Tectono-stratigraphic evolution of the Mesozoic continental

Tectono-stratigraphic evolution of the

Mesozoic continental margins

of the Central Atlantic

Max Anthony Casson

A thesis submitted to the University of Manchester

for the degree of Doctor of Philosophy (Ph.D.)

in the Faculty of Science and Engineering

2020

School of Earth & Environmental Science

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TABLE OF CONTENTS

LIST OF FIGURES ...................................................................................................................................................... 5

LIST OF TABLES ...................................................................................................................................................... 12

ABBREVIATIONS ..................................................................................................................................................... 13

ABSTRACT ............................................................................................................................................................ 18

DECLARATION ....................................................................................................................................................... 19

COPYRIGHT STATEMENT .......................................................................................................................................... 19

ACKNOWLEDGEMENTS ............................................................................................................................................ 20

THESIS OUTLINE .................................................................................................................................................... 21

1 INTRODUCTION ........................................................................................................................................... 24

1.1 SCOPE OF THE THESIS ....................................................................................................................................... 25

1.2 BASIN PHYSIOGRAPHY ....................................................................................................................................... 29

1.3 GEOLOGICAL HISTORY OF THE CENTRAL ATLANTIC .................................................................................................. 30

1.4 DATASET ........................................................................................................................................................ 38

1.4.1 Field Campaigns ................................................................................................................................... 39

1.4.2 Well Data ............................................................................................................................................. 39

1.4.3 Seismic Reflection Data ........................................................................................................................ 40

1.5 METHODOLOGY ............................................................................................................................................... 41

1.5.1 Stratigraphic Analysis........................................................................................................................... 41

1.5.2 Seismic Interpretation .......................................................................................................................... 44

1.6 REFERENCES ................................................................................................................................................... 45

2 DEEP SEA ROCK RECORD EXHUMED ON OCEANIC VOLCANIC ISLANDS: THE CRETACEOUS SEDIMENTS OF

MAIO, CAPE VERDE ......................................................................................................................................... 52

2.1 ABSTRACT ...................................................................................................................................................... 53

2.2 INTRODUCTION ................................................................................................................................................ 54

2.3 REGIONAL SETTING AND STRATIGRAPHY ................................................................................................................ 55

2.4 METHODS ...................................................................................................................................................... 57

2.4.1 Sedimentology ..................................................................................................................................... 57

2.4.2 Biostratigraphy .................................................................................................................................... 58

2.5 RESULTS ......................................................................................................................................................... 58

2.5.1 Ribeira do Morro Section (Sample prefix: RDM) ................................................................................... 61

2.5.2 Monte Esgrovere Section (Sample prefix: ESG) .................................................................................... 67

2.5.3 Monte Carquiejo and River Cut Sections (Sample prefix: MC & RC) ..................................................... 69

2.6 DISCUSSION .................................................................................................................................................... 72

2.6.1 Stratigraphy ......................................................................................................................................... 73

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2.6.2 Regional Correlation ............................................................................................................................ 73

2.6.3 Paleo-Environmental Evolution ............................................................................................................ 75

2.7 CONCLUSIONS ................................................................................................................................................. 76

2.8 ACKNOWLEDGEMENTS ...................................................................................................................................... 77

2.9 SUPPLEMENTARY DATA ..................................................................................................................................... 77

2.10 REFERENCES ................................................................................................................................................. 84

3 AN INTEGRATED STRATIGRAPHIC RE-EVALUATION OF KEY CENTRAL ATLANTIC DSDP SITES ............................ 88

3.1 ABSTRACT ...................................................................................................................................................... 89

3.2 INTRODUCTION ................................................................................................................................................ 90

3.3 REGIONAL SETTING .......................................................................................................................................... 93

3.3.1 Scientific Drilling in the Oceanic Domain .............................................................................................. 94

3.3.2 Proximal Continental Margin Evolution ............................................................................................... 95

3.4 DATASET & METHODS ...................................................................................................................................... 96

3.4.1 Data ..................................................................................................................................................... 96

3.4.2 Methods ............................................................................................................................................... 96

3.5 RESULTS ......................................................................................................................................................... 99

3.5.1 Stratigraphic Revision .......................................................................................................................... 99

3.5.2 Organic Geochemistry ........................................................................................................................ 108

3.5.3 Seismic Stratigraphy .......................................................................................................................... 112

3.6 DISCUSSION .................................................................................................................................................. 117

3.6.1 Stratigraphic Evolution ....................................................................................................................... 117

3.6.2 Regional Extent and Drivers of Major Unconformities ....................................................................... 119

3.6.3 Seaward Dipping Reflector (SDR) Occurrence & Volcanism in the Central Atlantic ............................ 121

3.7 CONCLUSIONS ............................................................................................................................................... 121

3.8 ACKNOWLEDGEMENTS .................................................................................................................................... 124

3.9 SUPPLEMENTARY DATA ................................................................................................................................... 125

3.10 REFERENCES ............................................................................................................................................... 133

4 CRETACEOUS CONTINENTAL MARGIN EVOLUTION REVEALED USING QUANTITATIVE SEISMIC

GEOMORPHOLOGY, OFFSHORE NORTHWEST AFRICA .................................................................................... 139

4.1 ABSTRACT .................................................................................................................................................... 140

4.2 INTRODUCTION .............................................................................................................................................. 141

4.3 REGIONAL SETTING ........................................................................................................................................ 143

4.4. DATASET & METHODS ................................................................................................................................... 145

4.4.1 Data ................................................................................................................................................... 145

4.4.2 Methods ............................................................................................................................................. 145

4.5 RESULTS ....................................................................................................................................................... 147

4.5.1 Lithological & Stratigraphic Control ................................................................................................... 147

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4.5.2 Margin Structure ................................................................................................................................ 149

4.5.3 Shelf-Edge Delta Evolution ................................................................................................................. 151

4.5.4 Canyon Incision .................................................................................................................................. 154

4.5.5 Quantitative seismic geomorphology ................................................................................................. 154

4.5.6 Canyon Classification ......................................................................................................................... 156

4.5.7 Formation Processes .......................................................................................................................... 156

4.5.8 Base-of-slope to Basin Floor Deposits ................................................................................................ 157

4.5.9 Spatio-temporal evolution ................................................................................................................. 161

4.6 DISCUSSION .................................................................................................................................................. 162

4.6.1 Mixed System Margin Morphology .................................................................................................... 162

4.6.2 Canyon Incision Evolution .................................................................................................................. 163

4.6.3 Sediment Transfer from Shelf to Basin ............................................................................................... 164

4.6.4 Regional Controls on Stratigraphic Evolution ..................................................................................... 166

4.7 CONCLUSIONS ............................................................................................................................................... 167


4.9 REFERENCES ................................................................................................................................................. 168

5 EVALUATING THE SEGMENTED POST-RIFT STRATIGRAPHIC ARCHITECTURE OF THE GUYANAS CONTINENTAL

MARGIN ....................................................................................................................................................... 176

5.1 ABSTRACT .................................................................................................................................................... 177

5.2 INTRODUCTION .............................................................................................................................................. 178

5.3 REGIONAL SETTING ........................................................................................................................................ 181

5.3.1 Previous Studies ................................................................................................................................. 182

5.4 DATASET & METHODS .................................................................................................................................... 183

5.4.1 Data ................................................................................................................................................... 183

5.4.2 Methods ............................................................................................................................................. 184

5.5 RESULTS ....................................................................................................................................................... 186

5.5.1 Sedimentological & Stratigraphic Control .......................................................................................... 186

5.5.2 Organic Geochemistry ........................................................................................................................ 200

5.5.3 Margin Architecture ........................................................................................................................... 203

5.5.4 Structural Evolution ........................................................................................................................... 208

5.5.5 Chronostratigraphic Analysis ............................................................................................................. 211

5.5.6 Palaeogeographical Reconstructions ................................................................................................. 214

5.6 DISCUSSION .................................................................................................................................................. 218

5.6.1 Comparison to the Conjugate Margin – Guinea Plateau .................................................................... 218

5.6.2 Margin Heterogeneity Influenced by Structural Inheritance .............................................................. 219

5.7 CONCLUSIONS ............................................................................................................................................... 220


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5.9 SUPPLEMENTARY DATA ................................................................................................................................... 223

5.10 REFERENCES ............................................................................................................................................... 233

6 SYNTHESIS ................................................................................................................................................. 241

6.1 INTRODUCTION .............................................................................................................................................. 242

6.2 PALAEOGEOGRAPHICAL RECONSTRUCTIONS ......................................................................................................... 246

6.2.1 Middle Berriasian unconformity (142 Ma) to Upper Valanginian maximum flooding surface (135 Ma)

.................................................................................................................................................................... 246

6.2.2 Base Aptian unconformity (125 Ma) to base Albian unconformity (113 Ma) ..................................... 248

6.2.3 Base Albian unconformity (113 Ma) to intra Late Albian unconformity (102 Ma).............................. 251

6.2.4 Intra Late Albian unconformity (102 Ma) to Cenomanian-Turonian boundary (94 Ma) ..................... 255

6.2.5 Cenomanian-Turonian boundary (94 Ma) to Middle Campanian unconformity (78 Ma) ................... 258

6.3 SUMMARY .................................................................................................................................................... 260


6.5 REFERENCES ................................................................................................................................................. 261

7 CONCLUSIONS ........................................................................................................................................... 264

7.1.1 Central Atlantic Stratigraphic Framework .......................................................................................... 265

7.1.2 Continental Margin Evolution ............................................................................................................ 266

7.1.3. Geochemical Analysis ........................................................................................................................ 268

7.1.4. Unconformity Development .............................................................................................................. 268

7.2 FUTURE RESEARCH ......................................................................................................................................... 269

7.2.1 Sediment provenance of sands in the Senegal basin .......................................................................... 269

7.2.2 Geophysical studies of the MSGBC basin ........................................................................................... 269

7.2.3 Regional megasequence characterisation of the US Atlantic margin ................................................. 270

7.2.4 Re-examination of Mesozoic outcrops at Cap de Naze & Cap Rouge ................................................. 270

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LIST OF FIGURES

Fig. 1.1 – Highly schematic cross-section orientated east-west of the northwest African Atlantic continental margin partitioned into various domains after Peron-Pinvidic et al. (2013). COB – continent ocean boundary; SDRs – seaward dipping reflectors. The approximate location of the section is shown in Fig. 1.8. .............. 25

Fig. 1.2– Bathymetry and topography maps of northwest Africa (A) and north-eastern South America (B) highlighting the location of data used during the thesis. Additional information on the seismic reflection data is provided in Table 1.1. More detailed maps are presented in each chapter. ............................................ 28

Fig. 1.3 – Chronostratigraphy of northwest Africa, MSGBC basin showing hydrocarbon occurences and DSDP lithostratigraphic units (Jansa et al., 1979). Adapted from Petrosen (2014). ............................................... 30

Fig. 1.4– Paleozoic basement terrane assembly of northwest Africa, South America (Gondwana) and North America (Laurentia). This model is an output from the Geognostics Earth Model (GEM, 2020). Np. – Neoproterozoic. ........................................................................................................................................... 31

Fig. 1.5– Paleogeographic reconstructions to early seafloor spreading in the Central Atlantic (175 Ma), opening of the Equatorial Atlantic (110 Ma) and post-rift / drift configuration (70 Ma) from Scotese (2016). White boxes indicate the conjugated study areas. CA – Central Atlantic; EA – Equatorial Atlantic; SA – South America. ....................................................................................................................................................... 31

Fig. 1.6 – Central Atlantic rift evolution from Late Triassic (205 Ma) to Middle Jurassic (165 Ma). This model is an output from the Geognostics Earth Model (GEM, 2020). Key to the basement terranes is from Fig. 1.4. DR – Demerara Rise; GP – Guinea Plateau. .................................................................................................. 33

Fig. 1.7– Equatorial Atlantic rift evolution from Aptian (124 Ma) to Late Albian (101 Ma). This model is an output from the Geognostics Earth Model (GEM, 2020). Key to the basement terranes is from Fig. 1.4. C.A. – Central Atlantic; CAMP – Central Atlantic Magmatic Province; DR – Demerara Rise; E.A. – Equatorial Atlantic; GP – Guinea Plateau. ...................................................................................................................... 36

Fig. 1.8– A structural synthesis of the northwest African Atlantic continental margin from the hinterland (West African Craton) in the east to the Central Atlantic Ocean in the west. To be used alongside Fig. 2A to reference the location of data used in the thesis. CDN – Cap de Naze (Cretaceous outcrop); CFR – Casamance failed rift; CSM – Casamance salt basin; KAF – Kaolack fault; KKI - Kédougou-Kéniba inlier; MFT – Mauritanide front thrust; MSB – Mauritania salt basin. Complied from Bellion and Crevola (1991), Davison (2005) and GEM (2020). The approximate location of the section in Fig. 1.1 is displayed. ............................................ 38

Fig. 2.1 (A) – Location map of the Cape Verde archipelago with magnetic anomalies (M0 ~125 Ma, Barremian-Aptian boundary; M10 ~130 Ma; M16 ~145 Ma; M21 ~148 Ma; M25 ~154 Ma; Seton et al., 2014), DSDP boreholes and location of Fig. 2.2 displayed. Bathymetric contours every 1000 m. (B) Geological map of Maio after Stillman et al. (1982), with the locations of four studied sections presented in this paper. (C) Schematic cross-section of Maio, location displayed on (B), adapted after Robertson et al. (1984). .......... 55

Fig. 2.2 – Schematic cross-section through the NW African Atlantic passive margin highlighting the main stratigraphic packages and architecture of the basin. Approximate locations of DSDP 367 and magnetic anomalies (Seton et al., 2014) shown. Location of section detailed in Fig. 2.1A. ......................................... 56

Fig. 2.3 – Chronostratigraphic summary chart for the geological evolution of Maio. Inset – references. Kindly provided by Steve Lawrence (pers. comms. 2018). ...................................................................................... 57

Fig. 2.4 (next page) – Detailed sedimentary log with the majority of igneous intrusions removed from Ribeira do Morro, see location in Fig. 2.1B. Samples taken for the calcareous nannofossil biostratigraphy are annotated, five specimens are illustrated: (A) A. youngii, (B) N. steinmannii, (C) C. rothii, (D) E. turriseiffelli,

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(E) Z. scutula, and the distribution charts are provided in the supplementary data (Table S 2.1). Inset – a sketch geological map highlighting where the section was logged along in the river bank exposures and in subsurface quarries, the lack of surface exposure due to quarrying activities (see supplementary data Fig. S 2.1) and structural data recorded in the field. ............................................................................................. 59

Fig. 2.5 – Reconstructed sedimentary log of the complete Ribeira do Morro section after Stahlecker (1935) with macrofossil horizons (I – XIV) displayed. The approximate stratigraphic location of Fig. 2.4 is shown. A selection of the key ammonites are illustrated: (A) VII – Leptohamulina cf. distans (= Leptoceras aff. sabaudianum in Stahlecker, 1935); (B) VII – Lytocrioceras sp. (= Ancyloceras sp. in Stahlecker, 1935); (C) VII – Mascarellina gr. hamus (= Hamulina cf. hamus in Stahlecker, 1935); (D-E) VII – Eoheteroceras multicostatum (= Heteroceras giraudi in Stahlecker, 1935); (F) VII – Eoheteroceras multicostatum (= Heteroceras aff. heterocostatum in Stahlecker, 1935); (G) VIII – Pulchellia sp. (= Pulchellia rhombocostata in Stahlecker, 1935); (H, I) X – Toxancyloceras gr. vandenheckii (= Ancyloceras matheronianum in Stahlecker, 1935); (J) XI – Heinzia sp. (= Douvilleiceras irregulare in Stahlecker, 1935); (K) XII – Heinzia sp. (= Pulchellia hoplitiformis in Stahlecker, 1935). Location detailed in Fig. 2.1B and key in Fig. 2.4. Note the change in scale, each bar represents 10m. All ammonites are natural size except Fig. J. (x2). .............................................. 63

Fig. 2.6 (next page) – Detailed sedimentary log of the Monte Esgrovere section with photographs of the new collection of ammonites: (A) Neolissoceras (Vergoligeras) sp. juv. gr. salinarium; (B) Bochianites sp.; (C) “Busnardoites” sp.; (D) Kilianella sp. All ammonites are natural size except Fig. A and C (x2). Location detailed in Fig. 2.1B and key in Fig. 2.4. ..................................................................................................................... 65

Fig. 2.7 – Detailed sedimentary log of the Monte Carquiejo and River Cut section, separated by approximately 120 m. Samples taken for the calcareous nannofossil biostratigraphy are annotated and the distribution charts are provided in the supplementary data (Table S 2.1). One belemnite was identified and studied; the location in the stratigraphy is shown supporting the age interpretation from the calcareous nannofossils. Location detailed in Fig. 2.1B and key in Fig. 2.4. ................................................................... 69

Fig. 2.8 – Composite stratigraphic summary log of the Cretaceous succession of Maio integrating all new data from various sections documented (Fig. 2.4; Fig. 2.5; Fig. 2.6; Fig. 2.7), with the calpionellid dating of the Batalha Fm. by Fourcade et al. (1990). UTU – upper transitional unit of the Morro Formation; Dating of sections based on: N. – nannofossils; Am. – ammonites; Ap. – aptychi; C. – calpionellids........................... 72

Fig. 3.1 – Reconstruction of the Central Atlantic to Aptian times (~125 Ma). Location of scientific boreholes and exploration wells (EXP) shown, the three revised wells are highlighted in orange, as well as outcrop studies from Maio, Cape Verde (Casson et al., 2020a) and Cap de Naze, Senegal (CDN). The reconstructed present-day onshore geology maps from the three continents, North America, South America and Africa are displayed highlighting the radial nature of the Central Atlantic Magmatic Province (CAMP) dykes. The onshore geology is clipped at the maximum transgressive coastline during the Cretaceous (Mourlot et al., 2018). Magnetic anomalies, Mx and their corresponding oceanic crust ages from Gradstein et al. (1994) with offsetting fracture zones (FZ). Additional magnetic anomalies (i.e. ABSMA) mapped by Labails et al. (2010) are displayed. The reconstructed location of the seismic data (Fig. 3.9) and estimated line of section for the Wheeler diagram (Fig. 3.11) shown. The conjugate South American study area (Casson et al., 2020b) is displayed as a black dashed box. ABSMA – African Blake Spur magnetic anomaly; BB – Bove Basin; BBB – Blake-Bahama Basin; BP – Blake Plateau; BSMA – Blake Spur magnetic anomaly; DR – Demerara Rise; ECMA – East Coast magnetic anomaly; GP – Guinea Plateau; MSGBC – Mauritania-Senegal-Guinea Bissau-Conarky basin; WACMA – West African Coast magnetic anomaly. ............................................................................ 92

Fig. 3.2 – Litho-stratigraphic summary chart for DSDP wells from the Central Atlantic, and Maio, Cape Verde after Casson et al. (2020a). Displaying litho-stratigraphic units/formations1 defined by Jansa et al. (1979) and events by Müller et al. (1983; 1984), key seismo-stratigraphic markers2 of Tucholke & Mountain (1979), and those defined in this study. Numbers relate to the core number. Black lines between cores indicate core gaps, and no lines indicate a hiatus. BAU – base Albian unconformity; BTU – base Tertiary unconformity;

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MBU – middle Berriasian unconformity; TC – top Cenomanian; TOC – top oceanic crust; TV – top Valanginian. ..................................................................................................................................................................... 94

Fig. 3.3 (next page) – A re-evaluation of DSDP Leg 41 Site 367 stratigraphy displaying nannofossil events (Table S 3.2) and palynology results (Fig. S 3.1), depth of an ichthyodectiform reported in Casson et al. (2018), total organic carbon (TOC; Table S 3.1) measurements and key stratigraphic surfaces. Palynology abbreviations: ABN – abundant, AOM – amorphous organic matter, FDO – first downhole occurrence, FDCO – first downhole common occurrence, FDAO – first downhole abundant occurrence, FDSAO – first downhole superabundant occurrence, INCR – increase in abundance, PRES - presence, CMN - common, SABN – superabundant, TNS – top not seen. ............................................................................................................ 97

Fig. 3.4 (next page) – A litho-stratigraphic summary of the Mesozoic sediments recovered at DSDP Leg 41 Site 367 displaying key stratigraphic units after Lancelot et al. (1976). Total organic carbon (TOC) maximum and average values per unit displayed from new geochemical analysis (Table S 3.1). ACD – aragonite compensation depth; CCD – calcite compensation depth. .......................................................................... 99

Fig. 3.5 – Photographs of Core 32 from DSDP Leg 41 Site 367 with analysed samples displayed by red arrows, highlighting the middle Berriasian unconformity (MBU) separating Late Tithonian-aged unit 6, reddish brown nannofossil-bearing argillaceous limestone, marl, clays and cherts from the overlying early Berriasian-aged Unit 5B, white grey nannofossil limestone, marl & chert (Lancelot et al., 1976). Tith. – Tithonian; Berr. – Berriasian. Scale in cm. ............................................................................................................................... 101

Fig. 3.6 – A re-evaluation of DSDP Leg 41 Site 368 stratigraphy displaying nannofossil events (Table S 3.2), total organic carbon (TOC; Table S 3.1) measurements, palynology results (Fig. S 3.1) and key stratigraphic surfaces. ..................................................................................................................................................... 104

Fig. 3.7 – A re-evaluation of DSDP Leg 76 Site 534a stratigraphy displaying nannofossil events (Table S 3.2), total organic carbon (TOC; Table S 3.1) measurements and key stratigraphic surfaces. ............................ 106

Fig. 3.8 – Classification of kerogen types using hydrogen and oxygen indices plotted on a modified van Krevelen diagram displaying the results of the Rock-Eval pyrolysis. The symbology reflects the age of each sample analysed, data from DSDP Site 367 and Site 368 is filled white and black respectively. The tabulated data is presented in the supplementary material (Table S 3.1). ................................................................. 108

Fig. 3.9 (next page) – Dip-orientated two-way time seismic sections from the North West African Atlantic margin, Mauritania to Guinea Bissau, displaying megasequence architecture extrapolated from the re-evaluated well stratigraphy. Location displayed on Fig. 3.1 and the inset map. A zoom-in on possible outer seaward dipping reflectors (SDRs) is shown at 2x magnification. M25 magnetic anomaly intersection (~154 Ma = Kimmeridgian) after Labails et al. (2010). COB – Continent ocean boundary. Seismic data courtesy of Spectrum Geo. ........................................................................................................................................... 110

Fig. 3.10 – A correlation between the stratigraphy studied in the DSDP cores of Site 367 (Fig. 3.3) and the two-way time seismic section displayed in Fig. 3.9B, where the location of this zoom is highlighted. DSDP unit numbers are shown on the lithology log. The main seismic markers are coloured and named following the symbology in Fig. 3.9. Note there are no wireline logs from this borehole, therefore a seismic-well tie is not possible. Type II and Type II/III refers to the predominate kerogen type, i.e. marine and mixed, respectively, for those particular intervals. OC – oceanic crust; SF – sea floor; SR – source rock. ............. 113

Fig. 3.11 (next page) – A dip-orientated Wheeler diagram constructed from the oceanic domain (left) to distal and proximal domains of onshore Senegal, northwest Africa Atlantic margin (right) detailing the stratigraphic evolution of the continental margin, from pre-rift to the top of the Cretaceous. The horizontal axis is not accurately to scale. Pin stripe vertical lines indicate hiatus’ corresponding to various regional unconformities dated in the stratigraphic analysis. Dash black and white lines indicate revised wells in this study. The geological time scale (GTS 2018) is non-linear. Hydrocarbon occurrences are shown. Outcrop

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studies from Maio, Cape Verde (Casson et al., 2020a) and Cap de Naze, Senegal (CDN) displayed. BFF – basin floor fan; TD – total depth. ......................................................................................................................... 115

Fig. 4.1 (next page) (A) – Shaded bathymetric and topographic map of northwest Africa showing the present-day structure of the continental margin, with major river systems delineated (blue lines). The M25 (154 Ma) magnetic anomaly is shown as a black line and the continent-ocean boundary (COB) as a red dashed line after Labails et al. (2010). 3D seismic reflection dataset in hydrocarbon exploration blocks A1 and A4, offshore The Gambia (WGS 1984 UTM Zone 28N) is tied to Deep Sea Drilling Project (DSDP) sites 367 and 368 by regional 2D seismic reflection data. The study area covers the present-day basin-to-shelf transition. The location of the well correlation in Fig. 4.2 is shown; see Fig. 4.2 inset for a more detailed map naming the exploration wells. Hydrocarbon accumulations along the margin are displayed. The eastern margin of the Mauritania-Senegal-Guinea-Bissau-Conakry (MSGBC) Basin is defined by the Mauritanide front (Labails et al., 2010). The Mesozoic shelf edge (after Purdy, 1989), Late Cretaceous shoreline and erosion (after Mourlot et al., 2018a), and Casamance failed rift arm (after Long, 2016) are mapped. Present-day canyon systems locations from Wynn (2000a). (B) – Regional cross section based on the 2D seismic line. See Fig. 4.1A for location. TB – Top Basement; TJ – Top Jurassic; TAp – Top Aptian; TA – Top Albian; RCU – Regional Composite Unconformity; BTU – Base Tertiary Unconformity; SF – Seafloor. ........................................... 142

Fig. 4.2 – Senegal-Gambia stratigraphy. Regional well correlation, datum the base Tertiary unconformity, along a 200 km strike profile of the NWAAM. Biostratigraphy and formation tops evaluated from well reports. Average interval velocities (m/s) above and below the regional composite unconformity are displayed. Data courtesy of Petrosen. Jammah-1 data from Clayburn (2017). Inset maps shows location of the wells, study area, paleo-shelf edge and hydrocarbon discoveries (green). .......................................... 147

Fig. 4.3 (A) – East-West two-way time seismic section with interpreted key stratigraphic surfaces. The regional composite unconformity (RCU) surface on the adjacent interfluve is projected onto the dip profile (dashed red line) highlighting the amount of erosion in canyon H. Intersections shown in (C). (B) – Inset seismic section focusing on seismic facies identified at the base of the canyon, MTD – mass transport deposit. (C) – North-South two-way time seismic section with canyon axes displayed. See inset map (A) for the line locations. Seismic data courtesy of TGS. .................................................................................................... 149

Fig. 4.4 (A) – Interpreted dip two-way time seismic section of the progradational shelf edge delta shown in Fig. 4.3A. Section flattened on the top Aptian surface shown in Fig. 4.3A to ‘restore’ the depositional geometry. (B) – Interpreted strike two-way time seismic section. Only seismic data between the regional composite unconformity (RCU) and -20 ms TWT below the top Aptian is shown. See inset map (A) and Fig. 4.5C for the line locations. Seismic data courtesy of TGS. .......................................................................... 150

Fig. 4.5 – Isochore maps (ms TWT) showing the progradation of an Albian-aged shelf-edge delta system across the platform, truncated by RCU erosion at the carbonate escarpment margin. (A) – Isochore map of Lobe 1. See inset map for location of displays in the study area (red box). (B) – Isochore map of Lobe 2 highlighting the progradation of the system. (C) – Total isochore for the shelf-edge delta. See Fig. 4.4 for the seismic horizons mapped for lobe 1 and 2. ................................................................................................ 151

Fig. 4.6 (next page) (A) – Depth structure map (contours), draped over a dip magnitude map, showing the regional composite unconformity (RCU) surface and the heavily canyonised carbonate escarpment margin. Arc Hydro™ computed flow pathways are displayed (solid white lines), lettered and cross-referenced in the following figures. (B) – Rose diagram showing the flow direction of each vertices from the flow pathways. (C) – Talweg longitudinal slope profiles of 13 canyons and a interfluve surface shown in (A). A major knickpoint zone exists between -3600 and -4100 m present-day depth (shown in grey shading) corresponding to the change in lithology at the subcrop of the top carbonate, see (A). (D) – Slope angle versus length along talweg longitudinal profile for two major canyons. Fine line sampled every vertices, bold averaged over 10 vertices. (E) – Canyon cross-profiles sampled every 1.5 km along the talweg longitudinal profile, locations displayed on Fig. 4.6A (white dashed lines). ................................................................... 152

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Fig. 4.7 – Spectral decomposition at 20, 30 and 40 Hz extracted on two surfaces, Albian-aged T1 (A) and Late Cretaceous-aged T2 (B), see above for the seismic horizons mapped. These images document the two phases of margin evolution. (A) – Inset rose diagram showing the orientation of each vertices from the sediment wave crest polylines. Carbonate escarpment mapped (white line). (B) – Inset zoom in on the basinal area showing glide tracks and carbonate blocks. ............................................................................................... 157

Fig. 4.8 – RMS amplitude maps extracted from a +/- 12 ms window around an intra-Albian horizon (A) and T1 (B), displaying the two end-member types of lobes (debris-poor vs. debris-rich). Location of the maps are shown in Fig. 4.6A. ..................................................................................................................................... 159

Fig. 4.9 – Summary of depositional systems active on the platform and in the basin through time, linked to each canyon system displayed in Fig. 4.6A. The line thickness indicates the volume of each geobody/deposit. Canyon K is omitted as this directly feeds the basin system of canyon L and M. Canyon M is also omitted as the majority of the deposits is beyond the dataset. Created through the interpretation of a 200-surface horizon stack generated in PaleoScan™ between the top Aptian and base Tertiary unconformity. The stratigraphic surfaces T1 and T2 are indicated. This is correlated to the geodynamical events effecting the Central Atlantic, with references shown. BTU – Base Tertiary Unconformity; DP – debris-poor lobes; DR – debris-rich lobes; MTD – mass transport deposit; ORI – organic-rich interval; RCU – regional composite unconformity; RSL – relative sea level. ....................................................................................................... 161

Fig. 4.10 (A) – Volume of deposit (derived from geobody interpretation) plotted with uncertainty against relative time (estimated from the PaleoScan™ horizon stack i.e. horizon 100 to 200 from oldest to youngest), coloured by facies. (B) – Run-out distance plotted against relative time. Trend lines coloured by facies. (C) – Cumulative volumes of sediment transported through each canyon system. ........................................... 162

Fig. 5.1 (A) – Shaded bathymetric and topographic location map of northeast South America showing the structure of the Guyanas continental margin and subsurface dataset. Exploration wells and scientific boreholes used in this study are shown; orange circles highlight where new stratigraphic analysis has been performed. The ION Geophysical GuyanaSPAN 2D seismic reflection survey, the location of the composite seismic section (Fig. 5.11A), dip section SR1-5400 (Fig. 5.11B) and the isochore maps are shown (Fig. 5.12). Dredge samples recovered basalts and rhyolites zircon-dated at 173.4 ± 1.6 Ma (Basile et al., 2020) from the seabed (white star). Onshore, the limit of sedimentary cover and hence the location of the Archean Guiana Shield is mapped (Cordani et al., 2016). Hydrocarbon discoveries and the limits of Cretaceous source kitchens after Kosmos (2018). DR – Demerara Rise; WA – Waini Arch. (B) – Structural framework of the Guyanas continental margin with a top basement depth structure map interpreted from the ION Geophysical GuyanaSPAN 2D seismic reflection survey. The ‘top basement’ map was constructed from a merge between the top oceanic crust and top basement surfaces. The onshore geological map is from the Geological Map of South America (CGMW, CPRM, DNPM, 2003). Structural features are mapped after Gouyet et al. (1994), Yang and Escalona (2011), Reuber et al. (2016), Sapin et al. (2016), crustal thickness modelled from 3D gravity anomaly inversion by Kusznir et al. (2018), predicted Jurassic graben offshore (Griffith, 2017), and volcanics from Gouyet et al. (1994) and Mourlot (2018). .......................................................................... 179

Fig. 5.2 – Tectono-stratigraphic framework for the Guyanas continental margin, offshore Suriname and Guyana. The major sequence stratigraphic surfaces identified in this study are indicated, linked to key biostratigraphy events. Lithostratigraphy is based on seismic profile SR1-5400 (Fig. 5.11B) and adapted from Nemčok et al. (2016), key in Fig. 5.15. The main seismic markers and megasequences used in this study are highlighted. Calculated sedimentation rates (sedi-rates) displayed in metres per million years (m/Myr). Relative sea level curve after Haq (2014). AF – Albian flooding surface; CAMP – Central Atlantic Magmatic Province; CF – Cenomanian flooding surface; OAE – oceanic anoxic event; SDRs – seaward dipping reflectors; TB – top basement. .................................................................................................................................... 182

Fig. 5.3 – A re-evaluation of the Guiana-Maritime GM-ES-3 well stratigraphy displaying nannofossil events (Table S 5.2), total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Location displayed on Fig. 5.1A. ................................................................................................................................ 187

10

Fig. 5.4 – A re-evaluation of the French Guiana 2-1 (FG2-1) well stratigraphy displaying nannofossil events (Table S 5.2), foraminifera and palynology results, total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Location displayed on Fig. 5.1A. ....................................................................... 189

Fig. 5.5 (next page) – A re-evaluation of the Demerara A2-1 well stratigraphy displaying nannofossil events (Table S 5.2), foraminifera and palynology results, total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Oil shows indicated on lithology column as green stars. Palynology abbreviations: CMN – common, FDCO – first downhole common occurrence. Location displayed on Fig. 5.1A. ............. 191

Fig. 5.6 – A re-evaluation of the ODP Leg 207 Site 1258C stratigraphy displaying nannofossil events (Table S 5.2), total organic carbon (TOC; Table S 5.1) data compiled from Meyers et al. (2006) and key stratigraphic surfaces. A 12 m correction has been applied to the gamma ray log, where LD is logger’s depth and DD is driller’s depth. Early Late Albian ammonites identified in cores 30 and 31 by Owen & Mutterlose (2006) are annotated, as well as the cores displayed in Fig. 5.7. Location displayed on Fig. 5.1A. .............................. 195

Fig. 5.7 – Photographs of two cores, 15 and 27 from ODP Leg 207 Site 1258C with analysed samples and interpreted ages displayed by red arrows, highlighting the Cretaceous stratigraphy and unconformities present in the borehole (Erbacher et al., 2004a). Inset – zoom in on the sharp contact between the calcareous nannofossil clay of Unit 3 and black shale of Unit 4 representing the middle Campanian unconformity (MCU) and a ca. 12 Myr hiatus (Erbacher et al., 2004b). Ceno. – Cenomanian; Camp. – Campanian. Scale in cm. ............................................................................................................................. 196

Fig. 5.8 – A re-evaluation of the DSDP Leg 14 Site 144 stratigraphy displaying nannofossil events (Table S 5.2), total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Location displayed on Fig. 5.1A. ................................................................................................................................ 199

Fig. 5.9 – Classification of kerogen types using hydrogen and oxygen indices plotted on a modified van Krevelen diagram displaying the results of the Rock-Eval pyrolysis. The symbology reflects the age of each sample analysed. New data generated in this study from four of the revised wells (A2-1, DSDP Site 144, FG2-1 and GM-ES-3) is amalgamated with data presented in Meyers et al. (2006) from ODP Site 1258C, the ages are updated following the new biostratigraphy results. The tabulated data is presented in the supplementary material (Table S 5.1). ................................................................................................................................ 201

Fig. 5.10 – Synthetic seismogram calculated for two exploration wells, Demerara A2-1 (Fig. 5.5) and French Guiana FG2-1 (Fig. 5.4), providing the well to seismic correlation of key horizons and megasequences identified in this new stratigraphic study. Extracted statistical wavelets presented. Location of the two wells displayed on Fig. 5.1A. ................................................................................................................................ 204

Fig. 5.11 (A) – Composite seismic section in depth displaying megasequence architecture along a >1000 km length of the Guyanas continental margin. Location displayed on Fig. 5.1A. Erosional truncation (red arrows) and onlap (black arrows) marked. BFF – basin floor fan; MFS – maximum flooding surface. (B) – Conjugate dip-orientated seismic depth sections from the Demerara Rise (2D line – SR1-5400, clipped at 20 km depth) and Guinea Plateau (after Edge, 2014) displaying megasequence architecture. Location displayed on Fig. 5.1A and reconstructed location on Fig. 5.16A. Note change of horizontal and vertical scale from (A). COB – continent-ocean boundary. Seismic data courtesy of ION Geophysical. .................................................... 205

Fig. 5.12 (left) – Isochore thickness maps for three megasequences, MS1 – top basement (seaward dipping reflectors, continental and oceanic crust) to upper Valanginian maximum flooding surface (VF); MS2 – VF to base Albian unconformity (BAU); MS3 – BAU to base Tertiary unconformity (BTU). Cont. – continental; GP – Guinea Plateau; TJ – top Jurassic. ............................................................................................................... 205

Fig. 5.13 (right) – A fence diagram constructed from 7 dip-orientated (N-S) seismic depth sections across the Demerara Rise, interpreted with the megasequences, structural domains and underlying basement structure. BAU – Base Albian unconformity; COB – continent-ocean boundary. Seismic data courtesy of ION Geophysical. Location inset. ....................................................................................................................... 205

11

Fig. 5.14 – Sequential restoration by horizon flattening for a segment of the strike seismic profile displayed in Fig 11A, at three key time stages, (D) Valanginian, (C) Aptian and (B) Albian revealing the structural evolution of the continental margin to (A) present day. A zoom in on the seismic around Demerara A2-1 with a projection of the uppermost truncated seismic reflection (black dashed line) revealing approximately a kilometre of erosion at the well location is shown. MFS – maximum flooding surface. Fig. 5.1A for location of the section. ............................................................................................................................................ 209

Fig. 5.15 (next page) – A Wheeler diagram constructed along strike from Guyana (left) to Brazil (right) detailing the stratigraphic evolution of the segmented Guyanas continental margin. Pin stripe vertical lines indicate hiatus’ corresponding to various regional unconformities dated in the stratigraphic analysis. Dash black and white lines indicate revised wells in this study. The geological time scale (GTS 2018) is non-linear. Hydrocarbon occurrences are shown. Average TOC values for the Canje Formation displayed, AR-1 data from Mourlot (2018). .......................................................................................................................................... 211

Fig. 5.16 (next page)– Gross depositional environment (GDE) maps for four key time stages, defined by the stratigraphic analysis, in the evolution of the Guyanas continental margin. (A) Upper Valanginian (135 Ma); (B) Aptian (115 Ma); (C) Latest Albian (101 Ma) and (D) Santonian (85 Ma). The reconstructed location of the conjugate seismic sections (Fig. 5.11B) are displayed in (A). Facies distribution (%) for the interval encountered in each well is shown. Geometries were reconstructed following the Geognostics Earth Model (GEM™). BFF – basin floor fan; DR – Demerara Rise; FZ – fracture zone; GP – Guinea Plateau. ................ 214

Fig. 6.1 (next page) – Chronostratigraphic summary of the key revised DSDP/ODP boreholes, exploration wells and outcrop locality (Maio, Cape Verde) of the Central Atlantic. Total organic carbon (TOC) data produced in this study is averaged over sub-stage intervals. A compilation of tectonic phases and regional events documented during this study, and synthesised from previous work is provided, alongside the relative sea level curve (Haq, 2014). A geological sketch based on regional two-dimensional seismic data profiles from the Central to Equatorial Atlantic, through the Demerara Rise is shown to display the relative positions, depths of penetration for each of the revised wells and stratigraphic architecture. DSDP 368 and Maio are not displayed on the geological section. .................................................................................................... 242

Fig. 6.2 – Palaeogeographical reconstruction to the interval, Middle Berriasian unconformity (142 Ma) to Upper Valanginian maximum flooding surface (MFS; 135 Ma). The map shows the depositional systems at maximum transgression. Facies distribution (%) for the interval encountered in each well is shown. A key is provided for reference in the following maps. ........................................................................................... 246

Fig. 6.3 – Palaeogeographical reconstruction to the interval, base Aptian unconformity (125 Ma) to base Albian unconformity (113 Ma), effectively representing the Aptian stage. ............................................... 248

Fig. 6.4 – Palaeogeographical reconstruction to the interval, base Albian unconformity (113 Ma) to intra Late Albian unconformity (102 Ma), effectively representing the Albian stage. ................................................ 251

Fig. 6.5 – Palaeogeographical reconstruction to the interval, intra Late Albian unconformity (102 Ma) to Cenomanian-Turonian boundary (94 Ma), effectively representing the major organic-rich interval. ........ 255

Fig. 6.6 – Palaeogeographical reconstruction to the interval, Cenomanian-Turonian boundary (94 Ma) to Middle Campanian unconformity (78 Ma). ................................................................................................ 258

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LIST OF TABLES

Table 1.1– Summary of seismic reflection datasets available for the study. ................................................ 40

Table 1.2 – Comparison of biostratigraphic techniques employed and integrated in this study. PD – present day. ............................................................................................................................................................... 43

Table 4.1 – Geomorphological data extracted from the sediment flow pathways (Arc Hydro) and regional composite unconformity (RCU) surface. Shelf-un – shelf-incising ungraded canyons; shelf-gr – shelf-incising graded canyons; slope – slope-confined canyons. Bold values signify the sediment flow pathway extended beyond the study area. .............................................................................................................................. 155

Table 4.2 – Geomorphological data extracted from the PaleoScan™ horizon stack and interpreted geobodies. Bold values signify the deposit extended beyond the study area. DP – debris-poor lobes; DR – debris-rich lobes; MTD – mass transport deposit. ........................................................................................................ 158

Table 6.1 – Public data synthesised for the following palaeogeographical reconstructions. ..................... 245

13

ABBREVIATIONS

AAPG American Association of Petroleum Geologists

ABN Abundant

ABSMA African Blake Spur magentic anomoly

AFTA Apatite fission track analysis

AGC Agence pour la gestion et la coopération

AGM Annual general meeting

AOM Amorphous organic matter

Ati Apatite-tourmaline index

BAU Base Albian unconformity

BB Bove basin

BBB Blake-Bahamas basin

BCR Bremen Core Repository

BCU Base Cenomanian unconformity

BFF Basin floor fan

BGS British Geological Survey

BP British Petroleum

BSE Backscatter electron

BSMA Blake Spur magentic anomoly

BTU Base Tertiary unconformity

CA Central Atlantic

CAMP Central Atlantic magnetic province

CASP Cambridge Arctic Shelf Programme

CCD Calcite compensation depth

CDN Cap de Naze

CFR Casamance failed rift

CIC Central igneous complex

CM Casamance marine

CMN Common

CNOOC China National Offshore Oil Corporation

CO Common occurrence

COB Continent ocean boundary

CORB Cretaceous oceanic red bed

COST Contient ocean stratigraphic test

CSM Casamance salt basin

14

CT Cenomanian Turonian

CTBE Cenomanian/Turonian boundary event

DD Drillers depth

DEM Digital elevation model

DR Demerara Rise

DSDP Deep sea drilling project

EA Equatorial Atlantic

EAGE European association of geologists and engineers

ECMA East Coast magentic anomoly

ECORD European consortium for ocean research drilling

EDX Energy dispersive X-ray

EGC Eastern Greater Caucasus

ESG Esgrovere

EXP Exploration

FAD First appearance datum

FAR First Australian Resources

FDAO First downhole abundant occurrence

FDCO First downhole common occurrence

FDO First downhole occurrence

FDSAO First downhole super abundant occurrence

FG French Guiana

FO First occurrence

FZ Fracture zone

GDE Gross depositional environment

GE Georgia Embayment

GEM Geognostics Earth Model

GHG Gareth Harriman geochemistry

GIS Geographic information systems

GP Guinea Plateau

GSA Geological society of America

GTS Geological time scale

GZi Garnet-zircon index

HGS Houston geological society

HI Hydrogen index

HM Heavy minerals

HP High pressure

15

HRA High relative abundance

ICE International conference and exhibition

INCR Increase in relative abundance

IODP International ocean drilling program

ITCZ Intertropical convergence zone

KAF Kaolack fault

KKI Kédougou-Kéniéba Inlier

KT Cretaceous Tertiary

LAD Last appearance datum

LD Loggers depth

LO Last occurrence

LTT Low-temperature thermochronology

MA Million years

MB Mount Branco

MBU Middle Berriasian unconformity

MC Mount Carquiejo

MCU Middle Campanian unconformity

MD Measured depth

MFS Maximum flooding surface

MFT Mauritanide front thrust

MMU Middle Miocene unconformity

ms milli-second

MS Megasequence

MSB Mauritania salt basin

MSGBC Mauritania-Senegal-Guinea Bissau-Conarky

MSV Middle Senegal Valley

MTC Mass transport complex

MTD Mass transport deposit

NARG North Africa Research Group

NF Nannofossil

NWAAM Northwest Africa Atlantic margin

OAE Oceanic anoxic event

OC Oceanic crust

ODP Ocean drilling program

OI Oxygen index

ORI Organic rich interval

16

PD Present day

PESGB Petroleum Exploration Society of Great Britian

PL Picked lithology

PPL Plane polarised light

PRES Presence

PSDM Pre-stack depth migration

PSTM Pre-stack time migration

QFL Quartz lithic feldspar

RC River cut

RCU Regional composite unconformity

RDM Ribiera do Morro

RMS Root mean square

RSL Relative sea level

Rzi Rutile-zircon index

SA South America

SABN Super abundant

SC Slope channels

SDR Seaward dipping reflectors

SEG Society of Exploration Geophysicists

SEM Scanning electron microscope

SEPM Society for Sedimentary Geology

SF Sea floor

SP Shot point

SR Source rock

SWT Seismic well tie

TA Top Albian

TB Top basement

TC Top Cenomanian

TCF Trillion cubic feet

TD Total depth

TJ Top Jurassic

TMP Transform marginal plateau

TNS Top not seen

TOC Top oceanic crust / total organic carbon

TV Top volcanics

TWT Two-way time

17

UCAD Universite Cheikh Anta Diop

UHP Ultra high pressure

UK United Kingdom

US United States

USA United States of America

UTM Universal Transverse Mercator

UTU Upper transitional unit

VF Valanginian flooding surface

WA Waini arch

WAC West African craton

WACMA West African Coast magentic anomoly

WAM West African Monsoon

WGS World Geodetic System

XPL Cross polarised light

XRD X-ray diffraction

18

ABSTRACT

The geology of the continental margins of northwest Africa and northeast South America, surrounding the

southern Central Atlantic have been investigated through a fully integrated, multi-disciplinary study to

document the tectono-stratigraphic evolution of the Mesozoic post-rift sequence. These sedimentary basins

are some of the most prolific underexplored hydrocarbon provinces worldwide. Rejuvenated tectonism

associated with the opening of the Equatorial Atlantic in the Aptian interrupted the relatively ‘passive’ post-

rift subsidence and was a significant control on sedimentation. Across the southern Central Atlantic, this

impacted the source-to-sink system through hinterland uplift (source), tectonic deformation of the basin

(sink), and associated effects on sedimentary systems, routing and depositional style.

A high-resolution stratigraphic framework has been constructed integrating existing data with new results

from biostratigraphic and sedimentological analyses of outcrop localities on the island of Maio, Cape Verde

and the re-sampling of seven key scientific boreholes and three exploration wells. Margin-scale

chronostratigraphic charts have been constructed to investigate facies distribution and highlight significant

regional hiati to enhance understanding of temporal stratigraphic evolution. Major unconformities are

recognised extending thousands of kilometres across the Central Atlantic such as the base Albian

unconformity (BAU). Local stratigraphic breaks are also identified, typically restricted to one structural

domain, i.e. the Late Cretaceous regional composite unconformity (RCU) located on the distal escarpment

margin offshore Senegal and The Gambia.

The mechanisms generating these regional unconformities have been considered and data suggest plate-

scale tectonic events are the major drivers. The middle Berriasian unconformity (MBU) recognised for the

first time at DSDP Site 367 has an associated time gap of ca. 5 Myr, linked to far-field effects of North Atlantic

breakup within the Iberia-Newfoundland segment. The Aptian-aged transpressional rifting in the Equatorial

Atlantic heavily deformed the pre-Aptian carbonate platform stratigraphy on the Demerara Rise creating a

suite of compressional structures resulting in major margin collapse. Further observations along the

northwest African Atlantic margin suggest the effects of this compression extend ca. 500 km north to Dakar,

forming broad intra-oceanic crust folding (DSDP Site 367) and thrusting of the distal escarpment margin. On

the Demerara Rise, the deformed pre-Aptian stratigraphy is peneplained by a striking angular unconformity

termed the base Albian unconformity (BAU); up to 1 km of sediment has been removed.

In subsequent Albian times, shelf edge delta systems prograde to the edge of the escarpment margin

depositing siliciclastic sediment across the shelf and to a base-of-slope apron. Quantitative seismic

geomorphology offshore The Gambia reveals the submarine canyonisation of the distal escarpment margin

forming kilometre-scale canyons on the RCU surface. Submarine lobe deposits at the terminus of these

systems are generally debris-rich, containing eroded blocks up to 1 km3 of the underlying carbonate

platform. Further unconformities are recognised on the Demerara Rise related to the creation of oceanic

crust (intra Late Albian) and continental breakup between S. America (Demerara Rise) and Africa (Guinea

Plateau) in the earliest Cenomanian.

To aid source rock characterisation, geochemical analysis of 110 samples reveals organic-enrichment in a

well-constrained time interval from the Late Albian (NC10a upper nannofossil zone) through the peak (>30%

TOC) during the global oceanic anoxic event OAE-2 (Late Cenomanian) into the earliest Turonian (northwest

Africa), and Coniacian (northeast South America). This organic-rich interval is the major source rock

candidate for generating hydrocarbons along these prospective continental margins.

19

DECLARATION

No portion of the work referred to in the thesis has been submitted in support of an application for another

degree or qualification of this or any other university or other institute of learning.

COPYRIGHT STATEMENT

i. The author of this thesis (including any appendices and/or schedules to this thesis) owns certain copyright

or related rights in it (the “Copyright”) and he has given The University of Manchester certain rights to use

such Copyright, including for administrative purposes.

ii. Copies of this thesis, either in full or in extracts and whether in hard or electronic copy, may be made only

in accordance with the Copyright, Designs and Patents Act 1988 (as amended) and regulations issued under

it or, where appropriate, in accordance with licensing agreements which the University has from time to

time. This page must form part of any such copies made.

iii. The ownership of certain Copyright, patents, designs, trademarks and other intellectual property (the

“Intellectual Property”) and any reproductions of copyright works in the thesis, for example graphs and

tables (“Reproductions”), which may be described in this thesis, may not be owned by the author and may

be owned by third parties. Such Intellectual Property and Reproductions cannot and must not be made

available for use without the prior written permission of the owner(s) of the relevant Intellectual Property

and/or Reproductions.

iv. Further information on the conditions under which disclosure, publication and commercialisation of this

thesis, the Copyright and any Intellectual Property and/or Reproductions described in it may take place is

available in the University IP Policy (see http://documents.manchester.ac.uk/DocuInfo.aspx?DocID=24420),

in any relevant Thesis restriction declarations deposited in the University Library, The University Library’s

regulations (see http://www.library.manchester.ac.uk/ about/regulations/) and in The University’s policy on

Presentation of Theses.

20

ACKNOWLEDGEMENTS

The unwavering support of many individuals deserves to be recognised in the completion of my PhD project.

First and foremost, I thank Jonathan Redfern for his encouragement and support to continue exploring over

the last three years. From our escapades on the island of Maio to the dusty core store in Senegal, I have

thoroughly enjoyed your supervision and I gratefully appreciate the opportunities associated with the PhD.

This study was funded by the North Africa Research Group (NARG) and I acknowledge the financial and

scientific support of the consortium sponsors. The University of Manchester was a fantastic host for

conducting this research, I am appreciative of the additional supervision I received. Petrosen, the National

Oil Company of Senegal, and Shell are thanked for data provision. The European Consortium for Ocean

Research Drilling (ECORD) provided a grant to support our re-investigation of the legacy Deep Sea Drilling

Project data.

A few special acknowledgements are extended to the following. Jason Jeremiah, it has been a pleasure to

work with you, your guidance and willingness to contribute from day one is a testament to the gentleman

you are. I will always chuckle at that time you nearly missed the only return boat off Maio. Gérôme Calvès,

our chance meeting at Manchester paved way for a cracking virtual friendship. Volunteering your

supervision was very honourable of you. Thank you for taking me under your wing. The Bulots, I have always

felt very welcome in your family following our field work in Popenguine, and throughout the subsequent

international adventures together, thank you both. Luc Bulot, I raise my beer to you for always being on

hand and teaching me to work critically, ‘cheers mate’!

Last but by no means least, I thank my family and friends. To my mother, father and brother who throughout

the years chasing my aspirations have always been the solid foundation for me to rely upon. You gave me

the platform and encouragement to attain these goals, and despite being unconventional within the family,

you have followed with love and interest throughout. I hope I’ve made you proud. I extend this appreciation

to the remainder of my family, both with us and unfortunately absent. Friends in Manchester, within NARG

and the Basins group are thanked for helping make my PhD experience very pleasant and smooth. Finally, I

acknowledge the support of my friends outside academia and thank them for the lovely times where their

loyal friendship and advice has really helped guide me through my studies.

21

THESIS OUTLINE

The thesis has been prepared in the Journal Format outlined by the University of Manchester, consisting of

six chapters and three additional appendices. Chapter 1 starts with an introduction to continental margins

to provide context for the study, followed by the geological history of the Central Atlantic and by extension,

the surrounding continental margins of northwest Africa, northeast South America and the eastern US. The

approach adopted for the study is presented alongside the studied datasets.

Chapter 2 – ‘Deep sea rock record exhumed on oceanic volcanic islands: the Cretaceous sediments of Maio,

Cape Verde’

Published in Gondwana Research (Casson, M., Bulot, L.G., Jeremiah, J. and Redfern, J., 2020. Deep sea rock

record exhumed on oceanic volcanic islands: the Cretaceous sediments of Maio, Cape Verde. Gondwana

Research, 81, pp.252-264.), this chapter presents the results from one field campaign undertaken in January

2018 by the authors on the island of Maio, Cape Verde. This is supplemented by an extensive revision of the

historical palaeontological collection of Stahlecker (1935) located in the University of Tubingen, Germany. A

high-resolution stratigraphic framework is developed for the exhumed oceanic domain sediments

integrating multiple biostratigraphic techniques with field sedimentology.

Co-author contributions: Luc Bulot (palaeontology investigation, ammonoid identification, manuscript

review); Jason Jeremiah (field associate, calcareous nannofossil identification, manuscript review); Jonathan

Redfern (supervision, field associate, manuscript review).

Chapter 3 – ‘An integrated stratigraphic re-evaluation of key Central Atlantic DSDP sites’

The stratigraphy of three key Deep Sea Drilling Project (DSDP) sites, 367, 368 and 534A in the oceanic domain

of the Central Atlantic are revised following multiple sampling trips to the IODP core repository in Bremen,

Germany. These three wells are fundamental in constraining the Mesozoic stratigraphy within the basin.

New biostratigraphic, sedimentology and organic geochemical results are presented and correlated to

regional two-dimensional seismic profiles.

Co-author contributions: Jason Jeremiah (sampling assistant, calcareous nannofossil identification,

manuscript review); Gérôme Calvès (supervision); Frederic de Ville de Goyet (palynology); Luc Bulot

(manuscript review); Jonathan Redfern (supervision, manuscript review).

22

Chapter 4 – ‘Cretaceous continental margin evolution revealed using quantitative seismic geomorphology,

offshore northwest Africa’

Results from previous chapters establishing the stratigraphic framework are applied to a three-dimensional

seismic dataset, offshore The Gambia in hydrocarbon exploration blocks A1 and A4. This work is published

open access in Basin Research (Casson, M., Calvès, G., Huuse, M., Sayers, B. and Redfern, J., 2020. Cretaceous

continental margin evolution revealed using quantitative seismic geomorphology, offshore northwest Africa.

Basin Research). The location of the dataset allows coeval shelfal and basinal depositional systems to be

investigated revealing a complex tectono-stratigraphic evolution of the distal continental margin.

Co-author contributions: Gérôme Calvès (supervision, manuscript review); Jonathan Redfern (supervision,

manuscript review); Mads Huuse (manuscript review); Ben Sayers (dataset provider, manuscript review).

Chapter 5 – ‘Evaluating the segmented post-rift stratigraphic architecture of the Guyanas continental

margin’

Prepared to be submitted to Petroleum Geoscience, this chapter extends the existing work on the African

margin to the conjugate South American margin, offshore Guyana to French Guiana. Seven key scientific

boreholes and exploration wells are re-evaluated following further sampling in Bremen, and additional

sampling of the exploration wells provided by Shell in Houston, US. Stratigraphic results are incorporated

into a refined tectono-stratigraphic framework and applied to a two-dimensional deep-penetrating seismic

dataset provided by ION Geophysical. This basin-scale dataset is used to construction gross depositional

environment maps and perform structural restorations. Positioned at a crucial location within the Central

Atlantic, the stratigraphic and structural response to the opening of the Equatorial Atlantic is explored.

Co-author contributions: Jason Jeremiah (sampling assistant – Bremen, calcareous nannofossil

identification, GDE mapping guidance; manuscript preparation); Gérôme Calvès (supervision, manuscript

review); Frédéric de Ville de Goyet (palynology); Kyle Reuber (dataset provider, seismic interpretation

supervision, concept discussions); Mike Bidgood (foraminifera dating); Daniela Reháková (calpionellid

dating); Luc Bulot (biostratigraphic review); Jonathan Redfern (supervision, sampling assistant – Houston,

manuscript review).

Chapter 6 – Synthesis

Results from the previous chapters are synthesised into a Central Atlantic tectono-stratigraphic framework.

Five regional palaeogeographic maps are presented for the eastern Central Atlantic (Africa and South

America). The biostratigraphic constraints, organic-enrichment, tectonics and palaeogeography are all

discussed.

23

Chapter 7 – Conclusions

Additional Research

Casson, M., Cavin, L., Jeremiah, J., Bulot, L.G. and Redfern, J., 2018. Fishing in the Central Atlantic, an Earliest

Cenomanian Ichthyodectiform from DSDP Site 367, Cape Verde Basin. Journal of Vertebrate Paleontology,

38(5).

Cumberpatch, Z., Soutter, E., Kane, I.A. and Casson, M., 2020. Evolution of a mixed siliciclastic-carbonate

deep-marine system on an unstable margin: the Cretaceous of the Eastern Greater Caucasus, Azerbaijan.

Basin Research.

Mounteney, I., Casson, M., Ruston, J., Millar, I., Dethie, N. and Redfern, J. 2020. Discerning the provenance

record of fresh detritus versus recycled sediment in Tertiary to modern-day source-to-sink systems of

Senegal. Submitted to the Journal of African Earth Sciences.

24

1 Introduction

Introduction

25

1.1 SCOPE OF THE THESIS

Continental margins cover over a tenth of the Earth’s surface. Our geological and geophysical

characterisation of these sedimentary basins is still evolving. This research asks fundamental questions

about major earth systems and processes. From an applied perspective, rifted margins are the most

voluminous sediment accumulations on Earth, host essential energy and natural resources, and provide a

rich record of global climatic and environmental changes.

Rifted or Atlantic-type “passive” continental margins form by continental breakup and subsequent sea-floor

spreading. Models of rifting and their formation indicate a period of initial extension creating rifts followed

by continental breakup and oceanic crust formation (McKenzie, 1978). The magnitude and orientation of

strain rate, presence of fluids, and the crustal and mantle rheology dictates the final geometry of rifted

margins (Peron-Pinvidic & Manatschal, 2019). This can also be influenced by other parameters such as: rift

obliquity, structural inheritance, and sedimentary and magmatic volumes during rifting. Along a dip profile

(Fig. 1.1), the margin can be divided into different domains (proximal – necking – continental-ocean

boundary/COB – distal – oceanic) and are typically classified as volcanic versus non-volcanic depending on

the magma volume during rifting (Franke, 2013).

Fig. 1.1 – Highly schematic cross-section orientated east-west of the northwest African Atlantic continental margin partitioned into various domains after Peron-Pinvidic et al. (2013). COB – continent ocean boundary; SDRs – seaward dipping reflectors. The approximate location of the section is shown in Fig. 1.8.

The overlying sedimentary fill is heterogeneous through these domains recording a complex interplay

between major Earth system processes. Accommodation is controlled by tectonic and thermal subsidence,

as well as isostasy. Erosion, which is influenced by eustasy and climate, governs sediment transfer through

sedimentary systems thousands of kilometres long, from the hinterland to the basin floor. Sedimentation

occurs in all of the domains, although over time and repeated erosional cycles most sediment will be

transported and deposited in the oceanic domain. Here in the ‘sink’, the stratigraphy is a major archive of

Chapter 1

26

past climates, oceanography and globally significant events (e.g. oceanic anoxic events – OAEs). Studying

the entire length of these sedimentary systems has been coined source-to-sink analysis (Allen, 2008; Clift et

al., 2008; Sømme et al., 2009; Martinsen et al, 2010).

This PhD study falls under a wider source-to-sink project undertaken by the North Africa Research Group

(NARG) that aims to understand the geological evolution of the continental margins of northwest Africa.

Previous work by NARG had focussed on the Moroccan onshore geology due to the abundance of

outcropping Mesozoic strata related to Alpine inversion. Studies targeted the full source-to-sink extent of

the continental margin. Charton (2018) documented kilometre-scale post-rift exhumation of the Moroccan

hinterland using low-temperature thermochronology, this novel dataset has now been expanded southward

along the Mauritanides revealing the whole margin has a dynamic rather than ‘passive’ post-rift uplift history

(Gouiza et al., 2019). To supplement this, multiple projects characterised the Mesozoic shelfal to non-marine

depositional systems from outcrops in the Essaouira-Agadir and North Aaiun-Tarfaya basins (Luber, 2017;

Arantegui, 2018; Duval-Arnould, 2020). Primarily these studies combined two key methods, outcrop

sedimentology and biostratigraphy. Due to the position in the depositional system, i.e. shallow marine, these

outcrops have high macro- and micro-palaeontological recovery and hence make ideal candidates to create

‘type’ sections of the Central Atlantic (i.e. Luber et al., 2019). NARG has been building a high-resolution

Mesozoic stratigraphic framework more applicable to the Central Atlantic than traditional schemes

correlating to the Tethyan and Boreal realms. Muniz-Pichel (2018) was the first NARG PhD to apply this

knowledge to a seismic dataset offshore Morocco to understand how salt tectonics controlled depositional

systems in the sink.

By 2016, hydrocarbon exploration companies and sponsors of NARG had shifted their frontier exploration

campaigns further south to the emerging hydrocarbon province of the Mauritania-Senegal-Guinea Bissau-

Conakry (MSGBC) basin. A report from the United States Geological Survey estimates hydrocarbon volumes

of 2.3 billion barrels of oil and 18.7 billion cubic feet of gas (Brownfield and Charpentier, 2003). Recent

exploration, 2014 to present day, has begun proving up these reserves. Offshore Senegal, Cairn Energy and

partners discovered the Sangomar field (previously SNE) containing 641 million barrels of oil in Albian-aged

reservoirs locaed at the paleo-shelf edge, and additional reserves in the equivalent downdip base-of-slope

fans (FAN and FAN-South; Clayburn, 2017). BP and Kosmos Energy estimate that their acreage offshore

Senegal and Mauritania contains between 50-100 trillion cubic feet of gas, already proving up most of this

volume in the Greater Tortue Ahmeyim field, Yakaar-Teranga discoveries and BirAllah area in basin-floor

turbidite reservoirs (Kosmos Energy, 2019).

Due to these recent successes that demonstrate the world-class nature of the MSGBC basin, NARG, through

the initiation of this study and subsequent PhD projects, aims to expand on and apply the knowledge

generated in North Africa to this prolific area. I was the first student from NARG working in the basin, and

Introduction

27

this thesis documents significant research undertaken to understand existing studies and generate new

datasets. Following a multi-disciplinary approach integrating a variety of datasets, outcrop, wells, seismic

reflection data, the aims were to:

- Apply and build on previous NARG studies to establish a ‘Central Atlantic stratigraphic framework’,

delivering high-resolution, multi-disciplinary biostratigraphy, and leveraging findings from the

reference sections established in Morocco.

- Investigate Mesozoic continental margin evolution across the full length of the basin, from proximal

to oceanic domains, and understand how the depositional sequences change spatially and

temporally.

- Identify and characterise any regional unconformities, determine spatial distribution and

subsequent impact on the evolution of the continental margins.

- Characterise geochemically organic-rich intervals.

- Ascertain the drivers, i.e. tectonics, eustasy, climate, behind continental margin evolution to

construct a tectono-stratigraphic framework.

During the project, the study area was expanded to include the conjugate margins of northeast South

America (Guyanas) and US Atlantic to compare and contrast continental margin evolution and evaluate the

regional aspects of the Central Atlantic geology.

Chapter 1

28

Fig. 1.2– Bathymetry and topography maps of northwest Africa (A) and north-eastern South America (B) highlighting the location of data used during the thesis. Additional information on the seismic reflection data is provided in Table 1.1. More detailed maps are presented in each chapter.

Introduction

29

1.2 BASIN PHYSIOGRAPHY

The continental margins surrounding the Central Atlantic extend from Morocco to Guinea (northwest Africa;

Davison, 2005), Brazil to Venezuela (northeast South America; Yang & Escalona, 2011), and Cuba to Canada

(east coast US; Withjack & Schlische, 2005; Miall, 2008). The northwest African Atlantic margin (NWAAM) is

bordered to the east by the West African Craton (WAC) composed of various terrains at high elevations (Rif

and Atlas belts) and eroded remnants of old massifs and orogenic belts (Reguibat, Mauritanides, Bassarides,

Rokelides, Leo Man Shield; Fig. 1.2A). Between the WAC and the Central Atlantic, the low-lying coastal plains

have little relief. The climate varies from dry (Saharan) to sub-tropical and humid. Continental shelf width

varies along the margin, from its narrowest in Mauritania (50 km), bulging to a maximum on the Guinea

Plateau (275 km). The oceanic volcanic islands of the Canaries and Cape Verde puncture through the Central

Atlantic abyssal plain.

The northeast South American margin borders the Archean Guyana Shield with a narrow coastal plain and

shelf (150 km), that extends to form the shallow bathymetric feature, the Demerara Rise (Fig. 1.2B). From

the tropical Bahamas, Cuba and Florida, the shelf is widest (375 km), becoming narrower northward beyond

Cape Hatteras and bounded to the west by the Appalachian Mountains. The Gulf Stream tracks the along

the margin bringing warm weather systems north.

The main focus of the thesis is the geology of the Central Atlantic from the Kane to Guinea fracture zones,

though Chapter 5 explores further into the neighbouring Equatorial Atlantic.

Chapter 1

30

1.3 GEOLOGICAL HISTORY OF THE CENTRAL ATLANTIC

Fig. 1.3 – Chronostratigraphy of northwest Africa, MSGBC basin showing hydrocarbon occurences and DSDP lithostratigraphic units (Jansa et al., 1979). Adapted from Petrosen (2014).

A general overview of the Central Atlantic geological history is provided, biased to the African margin. This

is augmented in each of the following chapters with more detail review relevant to that particular study.

Extracts from the Geognostics Earth Model (GEM, 2020) and Scotese (2016) palaeogeographic maps,

alongside a MSGBC basin chronstratigraphic chart (Fig. 1.3) are used to understand the Central Atlantic

basement terrane assembly and rift to drift evolution of the Central Atlantic (Fig. 1.4; Fig. 1.5).

Introduction

31

Fig. 1.4– Paleozoic basement terrane assembly of northwest Africa, South America (Gondwana) and North America (Laurentia). This model is an output from the Geognostics Earth Model (GEM, 2020). Np. – Neoproterozoic.

Fig. 1.5– Paleogeographic reconstructions to early seafloor spreading in the Central Atlantic (175 Ma), opening of the Equatorial Atlantic (110 Ma) and post-rift / drift configuration (70 Ma) from Scotese (2016).

Chapter 1

32

White boxes indicate the conjugated study areas. CA – Central Atlantic; EA – Equatorial Atlantic; SA – South America.

Pre-rift – Prior to Central Atlantic rifting and fragmentation of Gondwana, the pre-Mesozoic geological

history involved numerous orogenic events accreting various terranes to the relatively stable Precambrian

cratons, the WAC and Amazonia Craton (Kennedy, 1964; Binks & Fairhead, 1992). Two Archean shields are

exposed present-day within the WAC, the Reguibat and Leo Man (Gueye et al., 2007; Villeneuve, 2008;

Villeneuve et al., 2015). Smaller exposed inliers also exist, i.e. the Kédougou-Kéniéba inliers (Ledru et al.,

1991; Milési et al., 1992). The Guyana Shield, part of the exposed Amazonia Craton, is built of several

Archean to Proterozoic terrains accreted in multiple orogenic episodes, (1) Trans-Amazonian

(Paleoproterozoic), (2) Late Mesoproterozoic, and (3) Araguaia (Neoproterozoic; Almeida et al., 2000). The

fundamental geological events that formed the basement terrane framework are summarised in Fig. 1.4. At

the end of the Neoproterozoic (Fig. 1.4A), the Florida and Yucatan blocks remained sutured to Amazonia,

which at the time was being subducted via an east-dipping subduction zone. This bordered the WAC, i.e. on

the western boundary of the Guinea Wedge, a latest Pan-African (580-520 Ma) accretionary complex

interpreted south of Dakar (GEM, 2020). Accreted Neoproterozoic oceanic crust was also subducted

between the two cratons. By Middle Cambrian times (500 Ma; Fig. 1.4B) continent-continent collision

between Amazonia and Central Gondwana formed the Araguaia orogenic belt stretching through Brazil

(Almeida et al., 2000). This deformation continued north along the western margin of Gondwana forming

the Rockelides Orogeny; rocks of this age, i.e. late Pan-African (550-520 Ma) are exposed present-day in

Sierra Leone (Villeneuve, 2008). Due to this continental-continental collision and closure in the south,

subduction north of the Demerara Rise ceased, this left stranded Neoproterozoic oceanic crust within the

proto-Central Atlantic south of Dakar (GEM, 2020).

Closure of the Rheic Ocean occurred in the Late Paleozoic as Gondwana and Laurussia (North America)

docked to form the supercontinent Pangea (Fig. 1.4C). Across the Gondwana continent, several Paleozoic

cratonic basins filled with sedimentary cover; the Bove Basin in southern Senegal to Guinea, and the

Taoudeni Basin in Mauritania and Mali (Culver & Hunt, 1991; Boudzoumou et al., 2011). It is interpreted that

the thermal sag extended over the stranded Neoproterozoic oceanic crust and overlying Guinea Wedge

based on deep seismic reflection data; thick Paleozoic-Early Mesozoic oceanic sediment accumulated here

(GEM, 2020). Continental collision between Gondwana and Laurussia from End Carboniferous to Late

Permian (Fig. 1.4D) created a series of orogenic belts along the sutured US continental margin, Ouachita,

Appalachian, Alleghenian, Variscan/Hercynian (Pindell, 1985; Poag & Sevon, 1989). On the African margin,

the older Rokelide and Bassaride Pan-African belts are crosscut by the Hercynian Mauritanide fold-thrust

belt (Deynoux, 2006).

Introduction

33

Fig. 1.6 – Central Atlantic rift evolution from Late Triassic (205 Ma) to Middle Jurassic (165 Ma). This model is an output from the Geognostics Earth Model (GEM, 2020). Key to the basement terranes is from Fig. 1.4. DR – Demerara Rise; GP – Guinea Plateau.

Syn-rift – Rifting in this part of Pangea began during the Middle to Upper Triassic until the Lower Jurassic

times (240-190 Ma; Withjack et al., 1985; Olsen, 1980; Labails et al., 2010; Frizon de Lamotte et al., 2015)

followed the grain of pre-existing orogenic belts. The latest stage associated with fissure igneous activity

resulted in the massive outpourings of the Central Atlantic Magmatic Province at ca. 201 Ma (CAMP; Davies

et al., 2017). Triassic rift basins formed along the length of the proto-Central Atlantic, from Morocco (Jebliet-

High Atlas system; Hafid et al., 2000) to Canada (Fundy basin; Withjack et al., 1985), US (Newark basin; Olsen,

1980; Olsen, 1997; Withjack et al., 2013), South America (Takutu Graben; Crawford et al., 1985), and are

interpreted to be in the subsurface in Mauritania and Senegal-The Gambia (Casamance failed rift; Burke,

1976). Syn-rift deposits are characterised by Triassic continental to marine red beds followed by Lower

Chapter 1

34

Jurassic salt in the later stages of rifting (Le Roy & Piqué, 2001). Two salt basins are delineated in the MSGBC

basin defining separate sub-basins; north of Dakar is the Mauritanian salt basin, south of Dakar is the

Casamance salt basin bounded by the Bissau-Kidira-Kayes shear zone (Davison, 2005). An overview of the

rift evolution is provided below (Fig. 1.6):

- A – Late Triassic (205 Ma). Rifting north of Dakar (segment A; Fig. 1.6), linked to the Moroccan-

Canadian rifts, initiated first (240-200 Ma; Olsen, 1980; Olsen, 1997; Withjack et al., 2013), this

resulted later in hyperextension of the continental crust offshore Mauritania and possibly exhumed

mantle (Whittaker, 2018). The final breakup in this segment was asymmetric, leaving a narrower

margin on the American margin. A rift triple junction was located near Dakar, with a narrow rift

segment propagating south (segment B; Fig. 1.6) between south Senegal and Florida/Blake Plateau.

Northeast orientated Triassic rifting also propagated through the Demerara Rise, forming the

Nickerie and Commeqijine grabens, and continuing onshore into the Takutu Graben, Brazil

(Crawford et al., 1985). The rift arm (segment C; Fig. 1.6) that extended west formed sinistral pull-

apart basins in South Georgia, linked to proto-Gulf of Mexico rifting. Movement was accommodated

along a major transfer zone that formed the terrane boundary between Florida and North America,

linked to the Kaolack fault (KAF) onshore Senegal, which itself forms the terrain boundary between

the Mauritanides to the north and remnants of the Rockelides and Bove Basin to the south.

Intrusion of the Freetown Igneous Complex occurred during the Triassic linked to the underlying

CAMP plume head (Briden et al., 1971). At the end of the Triassic, ca. 201 Ma, magmatism from the

arrival of the CAMP plume emplaced mafic dykes and sills in the cratons of all three continents

(McHone, 2000). Coevally the magmatism produced major seaward dipping reflector sequences

(SDRs) and associated magnetic anomalies following the earlier rift structures (ECMA – East Coast

magnetic anomaly; Keller et al., 1954; Austin et al., 1990). This was followed by flood basalts dated

until ca. 190 Ma (Davies et al., 2017).

- B – Early Jurassic (175 Ma). Continental breakup occurred in the northern Central Atlantic first

between Morocco and Nova Scotia (ca. 187 Ma), followed by north Senegal/Mauritania and North

America (segment A; ca. 178 Ma; Müller et al., 2019) and latterly in the southern segment between

Senegal (south of Dakar) and Florida (segment B; Fig. 1.6). Slow spreading rates (0.8 cm/year) during

initial rifting in segment A meant seafloor spreading did not occur until 185-175 Ma (Sapin &

Maurin, 2018). The CAMP plume head migrated northwest intruding volcanics below the proto-

Bahamas Plateau (Nomade et al., 2007). Extension in the Central Atlantic was accommodated by

transtensional movement between Florida and North America.

- C – Middle Jurassic (170 Ma). Around the rift triple junction, a major ridge jump in the oceanic

spreading centre (171 Ma; GEM, 2020) stranded older oceanic crust on the North American margin

Introduction

35

(Klitgord & Schouten, 1986). The rift arm between Florida and North America (segment C; Fig. 1.6)

failed allowing east-west orientated extension to propogate further south along segment B to the

western margin of the Demerara Plateau. Here, excessive magmatism related to the CAMP plume

head significantly thickened the oceanic crust below the Bahamas Plateau. Sapin & Maurin (2019)

reported that oceanic crust in this segment (B) was abnormally thick at 12-14 km, compared to the

6 km thick oceanic crust in segment A (Fig. 1.6). In segment B, i.e. south of Dakar the continental

crust is barely thinned and the transition to oceanic crust is abrupt (Uchupi, 1989).

- D – Middle Jurassic (165 Ma). Final breakup of the Central Atlantic within segment B occurred

between the Demerara Rise/Guinea Plateau and the Bahamas Plateau. The sinistral movement

north and south of Florida accommodated the seafloor spreading in the Central Atlantic. At this

time, a marine connection was established between the Central Atlantic and proto-Caribbean.

North of Florida, segment C, formed a failed rift arm. Gradual opening of segment A, followed by

segment B resulted in diachronous initiation of passive margin formation along the African margin,

younging from north to south. Post break-up spreading rates according to Labails et al. (2010) model

increase gradually through the Jurassic from 2 to 6 cm/year, before sharply decreasing at magnetic

anomaly M22 (ca. 150 Ma).

Post-rift – Early in the post-rift history, ca. 158 Ma according to Reuber et al. (2016) or 173 Ma (Basile et al.,

2020), SDRs have been interpreted below the Demerara Rise related to the Bahamas or Sierra Leone hotspot

respectively and continued Central Atlantic spreading.

Onshore, the western distal part of the MSGBC basin is characterised by higher subsidence rates, this domain

is to the west of a ‘hinge zone’ or ‘rift onset’ that trends north-south separating a more stable domain to

the east (Flicoteaux, 1988). Several basement lineaments, generally trending east-west, can be mapped

linked to fracture zones offshore.

Post-rift sedimentation initiated with the establishment of an extensive, basin-fringing carbonate ramp

around the circumference of the Central Atlantic (Davison, 2005; Eliuk & Prather, 2005). Recent work by

Mourlot (2018) highlights the escarpment-type geometry of the carbonate platform on the African margin,

generally controlling the location of the shelf edge throughout the Meso-Cenozoic. Platform width increases

in the southern segment of Central Atlantic and is at its widest on the Florida margin and in the south-

eastern corner of the Central Atlantic forming the conjugate Demerara Rise and Guinea Plateau (Gouyet,

1988; Davison, 2005; Edge, 2014). The Mesozoic carbonate escarpment follows the continent-ocean

boundary (COB) in Senegal, it is offset north of Dakar and in Mauritania sits more proximally. Continuous

carbonate sedimentation is punctuated by the arrival of siliciclastic systems at the end of the Aptian stage

(MSGBC basin) related to the opening of the Equatorial Atlantic.

Chapter 1

36

Fig. 1.7– Equatorial Atlantic rift evolution from Aptian (124 Ma) to Late Albian (101 Ma). This model is an output from the Geognostics Earth Model (GEM, 2020). Key to the basement terranes is from Fig. 1.4. C.A. – Central Atlantic; CAMP – Central Atlantic Magmatic Province; DR – Demerara Rise; E.A. – Equatorial Atlantic; GP – Guinea Plateau.

During the Aptian (124-114 Ma; Fig. 1.7A), northeast-southwest orientated extension induced rifting of the

Equatorial Atlantic, exploiting weaknesses along basement terrane boundaries. Narrow rift basins formed

between the Demerara Rise and Guinea Plateau, continuing through to the proto-Equatorial Atlantic, i.e.

offshore French Guiana into the Cacipore Graben (Brazil). A change in the orientation of extension induced

by the African plate rotating anticlockwise away from South America (Sibuet and Mascle, 1978) occurred in

Early Albian times (114-108 Ma; Fig. 1.7B). This tectonic stress regime formed deep isolated oceanic dextral

pull-apart basins (i.e. French Guiana), separated by dextral transpressional segments that would later form

the oceanic fracture zones (Pindell, 1985; Greenroyd et al., 2007, 2008a; Basile et al., 2013; Davison et al.,

2016). An intra-oceanic transpressional fold-thrust belt formed north of the Demerara Rise within the

Central Atlantic creating a new plate boundary (GEM, 2020). Throughout the Demerara Rise and Guinea

Plateau, the transpressional tectonics induced deeply-rooted inversion, uplift and shelf margin collapse

(Gouyet, 1988; Olyphant et al., 2017). Volcanism linked to Equatorial Atlantic rifting is locally developed on

both Equatorial margins (Gouyet, 1988; Greenroyd et al., 2008b; Olyphant et al., 2017). The far-field effects

of the Equatorial and South Atlantic rifting caused the landward tilt and uplift of the shelf margin of the

Central Atlantic Mesozoic carbonate platform, south of Dakar, inversion (thurst fault and fold) at the base-

of-slope (Fig. 7B) and ceasing at the basement terrane boundary (KAF). By Late Albian times (108-101 Ma),

the transpressional transform segments ‘release’, margins become divergent and passive, seafloor

spreading extends throughout the Equatorial Atlantic linking with the Central Atlantic to form an apparent

juxtaposition of Jurassic-aged and Cretaceous-aged oceanic crust within the Guyana-Suriname basin and

either side of the Demerara Rise (Fig. 1.7C).

Consequential uplift of the hinterland evidenced by low-temperature geochronology data (Gouiza et al.,

2019) increased denudation providing the first major delivery of siliciclastic sediment to the MSGBC basin

and Central Atlantic continental margin. Albian-aged deltas prograded to the shelf edge (Mourlot et al.,

Introduction

37

2018a). Subsequent Cenomanian transgression and coeval establishment of coastal upwelling of deep

oceanic water masses resulted in the deposition of a thick organic-rich interval throughout oceanic anoxic

event 2 (OAE-2) and the Cenomanian-Turonian boundary event (Arthur et al., 1984). This transgression

created the Florida Straits and Bahama channels (Sheridan et al., 1983). Far-field tectonic stresses, i.e. the

Santonian compressional event (84-80 Ma) associated with Africa-Europe convergence and a change in the

pole of rotation in the opening Central Atlantic, created the regional Senonian unconformity across the

African continental margin (Martin et al., 2010). During the Maastrichtian, the MSGBC was nearly fully

transgressed to the present-day location of the Mauritanides (Mourlot et al., 2018a). The Cretaceous

sequence is commonly capped by an erosive base Tertiary unconformity across the Central Atlantic (Davison,

2005).

Volcanism and uplift of the Cape Verde archipelago, and an associated basement bulge is postulated to co-

occur in the Late Cretaceous through to emergence in the Miocene (Bellion & Crevola, 1991; Patriat &

Labails, 2006; Hansen et al., 2008; Holm et al., 2008). Seamounts related to the Canaries Island are dated

between 142 and 91 Ma (van den Bogaard, 2013), indicating earlier Lower Cretaceous-aged volcanism along

the African margin. Localised volcanic intrusions are scattered throughout the MSGBC basin exploiting pre-

existing basement lineaments, i.e. the Leona Dome near St. Louis (Maastrichtian; Bellion & Crevola, 1991;

Ritz & Bellion, 1994), extensive subsurface Miocene volcanic intrusions (sills and dykes) offshore Senegal,

and similarly timed intra-plate volcanic events leading to the formation of the Cayar seamount and Cap-Vert

peninsula (Hansen et al., 2008). Cap Vert volcanism likely exploited the structural weaknesses at the paleo-

triple junction of the Central Atlantic located near Dakar (Fig. 1.6). This surface exposure has been dated at

ca. 35 Ma (latest Eocene; Bellion & Crevola, 1991; Lo et al., 1992), and is likely part of a much larger volcanic

province extending to east of Thiès, Senegal. The volcanism is thought to be associated with passage of the

African plate above an active mantle hotspot, as Africa collided with Europe (Lo et al., 1992). Holm et al.

(2008) concluded from 40Ar‐39Ar dating of volcanic rocks exposed on the Cape Verde islands that the Rise

was fully established by early Miocene times with associated alkaline volcanism. This volcanism exhumed

Cretaceous basin floor sediments and underlying pillow basalts representing oceanic crust on the island of

Maio. Further volcanism on the eastern chain of islands (Sal, Bao Vista, Maio) occurred through the Miocene

and Pliocene (Holm et al., 2008). Upwelling shallow mantle associated with the Cape Verde volcanism

resulted in downwelling below the continental margin of Mauritania, creating excess subsidence (Lodhia et

al., 2018). A synthesis of the present-day structural configuration is presented in Fig. 1.8.

Chapter 1

38

Fig. 1.8– A structural synthesis of the northwest African Atlantic continental margin from the hinterland (West African Craton) in the east to the Central Atlantic Ocean in the west. To be used alongside Fig. 2A to reference the location of data used in the thesis. CDN – Cap de Naze (Cretaceous outcrop); CFR – Casamance failed rift; CSM – Casamance salt basin; KAF – Kaolack fault; KKI - Kédougou-Kéniba inlier; MFT – Mauritanide front thrust; MSB – Mauritania salt basin. Complied from Bellion and Crevola (1991), Davison (2005) and GEM (2020). The approximate location of the section in Fig. 1.1 is displayed.

1.4 DATASET

During this PhD project, a wealth of data has been accessed and new data generated across the Central

Atlantic, discussed below. All remaining rock samples are stored in the NARG collection at the University of

Manchester.

Introduction

39

1.4.1 Field Campaigns

Senegal – Mesozoic sediments in the MSGBC basin rarely outcrop due to Cenozoic cover. Outcrops are

located in the hinterland on the fringes of the Mauritanides and along the Atlantic coastline of Senegal at

Cap de Naze (Popenguine; Fig. 1.8), Cap de Rouge (Nditarh), and in small quarries at Paki. This is due to

Cenozoic uplift of the Ndiass horst (Tessier et al., 1952). Jonathan Redfern and Luc Bulot guided by Petrosen

(Senegalese National Oil Company) and the Université Cheikh Anta Diop de Dakar (UCAD) visited these

outcrops for reconnaissance in June, 2017. This was followed-up with a field campaign in November-

December 2017 with Max Casson, Luc Bulot and Elsa Bulot to collect samples from Cap de Naze for

biostratigraphy, log the sedimentary architecture and capture a photogrammetry dataset. The datasets

captured were worked up by an MSc student, Andreas Bonilla, supervised over summer 2018, the results

are available in his MSc thesis. In November 2018, I led a field course to these outcrops for partners in the

Sangomar field development, Woodside, Cairn Energy, FAR, Petrosen. Additional fieldwork as part of Ian

Mounteney’s PhD project took place in April 2019, sampling sands from the modern river systems of Senegal

and The Gambia.

Maio, Cape Verde – During one field season in January 2018, Prof. Jonathan Redfern and myself completed

a thorough reconnaissance of the island’s geology, supplemented by an extensive literature review. This

highlighted four key sections to log and sample the full extent of the deep-water Mesozoic stratigraphy

brought to surface during the exhumation of the volcanic islands. With Jason Jeremiah, 152 hand specimens

were collected for subsequent analysis. Due to intensive quarrying activities, the collection of new

macrofossils (ammonites) was challenging. Therefore, to complement the analysis of new material collected

during the field season, a visit to the Palaeontological Museum of the University of Tübingen in December

2018 revealed the paleontological collection of Stahlecker (1935), where all remaining specimens were

documented and photographed with Luc Bulot and Elsa Bulot. These four sedimentary logs and detailed

field mapping, plus integration with a reconstruction of Stahlecker’s log (1935), provided a composite

reference section for Maio. These rock samples are recorded in Chapter 2.

1.4.2 Well Data

International Ocean Drilling Project (IODP) Bremen Core Repository BCR – Cores taken during expeditions

of the Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) within the Central Atlantic are stored

in the MARUM core repository at the University of Bremen, Germany. A wealth of legacy data is hosted here

curated by Holger Kuhlmann. During several visits (August and November, 2017 – Jason Jeremiah; December

2018 – Orrin Bryers) core from seven DSDP/ODP sites were logged and sampled, partially supported by an

European Consortium for Ocean Research Drilling (ECORD) Research Grant awarded in June 2018. These

Chapter 1

40

sampling visits and subsequent requests for infill samples were registered under the following

identifications: 054376IODP, 065859IODP and 077865IODP. Sample tables are provided in Chapter 3.

Senegal Exploration Wells – Through an agreement with Petrosen, samples of drill cuttings and core, as well

as wireline logs and end-of-well reports were provided for the study. Sampling and logging took place in

March 2018 with Jonathan Redfern, collecting samples for biostratigraphy. During an additional visit (April

2019) to the Petrosen office in Dakar, Senegal, Ian Mounteney and myself collected samples of any sands

encountered in these wells for provenance analysis in Ian’s PhD.

Suriname-French Guiana Exploration Wells – Samples of drill cuttings from two exploration wells located

offshore Suriname, Demerara A2-1 and French Guiana, FG2-1 were collected from the CGG storage facility

in Schulenburg, Texas, assisted by Jonathan Redfern during a visit to Houston in September 2018. This data

was provided through an agreement with Shell (NARG sponsor). Tyrone Sigur assisted us with shipping infill

samples following the visit. The Demerara A2-1 is one of the deepest stratigraphic tests to date along the

northeast South American margin, as such is an excellent dataset to extend the stratigraphic framework

across the Central Atlantic. Additionally, drill cutting samples from exploration well GM-ES-3 offshore French

Guiana were shipped in January 2020. All samples are listed in Chapter 5. Peter Osterloff, Shell, provided

wireline data from the three exploration wells to assist with the seismic interpretation.

1.4.3 Seismic Reflection Data

An overview of the seismic reflection datasets available for the PhD is provided in Table 1.1, this is

supplemented in each chapter with the specific configurations of each survey used.

Table 1.1– Summary of seismic reflection datasets available for the study.

Name Location Provider 2D/3D Vintage Time / depth

Total line km / area

km2

Record length

Gambia Blocks A1/A4

The Gambia TGS 3D PSTM

2012 time 2,566 km2

13 secs

GuyanaSPAN Suriname-French Guiana

ION Geophysical

2D PSDM

2013 depth 7970 km 40 km / 25 km

VER01 MWT MSGBC basin Spectrum Geo (now TGS)

2D PSTM

2016-2017

time 1728 km 12.5 secs

Introduction

41

1.5 METHODOLOGY

Various basin analysis techniques outlined in Allen & Allen (2013) have been integrated to understand the

basin evolution and aid paleoenvironmental reconstruction. Primarily this involved revisiting the original

material, wells and outcrop, resampling and reanalysing with updated methodologies and new techniques

previously not applied to these legacy datasets. After an exhaustive literature review including Senegalese

publications in French, the project, and its chapters, typically developed in two overlapping phases beginning

with the analysis of the re-sampled material (outcrop/wells) to build an integrated stratigraphic framework.

Subsequent results were applied to seismic reflection datasets. An overview of these phases is provided

below. During this process, any data captured or generated was added to a personal ArcGIS database,

latterly input into the official NARG Geodatabase.

1.5.1 Stratigraphic Analysis

Through the Mesozoic ammonoids are the primary standard for biochronology with the highest precision

for dating. However, ammonoids are not present and/or preserved in all strata as they are restricted to

specific depositional environments. Recovery is also rare when primarily working with well data

(core/cuttings). Therefore, it is essential to rely on chronometers that are recorded in small quantities (ca.

10 g) of sediment, i.e. microfossils. NARG research in Morocco and across North Africa, where there is

abundant outcrop due to exhumation associated with the Alpine orogeny has focused on establishing

reference sections for the Mesozoic stratigraphy of the Central Atlantic (Luber et al., 2017; 2019; Duval-

Arnold et al., 2020). Typically, these outcrops yield abundant macrofossils, good recovery of microfossils and

carbon isotopes can be measured (δ13C). Thus, key microfossil events can be calibrated against the global

ammonoid scale and chemo-chronological framework to define biozones (Callomon, 1994). A summary of

the biostratigraphic techniques employed in this study are listed in Table 1.2.

Alongside the dating of the sediments, several techniques to further characterise the sedimentology, organic

geochemistry and petrography were used to leverage geological knowledge. Logs recorded in the field and

from core/cuttings recorded the sedimentology, further characterisation of the lithologies was achieved by

analysing thin sections under a light microscope. Additional quantitative data on the lithology was extracted

using x-ray diffraction (XRD) of the whole-rock and clay fraction (Snyder & Bish, 1989). Descriptive

petrographic sandstone classification was performed following the methodology of Garzanti (2016) to

classify the relative percentages of quartz-lithic-feldspar grains (QFL) and determine source provenance. Ian

Mounteney’s PhD will investigate the MSGBC basin sediment provenance in more detail. To quantify the

organic richness of samples, total organic carbon (TOC) was measured. Additional characterisation of the

organic matter, i.e. type and maturity, was conducted using Rock-Eval 6 pyrolysis.

Chapter 1

42

Introduction

43

Table 1.2 – Comparison of biostratigraphic techniques employed and integrated in this study. PD – present day.

Micropaleontology technique

Definition Depositional environment

Type of sediment

Age range Methodology Additional data generated Caveats

Calcareous nannofossils

Nanometre-sized (<0.1 mm) calcareous

nannoplankton i.e. coccoliths

Planktonic (photic zone) – middle shelf to

abyssal

Calcareous mudstones

Triassic to PD

Picking brush method (Jeremiah, 2001) under light

microscope

N/A Limited paleoenvironmental

use

Small size – easily reworked

Foraminifera Mineralised microfossils (0.1

mm – cms)

Planktonic – mid-shelf to lower

bathyal

Benthic – shelf (top 10 cm of

substrate)

Marine Planktonic – Middle

Jurassic to PD

Benthic – Cambrian

to PD

Thin section (limestones) under

light microscope

Benthics – dissolved out using hydrogen peroxide

Excellent paleoenvironmental, palaeobathymetric indicators

N/A

Calpionellids Mineralised microfossils (0.1

mm – cms)

Planktonic – shelf Micritic limestones or

marly limestones

Jurassic to Cretaceous

Thin section under light microscope

Lithological description Restricted to a specific

depositional environment

Palynology Nanometre-sized (<0.1 mm) organic-

walled fossils i.e. dinoflagellates, spores, pollen

Spores/pollen – terrestrial to inner shelf

Dinoflagellates – deltaic/estuarine to upper bathyal

Siliciclastic Paleozoic to PD

Carbonate removed using

hydrochloric acid, washed, stained,

mounted and inspected under light microscope

Excellent paleoenvironmental indicators

Plus, indicative of the environment on land i.e. hot,

dry

Dinoflagellates typically the only fossil in sandstones

Palynofacies

Particularly susceptible to

degradation by oxidising agents

Chapter 1

44

1.5.2 Seismic Interpretation

Seismic imaging of the subsurface provides high-resolution spatial-temporal datasets. Integrated with well

data recorded at a much finer temporal resolution, provides a powerful tool to image the subsurface geology

and perform basin analysis (Cox et al., in press). Several seminal works describe the process of interpreting

seismic reflection data to acquire geological knowledge i.e. Payton (1977), Badley (1985), Avseth (2005) and

Posamentier (2005). These techniques rely on sequence stratigraphic principles defined by Mitchum et al.

(1977); i.e. depositional sequences are stratigraphic units composed of a relatively conformable succession

of genetically related strata bounded by unconformities or their correlative conformities. Different scales of

observations may lead to the assignment of hierarchical orders of depositional sequences and their

bounding surfaces (Catuneanu et al., 2006). First-, second-, and third-order sequences are defined based on

seismic interpretation by Vail et al. (1977) with durations of 200-300 Myr, 10-80 Myr, and 1-10 Myr,

respectively. Sub-third-order sequences and the associated stratal stacking patterns are preserved in rock

data (Catuneanu et al., 2006). Seismic datasets commonly provide knowledge of third-order, maybe fourth-

order systems, documenting basin infill, erosional processes and the interaction of accommodation and

sediment supply.

Schlumberger’s Petrel software was used as the main seismic interpretation package. Cox et al. (in press)

provides an up-to-date review of the seismic interpretation process. Key steps are summarised:

- Data import: Seismic reflection data, 2D and/or 3D, in the time or depth domain is imported into a

project with a suitable co-ordinate reference system. In addition, well data (wireline logs, formation

tops – determined from the stratigraphic analysis) is loaded.

- Seismic-well tie (SWT): If wireline data is available, the SWT bridges the gap between geological

(depth domain) and geophysical (commonly time domain) data. This step provides calibration

between the geological information and different seismic packages, highlighting unconformities

etc. for further investigation.

- Horizon interpretation: Detailed mapping of key reflections, termed ‘horizons’, allows stratal

architecture and facies variations to be understood. Features, such as amplitude, strata

terminations (top lap, down lap, onlap) and geometry are used to describe the seismic stratigraphic

architecture (Payton, 1977). Structure and thickness maps at multiple time intervals can then be

used to understand the spatial-temporal change in depositional and erosional patterns.

- Structural interpretation: Structural features, i.e. faults, intrusions, deformation, are recorded and

integrated with the horizon interpretation to understand the structural controls.

- Seismic attributes: Additional seismic volumes and surface attributes of variance, amplitude, and

coherency etc. can be generated to emphasise structural features and/or depositional system

distribution across a time-equivalent surface.

Introduction

45

Additional advanced techniques are applied and documented in detail in various chapters to extract further

knowledge from the seismic datasets. Depth conversion is used to better constrain the present-day and

palaeo-structure of key surfaces. Spectral decomposition performed in GeoTeric software, of the seismic

data breaks down the seismic signal into frequency bands, colours are assigned to the respective bands and

blended to reveal heterogeneities in the lithology/stratal architecture for better imaging of seismic

geomorphology (Partyka & Gridley, 1999; Posamentier, 2005). Semi-automated seismic interpretation using

PaleoScan™ semi-automates the horizon picking process attempting to pick every possible time-

transgressive horizon to produce ‘horizon stacks’, where it is possible to scroll through depositional surfaces

and extract seismic attributes. Firstly, the model should be constrained by key stratigraphic surfaces

interpreted traditionally to ensure geological accuracy, particular attention is paid to structurally complex

areas i.e. angular unconformities. This methodology is becoming commonplace in seismic geomorphological

studies (i.e. Smit et al., 2017). Data generated from the seismic interpretation process can then be integrated

with GIS software (ArcGIS) to build palaeogeography maps and apply geostatistical and geospatial processing

tools. Structural reconstructions using horizon flattening and sediment decompaction can be carried out in

Petex’s MOVE and/or Petrel to improve understanding of depositional geometries and structural features,

and estimate shortening/extension, by removing sediment overburden. Integrating many techniques from

the micro- to regional-scale provides a comprehensive evaluation of basin evolution.

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52

2 Deep sea rock record exhumed on oceanic

volcanic islands: the Cretaceous sediments of Maio, Cape Verde

Max Casson1, Luc G. Bulot2,1, Jason Jeremiah3, Jonathan Redfern1

1North Africa Research Group, University of Manchester, Oxford Road, M13 9PL

2Aix-Marseille Université, CNRS, IRD, Collège de France, INRA, Cerege, Site Saint-Charles, Case 67, 3, Place

Victor Hugo, 13331, Marseille Cedex 3, France

3Golden Spike Geosolutions Ltd., 20 Ten Acres Crescent, Stevenage, Hertfordshire, SG2 9U

Casson, M., Bulot, L.G., Jeremiah, J. and Redfern, J., 2020. Deep sea rock record exhumed on oceanic volcanic

islands: the Cretaceous sediments of Maio, Cape Verde. Gondwana Research, 81, pp.252-264.

Chapter 2

53

2.1 ABSTRACT

Revising the deep water stratigraphy exposed on Maio offers a key section recording the sedimentary

evolution in the distal domain of the Central Atlantic and the related North West African Atlantic margin

(NWAAM). The oceanic volcanic island is one of nine islands in the Cape Verde archipelago, and is unique to

the Central Atlantic due to the exposures of ophiolites and the overlying Mesozoic deep water sediments

uplifted during the Cenozoic. This provides the opportunity to assess at outcrop, the exhumed sediments,

stratigraphy and paleo-environments of the early Central Atlantic and contribute towards the knowledge of

passive margin evolution along the NWAAM, part of the largest continental remnant of Gondwana.

Combined with the previous recording of calpionellids, the first collection of lower Valanginian ammonites

from the lowest sedimentary succession provides conclusive evidence that Jurassic sediments are not

present on Maio. Bed-by-bed sampling and ensuing micro-palaeontological analysis of these 71 samples,

together with a re-interpretation of Stahlecker’s remaining historical palaeontological collection providing a

comprehensive dataset to build a high-resolution stratigraphic framework for the Mesozoic sediments. This

reveals pelagic deepwater limestones of the Morro Fm. were deposited until the upper Barremian. A major

lithological change from carbonate- to siliciclastic-dominated facies, corresponding to the Morro-Carquiejo

Fm. boundary is recognised as a regional hiatus spanning part of the Aptian identified across the Central

Atlantic. The overlying Albian and younger Carquiejo Fm. is seen as an equivalent to the Albian-Cenomanian

black shales of DSDP Leg 41, yet organic content is absent due to degradation. Future studies can build on

this multi-disciplinary investigation and rely on the revision of the stratigraphy of Maio.

Key words: distal domain; stratigraphy; Central Atlantic; Maio; exhumed oceanic volcanic islands

Cretaceous sediments of Maio

54

2.2 INTRODUCTION

Exhumed sediments on oceanic volcanic islands offer the opportunity to examine at outcrop deep sea

sediments deposited in passive margin basins that are otherwise only penetrated by the drill bit and/or

imaged using seismic reflection techniques. The fortuitous uplift of these sediments surrounding the igneous

complex allow a comprehensive analysis of deep-water stratigraphy; allowing a stratigraphic framework to

be developed for the distal domain and post-rift sedimentology to be fully examined using conventional

fieldwork and ensuing laboratory analysis.

The study of the island of Maio in the Cape Verde archipelago provides an opportunity to assess the paleo-

environmental evolution of the early Central Atlantic and contribute towards the knowledge of the evolution

of the NWAAM. This margin is part of the largest remnant of early Gondwana, the African continent. New

findings are integrated with results from the Deep Sea Drilling Project (DSDP) and comparisons made with

Mesozoic outcrops of Cuba and more generally with the Maiolica facies across the Central Atlantic to

correlate interpretations regionally.

This multi-disciplinary analysis refines the stratigraphic scheme developed by geologists, palaeontologists

and stratigraphers since the early 20th century (see Fourcade et al., 1990 with references). We also

document the first collection of ammonites from the lowest part of the sedimentary succession, with bed-

by-bed sampling and high-resolution micro-palaeontological analysis, combined with a re-interpretation of

the remainder of the palaeontological collection of Stahlecker (1935). This provides a comprehensive

dataset that allows definition of a high-resolution stratigraphic framework to address uncertainties

surrounding the dating of the Mesozoic stratigraphy of Maio.

Chapter 2

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2.3 REGIONAL SETTING AND STRATIGRAPHY

Fig. 2.1 (A) – Location map of the Cape Verde archipelago with magnetic anomalies (M0 ~125 Ma, Barremian-Aptian boundary; M10 ~130 Ma; M16 ~145 Ma; M21 ~148 Ma; M25 ~154 Ma; Seton et al., 2014), DSDP boreholes and location of Fig. 2.2 displayed. Bathymetric contours every 1000 m. (B) Geological map of Maio after Stillman et al. (1982), with the locations of four studied sections presented in this paper. (C) Schematic cross-section of Maio, location displayed on (B), adapted after Robertson et al. (1984).


56

The Cape Verde archipelago is located in the Atlantic Ocean, ca. 500 km west of Dakar, Senegal and ca. 2000

km east of the present-day Mid-Atlantic Ridge (Fig. 2.1A). It encompasses 9 major active and inactive volcanic

islands. The island of Maio is part of the eastern N-S orientated chain, interpreted to be older (10-20 Ma)

than the western chain (<8 Ma; Holm et al., 2008). The islands rise 2-4 km above the surrounding seafloor

(Hayes & Rabinowitz, 1975), where magnetic anomalies have been identified suggesting mid-plate

emplacement on oceanic lithosphere between M11 (~136 Ma) and M16 (~145 Ma; Fig. 2.1A; Gradstein et

al., 2012). The archipelago formed in the southwestern corner of the Cape Verde Rise, one of the largest

bathymetric swells in the world, elevated ca. 2.2 km above the expected depth of the seafloor (Pim et al.,

2008). It is generally accepted that the islands and swell formed above a deep mantle plume with associated

hot spot activity (Crough, 1978; Lodhia et al., 2018; Carvalho et al., 2019) and postulated dynamic uplift (Pim

et al., 2008). Flexure of the surrounding plate by Early Miocene volcanic loading created a concentric flexural

moat with 2 km of stratigraphic infill (Ali et al., 2003).

Fig. 2.2 – Schematic cross-section through the NW African Atlantic passive margin highlighting the main stratigraphic packages and architecture of the basin. Approximate locations of DSDP 367 and magnetic anomalies (Seton et al., 2014) shown. Location of section detailed in Fig. 2.1A.

Maio is unique among the Cape Verde archipelago as it hosts a complete sedimentary sequence resting on

ocean floor extending to the volcaniclastic sediments that record emergence of the oceanic island (Fig. 2.1;

Fig. 2.2). These outcrops offer the only opportunity to study exposed deepwater Cretaceous successions at

outcrop in the Mauritania-Senegal-Guinea Bissau-Conarky (MSGBC) Basin. The stratigraphy was summarised

by Fourcade et al. (1990) and the chronostratigraphic events from previous workers are presented in Fig.

2.3. Exposed at the core of Maio is the Central Igneous Complex (CIC), an unroofed alkaline plutonic body

intensely intruded by swarms of sills and dikes with mafic to intermediate composition (Serralheiro, 1968).

The Mesozoic stratigraphy is exposed in a ring of outcrops, radially dipping away from the CIC (Fig. 2.1B),

consisting of 4 formations: the Batalha Formation – normal-type mid-ocean ridge tholeiitic pillow basalts

(de Paepe et al., 1974); the Morro Formation – homogeneous thick bedded fossiliferous pelagic limestones

becoming thin bedded with interbedded marls upwards (informally termed the ‘upper transitional unit’ by

Robertson, 1984), with a basal ferruginous facies; the Carquiejo Formation – heterogeneous unit of shales,

siltstones and limestones; and the Coruja Formation – tuffs, sandstones and conglomerates (Stillman et al.,

Chapter 2

57

1982; Robertson, 1984). The Mesozoic stratigraphy is unconformably overlain by Tertiary and Quaternary

formations associated with Maio’s emergence.

Fig. 2.3 – Chronostratigraphic summary chart for the geological evolution of Maio. Inset – references. Kindly provided by Steve Lawrence (pers. comms. 2018).

2.4 METHODS

A multi-disciplinary approach has been adopted to the analysis of Maio sediments to build on existing studies

and utilise previously captured data. New ammonoid findings and key calcareous nannofossil species are

fully illustrated for future reference.

2.4.1 Sedimentology

Detailed sedimentary logging was performed during one field season and samples collected for subsequent

petrographical investigation. Five black shale samples were selected for organic geochemical analysis using


58

a Shimadzu TOC-V CPN and Solid Sample Module (SSM), calibrated to sodium carbonate and glucose to

measure inorganic and total carbon respectively. None of the samples yielded any organic carbon content.

2.4.2 Biostratigraphy

Calcareous nannofossil biostratigraphy

71 samples from Maio were analysed with standard techniques described by Bown (1998), and the picking

brush method of Jeremiah (1996). Samples were analysed semi-quantitatively, with the first 30 fields of view

counted and the remaining slide scanned for rare specimens. Sampling focused on the upper transitional

unit and overlying Carquiejo Fm. where marls were abundant, however recovery was generally poor. Key

specimens from the section are illustrated with the associated log.

Macro-fossil biostratigraphy

Due to intensive quarrying activities, the collection of new macro-fossils was challenging. However, a new

assemblage of limonitic ammonites was made at Monte Esgrovere (Fig. 2.1B), belemnite specimens

recovered from Monte Carquiejo (Fig. 2.1B) and Aptychi discovered throughout the sections. To

complement the analysis of new material, the authors accessed the macro-fossil collection of Stahlecker

hosted in the Palaeontological Museum of the University of Tübingen, where all remaining specimens were

documented and photographed.

Foraminiferal biostratigraphy

10 samples were chosen with relatively abundant calcareous nannofossil content and prepared using the

standard methodology described by Armstrong and Brasier (2005). All samples except one, RC-6, yielded no

visible microfossils, likely due to the altered nature of the lithology.

Calpionellid biostratigraphy

Following the report of calpionellids by Fourcade et al. (1990), four samples from Monte Esgrovere were cut

for thin sections in two planes. Unfortunately, there were no notable calpionellid occurrences.

2.5 RESULTS

Five sections were selected for detailed bed-by-bed logging and sampling after thorough reconnaissance

following the geological map of Stillman et al. (1982). Since the earlier work of Stahlecker (1935) and

Serralheiro (1975; see their Fig. 4) the nature of the outcrops have been affected by local quarrying.

Unpublished field photographs in the collection of Stahlecker Tubingen Museum, and photographs

Chapter 2

59

published by Serralheiro (1975) show abundant surface exposure at Ribeira do Morro, but most of this has

now been removed and quarried (see supplementary data Fig. S 2.1). Although more complex, access to the

sections is still possible.

Data was attained from both flanks of the island to provide spatial coverage, with a maximum distance

between sections of ca. 10 km East-West. The definition of the Morro-Carquiejo Fm. boundary by Stillman

et al. (1982) was recognised and followed; this contact is commonly intruded by younger intrusives

exploiting the rheological weakness between the different lithologies. On the eastern flank, the authors are

in agreement with Stillman et al. (1982) that the stratigraphy has been thrusted.

Fig. 2.4 (next page) – Detailed sedimentary log with the majority of igneous intrusions removed from Ribeira do Morro, see location in Fig. 2.1B. Samples taken for the calcareous nannofossil biostratigraphy are annotated, five specimens are illustrated: (A) A. youngii, (B) N. steinmannii, (C) C. rothii, (D) E. turriseiffelli, (E) Z. scutula, and the distribution charts are provided in the supplementary data (Table S 2.1). Inset – a sketch geological map highlighting where the section was logged along in the river bank exposures and in subsurface quarries, the lack of surface exposure due to quarrying activities (see supplementary data Fig. S 2.1) and structural data recorded in the field.


60

Chapter 2

61

2.5.1 Ribeira do Morro Section (Sample prefix: RDM)

The most complete succession, previously documented, is now a more complex exposure of isolated small

quarries and small outcrops along the ephemeral Morro River (Fig. 2.4). It was possible to log the exposures

in the river bank as shown in Fig. 2.4 (map inset) and construct a composite log. This can be correlated with

the graphical reconstruction of Stahlecker’s log of the full Ribeira do Morro sequence, shown in Fig. 2.5, with

the palaeontological horizons annotated. The stratigraphic location of our composite log (Fig. 2.4) is

displayed on the complete log (Fig. 2.5). These were well documented and the specimens in the Tübingen

collection viewed and re-described as part of this study.

Lithofacies

Batalha Formation

Basaltic Pillow Lava – The base of the section exposes coarse-fine grained, dark green-grey basaltic pillows

with a maximum diameter of 60 cm, surrounded by thermally altered meta-sediments. These crop out in

isolated exposures at the head of the Morro River, 2.2 km ENE of Morro village. Traversing west (Lat.:

15.18357°, Long: -23.20195°), the Mesozoic sequence can be followed downstream. Faulting is inferred

from deformation of bedding and dips, and intrusions are common. The contact between the Batalha and

Morro Fm. is placed in a heavily deformed zone with fault breccias and dikes.

Morro Formation

Massive to bedded limestone facies – The lowermost Morro Fm., above this ill-defined contact, is composed

of dark grey-black, thickly-bedded (av. 30 cm) to massive cyclical limestone with common stylolites and

calcite veining. The limestones contain vitreous black chert horizons and nodules and show minor parallel

laminations. Partings are undulating and marls absent. Sample RDM-12 is a typical Morro Fm. limestone,

which in thin section records a micritic matrix with a wackestone texture, also containing recrystallized

radiolarian and pyrite (see supplementary data Fig. S 2.2). A stratigraphic gap of estimated 100 m thickness

exists between this exposure in the stream bed and the first subsurface quarry, this interval is also cut by

small faults, which can be observed offsetting the stratigraphy between exposures, and folded in places (see

supplementary data Fig. S 2.3A). Within the first quarry, the almost vertical Morro limestones revealed

common apytchi on certain bedding planes. Chert content decreases and the limestone is generally a lighter

grey colour and up-section the beds become thinner. Sample RDM-30 contains abundant pyrite within the

nodular texture of the micritic limestone. The limestones have undergone the early stages of the pressure-

solution processes, with stylolites beginning to form (see supplementary data Fig. S 2.32).

Slow accumulation of the massive to bedded limestone facies occurred in a deep-water setting by pelagic

deposition, above the calcite compensation depth (CCD). The repetitive nature of the beds with consistent


62

lateral continuity indicates steady cyclical sedimentation across the sea floor with minor current activity

producing undulating partings (Stillman et al., 1982). Our analysis of thin sections has failed to find any quartz

within this facies; this is in agreement with Robertson’s (1984) interpretation that this part of the basin was

isolated from terrigenous sediment during deposition of this facies.

Upper Transitional Unit

Flaggy limestone facies – Exposure of flaggy limestone beds are observed in the river bank upstream and

downstream of a small dam (Lat.: 15.18429°, Long: -23.20429°). The flaggy limestone beds are generally

thinner bedded (av. 10 cm), increasingly laminated and less silicified. Interbedded bituminous, fissile,

calcareous mudstones were sampled for nannofossil content (RDM-36 to 67, Fig. 2.4). An ichnofacies is

recorded in these sediments at the MC section. Horizons of mm-scale iron concretions occur in the flaggy

limestones. A fairly large number of aptychi, fish remains and ammonites were collected from this part of

the succession, some of which were published by Stahlecker (1935) and revised below.

The contrasting facies of the upper transitional unit to the main Morro Fm. was deposited by distal turbidites

and the thinner bedded nature of the flaggy limestones indicates less continuous pelagic sedimentation

between events. The increasing clay content suggests terrigenous material reached the deep basin. These

depositional conditions favoured the preservation of calcareous nannofossils, trace fossils and ammonites.

Carquiejo Formation

Non-calcareous silicified mudstone facies – The change from calcareous to non-calcareous dominated

sedimentation and the absence of competent limestone beds is taken as the Morro-Carquiejo Fm. boundary.

A regional 70 cm-thick sill is observed at the lithological contact on either flank of Maio that obstructs direct

observation of the sedimentary boundary with the overlying unit of non-calcareous, green-orange

weathered, silicified mudstone of the Carquiejo Fm. This 4-5 m thick mudstone unit is commonly heavily

fractured and has no internal structure, bar a singular 30 cm-thick limestone bed. RDM-68 records a non-

calcareous mudstone of the Carquiejo Fm, with no visible lamination and minor organic matter (see

supplementary data Fig. S 2.2).

Above this unit, the Carquiejo Fm. is typically heterogeneous, composed of thin-bedded shales, siltstones

and laminated limestones. Exposure is absent below a fence crossing the river (Lat.: 15.18430°, Long: -

23.20428°), where the stratigraphy is folded and heavily eroded.

The non-calcareous mudstones are interpreted as being deposited below the CCD with a marked increase

in terrigenous input from the NWAAM. Presence of wood material (see Section 2.5.3) in these deposits

supports this interpretation. During diagenesis, reducing conditions prevailed as the facies has a ferruginous

Chapter 2

63

staining. The overlying heterogeneous unit was deposited by turbidity currents relatively rapidly in

comparison to the pelagic Morro Fm.

Ammonite Biostratigraphy

The following biostratigraphic interpretation is based on the re-examination of the material collected and

published by Stahlecker (1935). The ammonite collection made by Stahlecker (1935) originates from the

upper part of the Morro Fm. (levels I to V) and the Upper Transition Unit (levels VII to XIV) (Fig. 2.5). The

uppermost part of the Morro Fm. is marked by a barren interval.

Fig. 2.5 – Reconstructed sedimentary log of the complete Ribeira do Morro section after Stahlecker (1935) with macrofossil horizons (I – XIV) displayed. The approximate stratigraphic location of Fig. 2.4 is shown. A selection of the key ammonites are illustrated: (A) VII – Leptohamulina cf. distans (= Leptoceras aff. sabaudianum in Stahlecker, 1935); (B) VII – Lytocrioceras sp. (= Ancyloceras sp. in Stahlecker, 1935); (C) VII – Mascarellina gr. hamus (= Hamulina cf. hamus in Stahlecker, 1935); (D-E) VII – Eoheteroceras multicostatum (= Heteroceras giraudi in Stahlecker, 1935); (F) VII – Eoheteroceras multicostatum (= Heteroceras aff. heterocostatum in Stahlecker, 1935); (G) VIII – Pulchellia sp. (= Pulchellia rhombocostata in Stahlecker, 1935); (H, I) X – Toxancyloceras gr. vandenheckii (= Ancyloceras matheronianum in Stahlecker,


64

1935); (J) XI – Heinzia sp. (= Douvilleiceras irregulare in Stahlecker, 1935); (K) XII – Heinzia sp. (= Pulchellia hoplitiformis in Stahlecker, 1935). Location detailed in Fig. 2.1B and key in Fig. 2.4. Note the change in scale, each bar represents 10m. All ammonites are natural size except Fig. J. (x2).

Stahlecker’s original material is preserved in the Palaeontological collections of the University of Tubingen

(Germany) but most of the specimens that were re-examined in the late 1980’s by the late Robert Busnardo

(Fourcade et al., 1990) from the Morro Fm. are missing.

Based on Busnardo’s interpretation of the fauna, Fourcade et al. (1990) assigned a late Hauterivian age to

this interval. Even so we could not access the material, we support this view since level I to V are

characterized by the occurrence of fairly abundant Didayilamellaptychus of the angulicostatus group,

including the type specimen of Didayilamellaptychus atlanticus (Hennig, 1914). It is clearly established that

these taxa characterise the Upper Hauterivian (Měchová et al., 2010; Vašíček et al., 2016). We also agree

with Fourcade et al. (1990) that the ammonoids from the topmost Morro Fm. (level VI) are not diagnostic.

The overlying level VII is marked by a fairly diverse fauna dominated by heteromorphic ammonoids. The

overall preservation as crushed impressions, is fairly poor, but was thought sufficiently distinctive by

Stahlecker to allow the introduction of new taxa such as Heteroceras multicostatum, Toxoceras filicostatum,

Ancyloceras maioense and Bochianites hennigi.

According to Busnardo in Fourcade et al. (1990), these forms should be re-interpreted as an assemblage of

Sabaudiella (= Eoleptoceras in Fourcade et al., 1990), Acrioceras and Hamulina of late Hauterivian age. In

our opinion this view is to be reconsidered in the light of the extensive recent literature on the upper

Hauterivian and lower Barremian heteromorphic ammonoids (see references in Klein et al., 2007;

Vermeulen, 2010a; Vermeulen et al., 2014; Leroy et al., 2016). The most significant taxa are illustrated on

Fig. 2.5A-F.

In our views, the genus Lytocrioceras as interpreted by Delanoy and Poupon (1992) and Ebbo et al. (1999) is

represented by open spires (such as T. filicostatum) and large proversum fragments (Fig. 5B and A.

maioense). Heteroceras multicostatum has been variously interpreted in the literature (see comments in

Vašíček and Wiedmann, 1994; Vašíček & Klajmon, 1998). In our opinion, it should rather be included in

Eoheteroceras and it is closely allied to E. norteyi (Myczyński and Triff).

The fauna also includes a number of small sized Anahamulinidae that show two distinct morphologies. The

smaller forms (Fig. 2.5C) are close to Mascarellina hamus (Quendstedt). The highly divergent shaft and

proversum of the larger forms (Fig. 2.5A & F) recalls Leptohamulina distans (Vašíček), and to a lesser extent,

Vasicekina autinae (Vermeulen). Due to the state of preservation of the Maio specimens, full identity cannot

be established, but the overall morphology is that of Leptohamulina. It should be noted that a fairly similar

specimen was illustrated by Myczyński and Triff (1986, pl. 3, Fig. 10), and as a whole the assemblage from

Chapter 2

65

level VII is very similar to the fauna from the Polier Fm. of Cuba. Based on the known occurrence of

Lytocrioceras in France and Eoheteroceras in Cuba, we retain an early Barremian age for this assemblage.

The occurrence of Lytocrioceras strongly suggests that the association cannot be any older than the K.

nicklesi ammonite Zone.

The occurrence of Pulchelliidae from level VIII to level XIV is of major biostratigraphic significance. Three

representative specimens are illustrated herein (Fig. 2.5G, J and K). Identification at the species level is

handicapped by the preservation of the material but we are confident that the ornamental features are

those of the late early (level VIII) to early late Barremian (level X to XIV) forms of the genera Pulchellia (Fig.

2.5G) and Heinzia (Fig. 2.5J-K) (Vermeulen, 2003; Patarroyo, 2004). The base of the upper Barremian is

placed at level X based on the occurrence of Toxancyloceras of the vandenheckii group (Fig. 2.5H-I) (Delanoy,

2003; Bert et al., 2018).

Calcareous Nannofossil Biostratigraphy

The basal intercalated mudstones from the Morro Fm. sampled between RDM-27 and RDM-38 are

extremely poor, no age assigned (Fig. 2.4; Table S 2.1). Nannofossil recovery improves from RDM-40 upwards

within the upper part of the Morro Fm. A poorly preserved, moderate diversity assemblage yields

Zeugrhabdotus scutula, Assipetra terebrodentarius youngii and Nannoconus steinmannii. This association is

indicative of a latest Barremian through earliest Aptian age. Above sample RDM-51, nannoconid abundance

drops significantly with N. steinmannii only sporadically identified (RDM-63 & RDM-66). Conusphaera rothii

is not recorded from this section, this probably more of a preservational response than a true stratigraphic

event.

The Carquiejo Fm yields a low diversity assemblage characterised by the continued occurrence of A.

terebrodentarius youngii and the appearance at RDM-70 of Eprolithus floralis (Fig. 2.4; Table S 2.1). The

presence of these two markers indicate a lower Aptian to earliest Albian age range. Preservational bias

affects the actual top/base of nannofossil events, rather than true FO/LO.

Fig. 2.6 (next page) – Detailed sedimentary log of the Monte Esgrovere section with photographs of the new collection of ammonites: (A) Neolissoceras (Vergoligeras) sp. juv. gr. salinarium; (B) Bochianites sp.; (C) “Busnardoites” sp.; (D) Kilianella sp. All ammonites are natural size except Fig. A and C (x2). Location detailed in Fig. 2.1B and key in Fig. 2.4.


66

Chapter 2

67

2.5.2 Monte Esgrovere Section (Sample prefix: ESG)

Patchy exposure across the Monte Esgrovere hillside can be correlated to produce a detailed log (Fig. 2.6),

with the inferred igneous units in Fig. 2.4. At the location defined by Fourcade et al. (1990) there was no

present-day surface exposure, with evidence of quarrying, hence a section was selected 1 km to the ESE

(Lat.: 15.16296°, Long: -23.18191°). This is the only location on the island preserving a complete section

from Batalha Fm. lavas, through the basal ferruginous facies to the main pelagic limestones of the Morro

Fm.

Lithofacies

Batalha Formation

Silicified limestone facies – The inter-lava sediments within the Batalha Fm. comprise red-purple silicified

limestones and chert previously described by Fourcade et al. (1990). These are observed in two outcrops

separated 5 m apart along strike, have a thickness of ca. 1 m, interbedded with inferred pillow lavas (ESG-0,

see supplementary data Fig. S 2.2). The sediments show undulated bedding. Sample ESG-0 is a red

ferruginous mudstone with a banded fabric (see supplementary data Fig. S 2.2). The micritic matrix contains

quartzose silt and calcified radiolarian, with a dark black band of opaque hematite. Above this, isolated

exposure of the interlava sediments is ca. 20 m of poorly exposed pillow lavas. The contact between the

Batalha and Morro Fm. is not directly observable, but is inferred as the break in slope before the more

competent Morro Fm. limestone crops out.

Stillman et al. (1982) assumes that the variolitic texture of the pillow lava indicates eruption of the mid-

ocean ridge basalts between 1000-1500 m water-depth. In the latter episodic stages of pillow lava

formation, silicified limestones accumulated above the CCD and were reworked by current activity during

periods of volcanic quiescence.

Morro Formation

Ferruginous limestone facies – At this location, the basal limestone has weathered to a bright orange colour

due to ferruginous enrichment (Stillman et al., 1982), gradually fading to the typical grey of the Morro Fm.

The limestone is thickly bedded, occasionally with finely laminated, mm-scale, horizons of iron concretions,

containing a diverse macro-fossil assemblage. Thin sections of two samples from this interval show different

characteristics. Sample ESG-12 has a mudstone texture containing thin-shelled bivalve fragments and

recrystallised radiolaria (see supplementary data Fig. S 2.2). This microfacies shows a nodular pseudo-

laminated fabric with abundant dark, wavy seams of organic material. Sample ESG-16 has a similar

microfacies (top and base; see supplementary data Fig. S 2.2) punctuated by a normally-graded bed, where

the boundary appears stylolitized. Micro-faulted calcite veins cross-cut the sample. A thin intraformational


68

conglomerate is present within the basal facies containing rounded clasts of altered volcanic glass and pellets

of chlorite in a ferruginous micritic matrix (Robertson, 1984). The transition to typical Morro Fm. limestones

is gradual observed along the exposure as it continues across the hill, where surface mining is currently

active.

The pelagic limestones formed in a hydrothermal field active during and sometime after the latter stages of

volcanism, causing metalliferous enrichment that gradually waned (Stillman et al. 1982). Robertson (1984)

highlights the geochemical similarities between this Fe-enriched and Al-depleted facies and oceanic pelagic

sequences in the Pacific seamount chains, but suggests deposition occurred in a topographic low evidenced

by laminated sedimentation.

Biostratigraphy

The newly collected material from the base of Morro Fm. is preserved as limonitic internal moulds of

juveniles. It includes Vergoliceras of the salinarium group (Fig. 2.6A), Bochianites sp. (Fig. 2.6B), Kilianella sp.

(Fig. 2.6D), olcostephanids, and a poorly preserved neocomitid that is tentatively assigned to “Busnardoites”

sp. (Fig. 2.6C). Co-occurrence of Vergoliceras and Kilianella leaves no doubt about the middle early

Valanginian age of the assemblage (Neocomites neocomiensiformis Zone, see Company and Tavera, 2015

with references).

Re-evaluation of the calpionellid illustrated by Fourcade et al. (1990) by Daniela Reháková (pers. comms.

2019) suggests that the Calpionellites species identified by those authors rather marks the upper part of the

Calpionellites Zone, e.g. the Major Subzone. This subzone indicates the middle to late Lower Valanginian

(Petrova et al., 2011), supporting the age assignment from the ammonite biostratigraphy.

Chapter 2

69

2.5.3 Monte Carquiejo and River Cut Sections (Sample prefix: MC & RC)

Fig. 2.7 – Detailed sedimentary log of the Monte Carquiejo and River Cut section, separated by approximately 120 m. Samples taken for the calcareous nannofossil biostratigraphy are annotated and the distribution charts are provided in the supplementary data (Table S 2.1). One belemnite was identified and studied; the location in the stratigraphy is shown supporting the age interpretation from the calcareous nannofossils. Location detailed in Fig. 2.1B and key in Fig. 2.4.

Lithofacies

Located northwest of Monte Carquiejo (Lat.: 15.20829°, Long: -23.12218°), the Morro and Carquiejo Fm.

boundary is well exposed for ca. 10 m in a small stream valley (MC; Fig. 2.7). The upper transitional unit and

Carquiejo Fm. has many similarities to the Ribeira do Morro section (RDM).


70

The upper transitional unit is composed of cyclic bedded small packages (av. 20 cm thick total) of bituminous

dark grey calcareous mudstones, interbedded with very thin (<5 mm) beds of limestone. Limestone content

increases upward, cumulating in a massive flaggy limestone (av. 10 cm thick). These thin-bedded limestones

contain numerous horizons of mm-scale iron concretions, some of which are lenticular in shape. A

belemnite-rich horizon is recorded within this unit that can be correlated around the flank of Monte

Carquiejo. At this location a sill is also intruded at the contact between the formations. The stratigraphy

appears conformable, with no apparent change in the dip of the bedding (see supplementary data Fig. S

2.3B). The overlying Carquiejo Fm. is again heterogeneous; comprising lowermost beds of non-calcareous

weathered-orange blocky mudstone up to 1.5 m in thickness. A small package of thin-bedded limestone sits

above this, where a 20 cm long piece of wood debris was observed (see supplementary data Fig. S 2.3C).

Exposed across the NE slopes of Monte Branco and Monte Carquiejo, along strike from the Monte Carquiejo

section (MC) and down dip within the main Morro Fm., a distinct 30 cm-thick bed of pale orange to tan

limestone has a moderately preserved assemblage of trace fossils on the dolomitized base of the bed (see

supplementary data Fig. S 2.3D-E). Narrow 1-3 mm in diameter, non-branching, structureless Planolites

burrows are relatively abundant. Larger >10 mm in diameter, Y-branched Thalassinoides burrows are

postulated. At the Monte Carquiejo section (MC), in bed MC-7 within the upper transitional unit, narrow <1

mm in diameter, Y-shaped branching Chrondrites burrows weather a dark orange colour in comparison to

the grey limestone sediment (see supplementary data Fig. S 2.3F). Collectively, these trace fossils likely

represent the Nereites ichnofacies and consequently, is the first ichnofacies description from Maio providing

evidence of a deep offshore marine palaeo-environment (after Gerard & Bromley, 2008).

Approximately 120 m east (Lat.: 15.18457°, Long: -23.20481°), the Carquiejo Fm. crops out in the eroded

river bank (RC), this is the youngest stratigraphy analysed in the paper (Fig. 2.7). The section ca. 5 m thick is

heterogeneous composed of thin-bedded limestones, non-calcareous and calcareous mudstones. Above

this, a band of white stained debris appears in the river bank, which is thought to represent heavily eroded

bleached black shales.

Biostratigraphy

Sixteen samples from the marls of the upper transitional unit of the Morro Fm. were investigated. All yielded

low diversity assemblages characterised by Assipetra terebrodentarius and A. terebrodentarius youngii, its

presence indicating an age no older than latest Barremian (Fig. 2.7; Table S 2.1). Nannoconus spp. are rare

throughout the section and not recorded above MC-12. Nannoconus steinmannii is restricted to the bottom

sample analysed, MC-5. Isolated occurrences of Zeugrhabdotus scutula are recorded from samples MC-12

and MC-17 and indicate an age no younger than earliest Aptian. Conusphaera rothii was not recorded from

the Monte Carquiejo samples analysed, this considered more a reflection of poor recovery than absolute

stratigraphic ranges.

Chapter 2

71

The belemnites recovered from the upper transitional unit are juvenile forms most probably Mesohibolites,

although not identifiable at the species level (Fig. 2.7). This genus has an age range from the late Barremian

to earliest Aptian and is supportive of the MC nannofossil datings.

The youngest Cretaceous succession with nannofossil recovery was investigated at the Monte Carquiejo

River Cut (RC). Nine samples were analysed, two samples barren of nannofossils (RC-11 & RC-14), the

remainder yielding a poorly preserved, moderate diversity assemblage (Fig. 2.7; Table S 2.1). The presence

of Eiffelithus turriseiffelii in the absence of Gartnerago nanum / G. theta, Acaenolithus cenomanicus and the

Broinsonia signata / B. enormis plexus indicates a stratigraphic level within the upper part of the late Albian.

Additional support for this age assignment is provided by the presence of Hayesites albiensis in the basal

sample RC-5 and occurrence of Watznaueria britannica (samples RC-7 & RC-10), both species having

documented LAD’s close the top Albian.

Sample RC-6 produced very abundant planktonic foram chambers observed semi-buried in lithic fragments.

Despite lithic material remaining attached to the specimens, Globigerinelloides and Hedbergella are

identified, although unidentifiable at a species level are consistent with the late Albian age assigned. There

is one specimen resembling G. bentonensis which is not older than mid-late Albian. The abundance of the

planktonics (which is high) suggests strong, open ocean, well oxygenated marine conditions within the upper

water column.


72

2.6 DISCUSSION

Fig. 2.8 – Composite stratigraphic summary log of the Cretaceous succession of Maio integrating all new data from various sections documented (Fig. 2.4; Fig. 2.5; Fig. 2.6; Fig. 2.7), with the calpionellid dating of the Batalha Fm. by Fourcade et al. (1990). UTU – upper transitional unit of the Morro Formation; Dating of sections based on: N. – nannofossils; Am. – ammonites; Ap. – aptychi; C. – calpionellids.

Chapter 2

73

2.6.1 Stratigraphy

Despite previous efforts the stratigraphy of Maio has remained poorly dated and significant uncertainties

have persisted throughout publications. Our comprehensive analysis of new fieldwork data complementing

an exhaustive re-interpretation of existing data has contributed towards resolving these issues and

improving the stratigraphic resolution (Fig. 2.8). The unpublished geological report of Rigassi (1972)

underpins the dating of the sedimentary sequence of Maio and was studied as part of our analysis. The ages

assigned to the stratigraphy are not supported by any macro-/micro-fossil plates or sedimentary logs leaving

little scientific value for use in this paper. One of the uncertainties regards the Tithonian age reported in the

literature for the lowermost stratigraphy exposed on the East flank of Maio. Our study joins Robertson and

Bernoulli (1982), Stillman et al. (1982), Robertson (1984) and Fourcade et al. (1990) in recognising the

absence of any Jurassic paleontological evidence to support this interpretation. The new ammonite

assemblage documented at ESG, complementing the calpionellid dating of Fourcade et al. (1990) validates

that the interlava sediments of the Batalha Fm. and overlying basal facies of the Morro Fm. are Lower

Valanginian in age, part of the Neocomites neocomiensiformis Zone. This is in agreement with the positions

of magnetic anomalies M11 and M16 relative to Maio (Fig. 2.1A).

Age definition for the upper transitional unit of the Morro Fm. is now robust; independent palaeontological

analyses of sections on each flank of the island provide strong evidence of a late Barremian age, even so an

early Aptian age cannot be excluded for the top of formation. Our new dating of the Carquiejo Fm. supports

the Albian age interpretation of Fourcade et al. (1990), and as a consequence, the recognition of a hiatus or

discontinuity spanning part of the Aptian and separating the contrasting lithologies of the Morro and

Carquiejo Formations (Stillman et al. 1982). Our youngest age attributed to the Carquiejo Fm. from the RC

section is of Late Albian age. This is not representative of the true youngest age for the formation as

stratigraphy exposed higher up in this formation yielded no age data, and in addition, the overlying

unconformity may have eroded section. Therefore, we are unable to determine the youngest age for the

Carquiejo Fm. and hence, the possible oldest most age for the volcanism on Maio due to the volcanic origin

of the overlying Coruja Fm.

2.6.2 Regional Correlation

By correlating the results from Maio to additional data available in the Central Atlantic (DSDP results,

outcrops in Cuba and more generally to the Maiolica facies of the Western Tethys) allows the Maio

sediments to be considered within a regional context. DSDP Site 367 is the nearest penetration (ca. 450 km

SE, Fig. 2.1B) of the Cretaceous stratigraphy (Lancelot et al. 1976). A comparison of stratigraphic thickness

is not directly proposed due to the imprecision of measurements on Maio. However, Ali et al. (2003)

highlight from seismic reflection data that this package thickens from west to east in response to sediment


74

loading and flexure at the West African continental margin. As such a thinning from Site 367 (ca. 225 m) to

Maio is postulated, but may not be representative as DSDP Site 367 was drilled on a structural high (Lancelot

et al. 1976). As discussed by Robertson (1984), red-brown argillaceous limestone facies encountered at Site

367 (Unit 6; “Rosso Ammonitico” sensu Farinacci & Elmi, 1981) below the white nannofossil limestones (Unit

5) were not recognised on Maio (Lancelot et al. 1976). In light of the biostratigraphic results for the

lowermost stratigraphy indicating a Lower Valanginian age (see Section 2.5.2) we would not expect to

encounter these Jurassic sediments on the island.

The pelagic deep water limestones with chert of the Morro Fm. resemble lithologically, paleontologically

and stratigraphically the Maiolica facies of the Western Tethys and Atlantic (Wieczorek, 1988), and are

drilled across the Central Atlantic by the DSDP (Müller et al. 1983). Generally, the Maiolica facies is white to

grey, compact, well stratified, pelagic limestone with dark nodular/layered chert, structured in 5-30 cm thick

beds with little internal bedding due to intense bioturbation (Wieczorek, 1988). Lithological variations exist,

exemplified by the comparison of stratigraphically equivalent Maio sediments to Unit 5 of DSDP Site 367

where marl interbeds are more common, related to the relative proximity to terrigenous supply from the

NWAAM. Aptychi dominate the macro-fossil assemblage of the Maiolica facies and as such are prevalent in

Unit 5 (DSDP Site 367; Renz, 1983) and observed in the Morro Fm. The Polier Fm. exposed on Cuba offers

the nearest outcrop occurrence of a similar sedimentary sequence to the Morro Fm. (Pszczółkowski &

Myczyński, 1999), albeit there is an overprint of clastic turbidite sandstones. There is a strong resemblance

between the facies, ammonite fauna and associated preservation style as once the Central Atlantic is

reconstructed to Lower Cretaceous times, the sediments now exposed on Maio and Cuba would have been

deposited at similar paleo-latitude and water depth (Davison, 2005).

The upper transitional unit records a discernible shift in the sedimentation style from the main Morro Fm.

as more clay is introduced into the Central Atlantic and anoxic conditions commence (Chamley et al. 1988).

This is reflected in the top of Unit 5 (Core 25 to 26, DSDP Site 367; Lancelot et al. 1976) where light grey

limestones interbedded with olive black marl were encountered (see Fig. 3.2 and Fig. 0.1 for a correlation

between the DSDP stratigraphy and Maio). Similarly, this transitional facies is cropping out within the upper

Polier Fm. (Pszczółkowski, 1978), and more widespread across both margins of the Tethys, Alps, Central

Atlantic and Pacific (de Graciansky et al. 1981). On Maio, the Morro-Carquiejo sharp transition between

calcareous and argillaceous dominated facies is clear. This, along with the biostratigraphy results, supports

the interpretation of a regional hiatus recorded in the Western Tethys and Central Atlantic between the

latest Early Aptian into the Late Aptian to Albian interval (Event E1 - Müller et al. 1983). Robertson (1984)

generally links the overlying Carquiejo Fm. stratigraphy to the upper Mid-Cretaceous black shale facies

drilled at DSDP Sites 367 and 368, whilst we agree with this broad interpretation further definition is

possible. The non-calcareous claystones exposed at both the RDM and MC sections are seen as equivalent

to the facies encountered in Core 24, DSDP Site 367 and not penetrated at DSDP Site 368 (Lancelot et al.

Chapter 2

75

1976). The limited exposure of the upper Carqueijo Fm. prevents complete integration with the DSDP

results; however the late Albian RC section is likely to be a distal equivalent of this upper Mid-Cretaceous

black shale facies.

2.6.3 Paleo-Environmental Evolution

Ocean floor formation occurred during the lower Valanginian above the CCD, where interlava sediment was

able to develop in quiescence periods of volcanism. The similarities in age between the interlava sediments

(Fourcade et al. 1990) and basal Morro Fm. suggests that there was no break in sedimentation. A prolonged

period of terrigenous starvation occurred extending from the lower Valanginian to Hauterivian resulting in

the deposition of thick pelagic limestones in a deep water basinal environment. During this period,

aggradational carbonate platforms extending around the circumference of the Central Atlantic were the

focus of sedimentation preventing terrigenous material reaching the deep basin (Mourlot et al. 2018). The

Morro Fm. pelagic limestones and Maiolica facies were deposited above the aragonite compensation depth

(ACD) and above the CCD, due to the occurrence of calcitic aptychi and ammonites, both having aragonitic

shells, in a basin starved of terrigenous input. Wieczorek (1988) highlights that these observations do not

specify paleo-water depths, as suggested by Robertson (1984). Benthic life in the deep water basinal

environment is indicated by the ichnofacies observed within the Morro Fm.

The presence of black shale facies interbedded in the upper transitional unit is not supported by TOC

measurements, however the presence of fish remains and planktonic ammonites hints to dysoxic conditions.

The co-occurrence of ornamented pulchellids and heteromorphic ammonoids is most typical of the shaley

interlayers within the Maiolica facies (Cecca et al. 1995). The faunal assemblages are largely dominated by

small size heteromorphs, a morphology that is known to indicate dysaerobic environments (see discussion

in Frau et al. 2016). Organic geochemical analysis of the equivalent section at DSDP Site 367 reveals a high

TOC content, 4-25% within the marls (Lancelot et al. 1976); as such this anoxic environment is postulated in

the upper transitional unit during the upper Barremian.

The regional hiatus occurs in a variety of depositional settings from carbonate platforms to pelagic

environments, recording a significant facies contrast that is attributed to the raising of the CCD in response

to a sea level-rise (Hancock, 1975; Vail et al., 1980; de Graciansky et al., 1981), and occurs coevally with the

rifting phase in the North Atlantic and Equatorial Atlantic (Sibuet et al., 1980; Olyphantet al., 2017). The

introduction of terrigenous material in the lower Carquiejo Fm. and identified in DSDP Site 367 (Core 24)

corresponds to the increased delivery of argillaceous sediment by shelf edge deltas along the NW African

Atlantic margin (Luber et al., 2019; Mourlot et al., 2018), introducing abundant plant debris. Evidence for

early volcanism in the Cape Verde archipelago was suggested by the presence of tuffs within the Carquiejo

Fm. (Serralheiro, 1968, 1970); however our field work supports Robertson’s (1984) lack of identification of


76

volcanic material in the formation. Consequently we follow previous interpretations that volcanism began

in Paleogene to Miocene times. Although, the possibility is not dismissed as Van de Bogaard (2013) dates 4

seamounts of Lower Cretaceous age (142-119Ma) using 40Ar/39Ar ratios within the Canary Island Seamount

Province, and volcanic glass is present in Late Cretaceous to Tertiary succession of DSDP Site 368 (Lancelot

et al. 1976).

2.7 CONCLUSIONS

This multi-disciplinary study has revised the stratigraphy for the Cretaceous sediments exposed on Maio and

provides a key section to define the stratigraphic framework in the distal domain of the Central Atlantic.

Dating of a new collection of ammonites from the basal Morro Fm. definitively indicates a lower Valanginian

age for the oldest sediments on Maio, revising the previous interpretations of a Jurassic age. The ferruginous

limestone facies were deposited by pelagic processes in a metalliferous hydrothermal field resulting in Fe-

enrichment. Re-interpretation of the original collection of macro-fauna collected by Stahlecker was

undertaken, essential to any stratigraphical study of these sediments, as this collection is likely to be

irreplaceable due to intensive quarrying on the island. Combined with the first substantial nanno-fossil study

of 71 samples and integration with new macro-fossils collected as part of this study, a refined stratigraphy

is proposed for the Morro Fm. This suggests the youngest Morro Fm. is of upper Barremian age. The

evolution from the main Morro Fm. massive to bedded limestone facies to the upper transitional unit flaggy

limestone facies is a result of increasing terrigenous supply.

Our new dating of the Morro-Carquiejo boundary and facies observations support the presence of a major

regional hiatus spanning part of the Aptian. This can be recognised widely across the Central Atlantic as it is

proposed to be related to major geodynamic events in the Atlantic and associated changes in oceanic

conditions. The youngest studied stratigraphy, the Carquiejo Fm., correlates well with the middle Upper

Cretaceous black shale facies drilled during DSDP expeditions across the Central Atlantic. These record

bleached black shale facies indicative of anoxic depositional environment. The organic content of the

mudstones on Maio is absent, most probably significantly degraded due to thermal alteration associated

with the volcanic activity and prolonged exposure at outcrop. Future biostratigraphical studies should aim

to date the uppermost Carquiejo Fm. and overlying Coruja Fm. to deduce the earliest possible age for the

volcanism related to the formation of this unique island and the remainder of the archipelago.

Chapter 2

77

2.8 ACKNOWLEDGEMENTS

This study is part of the lead authors PhD project at the University of Manchester, I thank the additional

authors for their support and encouragement. We thank the sponsoring companies of NARG for their

continued financial, logistical, and scientific support. The paper is dedicated to Chris Cornford who along

with Steve Lawrence paved the way for the field investigation. Mike Bidgood (GSS Geoscience Ltd.) and Nico

Janssen (TNO) are thanked for their contributions towards the foraminifera and belemnite analysis

respectively. We also thank Dr. Ingmar Werneburg from the Palaeontological Collection at the University of

Tübingen for their hospitality and open access to the Stahlecker palaeontological collection. Elsa Bulot’s

support and photography of specimens in Tübingen is greatly appreciated. Prof. Alastair Robertson is

acknowledged for helping access the report of Rigassi (1972). Richard Dixon (BP Exploration) is thanked for

making us aware of the exceptional geology exposed on this island. Miguel Company (University of Granada,

Spain), an anonymous reviewer and Gondwana Research associate editor, Andrea Festa’s constructive

reviews significantly improved this paper.

2.9 SUPPLEMENTARY DATA

Fig. S 2.1 – Photographs of the exposures at Ribiera do Morro showing the intense quarrying activities over the last century. Photograph from 1929 scanned from the Stahlecker collection.


78

Fig. S 2.2 – Photomicrographs of thin sections from various localities. Sample numbers can be cross referenced on logs and discussed in text (Fig. 2.4; Fig. 2.6).

Chapter 2

79

Fig. S 2.3– Compilation of field photographs taken during 2018 field season by authors. (A) Parasitic folding of Morro Fm. limestones in a subsurface quarry, Ribiera do Morro; (B) The Monte Carquiejo MC exposure logged in Fig. 2.7; (C) Wood debris found within the Carquiejo Fm., the white star in Fig. S 2.2B shows location; (D-E) Ichnofacies on the base of a dolomitized limestone bed of the Morro Fm., Monte Branco, Pl – Planolites, Th – Thalassinoides; (F) Ch – Chrondrites exposed on the base of a flaggy limestone of the upper transitional unit, Monte Carquiejo.


80

Fig. S 2.4 – Calcareous nanno-fossil zonation for the Central Atlantic. NC Zones of Roth (1978, 1983), Subzones of Bralower (1987) and Bralower et. al. (1993). Hayesites irregularis and Flabellites oblongus are not recorded from the Morro Formation due to the poor preservation. In offshore wells (pers. obs) the FAD of Assipetra terebrodentarius youngii occurs immediately below the FAD of F.oblongus. In the Central Atlantic, the FAD of Hayesites irregularis overlaps with the LAD of Rucinolithus radiatus, a very similar form under the light microscope which makes the true FAD of H. irregularis difficult to identify. The LAD's of Zeugrhabdotus scutula and Conusphaera rothii approximate to the top Barremian in the current study. Ongoing studies will ascertain whether one or both forms range up into the earliest Aptian. Research in Morocco (Luber et. al., 2017 & pers. obs) confirms LAD's below the base of the Deshayesites forbesi ammonite Zone.

Chapter 2

81

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RDM-76 1 2 150

RDM-75 17

RDM-73 2 5 5 3 2 1 410 P 4

RDM-71 1 1 1 11

RDM-70 1 1 2 1 P 2 1 1 2 200 P

Unassigned RDM-69 BARREN

RDM-67 60 42 1 3 2 2 2 420 7

RDM-66 13 5 3 5 1 `1 P 5 5 6 1 1 260 4 4

RDM-65 8 2 1 2 2 2 4 P 1 270 P 1

RDM-63 33 2 2 2 3 1` P 1 8 P 2 1 1 240 9 1 1

RDM-62 16 2 1 P 10 2 6 4 1 P 330 P 3

RDM-61 7 P P 1 3 1 1 9 4 P 7 7 P 4 P 390 1 P 3 P

RDM-60 30 P 2 6 1 1 8 5 P 1 22 6 2 1 P 430 P 2 2 1

RDM-59 7 1 4 5 5 P P 330 P 2

RDM-57 42 1 1 1 1 7 3 1 9 1 12 1 1 P 610 P 8 3 2

RDM-55 12 2 4 3 2 P 620 10 P

RDM-54 32 2 P 16 5 P 5 6 1 1 1 340 3 2 3

RDM-53 BARREN

RDM-51 2 P 1 2 1 13 1 3 1 1 3 1 57 1 P 2

RDM-50 BARREN

RDM-48 7 1 6 1 12 7 1 P 55 1 4 P 6 7 1 1 2 P 1 380 1 1 P

RDM-47 1 1 1 1 26

RDM-46 3 1 P 1 5 2 1 8 180 4 1

RDM-45 5 1 5 1 1 3 96 2

RDM-44 5 3 1 P 2 4 1 3 P 1 72 2

RDM-42 10 2 P 1 5 6 1 4 5 1 1 2 1 42 2 P P P

RDM-41 2 1 12

RDM-40 5 3 P 2 3 1 7 P 3 P 1 P 1 1 21 P P

RDM-38 BARREN

RDM-37 4

RDM-36 BARREN

RDM-31 2 3 1

RDM-27 3 1 1 3 P 1 6 P

NC

7a

- ?

NC

8a

NC

5d

- N

C6

aU

na

ss

ign

ed

Aptian - Early

Albian

Ca

rqu

iejo

Late

Barremian -

?Earliest

Aptian

Mo

rro

Earliest Aptian

& older


82

Monte Carquiejo (MC – Fig. 2.7)

Ag

e

Fo

rma

tio

n

NF

Zo

ne

De

pth

As

sip

etr

a t

ere

bro

de

nta

riu

s

As

sip

etr

a t

ere

bro

de

nta

riu

s s

sp

. y

ou

ng

ii

Cy

cla

ge

los

ph

ae

ra m

arg

ere

lii

Dis

co

rha

bd

us

ig

no

tus

Ha

qiu

s c

irc

um

rad

iatu

s

He

len

ea

ch

ias

tia

Lit

hra

ph

idit

es

sp

.

Mic

ran

tho

lith

us

ob

tus

us

Na

nn

oc

on

us

sp

p.

(to

p v

iew

)

Na

nn

oc

on

us

ste

inm

an

nii

Re

tec

ap

sa

sp

p.

Rh

ag

od

isc

us

as

pe

r

Ro

tela

pil

lus

cre

nu

latu

s

Tu

bo

dis

cu

s j

ura

pe

lag

icu

s

Wa

tzn

au

eri

a b

arn

es

ae

Wa

tzn

au

eri

a b

rita

nn

ica

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

rha

do

tus

sc

utu

la

MC-22 9 2 2 1 230 2

MC-21 7 3 1 2 1 1 240 2

MC-19 6 2 2 2 3 1 1 1 160 P

MC-18 3 1 1 1 1 72 1

MC-17 4 1 1 1 3 1 160 5 P

MC-16 8 2 2 1 1 132 2

MC-15 5 2 2 140 2

MC-14 3 P 3 4 1 160 4

MC-13 3 2 120 1

MC-12 22 3 4 P 6 190 5 2

MC-11 1 1 1 1 P 75

MC-10 5 P P 3 1 2 48 1

MC-9 7 P P 6 7 3 P 210 2

MC-8 2 2 66

MC-6 3 1 1 94 1

MC-5 3 1 P P 1 11 4 P 60 1 2

La

te B

arr

em

ian

- E

arl

ies

t A

pti

an

Mo

rro

Unassig

ned

NC

5d

- N

C6

a

Chapter 2

83

Table S 2.1 – Distribution charts of key calcareous nannofossils from the Ribiera do Morro (RDM – Fig. 2.4), Monte Carquiejo (MC – Fig. 2.7) and River Cut (RC – Fig. 2.7).

Ag

e

Fo

rma

tio

n

NF

Zo

ne

De

pth

Bis

cu

tum

co

ns

tan

s

Bro

ins

on

ia s

ten

os

tau

rio

n

Cre

tarh

ab

du

s l

ori

ei

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

tu

rris

eif

feli

i

Ep

roli

thu

s f

lora

lis

Fla

be

llit

es

ob

lon

gu

s

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

Ha

ye

sit

es

alb

ien

sis

He

len

ea

ch

ias

tia

He

mip

od

orh

ab

du

s g

ork

ae

Lit

hra

ph

idit

es

sp

.

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

mm

ato

ide

a

Pre

dis

co

sp

ha

era

co

lum

na

ta

Re

tec

ap

sa

sp

p.

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Sta

uro

lith

ite

s g

au

so

rhe

thiu

m

Te

gu

me

ntu

m s

tra

dn

eri

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

ph

ac

elo

su

s

Wa

tzn

au

eri

a b

arn

es

ae

Wa

tzn

au

eri

a b

rita

nn

ica

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

hrh

ab

do

tus

ho

we

i

Ze

ug

rha

do

tus

mo

ull

ad

ei

RC14 BARREN

RC-13 P P P 42 1

RC-12 P P 1 P P P P P 30 P P

RC-11 BARREN

RC-10 96 P 1 2 12 P 1 10 1 2 4 2 5 3 1 1 3 240 P 2 14 3

RC-8 3 P 3 1 93 2

RC-7 5 12 33 1 11 1 5 1 1 6 2 1 P 1 360 1 11 1

RC-6 1 1 1 1 170 1

RC-5 1 1 1 P 1 P 3 1 240 1 2

Ca

rqu

iejo

NC

10

a

La

te A

lbia

n


84

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Hayes, D.E. and Rabinowitz, P.D., 1975. Mesozoic magnetic lineations and the magnetic quiet zone off northwest Africa. Earth and Planetary Science Letters, 28(2), pp. 105-115.

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Jeremiah, J., 1996. A proposed Albian to Lower Cenomanian nannofossil biozonation for England and the North Sea Basin. Journal of Micropalaeontology, 15(2), pp. 97-129.

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Lancelot, Y., Seibold, E. et al., 1976. Initial Reports of the DSDP, Vol. 41. U.S. Government Printing Office, Washington, D.C., 1259 pp.

Leroy, L., Vermeulen, J., Lazarin, P., Lepinay, P., and Mascarelli, E., 2016. Nouvelles données sur la classification et l'évolution des Anahamulinidae Breistroffer, 1952 (Turrilitina, Ptychoceratoidea). Annales du Muséum d'Histoire Naturelle de Nice 31, pp. 1-25.

Lodhia, B.H., Roberts, G.G., Fraser, A.J., Fishwick, S., Goes, S. and Jarvis, J., 2018. Continental margin subsidence from shallow mantle convection: Example from West Africa. Earth and Planetary Science Letters, 481, pp.350-361.

Luber, T.L., Bulot, L.G., Redfern, J., Frau, C., Arantegui, A. and Masrour, M., 2017. A revised ammonoid biostratigraphy for the Aptian of NW Africa: Essaouira-Agadir Basin, Morocco. Cretaceous Research, 79, pp. 12-34.

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Měchová, L., Vašíček, Z., and Houša, V., 2010. Early Cretaceous ribbed aptychi – a proposal for a new systematic classification. Bulletin of Geosciences 85/2, pp. 219–274. Czech Geological Survey, Prague.

Mourlot, Y., Calvès, G., Clift, P.D., Baby, G., Chaboureau, A.C. and Raisson, F., 2018. Seismic stratigraphy of Cretaceous eastern Central Atlantic Ocean: Basin evolution and palaeoceanographic implications. Earth and Planetary Science Letters, 499, pp. 107-121.

Müller, C., Schaff, A. and Sigal, J., 1983. Biochronostratigraphy of Cretaceous Formations in DSDP boreholes in the North Atlantic 1. Revue de l’Institut Français du Petrole, 38(6), pp. 683-708.


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Myczynski, R., and Triff, J., 1986. Los ammonites del Cretácio Inferior de las provincias de Pinar del Río y Matanzas. Bulletin of the Polish Academy of Sciences, Earth Sciences 34, pp. 113-137.

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88

3 An integrated stratigraphic re-evaluation of

key Central Atlantic DSDP sites

Max Casson1, Jason Jeremiah2, Gérôme Calvès3, Frédéric de Ville de Goyet4,

Luc Bulot5,1, Jonathan Redfern1

1 North Africa Research Group (NARG), Department of Earth and Environmental Sciences, The University of

Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL, UK

2 Golden Spike Geosolutions Ltd., 20 Ten Acres Crescent, Stevenage, Hertfordshire, SG2 9US, UK

3 Université Toulouse 3, Paul Sabatier, Géosciences Environnement Toulouse, 14 avenue Edouard Belin,

31400, Toulouse, France

4 PetroStrat Ltd. Tan-y-Graig, Parc Caer Seion, Conwy, LL32 8FA, Wales, UK

5 Aix-Marseille Université, CNRS, IRD, Collège de France, INRA, Cerege, Site Saint-Charles, Case 67, 3, Place


Chapter 3

89

3.1 ABSTRACT

Re-sampling DSDP core from key Central Atlantic sites drilled over 30 years ago has defined an updated

stratigraphic framework. Biostratigraphic dating using calcareous nannofossils and palynology, has been

performed on 234 samples. This reveals a higher biostratigraphic resolution for regional correlation and

identification of major hiatus previously unrecognised within the oceanic domain stratigraphy. This work

builds on the pioneering work of these cruises, to utilise the valuable data for new age dating, supplemented

with new organic geochemistry analysis and a sedimentological characterisation to improve the

documentation of the Mesozoic strata. Results are extrapolated along the continental margins of northwest

Africa using regional two-dimensional seismic sections, providing a correlation between the oceanic domain

stratigraphy and shelfal depositional systems penetrated by hydrocarbon exploration wells.

At DSDP Site 367, a middle Berriasian unconformity is recognised for the first time from Core 33, where

middle Berriasian white pelagic limestones (Blake-Bahama Formation) sit unconformably on Early Tithonian

red argillaceous limestones (Cat Gap Formation), indicating a ca. 5 Myr hiatus at the Jurassic-Cretaceous

boundary. Marl interbeds within the pelagic limestones increase in occurrence through the Barremian,

reflecting increased terrigenous input, with associated total organic content (TOC) averaging 5%. A major

lithological break is reported at DSDP Site 367, interpreted as a base Albian unconformity, between the

Blake-Bahama and overlying Hatteras Formation. Sediments above are intra Late Albian variegated

claystones with abundant terrestrial detritus and distal turbidites. Seismic data that intersects the well

location show onlapping reflections of Early-Middle Albian strata landward of DSDP Site 367, indicating

paleo-topography prior to Albian deposition. These sediments are contemporaneous with a major

progradational phase on the shelf and sedimentary wedge at the base of the carbonate escarpment. Early

Albian sediments sit above an interpreted base Albian unconformity at DSDP Site 534A on the conjugate US

Atlantic margin, suggesting the super-regional nature of this event. The refined dating provides calibration

of a basin-wide unconformity recognised at this level, previously known from seismo-stratigraphic studies

as Reflector .

The Late Albian to Late Cenomanian strata (Hatteras Formation) is a 164 m thick organic-rich interval, up to

37% TOC, with internal facies and organic geochemical heterogeneity. This transgressive sequence is

associated with a flooding of the shelf. A temporal variation in the cessation of anoxia (earliest Turonian) is

observed at DSDP Site 368. This revised stratigraphic framework provides a solid foundation for future

Central Atlantic studies intending to use these sites as calibration of the oceanic domain stratigraphy.

Key words: stratigraphic framework; DSDP Site 367; Central Atlantic; MSGBC basin

Central Atlantic DSDP Sites

90

3.2 INTRODUCTION

Over fifty years ago, scientific drilling on the very first leg of the Deep Sea Drilling Project (DSDP) recovered

sediments from the Central Atlantic, establishing the foundations for a stratigraphic framework (Ewing et

al., 1969). After hundreds of additional boreholes, subsequent research has revealed the Meso-Cenozoic

evolution of one of the oldest oceans on Earth, and consequently the adjacent continents, investigating a

variety themes from plate tectonics to climate change. The principal aim of these early expeditions was to

recover samples of the oceanic crust and overlying sediments deposited on the ocean floor. Data generated

by this program forms the most complete and continuous stratigraphic record in the oceanic domain.

However, since the initial reports from the scientific drilling, few studies have revisited these cores to re-

sample and revise the stratigraphy, more commonly the original reported biostratigraphic data is merely re-

interpreted (Müller et al., 1983; 1984).

Unconformities represent a hiatus in the geological record (Blackwelder, 1909, Sloss et al., 1949). Identifying

these surfaces and characterising the sequences that they bound in the oceanic domain is critical to building

a framework for understanding the regional evolution of the surrounding continental margins. Within the

oceanic domain, i.e. the oceanic crust seaward of the continent-ocean boundary (COB), marine

unconformities/correlative conformities (sensu Posamentier & Allen, 1999) are generated by low

accommodation rates or non-deposition related to regional tectonics, global eustasy, and/or erosion by

turbidity or contour currents (Catuneanu, 2006). This surface marks the onset of relative sea-level fall and

the development of an overlying lowstand fan/wedge in siliciclastic systems. Maximum flooding surfaces

(MFS) form when marine sediments reach their most land-ward position, typically after flooding the

continental shelf and are associated with condensed sequences in the oceanic domain. These sequence

boundaries vary in spatial distribution related to their scale; first-order surfaces are typically super-regional

in scale recording plate to margin-scale events (e.g. Vail et al., 1980).

For this study, two key DSDP sites were selected that recovered the most complete Mesozoic stratigraphy,

sites 367, 368 offshore northwest Africa (Lancelot et al., 1978a; 1978b). These two African sites are the

principle calibration points for the oceanic domain stratigraphy within the emerging hydrocarbon province

of the Mauritania-Senegal-Guinea Bissau-Conakry (MSGBC) basin. A comparison is made to the re-evaluated

Early Cretaceous interval at DSDP Site 534A, within the Blake-Bahamas basin along the eastern US Atlantic

conjugate continental margin. The Mesozoic northwest African continental margin is characterised by an

escarpment-type carbonate platform, where the shelf (proximal to distal domains) and basin (oceanic)

depositional systems are decoupled across the escarpment unconformity surface (Casson et al., 2020b).

Therefore, there is difficulty extrapolating, using seismic reflection data, a stratigraphic framework from

exploration well data on the shelf and onshore basin, to the offshore beyond the paleo-shelf edge, where

the prospective slope to basin floor hydrocarbon plays exist. Understanding the margin evolution and

Chapter 3

91

petroleum systems relies on the stratigraphic framework and calibrations to the boreholes at DSDP sites

367, 368. Additional Mesozoic stratigraphical data can be leveraged from the fortuitous uplift of the oceanic

domain sediments on the volcanic island of Maio, Cape Verde, and as part of this integrated study these

outcrops were also recently re-investigated (Casson et al., 2020a).

In order to revise the stratigraphic framework for the Central Atlantic oceanic domain, we undertook new

biostratigraphic, sedimentological and organic geochemical analysis on 234 new samples collected from the

Bremen core repository. This would not have been possible without the meticulous curation and

preservation of the vintage data by the DSDP. A new age model, based on multiple biostratigraphic proxies

is proposed to calibrate the oceanic domain stratigraphy, providing re-dating of the Mesozoic sequences

and bounding regional surfaces, as well as insights into the timing and nature of organic-rich sedimentation.

This study examines the full dip-length of the depositional system by integrating a re-interpretation of

Senegalese exploration wells and regional seismic reflection profiles to construct a chronostratigraphic

framework.


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Fig. 3.1 – Reconstruction of the Central Atlantic to Aptian times (~125 Ma). Location of scientific boreholes and exploration wells (EXP) shown, the three revised wells are highlighted in orange, as well as outcrop studies from Maio, Cape Verde (Casson et al., 2020a) and Cap de Naze, Senegal (CDN). The reconstructed present-day onshore geology maps from the three continents, North America, South America and Africa are displayed highlighting the radial nature of the Central Atlantic Magmatic Province (CAMP) dykes. The onshore geology is clipped at the maximum transgressive coastline during the Cretaceous (Mourlot et al., 2018). Magnetic anomalies, Mx and their corresponding oceanic crust ages from Gradstein et al. (1994) with offsetting fracture zones (FZ). Additional magnetic anomalies (i.e. ABSMA) mapped by Labails et al. (2010) are displayed. The reconstructed location of the seismic data (Fig. 3.9) and estimated line of section for the Wheeler diagram (Fig. 3.11) shown. The conjugate South American study area (Casson et al., 2020b) is displayed as a black dashed box. ABSMA – African Blake Spur magnetic anomaly; BB – Bove Basin; BBB – Blake-Bahama Basin; BP – Blake Plateau; BSMA – Blake Spur magnetic anomaly; DR – Demerara Rise; ECMA – East Coast magnetic anomaly; GP – Guinea Plateau; MSGBC – Mauritania-Senegal-Guinea Bissau-Conarky basin; WACMA – West African Coast magnetic anomaly.

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3.3 REGIONAL SETTING

The Central Atlantic formed following the breakup of Gondwana in the early Mesozoic. Late Triassic rifting

throughout the Central Atlantic occurred contemporaneously, recorded in the onshore rift basins of

Morocco and Nova Scotia (Fig. 3.1; Withjack et al., 1985; Olsen, 1980; Olsen, 1997). During the early Jurassic

(around 201 Ma) the Central Atlantic and surrounding continental margins were affected by extensive

volcanism; the Central Atlantic Magmatic Province event (CAMP; Wilson, 1997; Hames et al., 2003). Onset

of seafloor spreading, and hence formation of oceanic crust is assumed to be diachronous from north to

south, commencing 185 Ma in the north (dependant on various models; Labails et al., 2010 and references

therein) with spreading commencing in the southern segment (study area) around 175 Ma. Kinematic

reconstructions of the Central Atlantic use the positioning and identification of two magnetic anomalies, the

Blake Spur Magnetic Anomaly (BSMA) and West African Coast Magnetic Anomaly (WACMA; Klitgord &

Schouten, 1986; Labails et al., 2010) and juxtaposed syn-rift salt basins reconstructed along fracture zones

(Davison, 2005). Oceanic crust basalts with resemblance to mid-ocean ridge lithologies are penetrated at

DSDP sites 100, 105 (Holister et al., 1972), 367 (Lancelot et al., 1978a) and are exposed on the volcanic island

of Maio, Cape Verde (Serralheiro, 1968; Casson et al., 2020a). Subsequent thermal subsidence of the Central

Atlantic conjugate margins persists to present day (Latil-Brun & Lucazeau, 1988).

Several geodynamic and tectono-stratigraphic events affected the sedimentary succession of the Central

Atlantic in the Cretaceous. The opening of the Equatorial Atlantic gateway caused by drifting of South

America from Africa in the latest Albian (105 Ma) altered paleo-circulation patterns in the Central Atlantic

influencing deep water depositional systems (Forster, 1978; Mourlot et al., 2018b). Cenomanian-aged

transgression and coeval establishment of coastal upwelling of deep oceanic water masses resulted in the

deposition of a thick organic-rich interval throughout global Oceanic Anoxic Event 2 (OAE-2) and the

Cenomanian-Turonian boundary event (Arthur et al., 1984). This transgression created the Florida Straits

and Bahama channels (Sheridan et al., 1983).

Far-field tectonic stresses, i.e. the Santonian compressional event (84-80 Ma) associated with Africa-Europe

convergence and a change in the pole of rotation in the opening Central Atlantic, caused destabilisation,

local inversion and tilting, resulting in canyonisation of the distal African continental margin during the Late

Cretaceous (Casson et al., 2020b). Volcanism and uplift of the Cape Verde archipelago, and an associated

basement bulge is postulated to co-occur in the Late Cretaceous through to emergence in the Miocene

(Patriat & Labails, 2006).


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3.3.1 Scientific Drilling in the Oceanic Domain

Fig. 3.2 – Litho-stratigraphic summary chart for DSDP wells from the Central Atlantic, and Maio, Cape Verde after Casson et al. (2020a). Displaying litho-stratigraphic units/formations1 defined by Jansa et al. (1979) and events by Müller et al. (1983; 1984), key seismo-stratigraphic markers2 of Tucholke & Mountain (1979), and those defined in this study. Numbers relate to the core number. Black lines between cores indicate core gaps, and no lines indicate a hiatus. BAU – base Albian unconformity; BTU – base Tertiary unconformity; MBU – middle Berriasian unconformity; TC – top Cenomanian; TOC – top oceanic crust; TV – top Valanginian.

A unified Mesozoic oceanic domain stratigraphy was conceived primarily following analysis of stratigraphic

data collected on R.V. Glomar Challenger during the many DSDP cruises across the Central Atlantic (Fig. 3.1).

Hollister et al. (1972) in their initial reports from DSDP Site 105, North American continental margin, were

the first to establish the stratigraphy. Subsequent scientific drilling on DSDP Leg 41 recognized a comparable

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stratigraphy offshore northwest Africa (Lancelot et al., 1978a; 1978b; Jansa et al., 1978). Following

documentation in the DSDP Initial Reports, the Mesozoic lithostratigraphic units were formally defined by

Jansa et al. (1979), later refined by Müller et al., (1983; 1984), as the Cat Gap Fm. (Kimmeridgian – Tithonian)

– red argillaceous limestone and marl (‘Rosso Ammonitico’ sensu Farinacci & Elmi, 1981); Blake-Bahama Fm.

(Berriasian – early Aptian) – white grey limestone, chert, chalk and marl; Hatteras (late Aptian – Cenomanian)

– carbonaceous claystone; and Plantagenet Fm. (Turonian – Senonian) – variegated clays (with ‘Cretaceous

oceanic red beds, CORBs’ sensu Hu et al., 2005). A correlation chart is provided in Fig. 3.2 summarising the

litho-stratigraphic units, linking with various seismo-stratigraphic schemes. Recent integrated stratigraphic

analysis by Casson et al. (2020a) of equivalent sediments exposed on Maio, Cape Verde provides calibration

of these sequences at outcrop. Two major unconformities sub-divide the Cretaceous formations, Event E1

(late Aptian) and Event E2 (Cenomanian – Turonian; Müller et al., 1983; 1984), interpreted to record

significant Central Atlantic palaeoceanographic events (Jansa et al., 1979). De Graciansky et al. (1987)

provides the most recent stratigraphic synthesis based on a compilation of previous biostratigraphy (Müller

et al., 1983; 1984) and organic geochemistry (Herbin & Deroo, 1982).

3.3.2 Proximal Continental Margin Evolution

Whilst the focus of this study is on the sediments of the oceanic domain, the depositional systems operating

in more proximal settings, on continental margins, are important to consider, as this is the source of much

of the sediment delivered into the deeper basins. These areas surrounding the Central Atlantic have been

subject to hydrocarbon exploration for decades, creating valuable well and seismic reflection datasets, often

yielding far more data in comparison to the relatively few penetrations in the oceanic domain. In the

adjacent onshore basins, the post-rift sediments can be studied at outcrop (i.e. Morocco – Luber et al.,

2019), although within the study area on both continental margins, thick Cenozoic sediments and lack of

Alpine-related exhumation means there are limited Mesozoic outcrops south of Morocco or on the North

American margin (with local exceptions such as Cap de Naze, Senegal; Sarr, 1995).

Recent work (Mourlot et al., 2019; Casson et al., 2020b) characterising the shelfal depositional systems of

the African continental margin can be summarised as follows: a carbonate escarpment margin fringes the

circumference of the Central Atlantic from Jurassic to Aptian times, with the first major delivery of siliciclastic

sediment to the shelf edge by deltaic systems during the Albian. In the Cenomanian to Turonian-aged,

transgression of the continental margin occurred, often extending into the onshore basins, and the Late

Cretaceous was a period of instability, with collapse of the distal continental margin associated

canyonisation.

The continental margin has a wide present-day shelf and the onshore sedimentary basins are characterised

by low topographic relief, with Mesozoic and younger sediments onlapping the post-rift unconformity and


96

bordering cratons. The location of the present-day shelf edge is spatially inherited and controlled by the

underlying Jurassic carbonate platforms; a feature that remains outcropping at the seafloor along the Blake

Escarpment on the conjugate margin (Jansa, 1981; Land et al., 1999), indicating the control the palaeo-shelf

edge trend had on succeeding depositional systems.

3.4 DATASET & METHODS

3.4.1 Data

Lithological Samples

Re-sampling the DSDP cores took place through 2017 to 2018 at the IODP Bremen Core Repository, Germany

(request ID: 054376IODP, 065859IODP and 077865IODP). The two key African DSDP sites 367 and 368 were

reanalysed. The late Early Cretaceous interval of DSDP Site 534A in the Blake-Bahama basin was used as a

comparison as it penetrated with high core recovery (56%; Sheridan et al., 1983) a similar Mesozoic

sequence to DSDP Site 367. These remaining samples are stored for reference in the North Africa Research

Group (NARG) collection at the University of Manchester. A sample summary is provided in the

supplementary data documenting the new analysis performed on each sample (Table S 3.1). Additional

organic geochemistry data was compiled from existing studies (Lancelot et al., 1978a; 1978b; Deroo et al.,

1978; Wagner, 2013; Mourlot, 2018a).

Subsurface Seismic and Well Data

The seismic reflection data offshore northwest Africa (WGS 1984 UTM Zone 28N) consists of four 2D seismic

reflection profiles (total of 1728 line km) from the Spectrum Geo (now TGS Geophysical) VER01 MWT

regional 2D survey reprocessed to broadband in 2016-2017. The survey ties key DSDP sites (367, 368) to the

continental margin, intersecting hydrocarbon exploration wells on the shelf (CVM-1, Jammah-1), and

providing a crucial well tie for the oceanic domain. The seismic data records to a depth of 12.5 seconds two-

way-travel time and was provided as Pre-Stack Time Migrated (PSTM) SEGY data. Hydrocarbon exploration

well data (wireline logs, end-of-well reports) from Senegal, courtesy of Petrosen, were available to expand

our investigation more proximally.

3.4.2 Methods

Biostratigraphy

Dependent on lithology various biostratigraphic analyses were performed to provide age constraints on the

stratigraphy. Calcareous nannofossils (JJ): 154 samples were analysed with standard techniques described

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by Bown (1998), and the picking brush method of Jeremiah (1996). Samples were analysed semi-

quantitatively, with the first 30 fields of view counted and the remaining slide scanned for rare specimens.

Palynology (FVG): 14 samples for palynological analyses were subject to the standard palynological

preparation technique which involves removal of all mineral material by hydrofluoric acid digestion and

sieving to produce a residue of the 10 micron and above size fraction for each sample. An initial count of

100 in situ palynomorph specimens was performed and abundance quantitatively assessed using percentage

of total palynoflora. Twenty-eight samples were cut for thin sections and dyed blue to analyse for the

occurrence of calpionellids within the limestones of the Blake-Bahamas and Cat Gap formation, DSDP Site

367. Unfortunately, the deep-water pelagic facies did not yield any calpionellids.

Organic Geochemistry

Forty-three samples were selected for organic geochemical analysis using a Shimadzu TOC-V CPN and Solid

Sample Module (SSM), calibrated to sodium carbonate and glucose to measure inorganic and total carbon

respectively. Additional geochemical data for DSDP Site 534A was incorporated from Herbin et al. (1983).

Pyrolysis of 17 samples yielding greater than 0.5% TOC was completed using a Rock-Eval 6 instrument at

GHGeochem by Gareth Harriman.

Fig. 3.3 (next page) – A re-evaluation of DSDP Leg 41 Site 367 stratigraphy displaying nannofossil events (Table S 3.2) and palynology results (Fig. S 3.1), depth of an ichthyodectiform reported in Casson et al. (2018), total organic carbon (TOC; Table S 3.1) measurements and key stratigraphic surfaces. Palynology abbreviations: ABN – abundant, AOM – amorphous organic matter, FDO – first downhole occurrence, FDCO – first downhole common occurrence, FDAO – first downhole abundant occurrence, FDSAO – first downhole superabundant occurrence, INCR – increase in abundance, PRES - presence, CMN - common, SABN – superabundant, TNS – top not seen.


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3.5 RESULTS

3.5.1 Stratigraphic Revision

DSDP Site 367

The scientific objectives of Site 367 were to “collect core to calibrate the lithological properties of the

acoustic stratigraphy and correlate this with sequences interpreted on the conjugate American margin”

(Lancelot et al., 1978a). In drilling Site 367, a full Mesozoic sequence was penetrated to oceanic basement,

providing the most complete record of the oceanic domain stratigraphy offshore northwest Africa (Fig. 3.3).

Site 367 was drilled above a basement high to a TD of 1153m, the lowermost three cores recovered basalts

dated using potassium-argon (K-Ar) whole rock and argon-argon (40Ar/39Ar) methods, yielding ages of 92.0

± 1.6 and 102.4 ± 2.0 Ma respectively (Duncan & Jackson, 1978). These relatively young ages (middle

Cretaceous) contradict with the age of the overlying sediments of the Cat Gap Formation,

Kimmeridgian/Oxfordian (~160 Ma; Lancelot et al., 1978a). This relatively young age may indicate the well

intersected dykes and sills intruded into and/or altered oceanic crust. Future work re-dating and describing

these basalts with modern techniques may yield ages that align with the age of the overlying sediments and

magnetic anomalies.

A lithostratigraphic summary from representative cores of the overlying Mesozoic units is provided in Fig.

3.4 detailing the sedimentary facies, organic content and interpreted depositional environments of DSDP

Site 367 (to be used in conjunction with the composite log, Fig. 3.3).

Fig. 3.4 (next page) – A litho-stratigraphic summary of the Mesozoic sediments recovered at DSDP Leg 41 Site 367 displaying key stratigraphic units after Lancelot et al. (1976). Total organic carbon (TOC) maximum and average values per unit displayed from new geochemical analysis (Table S 3.1). ACD – aragonite compensation depth; CCD – calcite compensation depth.


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Fig. 3.5 – Photographs of Core 32 from DSDP Leg 41 Site 367 with analysed samples displayed by red arrows, highlighting the middle Berriasian unconformity (MBU) separating Late Tithonian-aged unit 6, reddish brown nannofossil-bearing argillaceous limestone, marl, clays and cherts from the overlying early Berriasian-aged Unit 5B, white grey nannofossil limestone, marl & chert (Lancelot et al., 1976). Tith. – Tithonian; Berr. – Berriasian. Scale in cm.

Biostratigraphy – The presence of Triscutum beaminsterensis between 1135.51-1136.34 m indicates

penetration of lower Kimmeridgian (Bergen et. al., 2013). The assemblages are low diversity dominated by

Watznaueria manivitiae and W. barnesiae, other age diagnostic markers absent. Triscutum cf.

beaminsterensis at 1114.96 m could not be precisely allocated to the species and is probably a new species

of Triscutum sp. A low diversity, non-age diagnostic assemblage ranges as high as 1111.80 m.

Definitive Lower Tithonian sediments are confirmed at 1109.25 m with the FO and HRA of Polycostella

beckmannii and Conusphaera mexicana followed by the FO of Nannoconid spp. including Nannoconus infans


102

and N. compressus at 1088.82 m, here associated with Hexalithus / Polycostella transitional 7 rayed forms.

This assemblage ranges up to 1088.19 m. No Upper Tithonian assemblages are recorded.

Above the middle Berriasian unconformity, middle Berriasian nannofloras make their first appearance with

Assipetra infracretacea, Diazomatolithus lehmanii, Cruciellipsis cuvillieri, Nannoconus steinmannii minor and

Umbria granulosa ssp. granulosa all recorded at 1088.07 m, the FO of Rhagodiscus nebulosus following at

1087.70 m. Late Berriasian deposits are recorded from 1086.90 m with the FO of Rucinolithus wisei,

?Percivalia fenestrata and Nannoconus steinmannii. The LO’s of Conusphaera mexicana at 1085.72 m,

Rhagodiscus nebulosus and Umbria granulosa ssp. granulosa at 1083.40 m indicate an age no younger than

late Berriasian at the top of Core 32-2.

Early Valanginian sediments appear at the base of Core 31-2 with the FO of Calcicalathina oblongata at

1055.57 m and range as high as the top of Core 30 at 1024.75 m, here marked by the LO of Rucinolithus

wisei.

Overlying sediments between 998.20 m and 939.64 m yield a ranging Early Hauterivian to late Valanginian

nannoflora, nominate markers such as Eiffellithus striatus and E. windii both unrecorded from DSDP Site 367.

The LO of definitive Tubodiscus verenae, a form often used as an approximate top Valanginian datum is at

968.15 m, here coincident with the LO of Rhagodiscus dekaenelii. The occurrence range in DSDP Site 367 of

Lithraphidites bollii is between 942.20 m and 940.30 m. An age no younger than Early Hauterivian is

confirmed by the occurrence of an influx of Cruciellipsis cuvillieri at 939.64 m.

The base of Core 26 yields a condensed early Barremian to Late Hauterivian sequence. The LO of Speetonia

colligata occurs at 915.50 m whilst the LO of Calcicalathina oblongata is at 914.60 m.

DSDP Site 367, has a late Barremian assemblage which yields a low diversity nannoconid assemblage,

Nannoconus steinmannii remaining rare and part of the background nannoflora, this also true of both

Micrantholithus obtusus and Conusphaera rothii. This observation is comparable to time equivalent

sediments exposed on Cape Verde (Upper Transitional Unit – Morro Fm.; Casson et. al., 2020a).

The late Barremian assemblages are characterized by influxes of Assipetra terebrodentarius together with

the presence of Zeugrhabdotus scutula. The FO of Hayestites irregularis is at 897.32 m but the absence of

both Flabellites biforaminis and Assipetra terebrodentarius youngii suggests latest Barremian sediments are

absent.

Cores 24-3 through 23 are barren of nannofossils, the reappearance of calcareous mudstones at Core 22-6

(728.80 m) yielding a Late Albian nannoflora. The presence of an influx of Eiffellithus turriseiffelii above the

LO of E. monechiae indicates a level in the upper part of the Late Albian.

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Despite the poor recovery of the sample analysed from Core 24-3 (729.00 m), the palynoflora indicates

marine conditions with some current upwelling of nutrients, as suggested by the sole presence of marine

palynofloras (Subtilisphaera species; Prauss, 2011; Prauss, 2012). The presence of Subtilisphaera cheit

suggests the sediments are no older than Late Albian (only by analogy with the similar taxon

Palaeohystrichophora infusorioides, which ranges no older than intra Late Albian in northwest Europe; Costa

et al., 1992).The presence in the samples from cores 22-6 and 23-1 (729.00; 778.35 m) of Litosphaeridium

arundum (Eisenack et al., 1960; Davey, 1979; Costa et al., 1992), Litosphaeridium conispinum (Davey et al.,

1973; Costa et al., 1992), Afropollis jardinus (Doyle et al., 1982), Elaterosporites klaszii and Elaterosporites

verrucatus (Jardine, 1967; Jardine et al., 1965; Regali et al., 1974; Salard-Cheboldaeff, 1991), all together

indicate penetration of sediments no younger than Late Albian. A terrestrial input is noted to occur within

Core 23-1 (778.35 m) as evidenced by the high abundances of pollen and spores. This input is also

characterised by an important increase in Classopollis species, indicating sediments input from a hot and dry

hinterland (Doyle et al., 1982), but the overall palynofloras of this latter sample still indicates an open marine

palaeoenvironment.

The Albian / Cenomanian boundary (ca. 710.46 m) lies between cores 22-1 (721.80 m) and 21-6 (700.26 m).

The LO of H. albiensis is at 723.96 m; Cenomanian sediments confirmed at 700.26 m by the FO of an increase

in Broinsonia signata / enormis group and FO of Gartnerago chiastia. The LO’s of G. chiastia at 695.93 m and

Eiffellithus paragogus at 690.94m indicates and age no younger than Lower Cenomanian.

A break in the core coverage into the base of Core 19-4 yields assemblages characteristic of the Late

Cenomanian. The acme of Eprolithus spp. between 649.17 m and 642.77 m is particularly characteristic of

Late Cenomanian to earliest Turonian sediments. An age no younger than Late Cenomanian is confirmed by

the LAD’s of Axopodorhabdus albianus and Gartnerago praeobliquum at 642.77 m followed by Helenea

chiastia at 637.70 m.

Two samples analysed for palynology from cores 17-3 and 18-1 (620.10; 637.40 m) had very poor recovery

and the chronostratigraphic interpretation of these cores from ?Late Cenomanian to ?Late Albian is mainly

based on similar bio-events already noted to occur offshore West Africa and cannot therefore be identified

with certainty. An open marine to offshore deep water paleoenvironment still prevails in this interval.

The uppermost sample from Core 16-2 (541.63 m) yielded a poor recovery. However, the presence of

Oligosphaeridium complex indicates penetration of sediments no younger than Late Santonian (unpublished

Petrostrat data West Africa). Deposition under open marine conditions prevail as evidenced by moderately

rich dinocyst assemblages. However, the low diversity in dinoflagellates indicate some restriction in the

surface waters.


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DSDP Site 368

Fig. 3.6 – A re-evaluation of DSDP Leg 41 Site 368 stratigraphy displaying nannofossil events (Table S 3.2), total organic carbon (TOC; Table S 3.1) measurements, palynology results (Fig. S 3.1) and key stratigraphic surfaces.

Along with Site 367 (Fig. 3.3), Site 368 adds further lithological data captured in the oceanic domain offshore

northwest Africa (Fig. 3.6). The borehole was abandoned at 984.5 mMD, after intersecting two diabase sills

and associated gas in black shale facies, equivalent to those drilled at Site 367 (Lancelot et al., 1978b). K-Ar

whole-rock ages for the sills are 16.3-19.3 Ma (Duncan & Jackson, 1978), linked to Cape Verde volcanism.

Contact metamorphism increased the thermal maturity of the surrounding Hatteras Formation shales,

revealing their hydrocarbon generating potential (Dow, 1978). The notable difference in lithostratigraphy to

Site 367 is the increased presence of coarser-grained terrigenous turbidites, that decrease in abundance

upwards through Plantagenet Formation of Site 368 (Unit 2; Fig. 3.6). Decimetre-scale cyclical turbidite

packages have fine-grained to silt grade quartz sand bases with load casts grading to claystones, best

preserved in cores 53 to 59 (Fig. 3.6).

Biostratigraphy – The oldest sediments analysed for calcareous nannofossils from Core 63 (980.78 m) yield

an influx of Eprolithus floralis, which ranges to the top of Core 62-4 (973.51 m); this influx is characteristic

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of Late Cenomanian to earliest Turonian sediments. Definitive Late Cenomanian markers, Axopodorhabdus

albianus, Gartnerago praeobliquum and Corollithion kennedyi have FO’s at 979.75 m. The LO’s of

Axopodorhabdus albianus and Gartnerago praeobliquum at 975.97 m indicates an age no younger than Late

Cenomanian.

Fifteen samples analysed between cores 60-2 (951.24 m) and 50-2 (704.52 m) proved barren of nannofossils.

Therefore 8 samples were analysed for palynology.

The impoverished recovery from cores 59-3 to 62-4 (942.87; 973.54 m) precludes a biostratigraphic or

paleoenvironmental interpretation. An Early Coniancian? – ?Late Turonian has been tentatively assigned to

the Core 58-2 (923.55 m) following the presence of increased algal cysts, which is one of the events noted

to occur within this age assignment offshore northwest Africa. The low diversity in dinocysts in this sample,

supported by this increased number of algal cysts, could indicate environmental stress and some restriction

in the surface waters.

Three samples taken from cores 55-2, 56-3 and 57-2 (840.36; 849.3; 894.52 m) yielded a relatively good

palynological recovery. The presence of Oligosphaeridium species (O. complex, O. irregulare, O.

pulcherrimum, Oligosphaeridium spp.), Chatangiella spp. and Cretacaeiporites mullerii in those samples all

indicate penetration of Santonian or older sediments (unpublished Petrostrat data West Africa). The

occurrence of high numbers in Subtilisphaera species, an event which is consistent with Late Santonian

sediments offshore northwest Africa (unpublished Petrostrat data West Africa), also supports this

interpretation. There is a notable change in the paleoenvironment through this interval, from open marine

with surface water restrictions and with current upwelling of nutrients (as indicated by the bloom of

Subtilisphaera species) to middle neritic environment as suggested by the decrease in marine palynofloras

and the decrease in spores and pollen compared to the sample from Core 53-2 (752.03 m).

A possible middle Campanian age has been assigned to the samples from Core 53-2 (752.03 m), as indicated

by the presence of Xenascus ceratoides (unpublished Petrostrat data West Africa). A moderately rich and

diverse dinoflagellate cysts assemblage indicates a degree of oxygenated surface waters, while the absence

of terrestrial palynoflora suggests an offshore setting or limited terrestrial input.


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DSDP Site 534A

Fig. 3.7 – A re-evaluation of DSDP Leg 76 Site 534a stratigraphy displaying nannofossil events (Table S 3.2), total organic carbon (TOC; Table S 3.1) measurements and key stratigraphic surfaces.

Across the Central Atlantic in the conjugate Blake-Bahamas Basin, Site 534A penetrated a remarkably similar

lithostratigraphy to the African sites previously discussed (Fig. 3.7). This site was selected as a conjugate

comparison due to the high number of cores recovered (total core length recovered – 629.8 m) through the

sedimentary section to TD in oceanic basement (Sheridan et al., 1983). Three cores at the TD of Site 534A

recovered 31.5 m of dark greenish grey tholeiitic basalt and breccia (Logothetis, 1983). Biostratigraphic

dating of the overlying sedimentary sequence as middle-late Callovian (~164 Ma), along with the normal

paleo-magnetic polarity of the basement rocks supported the predicted minimum age of the oceanic crust

just seaward of the Magnetic Anomaly M-28 (Sheridan et al., 1983; Steiner, 1983). Consequently, older

sediment (unnamed formation) was recovered compared to Site 367, composed of predominantly red,

weakly laminated claystones with flattened burrows indicative of oxygenated bottom waters and strong

current activity (Sheridan et al., 1983). In comparison to the African sites, Jurassic limestone textures and

sedimentary structures (Cat Gap Formation) indicate these hemipelagic sediments have been redeposited

by slope and shelf-derived turbidites and modified by bottom-current transport (Sheridan et al., 1983).

Within this package, elevated organic enrichment is assumed to reflect input of organic matter from

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terrestrial sources reflected in the Type III organic matter (Herbin et al., 1983). The Lower Cretaceous Blake

Bahama Formation shows a gradual increase in carbonaceous claystone through a predominantly pelagic

limestone sequence mirroring Site 367. In the Hatteras Formation, black shales were deposited by distal

turbidity currents (Sheridan et al., 1983), supported in the terrestrial origin of the organic matter (Herbin et

al., 1983). Sediment starvation resulted in an unusually thin (41.0 m) Plantagenet Formation unconformably

overlying the Hatteras Formation (Sheridan et al., 1983).

Biostratigraphy – DSDP Site 534A has been studied extensively for nannofossils stratigraphy. The current

investigation focused on the Albian through Barremian sequence (Fig. 3.7), which has also been reviewed

by Roth, 1983 and Bergen, 1994). The Lower Cretaceous through Upper Jurassic sequence, not described

here, was the focus of studies by Roth, 1983; Bralower et. al., 1989; Cassellato, 2010 and Bergen et. al.,

2013).

The oldest samples analysed in the current analysis are Late Barremian in age. This is confirmed by the

presence of Zeugrhabdotus scutula above the LO of Calcicalathina oblongata and below the FO of Assipetra

infracretacea ssp. youngii at 952.04 m and the FO of Flabellites oblongus at 938.36 m. A ranging earliest

Aptian to late Barremian age is given for the interval between 914.50 m and 938.36 m based on the LO of

Zeugrhabdotus scutula, an influx of Assipetra terebrodentarius youngii and abundant Cyclagelosphaera

margerelii. Conusphaera rothii was completely absent from this section whilst other characteristic

nannofossils of the Barremian, Nannoconus steinmannii and Micrantholithus obtusus, were sporadic.

These assemblages are very similar to Barremian nannofloras from Cape Verde (Casson et al., 2020a) and

DSDP Site 367 (Fig. 3.3). The FO of Hayesites irregularis is also shown to range below the FO of Flabellites

oblongus at DSDP Site 534A (Fig. 3.7) and DSDP Site 367 (Fig. 3.3). Along the Atlantic Morocco margin, the

LO of Zeugrhabdotus scutula was found immediately below a condensed earliest Aptian ammonite bearing

section with Procheloniceras dechauxii and Deshayesites aff. euglyphus ammonites (Luber et. al., 2019; J.

Jeremiah., pers. obs.). The condensed nature of this section in Morocco, however, does not preclude Z.

scutula ranging up into the basal Aptian so a ranging age for the current interval is preferred.

Bergen (1994) utilised the FO of Rhagodiscus achlyostaurion in Core 45-4 to indicate a late Barremian age.

This species has not been found in sediments any older than latest Aptian by the author and was not found

below the Albian in the reinvestigation of DSDP Site 534A.

Cores 39-42 are barren of nannofossils. The DSDP preliminary investigation of DSDP Site 534A (Gradstein &

Sheridan, 1983 & Roth, 1983) did not yield definitive nannofossil or foraminiferal markers over this

sequence. The LO of the palynomorph, Druggidium deflandrei from Core 41-6 was utilised as an Aptian

marker but this form is known to range into the Lower Albian.


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Early Albian nannofloras appear at the base of Core 38-3 (873.04 m). The presence of Prediscosphaera

columnata and Rhagodiscus achlyostaurion at 873.04 m indicates and an age no older than Albian, the

occurrences of Assipetra terebrodentarius youngii and Crucibiscutum bosunensis indicating the early part of

the Early Albian, assemblages very similar to those recorded along the Atlantic coast of Morocco (Luber et.

al., 2019). Repagulum parvidentatum, a cold-water nannofossil is recorded from DSDP Site 534A, but unlike

Morocco, no influxes were recorded. The LO’s of A. t. youngii is at 863.03 m, an event also recorded from

Morocco (Luber et. al., 2019).

3.5.2 Organic Geochemistry

Fig. 3.8 – Classification of kerogen types using hydrogen and oxygen indices plotted on a modified van Krevelen diagram displaying the results of the Rock-Eval pyrolysis. The symbology reflects the age of each sample analysed, data from DSDP Site 367 and Site 368 is filled white and black respectively. The tabulated data is presented in the supplementary material (Table S 3.1).

Combined with the re-dating of sediments from the three DSDP sites studied, further organic geochemical

analysis was undertaken to characterise the organic-rich intervals encountered. TOC data is plotted against

depth and stratigraphy on the revised composite well logs (Fig. 3.3; Fig. 3.6; Fig. 3.7). Pyrolysis results are

displayed separately on a modified van Krevelen diagram (Fig. 3.8) and are tabulated in the supplementary

data (Table S 3.1). Deeper and older organic-rich intervals are encountered through the oceanic domain

stratigraphy at DSDP Sites 367 (Fig. 3.3). These generally occur in isolated marly horizons dispersed between

more competent limestone units and are usually less than 1 cm in thickness predominantly composed of

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fissile marl (Facies D – DSDP Site 367; Fig. 3.4). It is conceivable that these isolated horizons thicken

proximally, as indicated in the seismic architecture of these sediments (Fig. 3.9). TOC values at DSDP Site

367 from the Lower Cretaceous to Jurassic (TD) interval average 4.71%, with occasionally higher values up

to 25.07% (Core 26) taken from plant material. The pyrolysis results record a more Type III kerogen type

indicating terrestrial-derived organic matter (Fig. 3.8). The majority of the pyrolysis data from DSDP Site

534A (Herbin et al., 1983) also have low HI and high OI values indicating Type III organic matter derived from

terrestrial sources, and hence are more gas-prone (Fig. 3.8). An increase in TOC content is recorded in

Callovian-aged sediments from this borehole, unpenetrated elsewhere around the Central Atlantic reflecting

local terrestrial organic matter input (Herbin et al., 1983).

The two DSDP sites along the African margin have exceptionally elevated TOC levels in Cenomanian-aged

black shales, with average TOC values of 19.45% and 13.78% from DSDP Site 367 and 368, respectively. Tmax

values average 405 °C for the organic-rich sediments from DSDP Site 367 indicating the source rock is

immature. By comparison, the time-equivalent stratigraphy at DSDP Site 368 has average Tmax value of 429

°C, closer to the temperatures capable of generating hydrocarbons, probably due to thermal maturation

associated with the recorded volcanic intrusives (Dow, 1978). In more proximal settings along the

continental margin the Cenomanian organic-rich interval will be buried under a thicker sediment

accumulation, increasing the maturity and therefore making it capable of generating hydrocarbons, and this

is the predicted source of the oil in the Sangomar field (Clayburn, 2017). A Cenomanian-aged grouping of

data points on Fig. 3.8 with high HI (hydrogen index – 450 to 600+ mg hydrocarbons/g organic carbon) and

low OI values (oxygen index – 10 to 65 mg CO₂/g organic carbon) indicates Type II marine kerogen with oil

generating potential.

Both dating by palynology and calcareous nannofossils (Fig. 3.3) indicate a Late Cenomanian age throughout

cores 17 to 19 from DSDP Site 367. Previously, Müller et al., (1983) reported these cores as early Turonian

in age and this dating was used by Herbin et al. (1986) to characterise the organic-enrichment around the

Cenomanian-Turonian boundary event. Our new stratigraphic results indicate these sediments show a

temporal correlation to the global oceanic anoxic event 2 (OAE-2 ~Late Cenomanian, nannofossil zone UC5).

The equivalent OAE-2 interval is penetrated in DSDP Site 368 in Core 63 (Fig. 3.6). Isotope geochemical

results from these intervals are discussed in Kuypers et al. (2002) and van Bentum et al. (2012).

Differences in the geochemical properties of correlative organic-rich intervals drilled on the Senegalese

continental shelf are recorded by exploration wells (Casamance Marine – CM). Herbin et al. (1986) show

TOC values decreasing towards the paleo-coastline and kerogen type shifting to become more terrestrial

(Type III) in nature, reflecting the proximity to terrigenous input and decrease in the preservation potential

of planktonic (marine Type II) organic matter.


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The deeper penetration at DSDP Site 367 allows the full stratigraphical extent of the organic-rich interval to

be examined. Organic-rich sediments are recorded through to Core 23, which can be dated as intra Late

Albian age (Fig. 3.3). Therefore, the minimum thickness, due to a core gap between cores 23 and 24, of the

Albian-Cenomanian organic-rich interval is 164 m, with a maximum thickness up to 218 m. Core 24, DSDP

Site 367 is composed of variegated claystone, with no black shale or organic content recorded (Fig. 3.3).

The Albian-Cenomanian organic-rich interval is internally heterogenous at the bed-scale reflected in the

TOC, kerogen type and sedimentary facies (Fig. 3.4). Facies B, present in cores 18-1 to 18-3 (Late

Cenomanian) is a laminated carbonaceous shale with the highest TOC concentration up to 37.21%, and

average of 34.09%. TOC generally decreases with depth and increasing age, from an average 19.45% TOC

(cores 18/19) to 2.36% TOC (Core 23). Although in Core 22-5 and 22-6, TOC values spike up to a maximum

of 25.06% (Wagner et al., 2013), strictly from Facies D, a light grey nannofossil-rich marlstone (Fig. 3.44). By

comparison, the bed stratigraphically above this maximum Albian TOC value records only 2.80% from Facies

C, dark black carbonaceous claystone (Fig. 3.4).

Organic content is registered in Core 17 (Late Cenomanian) of the overlying Plantagenet Formation within

non-oxidised/-reduced beds with abundant plant debris and an average TOC of 4.08%. Pyrolysis results

reveal the changes in kerogen type through this interval (Fig. 3.8). Cores 18 to 21 (Late and earliest

Cenomanian), DSDP Site 367, and Core 63 (Late Cenomanian), DSDP Site 368 all have high HI (450-650 mg

hydrocarbons/g organic carbon) and low OI values (10-65 CO₂/g organic carbon) indicating Type II marine

kerogen with oil generating potential. There appears to be no correlation between facies and kerogen type.

Core 22 (Late Albian), DSDP Site 367 generally shows a mixed Type II/III signature. Examining extra data from

this core (Wagner et al., 2013) shows higher HI, lower OI values (Type II signature) are associated with Facies

D, with Facies C predominantly more terrestrially influenced (Type III). Low HI, high OI values from cores 17

and 23, DSDP Site 367 indicate a terrestrial source of organic matter (Fig. 3.8). Mixing of marine and

terrestrial organic matter can occur by sedimentary processes i.e. turbidites introducing plant matter as

recorded in Facies D. Cenomanian-aged (i.e. OAE-2) sediments of the Plantagenet Formation at DSDP Site

534A are truncated by the base Tertiary unconformity or not deposited due to exceptionally low

sedimentation rates (Fig. 3.7).

Fig. 3.9 (next page) – Dip-orientated two-way time seismic sections from the North West African Atlantic margin, Mauritania to Guinea Bissau, displaying megasequence architecture extrapolated from the re-evaluated well stratigraphy. Location displayed on Fig. 3.1 and the inset map. A zoom-in on possible outer seaward dipping reflectors (SDRs) is shown at 2x magnification. M25 magnetic anomaly intersection (~154 Ma = Kimmeridgian) after Labails et al. (2010). COB – Continent ocean boundary. Seismic data courtesy of Spectrum Geo.

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3.5.3 Seismic Stratigraphy

An overview of the seismic stratigraphy documenting the margin architecture is provided to extend

observations and the new age interpretations from the DSDP sites eastward to the continental margin (Fig.

3.9), linking with studies of the shelfal stratigraphy (Casson et al., 2020b). The broad present-day basement

bulge (sensu Patriat & Labails, 2006) of the Cape Verde Rise is subtly apparent on Fig. 3.9A forming a

bathymetric rise dipping towards the continental margin, reflected in the oceanic crust geometry. A semi-

continuous seismic reflection interpreted below the oceanic crust at 8.5 and 10 sTWT depth (Fig. 3.9A and

Fig. 3.9C, respectively) is possibly the Moho. Below the top oceanic crust, ca. 100 km southeast of DSDP Site

367, reflections are arcuate, curving to sub-vertical and dip basin/oceanward, over a distance of ca. 50 km

(Fig. 3.9C inset); normal oceanic crust exists to the northwest and southeast. The sediment-basement

reflection (i.e. top oceanic crust) is smooth, relative to the rugose oceanic crust topography further outboard

to the northwest (Fig. 3.9C). By comparison to Calvès et al. (2011), these features can be interpreted as

volcanic seaward dipping reflections (SDRs) produced by basaltic flows during early seafloor spreading. The

reflections extend ca. 50 km along the seismic profile (Fig. 3.9C). Labails et al. (2010) map two magnetic

anomalies along the northwest African continental margin, the African Blake Spur magnetic anomaly

(ABSMA) and the West African Coast magnetic anomaly (WACMA; Fig. 3.1); whether these magnetic

anomalies are associated with SDR packages remains to be proven. Their mapped extent stops south of the

Cap Vert fracture zone (Fig. 3.1). However, our work documents SDRs on trend with the African Blake Spur

magnetic anomaly (Fig. 3.1).

The oceanic crust is faulted and rugose further outboard, becoming smoother towards the continental

margin (Fig. 3.9A), as observed by Patriat & Labails (2006). Locating the continent-ocean boundary (COB) on

Fig. 3.9A is difficult due to the seismic line intersecting a fracture zone offshore Dakar and the acoustic

effects of the Cap Vert intrusive volcanism (Hansen et al., 2008). However, the COB on Fig. 3.9B is

identifiable within in The Gambia 3D dataset, where a landward-dipping normal fault separates oceanic crust

from a postulated syn-rift wedge and continental crust to the east. The oceanic crust and overlying Jurassic-

Lower Cretaceous stratigraphy in Fig. 3.9C is thrusted, forming roll-over structures in the overlying

stratigraphy, and again intersects east-west trending fracture zones causing pronounced steps. Imaging the

continental basement structure is limited by the seismic penetration on all profiles. All the overlying

stratigraphy thins onto oceanic crust and thickens considerably inboard. DSDP sites located outboard

therefore encounter condensed sequences, this is exaggerated at Site 367, which was drilled on a basement

high. Expanded and complete stratigraphic intervals are predicted from the seismic interpretation at the

base of carbonate margin (Fig. 3.9).

Both DSDP sites are located west of the Magnetic Anomaly M-25 (~154 Ma – Kimmeridgian), therefore latest

Jurassic stratigraphy is interpreted along all three profiles in the oceanic domain, as encountered at Site 367

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below the MBU (1088.52 m depth; Fig. 3.3; Fig. 3.5). Older Jurassic stratigraphy (and potential Jurassic

marine source rocks) were likely deposited on the oldest oceanic crust towards the continental margin, and

there is also potential for lacustrine sequences behind the carbonate platform. The Jurassic stratigraphy

below the present-day shelf forms a thick carbonate platform with an associated escarpment margin (Casson

et al., 2020b), present along the NWAAM and conjugate margins (Fig. 3.9; Casson et al., 2020c). Younger

stratigraphy onlaps this feature (Fig. 3.9B).

At the base of the carbonate escarpment, the basinal stratigraphy is deformed into a 5 km wavelength, tight

anticlinal fold (Fig. 3.9B). The fold axis trends north-south for at least 40 km (Casson et al., 2020b). This was

previously reported by Tari et al. (2003) as being salt induced, interpreting the deformation as being induced

by a salt pillow below the folded stratigraphy. Analysis of the 3D seismic data in The Gambia (Casson et al.,

2020b) does not detect any seismic reflections indicative of salt (no low amplitude, chaotic, weak

reflections), hence a tectonic mechanism for the deformation is preferred.

The high amplitude, well-stratified, continuous seismic facies of the overlying pelagic limestone (Blake

Bahama Formation; Fig. 3.3; Fig. 3.5; Fig. 3.9) clearly blankets the oceanic crust structure filling the rugose

topography and thinning over basement highs (Fig. 3.10). This unit is heavily faulted by low offset normal

faults further outboard (Fig. 3.9B).

Fig. 3.10 – A correlation between the stratigraphy studied in the DSDP cores of Site 367 (Fig. 3.3) and the two-way time seismic section displayed in Fig. 3.9B, where the location of this zoom is highlighted. DSDP unit numbers are shown on the lithology log. The main seismic markers are coloured and named following the symbology in Fig. 3.9. Note there are no wireline logs from this borehole, therefore a seismic-well tie is


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not possible. Type II and Type II/III refers to the predominate kerogen type, i.e. marine and mixed, respectively, for those particular intervals. OC – oceanic crust; SF – sea floor; SR – source rock.

Without a seismic-well tie calibration, due to the lack of wireline logs, there is uncertainty in definitively

assigning seismic reflections to the key stratigraphic surfaces established in the re-investigation of Site 367.

However, a most-likely interpretation based on the known unit thicknesses correlated to packages of

different seismic facies, is provided in Fig. 3.10. The BAU is inferred to occur between Core 24 (intra Late

Albian) and 25 (Late Barremian), with overlying Early-Middle Albian onlapping the BAU surface to the

northeast of the site. This explains why Early-Middle Albian strata are not present or at least very condensed

(and if present, located between cores 24 and 25) at Site 367. This observation and the clear thinning of the

Albian sequence suggests the formation of significant paleo-topography prior to Albian deposition. Mourlot

et al. (2018) attributed this to emplacement of sheeted contourite drifts.

Interpreting eastward on Fig. 3.9C to the present-day base of slope, the BAU bisects a series of undulating,

draping continuous reflections with km-scale wavelength that are interpreted as sediment waves. This

indicates that there was oceanic circulation at this time, as reported by Mourlot et al. (2018). Below the

most distal region of the Guinea Plateau (Fig. 3.9C), the pre-Albian sediments are anomalously thick with

minor thrust faults observed, interpreted as a collapsed part of the carbonate margin. A similar-aged

collapse feature is observed on the conjugate Demerara Rise (Casson et al., 2020c).

At Site 368, in the interval equivalent to the TD of the borehole, high amplitude seismic reflections are

observed that form elongated horizontal geobodies up to 5 km wide, disrupting underlying reflections (Fig.

3.9A). These are interpreted to represent the diabase sills encountered at TD of Site 368, intruded into

relatively undeformed oceanic domain stratigraphy (Fig. 3.6). Along the remainder of the profiles, no similar

geobodies/sills are identified.

The Hatteras Formation source rock (Late Albian – Late Cenomanian) encountered at both DSDP sites again

thickens towards the continental margin and has a distinctive seismic response, forming high amplitude,

continuous reflections (Fig. 3.10). The base of the source rock interval, i.e. the boundary between Unit 4A

and 4B at DSDP Site 367, is interpreted to correlate to the observed change in seismic amplitude and

continuity (Fig. 3.10). Displayed on Fig. 3.9A, near the top Cenomanian horizon, locally high amplitude,

lobate reflections are interpreted to represent basin floor fan systems (BFF) of equivalent up dip erosive

base of slope channel-lobe systems (SC; Posamentier & Kolla, 2003). The Yakaar-1 gas discovery (15 TCF)

encountered a 120 m hydrocarbon in high quality Lower Cenomanian reservoir sands (Kosmos Energy,

2019). The comparable sequence further south along the margin at the base of the escarpment (Fig. 3.9B),

shows significant thickening forming a wedge geometry, time-equivalent to a shelf-edge delta system

documented on the distal continental margin (Casson et al., 2020b). Subsequent canyonisation and erosion

of the shelf margin that occurred during the Late Cretaceous is recorded as the regional composite

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unconformity (RCU; Casson et al., 2020b), correlating approximately to the top Cenomanian (TC) in the

oceanic domain and the significant facies change between the Hatteras and Plantagenet Formations (Fig.

3.3).

Within the interval correlated to the Plantagenet Formation, chaotic and discontinuous reflections above

continuous sub-parallel basal shear surfaces are interpreted as mass transport deposits (MTDs; Fig. 3.9A;

Posamentier & Kolla, 2003) representing material associated with the margin collapse (Casson et al., 2020b).

The BTU erodes the Mesozoic stratigraphy primarily at the base of slope, forming slope canyons mirroring

earlier RCU-related canyons (Fig. 3.9B), completely truncating the Plantagenet Formation (Fig. 3.9C) and

subcropping on the present-day shelf due to Cap Vert volcanism and associated uplift in the Cenozoic.

Fig. 3.11 (next page) – A dip-orientated Wheeler diagram constructed from the oceanic domain (left) to distal and proximal domains of onshore Senegal, northwest Africa Atlantic margin (right) detailing the stratigraphic evolution of the continental margin, from pre-rift to the top of the Cretaceous. The horizontal axis is not accurately to scale. Pin stripe vertical lines indicate hiatus’ corresponding to various regional unconformities dated in the stratigraphic analysis. Dash black and white lines indicate revised wells in this study. The geological time scale (GTS 2018) is non-linear. Hydrocarbon occurrences are shown. Outcrop studies from Maio, Cape Verde (Casson et al., 2020a) and Cap de Naze, Senegal (CDN) displayed. BFF – basin floor fan; TD – total depth.


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3.6 DISCUSSION

3.6.1 Stratigraphic Evolution

Incorporating the new interpretations of the oceanic domain dating and revised stratigraphy with the

existing shelfal stratigraphy encountered in exploration wells, and new data from the outcrop studies on

Maio, Cape Verde (Casson et al., 2020a) and Cap de Naze, Senegal (pers. obs.), allows the full dip-extent of

the depositional systems and stratigraphic architecture to be investigated across the northwest African

continental margin (Fig. 3.11).

Basement rocks are encountered in the most proximal (onshore), easterly drilled Senegalese exploration

wells (17 total), where the overlying Meso-Cenozoic sedimentary sequence thins and gradually onlaps

basement. These penetrations reveal the heterogeneous nature in the pre-Mesozoic basement, summarised

by Villeneuve et al. (2015) and Ndiaye et al. (2016). Wells Dl-1 and Kb-1 (Fig. 3.11) recovered Silurian to

Permian-aged quartzites (biotite hornfels), shales and breccias that show affinity to Bove Basin Palaeozoic

strata (Fig. 3.11). Analogous meta-sediments radiometrically dated as Late Devonian in age are found at TD

on the conjugate North American margin in the COST GE-1 well (Poppe et al., 1995; Scholle, 1979). These

Palaeozoic sediments were widely distributed over the sutured African American continental margin (Sougy,

1962; Dillon & Sougy, 1974; Petters, 1979).

Syn-rift strata are inferred from seismic reflection data in the MSGBC basin (Tari et al., 2003), and by

comparison to similar sedimentary sequences exposed in neighbouring Central Atlantic basins (i.e. Morocco;

Davison, 2005; Pichel et al., 2019) and on the conjugate margin (Shipley et al., 1978). Late Triassic to Early

Jurassic continental clastics and salt were probably deposited in these rift graben systems, isolated by

basement highs into two mapped sub-basins: the Mauritania and Casamance salt basins. Salt has been

remobilised in both basins primarily into narrow, km-wide diapiric structures intruded into the overlying

sedimentary succession, drilled in offshore Casamance Maritime (CM) exploration wells, southern Senegal

and in Guinea Bissau. Conjugate syn-rift salt basins are predicted from tectonic reconstructions on the

American margin and occur further north in the Carolina Trough (Davison, 2005).

Early to Middle Jurassic post-rift strata are encountered in Senegalese exploration wells drilled close to the

paleo-shelf edge (i.e. DKM-2) consisting of interbedded micritic limestones, calcareous sandstones and marls

forming a carbonate platform with an oceanward escarpment margin (Casson et al., 2020b). The conjugate

is the Bahamas-Grand Banks carbonate platform and carbonate platforms are encountered surrounding the

Central Atlantic. Jurassic lacustrine/lagoonal shales located inboard of the escarpment margin are

postulated to be a source for the oil in the onshore Gadiaga and Diam Niado fields, based on biomarker

analysis (Carr et al., 2015; 2017).


118

Argillaceous limestones (Cat Gap Formation) from DSDP Site 367 are the time-equivalent basinal sediments

to Jurassic carbonate platform. Observed terrestrial organic material in these sediments is indicative of

terrigenous input into the deep basin, suggesting Jurassic deltas were present along the continental margin.

This stratigraphy is not recorded at outcrop on Maio, where the oldest sediments are of Lower Valanginian

age, resting on oceanic crust pillow lavas (Casson et al., 2020a).

The middle Berriasian unconformity identified in this study at DSDP Site 367 (Fig. 3.3; Fig. 3.5) represents

the Jurassic-Cretaceous boundary. On the conjugate margin, in the Georgia Embayment and along the

remainder of the American margin to the north, the carbonate platforms were drowned at this time by

Berriasian and younger siliciclastic systems (drowning unconformity sensu Schlager, 1989), however across

the Blake Plateau and the Bahamas, carbonate platforms persisted through the Early Cretaceous (Poag,

1991). The carbonate platform survived until Aptian times in the MSGBC basin (Casson et al., 2020b). Pelagic

limestones of the Blake-Bahamas Formation accumulated in the deep basin across the Central Atlantic. DSDP

Site 367 and outcrops on Maio record an upward increase in marl interbeds, reflecting additional terrigenous

input. A recent appraisal well on the Yakaar discovery, northern Senegal (Kosmos Energy, 2019) hinted at

the occurrence of Aptian basin floor fan systems at this time.

The base Albian unconformity is interpreted to occur across the oceanic domain of the Central Atlantic and

is recorded at multiple locations as a hiatus spanning most of the Aptian. On Maio and at DSDP Site 367 Late

Barremian sediments are recorded below this event, bracketing the timing of the unconformity. The

overlying stratigraphy of the Hatteras Formation varies in age from Early Albian (DSDP Site 534A) to Late

Albian (DSDP Site 367). At this time, karstification of the most distal edge of the African carbonate platform

preceded the first major siliciclastic input (Martin et al., 2010; Casson et al., 2020b). Shelfal wells record fine-

grained sandstones and seismic geomorphology reveals a shelf edge delta prograded through the Albian

across the relict carbonate margin in many areas of the MSGBC basin, spilling sediment over the escarpment

margin to form base-of-slope fans (Casson et al., 2020b). In the deep basin, the equivalent stratigraphy

records thin distal turbidites, with observed plant debris within interbedded mudstones and an increase in

terrestrially derived organic matter (Core 24, DSDP Site 367 – Fig. 3.3; Fig. 3.4). We postulate that these

sediments were introduced into the deep basin by the Albian shelf-edge delta systems.

A latest Albian flooding surface is recognised around the Central Atlantic, transgressing the shelf, and coeval

with the onset of organic-rich sedimentation. Minor carbonate production on the transgressed Senegalese

shelf at this time is interspersed within siliciclastics (Br-1; Ti-1). At DSDP Site 367, the organic enrichment

ceases in the Late Cenomanian, whereas 580 km northwest at DSDP Site 368 enrichment prevails into the

Turonian. Jones et al. (2007) reveals through regional seismic mapping of the top of the black shale

sequence, the diachronous nature of the interval extending into the Campanian south of the Guinea Fracture

Zone. A progradational phase in the Late Cenomanian delivers siliciclastic sediment to basin floor fans

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encountered in Yakaar wells, through the palaeo-Senegal river system, inboard of DSDP Site 368. The

continental margin is transgressed at the Cenomanian-Turonian boundary and this is followed by the onset

of margin collapse observed offshore The Gambia (Casson et al., 2020b). Debris-rich lobes form at the base

of submarine canyons redepositing eroded carbonate material from the underlying platform. A regional

composite unconformity, with erosion restricted to the shelf edge, is established, bypassing sediment

throughout the remainder of the Late Cretaceous. Non-calcareous mudstones and siltstones of distal

turbidites, part of the Plantagenet Formation are recorded through DSDP sites 367 and 368 (Fig. 3.11). Late

Cretaceous sediments of this age are not present on Maio due to postulated volcanic uplift (or are not

exposed). Shallow marine sands prograded across the Senegalese shelf in the Campanian to Maastrichtian

period, observed at the Cap de Naze outcrop as stacked progradational para-sequences of shallow marine

sandstones and shelfal siltstones (Barusseau et al., 2009). Development of a base Tertiary unconformity at

the Cretaceous-Tertiary boundary is associated with a major relative sea-level fall (Shipley et al., 1978).

3.6.2 Regional Extent and Drivers of Major Unconformities

This study refines the timing and nature of key unconformities that have previously been documented to

occur elsewhere in the oceanic domain of the Central Atlantic during the drilling of many DSDP legs

(summarised in Jansa et al., 1978), and in subsequent stratigraphic studies (Müller et al., 1983; 1984; de

Graciansky et al., 1987). A summary of these events is provided below, capturing their regional distribution

and postulated drivers behind their formation.

Middle Berriasian unconformity - MBU

At DSDP Site 367, the MBU and Jurassic-Cretaceous (J/K) boundary is located between the Cat Gap (red

argillaceous limestone) and Blake-Bahama (white-grey limestone with marl) formations (Fig. 3.5). This

unconformity at DSDP Site 367 is reported for the first time in this publication based on the new high-

resolution biostratigraphy. The original interpretation (Lancelot et al., 1978a) reported from all the

stratigraphy from Core 32 to TD as Kimmeridgian and older. We now reveal the unconformity records a ca.

5 million-year hiatus between the Early Tithonian and middle Berriasian and is equivalent to seismo-

stratigraphic Horizon C recognised across the Central Atlantic (Jansa et al., 1979). The interval on the

Moroccan shelf is characterised by multiple hard ground surfaces (NARG obs.). The Cat Gap Formation

shares remarkably similar lithological characteristics to the ‘Rosso Ammonitico’ facies (sensu Farinacci &

Elmi, 1981), more precisely to the ‘Rosso ad Aptici’ sub-facies, i.e. the basinal facies with abundant chert and

marl (sensu Rossi, 1975). The Rosso Ammonitico facies is characterised by red pelagic limestones and marls,

the development of hard grounds, condensed sequences, and ferro-manganese nodules, typically deposited

over topographic highs (Cecca et al, 1992). This facies is pervasive in the Mediterranean Tethys, and occurs

throughout the Central Atlantic, recovered at other DSDP sites (100, 105; Hollister et al., 1972a; 1972b).


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There are no known occurrences of the Rosso Ammonitico in late Berriasian or younger stratigraphy; the

disappearance is associated with, (1) major paleoceanographic circulation changes establishing a connection

between the Tethys and Caribbean, (2) increase in biogenic (rapid diversification of calcareous

nannoplankton) and siliciclastic sediment supply, (3) thermal subsidence following the end of Central

Atlantic rifting, (4) North Atlantic breakup in the Iberia-Newfoundland segment (Cecca et al, 1992). Further

examination of the J/K boundary at DSDP Site 534A (Tremolada et al., 2006) implied a significant

temperature increase in surface waters through the interval. Without further investigation it is difficult to

pinpoint what process is generating this unconformity within the Central Atlantic, our primary model is this

is related to North Atlantic breakup within the Iberia-Newfoundland segment; Pereira & Alves (2011)

reported an unconformity of this age.

Base Albian unconformity - BAU

The base Albian unconformity (BAU) is inferred to be located within the 47.5 m core gap between intra Late

Albian dated Core 24 (Hatteras Formation) and Late Barremian dated Core 25 (Blake-Bahama Formation) at

DSDP Site 367 (Fig. 3.3). The occurrence of the BAU is supported by seismic interpretation that recognises

an unconformity at this stratigraphic level (Fig. 3.10). The BAU is recorded throughout the Central Atlantic

(Reflector sensu Jansa et al., 1979), and as interpreted in the re-evaluation of DSDP Site 534A between the

Early Albian dated Core 38 (Hatteras Formation) and the earliest Aptian – latest Barremian dated Core 42

(Blake-Bahama Formation). This event corresponds to a major lithological change between carbonate (pre-

BAU) and siliciclastic-prone deposition (Fig. 3.11; de Graciansky et al., 1981). Locally to DSDP Site 105, pre-

Reflector strata (Blake-Bahamas Formation) onlap onto a similar basement structure (swell) to that drilled

by DSDP Site 367 (Tucholke & Mountain, 1979). Stratigraphy onlapping the BAU is also observed at DSDP

Site 367 (Mourlot et al., 2018). The BAU forms an angular unconformity peneplaining up to 1 km of sediment

across the Demerara Rise, ca. 500 km to the southeast (Casson et al., 2020c). The pre-BAU stratigraphy is

heavily deformed creating a suite of compressional structures. Thrust faults and associated folding of pre-

BAU stratigraphy are observed along the full length of Fig. 3.9C, (ca. 250 km northwest of the Demerara

Rise), additionally, a tight anticlinal fold at the foot of the carbonate escarpment is interpreted along Fig.

3.9B. These compressional features are thought to be associated with this tectonic activity, highlighting the

widespread nature of the Equatorial Atlantic tectonic deformation. There is also a major margin collapse off

the Demerara Rise at this time and we interpret the collapse observed on Fig. 3.9C to be the equivalent on

the Guinea Plateau. The rejuvenated tectonism associated with Equatorial Atlantic break-up is postulated to

have far-field effects across the Central Atlantic, potentially leading to hiatus on paleo-highs within the basin

(i.e. at DSDP Site 367). De Graciansky et al. (1981) suggest this event (E1) is recorded throughout the Central

Atlantic, in a variety of depositional environments, from the shelf to deep basin.

Chapter 3

121

Hatteras-Plantagenet Formation boundary

A transitional boundary between the Hatteras (black shale) and Plantagenet (variegated clays) formations is

recorded in Core 17 at DSDP Site 367, observed as an upward decrease of dark black carbonaceous claystone

(Facies C; Fig. 3.4). Previous work (Herbin et al., 1986 and references therein) placed the Cenomanian-

Turonian boundary in Core 18, whereas we record Late Cenomanian stratigraphy throughout Core 17, 10.5

m shallower, suggesting DSDP Site 367 did not recover any Turonian-aged sediments, as Core 16 is assigned

a late Santonian age. This new age dating has implications for the timing, distribution and correlation of

organic-enrichment based on the 13C curve in the Central Atlantic. Around the Cenomanian-Turonian

boundary, a major marine transgression is recorded over the shelf and extending to the present-day onshore

Senegal basin, shifting depositional systems proximally (Mourlot et al., 2018). This transgression correlates

to the global eustatic sea-level rise (Haq et al., 2014). The new stratigraphic data does not support the

interpretation of a second stratigraphic gap (Event E2; de Graciansky et al., 1981) at DSDP Site 367, where

most of the Cenomanian-aged strata was interpreted to be absent. Our new dating shows a complete

Cenomanian succession equivalent to the Hatteras Formation from Core 17 to 21 (Fig. 3.3).

3.6.3 Seaward Dipping Reflector (SDR) Occurrence & Volcanism in the Central Atlantic

Based on the interpretation of one regional 2-D seismic reflection profile (Fig. 3.9), SDRs are reported for

the first time along the northwest African continental margin. The location of these newly discovered SDRs

is on trend (parallel) with the African Blake Spur magnetic anomaly (Fig. 3.1) further to the north beyond the

Cape Vert fracture zone. No evidence has been presented thus far for the occurrence of SDRs tied spatially

to the two magnetic anomalies along the northwest African continental margin (Davison, pers. comms.

2020). Further volcanism during early Central Atlantic seafloor spreading resulting in the formation of SDR

sequences is documented on the conjugate margins of northeast South America below the Demerara Rise

(Reuber et al., 2016) and North American Atlantic margin within the Carolina trough and Blake Plateau basin

(Oh et al., 1995). Hence the continental margins in the southern Central Atlantic can be classified as volcanic

margins. Basile et al. (2020) suggests this volcanism is a related to the Sierra Leone hotspot.

3.7 CONCLUSIONS

Re-investigating the cores of key DSDP sites drilled across the Central Atlantic using modern multi-discipline

biostratigraphic techniques has yielded an updated stratigraphic framework that improves the timing and

resolution, as well as the identification of key stratigraphic events. Specifically, in relation to the two African

DSDP sites, 367 and 368, this is the first new investigation that includes re-sampling to have been published

in the last 30 years. The stratigraphic framework developed in the oceanic domain is extended and

correlated with depositional systems in data from the northwest African continental margin. A well-


122

constrained middle Berriasian unconformity is reported for the first time in Core 33 at DSDP Site 367, where

middle Berriasian white pelagic limestones (Blake-Bahama Formation) sit unconformably on Early Tithonian

red argillaceous limestones (Cat Gap Formation), indicating a ca. 5 Myr hiatus.

Organic content in the middle Berriasian to Late Barremian Blake-Bahamas Formation is recorded in isolated

marl horizons (cms-thick) with a terrestrial kerogen type that records total organic carbon content (TOC)

averaging 5% at DSDP Site 367. Seismic evidence indicates this package expands towards the carbonate

escarpment and hence may offer a prospective hydrocarbon source rock interval.

A major lithological change is recorded at DSDP Site 367 in the intra-Late Albian Core 24, where the facies

consists of variegated mudstones with abundant terrestrial detritus with a notable absence of any limestone

beds. A base Albian unconformity is inferred below this core at the boundary with the Hatteras Formation

(Barremian). Early-Middle Albian strata are interpreted onlapping the base Albian unconformity away from

Site 367, suggesting there was paleo-topography prior to Albian deposition. This unconformity is recorded

throughout the Central Atlantic postulated to be tectonically driven by far field stresses related to the

opening Equatorial Atlantic. This is evidenced by the re-evaluation of the corresponding interval

encountered at DSDP Site 534A, where Early Albian-aged sediments sit above this event, recognised on

seismic data previously as Reflector . A major margin collapse feature and evidence of compression, thrust

faulting and folding, is observed related to this tectonism from the Guinea Plateau to Senegal.

The onset of organic-rich sedimentation, and hence anoxic to dysoxic bottom-water conditions is well-dated

as occurring in the intra Late Albian at DSDP Site 367. Internal heterogeneity is observed between different

facies within this source rock interval that extends into the Late Cenomanian and earliest Turonian, in DSDP

Site 367 and 368 respectively. This indicates spatio-temporal changes in the cessation of anoxia along the

African margin. Dark black carbonaceous claystones have terrestrially-derived organic matter, whereas the

kerogen type is marine in origin within the light grey clayey nanno-fossil marlstone facies that record much

higher TOC values (up to 25%). Terrestrial organic matter is likely introduced by turbidity currents linked to

sediment input from shelf edge delta systems active on the African continental shelf.

The Late Cenomanian dark black laminated shales present in Core 18, DSDP Site 367, average 34% TOC,

time-equivalent to the global anoxic event, OAE-2. The organic-rich interval on the American margin is

truncated by a base Tertiary unconformity at DSDP Site 534A. Palynological dating of the non-calcareous

variegated clays of the overlying Plantagenet Formation span the remainder of the Late Cretaceous. A

transitional boundary is observed in Core 17, DSDP Site 367 suggesting the gradual cessation of anoxic

conditions within the oceanic domain, changes in sediment input and/or decrease in organic productivity.

In addition to the stratigraphic framework, evidence is presented for the occurrence of seaward dipping

reflectors (SDRs) northwest of the Guinea Plateau. SDRs have not been reported along this section of the

Chapter 3

123

African margin, demonstrating volcanicism during early seafloor spreading. There are similar volcanic

packages on the conjugate margins of the Central Atlantic indicating volcanic nature of this province during

early seafloor spreading.


124


This study is part of the lead authors PhD project at the University of Manchester. We thank the sponsoring

companies of NARG for their continued financial and scientific support. Funding to support the author’s (MC)

research associated with the Deep Sea Drilling Project (DSDP) data was granted by the European Consortium

for Ocean Research Drilling (ECORD) Research Grant 2018. Holger Kuhlmann provided excellent support

during our visits to the Bremen Core Repository and following requests to ship additional samples. Alastair

Bewsher at the University of Manchester is thanked for use of the organic geochemistry laboratory and

equipment training. Petrosen are gratefully acknowledged for providing access to the Senegalese

exploration well data, specifically Mamadou Faye, General Manager and Mamoudou Ka are thanked for

managing the transfer of data and hospitality during our visits. Gareth Harriman (deceased), GHGeochem

completed the pyrolysis analysis, may he rest in peace.

Chapter 3

125


Fig. S 3.1 – Palynology distribution charts from DSDP sites 367 and 368.

DSDP-368DSDP-368: Palynological Distribution Chart

Compiled by Frederic de Ville de GoyetChart date: 16-Jun-2020Scale: 1:2000ENCLOSURE 1

*1quantitative abundance, % panel

SP

FU

FT

DC

ALPR

ALBO

AL

100

740

760

780

800

820

840

860

880

900

920

940

960

980

Me

asu

red d

ep

th (

m)

Late Cretaceous

Pe

rio

d/E

poch

Santonian or older ?

Indeterminate

Middle Campanian ?

Early Coniacian ? - ?Turonian

Ag

e

FSE (P): PRES Xenascus ceratioides, Andalusiella mauthei

FDO Oligosphaeridium species (O. complex, O. irregulare, O. pulcherrimum, O. spp.); FDSAO Subtilisphaera cheit; FDO Trichodinium castanea

ACME Subtilisphaera species; FDO Chatangiella spp., Odontochitina costata

FDO Cretacaeiporites mullerii

FDSAO algal cyst (spinose); FDSAO algal cyst (granulate/scabrate and smooth)

Extremely poor recovery.

Extremely poor recovery.

LSE (P): Barren of palynomorphs

quantitative abundance (100 = 40mm, scale tick = 10 counts)

2 2 11 1 4 13 2 1 1

1

2

+

2

6

1

1

8

7

1

5

1

9

1

1

6

1

5

4

26

1

2 + + + + + +

+

+

+

2

3

1

1

1

1

57

46

12

11

21

39

15

1

1

1

1 3 1 1 +

1

*2

+

quantitative abundance (100 = 40mm)

5

58

2

17

2

23

3

6

5

4

2

11

3

1

+

*2

2

+

2

1

1

1

1

3

1

1

7

10

+

4

1

1

3

+ + +

+

+

+

*2

2

1

6

3

1

1

1

*2

1

*2

1

740

760

780

800

820

840

860

880

900

920

940

960

980

Me

asu

red d

ep

th (

m)


1

1

1

2

1

2 4 1 1 1 1 1 1 2 2

2

1

1

3

6

3 1

(Rw, Cv excluded)

WA

- T

richo

din

ium

casta

nea

(to

tal count)

80

1

1

(Rw, Cv excluded)

WA

- S

ub

tilis

ph

ae

ra s

pe

cie

s (

tota

l coun

t)

100

78

85

27

12

(Rw, Cv excluded)

WA

- O

ligosph

ae

rid

ium

sp

ecie

s (

tota

l co

unt)

80

+

+

(Rw, Cv excluded)

WA

- E

ph

ed

ripite

s s

pecie

s (

tota

l coun

t)

80

7

6

3

(Rw, Cv excluded)

WA

-

Alg

al cysts

(excl. s

pin

o (

tota

l co

unt)

80

8

5

21

4

34

6

1

(Rw, Cv excluded)

WA

- A

lga

l cysts

(sp

inose)

(tota

l co

un

t)

80

5

58

(Rw, Cv excluded)

Pra

sin

oph

yce

a (

tota

l coun

t)

80

15

3

6

3

9

3

(Rw, Cv excluded)

Bo

tryococcus &

Ped

iastr

um

spp

(to

tal cou

nt)

80

2

1

7

4

1

(Rw, Cv excluded)

Din

ocyst

Co

unt 1 (

AM

) (t

ota

l cou

nt)

100

69

92

80

30

(Rw, Cv excluded)

spore

s a

nd

po

llen

(cou

nt

1)

AM

(to

tal co

un

t)

80

1

7

(Rw, Cv excluded)

Din

ofla

gella

te c

ysts

(spe

cie

s r

ich

ne

ss)

80

16

20

14

4

7

1

(Rw, Cv excluded)

Sp

ore

s a

nd p

olle

n (

sp

ecie

s r

ichn

ess)

80

1

1

2

13

3

2

740

760

780

800

820

840

860

880

900

920

940

960

980

Me

asu

red d

ep

th (

m)

Me

asu

red d

ep

th (

m)

Chronostratigraphy

Palynology Comments

Dinoflagellate cysts A-...

Algae Prasinophycea Bot-ry......

T-......

F-......

Me

asu

red d

ep

th (

m)

Spores and Pollen WA -Trichodinium c...

WA - Subtilisphaeraspecies

WA - Oligosphae-ridium species

WA -Ephedripites sp...

WA - Algal cysts(excl. spino

WA - Algal cysts(spinose)

Prasinophycea Pediastrumspecies

Dinoflagellate CystsDinoflagellate Cysts

Spores andPollen

DinoflagellateCysts Diversity

Spores andPollen diversity

Palynology % Total Counts

Me

asu

red d

ep

th (

m)

Text Keys

*1 ('Paly Totals exclusion group' excluded)

*2 quantitative abundance (100 = 40mm, scale tick = 10 counts)

Boundary Types

Confident

Sampling

Cutting

Core

Sidewall Core

Taxon Categories

AC - Acritarchs

AL - Algae

ALBO - Botryococcus and Pediastrum

ALPR - Prasinophycea

DC - Dinoflagellate cysts

FT - Foram test linings

FU - Fungi

SP - Spores and pollen

DSDP Leg 41, Site 367ENCLOSURE 1: Leg 41, Site 367: Palynological Distribution Chart

Analysis by Frederic de Ville de GoyetChart date: 16-Jun-2020Scale: 1:3500

Interval: 520m - 860m


SP

FU

DC

ALPR

ALBO

AL

AC

100

600

700

800

Me

asu

red

de

pth

(m

)

Late Cretaceous

Early Cretaceous

?Late Cretaceous - ?Early Cretaceous

Peri

od

/Epo

ch

intra-Late Albian

?Late Santonian or older

?Late Cenomanian or older

?Late Cenomanian - ?Late Albian

Age

FSE (P): FDO Oligosphaeridium complex; FDAO/ACME (TNS) Subtilisphaera spp.; FDCO subtilisphaera cheit; PRES Classopollis spp. (small, <30 microns), Afropollis jardinus

FDSAO/ACME Subtilisphaera cheit

AOM; ACME algal cyst (smooth)

FDAO Litosphaeridium conispinum; FDO Litosphaeridium arundum; FDO (in situ) Afropollis jardinus, Classopollis spp. (small, <30 microns); FDSAO Prasinophycea algae (Pterospermellla spp.)

FDO Elaterosporites klaszii, E. verrucatus; FDSAO Classopollis species (C. spp.small, <30 microns, C.brasiliensis); INCR (ABN) Afropollis jardinus; INCR (SABN) Subtilisphaera spp.; FDO D.tuberculatum, T.castanea, S.agadirensis

LSE (P): PRES (CMN) Subtilisphaera cheit


1 ? 1 ? 1 1

3

2

6

2

1

3

5

8

81

3

8

15

6

12

17

7

61

3

1 1

+

6 19 1

1 1 1 1 1 3 1 1 2

*2

1

1

1

*2

3

2

8

2

2

8

53

2

1

1

4

+


1

1

2

4

9

12

92

2

+

+

+

2

1

3

15

5

2

1

+ + 1

*2

2

+

*2

1

7

1

600

700

800

Me

asu

red

de

pth

(m

)


1

1

1

+

2

1

2

1

1

2 1 1 1 1

2

2

1

6 Rw

2

2

33

1 Rw

1

23

1

2 5 + + 23 1 4 + 1 + + 1 + 1 1

1 Rw ?

(Rw, Cv excluded)

WA

- T

richo

din

ium

casta

nea (

tota

l cou

nt)

80

2

(Rw, Cv excluded)

WA

- S

ub

tilis

ph

aera

specie

s (

tota

l co

unt)

100

20

98

3

15

76

9

(Rw, Cv excluded)

WA

- O

ligosph

ae

rid

ium

spe

cie

s (

tota

l co

unt)

80

2

7

(Rw, Cv excluded)

WA

- C

lassop

olli

s s

pecie

s (

tota

l cou

nt)

80

2

2

57

(Rw, Cv excluded)

WA

- E

ph

ed

rip

ites s

pecie

s (

tota

l co

un

t)

80

2

1

3

(Rw, Cv excluded)

WA

- A

lgal cysts

(excl. s

pin

o (

tota

l count)

80

3

10

65

4

2

(Rw, Cv excluded)

WA

- A

lgal cysts

(sp

inose)

(tota

l co

unt)

80

1

1

(Rw, Cv excluded)

Pra

sin

op

hyce

a (

tota

l co

un

t)

100

5

13

29

101

4

1

(Rw, Cv excluded)

Botr

yoco

ccus &

Ped

iastr

um

sp

p (

tota

l co

un

t)

80

2

+

(Rw, Cv excluded)

Din

ocyst C

oun

t 1 (

AM

) (t

ota

l cou

nt)

90

28

75

3

11

48

9

(Rw, Cv excluded)

spo

res a

nd

po

llen

(cou

nt 1

) A

M (

tota

l coun

t)

80

13

3

3

2

49

(Rw, Cv excluded)

Din

ofla

ge

llate

cysts

(spe

cie

s r

ichn

ess)

80

8 ?

5

1

6

15

2

(Rw, Cv excluded)

Spo

res a

nd p

olle

n (

sp

ecie

s r

ichn

ess)

80

4

6

2

6

20

600

700

800

Me

asu

red

de

pth

(m

)

Me

asu

red

de

pth

(m

)

Chronostratigraphy

Palynology Comments

Dinoflagellate cysts A... Algae Prasinophycea B... ...

Me

asu

red

de

pth

(m

)

Spores and Pollen WA - Trichodini...WA - Trichodinium ca...

WA - Subtilisphaera... WA - Oligospha...WA - Oligosphaeridiu...

WA - Classopol...WA - Classopollis spe...

WA - Ephedripit...WA - Ephedripites sp...

WA - Algal cyst...WA - Algal cysts (excl...

WA - Algal cyst...WA - Algal cysts (spin...

Prasinophycea Pediastrum spe... Dinoflagellate Cy...Dinoflagellate Cysts

Spores and Poll...Spores and Pollen

Dinoflagellate C...Spores and Poll... Palynology % Total Counts

Me

asu

red

de

pth

(m

)

Text Keys



Boundary Types

Confident

Sampling

Cutting

Core

Sidewall Core

Taxon Categories

AC - Acritarchs

AL - Algae




FU - Fungi



126

EXP SITE CORE SECT TOP BOT MBSF_TOP MCD_TOP Sample ID Nan

no

s

Pal

yno

logy

Cal

pio

nel

lid

s

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

TOC

(%)

41 367 16 2 13 15 541.63 541.63 5103260 6

41 367 16 3 118 119 544.18 544.18 5103261

41 367 16 4 55 56 545.05 545.05 5103262

41 367 16 6 3 4 547.53 547.53 5046547

41 367 16 6 70 71 548.2 548.2 5103263

41 367 17 1 5 6 616.05 616.05 5046548

41 367 17 1 100 105 617 617 5103161

41 367 17 2 15 16 617.65 617.65 5103162

41 367 17 2 70 72 618.2 618.2 5046552 0.17

41 367 17 2 95 100 618.45 618.45 5103163

41 367 17 3 52 53 619.52 619.52 5103164

41 367 17 3 60 62 619.6 619.6 5046551 11.1 2.7 45.9 3.6 399 123 33.0 11.1

41 367 17 3 110 115 620.1 620.1 5103165 3

41 367 17 4 5 6 620.55 620.55 5046549

41 367 17 4 43 47 620.93 620.93 5103166

41 367 17 4 106 112 621.56 621.56 5103167

41 367 17 4 115 116 621.65 621.65 5046564 4.03

41 367 18 1 50 53 636.5 636.5 5103168

41 367 18 1 115 116 637.15 637.15 5046563 33.8

41 367 18 1 140 142 637.4 637.4 5103169 1

41 367 18 2 13 14 637.63 637.63 5046565

41 367 18 2 13 15 637.63 637.63 5103170

41 367 18 2 20 21 637.7 637.7 5054655

41 367 18 2 24 25 637.74 637.74 5046567 36.7 13.3 200 8.5 397 546 23.0 36.7

41 367 18 2 142 143 638.92 638.92 5046566

41 367 18 3 32 33 639.32 639.32 5046568 31.8

41 367 18 4 93 94 641.43 641.43 5046569

41 367 18 4 94 95 641.44 641.44 5046570 25.4 9.5 153 7.6 398 604 30.0 25.4

41 367 18 5 52 54 642.52 642.52 5046572 7.69

41 367 18 5 77 78 642.77 642.77 5046571

41 367 19 2 32 34 646.32 646.32 5046573 19.8 5.3 120 8.7 410 608 44.0 19.8

41 367 19 2 34 35 646.34 646.34 5046574

41 367 19 3 74 75 648.24 648.24 5046575

41 367 19 3 94 95 648.44 648.44 5046576 19.8

41 367 19 3 116 117 648.66 648.66 5046577 2.18

41 367 19 4 17 18 649.17 649.17 5046578

41 367 20 1 132 133 689.82 689.82 5046580 17.7 2.9 88.0 7.7 406 497 43.0 17.7

41 367 20 1 140 141 690.9 690.9 5103171

41 367 20 1 142 143 690.92 690.92 5046581 9.37 1.5 53.6 6.1 412 572 65.0 9.4

41 367 20 1 144 145 690.94 690.94 5046579

41 367 20 2 6 7 691.06 691.06 5046582

41 367 20 2 96 98 691.96 691.96 5103172

41 367 20 2 136 137 692.36 692.36 5046583

41 367 20 2 137 138 692.37 692.37 5046584

41 367 20 3 7 8 692.57 692.57 5046601

41 367 21 1 74 75 692.74 692.74 5046605

41 367 20 3 65 67 693.15 693.15 5103173

41 367 21 1 119 120 693.19 693.19 5103175

41 367 20 3 140 141 693.9 693.9 5046602

41 367 21 2 95 96 694.45 694.45 5046606

41 367 21 2 95 96 694.45 694.45 5103176

41 367 21 2 100 101 694.5 694.5 5046607 5.83

41 367 20 4 79 80 694.79 694.79 5046604 11.6

41 367 20 4 90 91 694.9 694.9 5103174

41 367 20 4 92 93 694.92 694.92 5046603

41 367 21 3 65 66 695.65 695.65 5046609 13.7

41 367 21 3 90 91 695.9 695.9 5103177

41 367 21 3 93 94 695.93 695.93 5046608

41 367 21 4 49 50 696.99 696.99 5103181

41 367 21 4 50 51 697 697 5046610

41 367 21 5 66 67 698.66 698.66 5046612

41 367 21 5 68 69 698.68 698.68 5103182

41 367 21 6 40 41 699.9 699.9 5046614

41 367 21 6 76 77 700.26 700.26 5046613

41 367 21 6 114 115 700.64 700.64 5103183

41 367 22 1 120 121 721.7 721.7 5103184

41 367 22 1 130 131 721.8 721.8 5046615

41 367 22 2 18 19 722.18 722.18 5046616

41 367 22 2 72 73 722.72 722.72 5046617 8.76

41 367 22 2 117 118 723.17 723.17 5103185

41 367 22 3 40 41 723.9 723.9 5103186

41 367 22 3 46 47 723.96 723.96 5046619

41 367 22 4 55 56 725.55 725.55 5046623

41 367 22 4 110 111 726.1 726.1 5046624 3.29

41 367 22 5 66 67 727.16 727.16 5046628 4.7 0.4 9.5 2.3 410 201 49.0 4.7

41 367 22 5 136 137 727.86 727.86 5046626

41 367 22 5 136 137 727.86 727.86 5103187

41 367 22 6 30 31 728.3 728.3 5046631

41 367 22 6 30 31 728.3 728.3 5103188

41 367 22 6 44 45 728.44 728.44 5046629

41 367 22 6 60 61 728.6 728.6 5103189

41 367 22 6 80 81 728.8 728.8 5103191

41 367 22 6 100 101 729 729 5103194 2

41 367 23 1 85 86 778.35 778.35 5103198 5

41 367 23 1 86 87 778.36 778.36 5046632 2.21 0.1 1.5 1.7 421 70 76.0 2.2

41 367 23 2 15 17 779.15 779.15 5103200

41 367 23 2 43 50 779.43 779.43 5103199

41 367 23 2 66 67 779.66 779.66 5046634

41 367 23 2 100 101 780 780 5103201

41 367 24 1 141 142 835.91 835.91 5029500

41 367 24 2 83 84 836.83 836.83 5029502

41 367 24 2 120 140 837.2 837.2 5103206

41 367 24 2 121 122 837.21 837.21 5029501

41 367 24 3 5 7 837.55 837.55 5103207 4

41 367 24 3 10 11 837.6 837.6 5029508

41 367 24 3 52 53 838.02 838.02 5029505

41 367 24 3 94 95 838.44 838.44 5029504

41 367 25 1 5 6 891.55 891.55 5054468 8.43 0.3 14.0 2.8 425 166 33.0 8.4

41 367 25 1 19 20 891.69 891.69 5029512

41 367 25 1 41 42 891.91 891.91 5029511

41 367 25 1 133 134 892.83 892.83 5054440 4.18

41 367 25 1 145 146 892.95 892.95 5029510

41 367 25 2 17 18 893.17 893.17 5029514

41 367 25 2 127 128 894.27 894.27 5029515

41 367 25 2 143 144 894.43 894.43 5029516

41 367 25 3 4 5 894.54 894.54 5029518

41 367 25 3 95 96 895.45 895.45 5029519

41 367 25 3 116 117 895.66 895.66 5029526

41 367 25 4 14 15 896.14 896.14 5029528

41 367 25 4 93 94 896.93 896.93 5029529

41 367 25 4 94 95 896.94 896.94 5054490 1.8

41 367 25 4 132 133 897.32 897.32 5029530

41 367 26 1 39 40 910.89 910.89 5054426

41 367 26 1 75 76 911.25 911.25 5051177

41 367 26 1 90 91 911.4 911.4 5054501 2.71

41 367 26 1 91 92 911.41 911.41 5054439

41 367 26 2 11 12 912.11 912.11 5054441

41 367 26 2 46 47 912.46 912.46 5054509 8.54 0.3 10.5 2.7 430 122 32.0 8.5

41 367 26 2 65 66 912.65 912.65 5051178

41 367 26 2 69 70 912.69 912.69 5054466

41 367 26 2 136 137 913.36 913.36 5054469

41 367 26 3 29 30 913.79 913.79 5054478

41 367 26 3 40 41 913.9 913.9 5054523 3.22

41 367 26 3 62 63 914.12 914.12 5054479

41 367 26 3 102 103 914.52 914.52 5054526

41 367 26 3 110 112 914.6 914.6 5051179 2.11

41 367 26 4 50 51 915.5 915.5 5051180

41 367 26 4 137 138 916.37 916.37 5054484

41 367 27 1 64 65 939.64 939.64 5054499

41 367 27 1 119 120 940.19 940.19 5054530 3.86 0.3 4.4 2.3 432 113 60.0 3.9

41 367 27 1 130 131 940.3 940.3 5051181

41 367 27 2 23 24 940.73 940.73 5054505

41 367 27 2 85 86 941.35 941.35 5051182

41 367 27 2 106 107 941.56 941.56 5054507

41 367 27 3 20 21 942.2 942.2 5051183

41 367 28 1 65 66 968.15 968.15 5051184

41 367 28 2 23 24 969.23 969.23 5054512

41 367 28 2 70 71 969.7 969.7 5051185

41 367 28 2 120 122 970.2 970.2 5054533 3.33

41 367 28 2 123 124 970.23 970.23 5054514

41 367 28 3 72 73 971.22 971.22 5051186

41 367 29 1 138 139 997.38 997.38 5054522

41 367 29 2 67 68 998.17 998.17 5054524

41 367 29 2 70 71 998.2 998.2 5051187

41 367 30 1 8 9 1024.58 1024.58 5051193

41 367 30 1 25 26 1024.75 1024.75 5051188

41 367 30 1 30 31 1024.8 1024.8 5051194

41 367 30 1 40 41 1024.9 1024.9 5054525

41 367 30 1 80 81 1025.3 1025.3 5051195

41 367 30 1 127 128 1025.77 1025.77 5051196

41 367 30 1 135 136 1025.85 1025.85 5051197

41 367 30 1 140 141 1025.9 1025.9 5051198

41 367 30 1 148 149 1025.98 1025.98 5054528

41 367 30 2 15 16 1026.15 1026.15 5051199

41 367 30 2 40 41 1026.4 1026.4 5051200

41 367 30 2 60 61 1026.6 1026.6 5051189

41 367 30 2 72 73 1026.72 1026.72 5051201

41 367 30 2 85 86 1026.85 1026.85 5051202

41 367 30 2 100 101 1027 1027 5051203

41 367 30 2 109 110 1027.09 1027.09 5051204

41 367 30 2 130 131 1027.3 1027.3 5051205

41 367 30 2 148 149 1027.48 1027.48 5054527

41 367 31 1 22 23 1053.22 1053.22 5051225

41 367 31 1 33 34 1053.33 1053.33 5051190

41 367 31 1 40 41 1053.4 1053.4 5051226

41 367 31 1 60 61 1053.6 1053.6 5051227

41 367 31 1 70 71 1053.7 1053.7 5054529

41 367 31 1 91 92 1053.91 1053.91 5051228

41 367 31 1 97 98 1053.97 1053.97 5054531

41 367 31 1 105 106 1054.05 1054.05 5051229

41 367 31 1 115 116 1054.15 1054.15 5051230

41 367 31 1 138 139 1054.38 1054.38 5051231

41 367 31 2 10 11 1054.6 1054.6 5051233

41 367 31 2 37 38 1054.87 1054.87 5051191

41 367 31 2 51 52 1055.01 1055.01 5051234

41 367 31 2 65 66 1055.15 1055.15 5051235

41 367 31 2 80 81 1055.3 1055.3 5051236

41 367 31 2 107 108 1055.57 1055.57 5054532 8.29 0.1 2.3 1.2 430 28 14.0 8.3

41 367 31 2 107 108 1055.57 1055.57 5054539

41 367 31 2 120 121 1055.7 1055.7 5051237

41 367 31 2 140 141 1055.9 1055.9 5051238

41 367 32 1 110 111 1082.6 1082.6 5051239

41 367 32 1 115 116 1082.65 1082.65 5054534

41 367 32 2 40 41 1083.4 1083.4 5051241

41 367 32 2 40 41 1083.4 1083.4 5054535

41 367 32 2 80 81 1083.8 1083.8 5051240

41 367 32 2 148 149 1084.48 1084.48 5054536

41 367 32 3 81 82 1085.31 1085.31 5051242

41 367 32 3 90 91 1085.4 1085.4 5054538

41 367 32 3 122 123 1085.72 1085.72 5051243

41 367 32 3 122 123 1085.72 1085.72 5054537

41 367 32 4 10 11 1086.1 1086.1 5054542

41 367 32 4 90 91 1086.9 1086.9 5051245

41 367 32 4 90 91 1086.9 1086.9 5051244

41 367 32 4 142 143 1087.42 1087.42 5054543

41 367 32 5 20 21 1087.7 1087.7 5054572

41 367 32 5 50 51 1088 1088 5051246

41 367 32 5 57 58 1088.07 1088.07 5054575

41 367 32 5 69 70 1088.19 1088.19 5054573

41 367 32 5 83 84 1088.33 1088.33 5054579

41 367 32 5 91 92 1088.41 1088.41 5054584

41 367 32 5 132 133 1088.82 1088.82 5054585

41 367 33 1 12 13 1105.62 1105.62 5054594 11.9 1.3 28.8 6.1 410 241 51.0 11.9

41 367 33 1 30 31 1105.8 1105.8 5051247

41 367 33 1 71 72 1106.21 1106.21 5054600

41 367 33 1 136 137 1106.86 1106.86 5054601

41 367 33 2 77 78 1107.77 1107.77 5051248

41 367 33 2 85 86 1107.85 1107.85 5051249

41 367 33 3 54 55 1109.04 1109.04 5051250

41 367 33 3 75 76 1109.25 1109.25 5051251

41 367 33 3 134 135 1109.84 1109.84 5054606

41 367 34 1 80 81 1111.8 1111.8 5054609

41 367 34 1 108 109 1112.08 1112.08 5054611

41 367 34 1 110 111 1112.1 1112.1 5051252

41 367 34 2 12 13 1112.62 1112.62 5054615

41 367 34 2 41 42 1112.91 1112.91 5051253

41 367 34 2 145 146 1113.95 1113.95 5054616

41 367 34 3 21 22 1114.21 1114.21 5054618

41 367 34 3 28 29 1114.28 1114.28 5051254

41 367 34 3 96 97 1114.96 1114.96 5054617

41 367 34 4 10 11 1115.6 1115.6 5054619

41 367 34 4 28 29 1115.78 1115.78 5051255

41 367 34 4 105 106 1116.55 1116.55 5054620

41 367 35 1 89 90 1120.39 1120.39 5051256

41 367 35 2 32 33 1121.32 1121.32 5051257

41 367 35 3 87 88 1123.37 1123.37 5051258

41 367 35 4 59 60 1124.59 1124.59 5051259

41 367 35 5 54 55 1126.04 1126.04 5051260

41 367 36 1 90 91 1128.4 1128.4 5051261

41 367 36 2 49 50 1129.49 1129.49 5051262

41 367 36 3 130 131 1131.8 1131.8 5051263

41 367 37 1 51 55 1135.51 1135.51 5103208

41 367 37 1 93 94 1135.93 1135.93 5051264

41 367 37 1 134 135 1136.34 1136.34 5103209

41 367 38 1 140 141 1143.4 1143.4 5103211

41 367 38 2 50 55 1144 1144 5103216

Total analysed samples 158 98 6 28 31 13

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

Sample Depths (m) Analysis

Pyrolysis

unused

unused


no

s

Pal

yno

logy

Cal

pio

nel

lid

s

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

TOC

(%)

41 367 16 2 13 15 541.63 541.63 5103260 6

41 367 16 3 118 119 544.18 544.18 5103261

41 367 16 4 55 56 545.05 545.05 5103262

41 367 16 6 3 4 547.53 547.53 5046547

41 367 16 6 70 71 548.2 548.2 5103263

41 367 17 1 5 6 616.05 616.05 5046548

41 367 17 1 100 105 617 617 5103161

41 367 17 2 15 16 617.65 617.65 5103162

41 367 17 2 70 72 618.2 618.2 5046552 0.17

41 367 17 2 95 100 618.45 618.45 5103163

41 367 17 3 52 53 619.52 619.52 5103164

41 367 17 3 60 62 619.6 619.6 5046551 11.1 2.7 45.9 3.6 399 123 33.0 11.1

41 367 17 3 110 115 620.1 620.1 5103165 3

41 367 17 4 5 6 620.55 620.55 5046549

41 367 17 4 43 47 620.93 620.93 5103166

41 367 17 4 106 112 621.56 621.56 5103167

41 367 17 4 115 116 621.65 621.65 5046564 4.03

41 367 18 1 50 53 636.5 636.5 5103168

41 367 18 1 115 116 637.15 637.15 5046563 33.8

41 367 18 1 140 142 637.4 637.4 5103169 1

41 367 18 2 13 14 637.63 637.63 5046565

41 367 18 2 13 15 637.63 637.63 5103170

41 367 18 2 20 21 637.7 637.7 5054655

41 367 18 2 24 25 637.74 637.74 5046567 36.7 13.3 200 8.5 397 546 23.0 36.7

41 367 18 2 142 143 638.92 638.92 5046566

41 367 18 3 32 33 639.32 639.32 5046568 31.8

41 367 18 4 93 94 641.43 641.43 5046569

41 367 18 4 94 95 641.44 641.44 5046570 25.4 9.5 153 7.6 398 604 30.0 25.4

41 367 18 5 52 54 642.52 642.52 5046572 7.69

41 367 18 5 77 78 642.77 642.77 5046571

41 367 19 2 32 34 646.32 646.32 5046573 19.8 5.3 120 8.7 410 608 44.0 19.8

41 367 19 2 34 35 646.34 646.34 5046574

41 367 19 3 74 75 648.24 648.24 5046575

41 367 19 3 94 95 648.44 648.44 5046576 19.8

41 367 19 3 116 117 648.66 648.66 5046577 2.18

41 367 19 4 17 18 649.17 649.17 5046578

41 367 20 1 132 133 689.82 689.82 5046580 17.7 2.9 88.0 7.7 406 497 43.0 17.7

41 367 20 1 140 141 690.9 690.9 5103171

41 367 20 1 142 143 690.92 690.92 5046581 9.37 1.5 53.6 6.1 412 572 65.0 9.4

41 367 20 1 144 145 690.94 690.94 5046579

41 367 20 2 6 7 691.06 691.06 5046582

41 367 20 2 96 98 691.96 691.96 5103172

41 367 20 2 136 137 692.36 692.36 5046583

41 367 20 2 137 138 692.37 692.37 5046584

41 367 20 3 7 8 692.57 692.57 5046601

41 367 21 1 74 75 692.74 692.74 5046605

41 367 20 3 65 67 693.15 693.15 5103173

41 367 21 1 119 120 693.19 693.19 5103175

41 367 20 3 140 141 693.9 693.9 5046602

41 367 21 2 95 96 694.45 694.45 5046606

41 367 21 2 95 96 694.45 694.45 5103176

41 367 21 2 100 101 694.5 694.5 5046607 5.83

41 367 20 4 79 80 694.79 694.79 5046604 11.6

41 367 20 4 90 91 694.9 694.9 5103174

41 367 20 4 92 93 694.92 694.92 5046603

41 367 21 3 65 66 695.65 695.65 5046609 13.7

41 367 21 3 90 91 695.9 695.9 5103177

41 367 21 3 93 94 695.93 695.93 5046608

41 367 21 4 49 50 696.99 696.99 5103181

41 367 21 4 50 51 697 697 5046610

41 367 21 5 66 67 698.66 698.66 5046612

41 367 21 5 68 69 698.68 698.68 5103182

41 367 21 6 40 41 699.9 699.9 5046614

41 367 21 6 76 77 700.26 700.26 5046613

41 367 21 6 114 115 700.64 700.64 5103183

41 367 22 1 120 121 721.7 721.7 5103184

41 367 22 1 130 131 721.8 721.8 5046615

41 367 22 2 18 19 722.18 722.18 5046616

41 367 22 2 72 73 722.72 722.72 5046617 8.76

41 367 22 2 117 118 723.17 723.17 5103185

41 367 22 3 40 41 723.9 723.9 5103186

41 367 22 3 46 47 723.96 723.96 5046619

41 367 22 4 55 56 725.55 725.55 5046623

41 367 22 4 110 111 726.1 726.1 5046624 3.29

41 367 22 5 66 67 727.16 727.16 5046628 4.7 0.4 9.5 2.3 410 201 49.0 4.7

41 367 22 5 136 137 727.86 727.86 5046626

41 367 22 5 136 137 727.86 727.86 5103187

41 367 22 6 30 31 728.3 728.3 5046631

41 367 22 6 30 31 728.3 728.3 5103188

41 367 22 6 44 45 728.44 728.44 5046629

41 367 22 6 60 61 728.6 728.6 5103189

41 367 22 6 80 81 728.8 728.8 5103191

41 367 22 6 100 101 729 729 5103194 2

41 367 23 1 85 86 778.35 778.35 5103198 5

41 367 23 1 86 87 778.36 778.36 5046632 2.21 0.1 1.5 1.7 421 70 76.0 2.2

41 367 23 2 15 17 779.15 779.15 5103200

41 367 23 2 43 50 779.43 779.43 5103199

41 367 23 2 66 67 779.66 779.66 5046634

41 367 23 2 100 101 780 780 5103201

41 367 24 1 141 142 835.91 835.91 5029500

41 367 24 2 83 84 836.83 836.83 5029502

41 367 24 2 120 140 837.2 837.2 5103206

41 367 24 2 121 122 837.21 837.21 5029501

41 367 24 3 5 7 837.55 837.55 5103207 4

41 367 24 3 10 11 837.6 837.6 5029508

41 367 24 3 52 53 838.02 838.02 5029505

41 367 24 3 94 95 838.44 838.44 5029504

41 367 25 1 5 6 891.55 891.55 5054468 8.43 0.3 14.0 2.8 425 166 33.0 8.4

41 367 25 1 19 20 891.69 891.69 5029512

41 367 25 1 41 42 891.91 891.91 5029511

41 367 25 1 133 134 892.83 892.83 5054440 4.18

41 367 25 1 145 146 892.95 892.95 5029510

41 367 25 2 17 18 893.17 893.17 5029514

41 367 25 2 127 128 894.27 894.27 5029515

41 367 25 2 143 144 894.43 894.43 5029516

41 367 25 3 4 5 894.54 894.54 5029518

41 367 25 3 95 96 895.45 895.45 5029519

41 367 25 3 116 117 895.66 895.66 5029526

41 367 25 4 14 15 896.14 896.14 5029528

41 367 25 4 93 94 896.93 896.93 5029529

41 367 25 4 94 95 896.94 896.94 5054490 1.8

41 367 25 4 132 133 897.32 897.32 5029530

41 367 26 1 39 40 910.89 910.89 5054426

41 367 26 1 75 76 911.25 911.25 5051177

41 367 26 1 90 91 911.4 911.4 5054501 2.71

41 367 26 1 91 92 911.41 911.41 5054439

41 367 26 2 11 12 912.11 912.11 5054441

41 367 26 2 46 47 912.46 912.46 5054509 8.54 0.3 10.5 2.7 430 122 32.0 8.5

41 367 26 2 65 66 912.65 912.65 5051178

41 367 26 2 69 70 912.69 912.69 5054466

41 367 26 2 136 137 913.36 913.36 5054469

41 367 26 3 29 30 913.79 913.79 5054478

41 367 26 3 40 41 913.9 913.9 5054523 3.22

41 367 26 3 62 63 914.12 914.12 5054479

41 367 26 3 102 103 914.52 914.52 5054526

41 367 26 3 110 112 914.6 914.6 5051179 2.11

41 367 26 4 50 51 915.5 915.5 5051180

41 367 26 4 137 138 916.37 916.37 5054484

41 367 27 1 64 65 939.64 939.64 5054499

41 367 27 1 119 120 940.19 940.19 5054530 3.86 0.3 4.4 2.3 432 113 60.0 3.9

41 367 27 1 130 131 940.3 940.3 5051181

41 367 27 2 23 24 940.73 940.73 5054505

41 367 27 2 85 86 941.35 941.35 5051182

41 367 27 2 106 107 941.56 941.56 5054507

41 367 27 3 20 21 942.2 942.2 5051183

41 367 28 1 65 66 968.15 968.15 5051184

41 367 28 2 23 24 969.23 969.23 5054512

41 367 28 2 70 71 969.7 969.7 5051185

41 367 28 2 120 122 970.2 970.2 5054533 3.33

41 367 28 2 123 124 970.23 970.23 5054514

41 367 28 3 72 73 971.22 971.22 5051186

41 367 29 1 138 139 997.38 997.38 5054522

41 367 29 2 67 68 998.17 998.17 5054524

41 367 29 2 70 71 998.2 998.2 5051187

41 367 30 1 8 9 1024.58 1024.58 5051193

41 367 30 1 25 26 1024.75 1024.75 5051188

41 367 30 1 30 31 1024.8 1024.8 5051194

41 367 30 1 40 41 1024.9 1024.9 5054525

41 367 30 1 80 81 1025.3 1025.3 5051195

41 367 30 1 127 128 1025.77 1025.77 5051196

41 367 30 1 135 136 1025.85 1025.85 5051197

41 367 30 1 140 141 1025.9 1025.9 5051198

41 367 30 1 148 149 1025.98 1025.98 5054528

41 367 30 2 15 16 1026.15 1026.15 5051199

41 367 30 2 40 41 1026.4 1026.4 5051200

41 367 30 2 60 61 1026.6 1026.6 5051189

41 367 30 2 72 73 1026.72 1026.72 5051201

41 367 30 2 85 86 1026.85 1026.85 5051202

41 367 30 2 100 101 1027 1027 5051203

41 367 30 2 109 110 1027.09 1027.09 5051204

41 367 30 2 130 131 1027.3 1027.3 5051205

41 367 30 2 148 149 1027.48 1027.48 5054527

41 367 31 1 22 23 1053.22 1053.22 5051225

41 367 31 1 33 34 1053.33 1053.33 5051190

41 367 31 1 40 41 1053.4 1053.4 5051226

41 367 31 1 60 61 1053.6 1053.6 5051227

41 367 31 1 70 71 1053.7 1053.7 5054529

41 367 31 1 91 92 1053.91 1053.91 5051228

41 367 31 1 97 98 1053.97 1053.97 5054531

41 367 31 1 105 106 1054.05 1054.05 5051229

41 367 31 1 115 116 1054.15 1054.15 5051230

41 367 31 1 138 139 1054.38 1054.38 5051231

41 367 31 2 10 11 1054.6 1054.6 5051233

41 367 31 2 37 38 1054.87 1054.87 5051191

41 367 31 2 51 52 1055.01 1055.01 5051234

41 367 31 2 65 66 1055.15 1055.15 5051235

41 367 31 2 80 81 1055.3 1055.3 5051236

41 367 31 2 107 108 1055.57 1055.57 5054532 8.29 0.1 2.3 1.2 430 28 14.0 8.3

41 367 31 2 107 108 1055.57 1055.57 5054539

41 367 31 2 120 121 1055.7 1055.7 5051237

41 367 31 2 140 141 1055.9 1055.9 5051238

41 367 32 1 110 111 1082.6 1082.6 5051239

41 367 32 1 115 116 1082.65 1082.65 5054534

41 367 32 2 40 41 1083.4 1083.4 5051241

41 367 32 2 40 41 1083.4 1083.4 5054535

41 367 32 2 80 81 1083.8 1083.8 5051240

41 367 32 2 148 149 1084.48 1084.48 5054536

41 367 32 3 81 82 1085.31 1085.31 5051242

41 367 32 3 90 91 1085.4 1085.4 5054538

41 367 32 3 122 123 1085.72 1085.72 5051243

41 367 32 3 122 123 1085.72 1085.72 5054537

41 367 32 4 10 11 1086.1 1086.1 5054542

41 367 32 4 90 91 1086.9 1086.9 5051245

41 367 32 4 90 91 1086.9 1086.9 5051244

41 367 32 4 142 143 1087.42 1087.42 5054543

41 367 32 5 20 21 1087.7 1087.7 5054572

41 367 32 5 50 51 1088 1088 5051246

41 367 32 5 57 58 1088.07 1088.07 5054575

41 367 32 5 69 70 1088.19 1088.19 5054573

41 367 32 5 83 84 1088.33 1088.33 5054579

41 367 32 5 91 92 1088.41 1088.41 5054584

41 367 32 5 132 133 1088.82 1088.82 5054585

41 367 33 1 12 13 1105.62 1105.62 5054594 11.9 1.3 28.8 6.1 410 241 51.0 11.9

41 367 33 1 30 31 1105.8 1105.8 5051247

41 367 33 1 71 72 1106.21 1106.21 5054600

41 367 33 1 136 137 1106.86 1106.86 5054601

41 367 33 2 77 78 1107.77 1107.77 5051248

41 367 33 2 85 86 1107.85 1107.85 5051249

41 367 33 3 54 55 1109.04 1109.04 5051250

41 367 33 3 75 76 1109.25 1109.25 5051251

41 367 33 3 134 135 1109.84 1109.84 5054606

41 367 34 1 80 81 1111.8 1111.8 5054609

41 367 34 1 108 109 1112.08 1112.08 5054611

41 367 34 1 110 111 1112.1 1112.1 5051252

41 367 34 2 12 13 1112.62 1112.62 5054615

41 367 34 2 41 42 1112.91 1112.91 5051253

41 367 34 2 145 146 1113.95 1113.95 5054616

41 367 34 3 21 22 1114.21 1114.21 5054618

41 367 34 3 28 29 1114.28 1114.28 5051254

41 367 34 3 96 97 1114.96 1114.96 5054617

41 367 34 4 10 11 1115.6 1115.6 5054619

41 367 34 4 28 29 1115.78 1115.78 5051255

41 367 34 4 105 106 1116.55 1116.55 5054620

41 367 35 1 89 90 1120.39 1120.39 5051256

41 367 35 2 32 33 1121.32 1121.32 5051257

41 367 35 3 87 88 1123.37 1123.37 5051258

41 367 35 4 59 60 1124.59 1124.59 5051259

41 367 35 5 54 55 1126.04 1126.04 5051260

41 367 36 1 90 91 1128.4 1128.4 5051261

41 367 36 2 49 50 1129.49 1129.49 5051262

41 367 36 3 130 131 1131.8 1131.8 5051263

41 367 37 1 51 55 1135.51 1135.51 5103208

41 367 37 1 93 94 1135.93 1135.93 5051264

41 367 37 1 134 135 1136.34 1136.34 5103209

41 367 38 1 140 141 1143.4 1143.4 5103211

41 367 38 2 50 55 1144 1144 5103216

Total analysed samples 158 98 6 28 31 13

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused


Pyrolysis

unused

unused

Chapter 3

127


no

s

Pal

yno

logy

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

41 368 50 2 46 47 704.46 704.46 5046641 0.12

41 368 50 2 52 53 704.52 704.52 5046640

41 368 50 3 76 77 706.26 706.26 5046644

41 368 51 2 38 39 713.88 713.88 5046649

41 368 51 3 98 99 715.98 715.98 5046652

41 368 52 1 139 140 722.89 722.89 5046653

41 368 52 2 26 27 723.26 723.26 5046654

41 368 52 4 113 114 727.13 727.13 5046655

41 368 53 1 138 139 751.38 751.38 5103257

41 368 53 2 53 55 752.03 752.03 5103258 1

41 368 53 2 66 67 752.16 752.16 5103259

41 368 55 2 136 138 840.36 840.36 5103223 2

41 368 55 3 13 15 840.63 840.63 5103231

41 368 56 3 13 16 848.13 848.13 5103234

41 368 56 3 130 132 849.3 849.3 5103235 3

41 368 57 1 13 14 892.63 892.63 5046656

41 368 57 1 30 31 892.8 892.8 5103236

41 368 57 2 52 65 894.52 894.52 5103237 4

41 368 57 2 84 85 894.84 894.84 5046658

41 368 57 2 134 135 895.34 895.34 5046657

41 368 57 3 41 43 895.91 895.91 5103238

41 368 57 3 42 43 895.92 895.92 5046670

41 368 57 3 89 90 896.39 896.39 5046671 0.08

41 368 57 4 53 65 897.53 897.53 5103239

41 368 57 4 80 81 897.8 897.8 5046672

41 368 58 2 103 104 923.53 923.53 5046673 1.1

41 368 58 2 105 110 923.55 923.55 5103240 5

41 368 58 3 74 75 924.74 924.74 5046676 1.53

41 368 58 3 114 116 925.14 925.14 5103241

41 368 58 4 90 91 926.4 926.4 5103242

41 368 58 5 50 51 927.5 927.5 5103244

41 368 58 5 95 96 927.95 927.95 5046682 1.32 0.1 1.6 0.5 411 119 38.0

41 368 58 5 96 97 927.96 927.96 5103243

41 368 58 5 140 141 928.4 928.4 5046680

41 368 58 6 21 22 928.71 928.71 5103246

41 368 58 6 100 105 929.5 929.5 5103245

41 368 58 6 104 105 929.54 929.54 5046685 6.31

41 368 59 1 55 56 939.05 939.05 5103248

41 368 59 2 92 96 940.92 940.92 5103249

41 368 59 2 122 123 941.22 941.22 5046690 9.44 1.4 42.4 1.1 421 450 12

41 368 59 3 137 138 942.87 942.87 5103250 6

41 368 60 1 90 92 950.4 950.4 5046693 4.55

41 368 60 1 110 111 950.6 950.6 5103251 7

41 368 60 2 24 25 951.24 951.24 5046694

41 368 60 2 60 61 951.6 951.6 5103252

41 368 60 3 90 91 953.4 953.4 5046695 7.77

41 368 60 3 134 135 953.84 953.84 5103253

41 368 60 4 60 61 954.6 954.6 5103254

41 368 62 3 145 146 972.95 972.95 5103255

41 368 62 4 51 52 973.51 973.51 5046696

41 368 62 4 54 55 973.54 973.54 5103256 8

41 368 62 4 69 70 973.69 973.69 5046697

41 368 63 1 35 36 975.35 975.35 5046702

41 368 63 1 97 98 975.97 975.97 5046703

41 368 63 2 44 45 976.94 976.94 5046705

41 368 63 2 45 46 976.95 976.95 5046704 6.35 2.0 32.2 1.1 436 507 18.0

41 368 63 2 106 107 977.56 977.56 5046706

41 368 63 3 17 18 978.17 978.17 5046708

41 368 63 3 82 83 978.82 978.82 5046709 22.1 10.9 141 2.1 430 641 9.0

41 368 63 3 128 129 979.28 979.28 5046710

41 368 63 4 25 26 979.75 979.75 5046713

41 368 63 4 117 118 980.67 980.67 5046712 19.8

41 368 63 4 128 129 980.78 980.78 5046714

Total analysed samples 43 23 8 12 4

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused


Pyrolysis

unused

unused

unused

unused

unused

unused

unused


128

Table S 3.1 – Sample table detailing the analysis performed on each sample, and organic geochemistry data generated.


no

s

Pal

yno

logy

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

76 534 27 1 2 3 764.52 764.52 5046766

76 534 27 3 123 124 768.57 768.57 5046770

76 534 28 1 107 108 775.07 775.07 5046771

76 534 34 2 128 129 833.34 833.34 5046780

76 534 35 1 1 2 840.51 840.51 5046783

76 534 35 3 5 6 843.55 843.55 5046785

76 534 37 3 53 54 863.03 863.03 5046787

76 534 38 3 36 37 872.36 872.36 5046796

76 534 38 3 66 67 872.66 872.66 5046793

76 534 38 3 104 105 873.04 873.04 5046794

76 534 41 4 91 92 901.41 901.41 5046800

76 534 41 4 134 135 901.84 901.84 5046801

76 534 43 1 50 51 914.5 914.5 5103342

76 534 43 1 77 79 914.77 914.77 5103339

76 534 43 1 105 106 915.05 915.05 5103341

76 534 43 2 2 3 915.37 915.37 5046806

76 534 43 2 89 90 916.24 916.24 5046807

76 534 43 2 121 122 916.56 916.56 5046808

76 534 44 1 52 53 923.52 923.52 5046814

76 534 44 1 144 145 924.44 924.44 5046815

76 534 44 2 76 77 925.26 925.26 5046817

76 534 44 3 129 130 926.99 926.99 5046819

76 534 44 4 66 67 927.86 927.86 5046821

76 534 44 5 10 11 928.8 928.8 5046823

76 534 45 1 103 104 933.03 933.03 5046825

76 534 45 2 55 56 934.05 934.05 5046827

76 534 45 3 74 75 935.55 935.55 5046830

76 534 45 4 65 66 936.96 936.96 5046832

76 534 45 5 55 56 938.36 938.36 5046833

76 534 45 6 10 11 938.76 938.76 5046834

76 534 46 1 20 21 941.2 941.2 5046810

76 534 46 1 87 88 941.87 941.87 5046811

76 534 47 2 54 55 952.04 952.04 5046836

Total analysed samples 33 33


Pyrolysis

Chapter 3

129

DSDP Leg 41 Site 367 (Upper Cretaceous)

Ag

e

NF

Zo

ne

De

pth

De

pth

(m

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od

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an

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na

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p

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nic

us

Unassigned 17-4 (5-6) 620.55 BARREN

18-2 (13-14) 637.63 3 1 2 10 2 1 1 4 8 P P P P 1 3 P 8 5

18-2 (13-15) 637.64 6 1 1 9 2 1 1 3 4 P P P P 3 2 P 3 3

18-2 (20-21) 637.70 2 3 P 1 2 3 P P P 8 4 P

18-2 (142-143) 638.92 7 4 1 1 2 P 1 3 3

18-4 (93-94) 641.43 1 P P 1 1 2 15 2

18-5 (77-78) 642.77 4 21 1 18 3 6 1 30 90 8 42 2 36 8 160 2 2 P P 4 1 210 4 240 2

19-2 (34-35) 646.34 P 30 1 P 36 P 1 1 21 21 1 6 4 2 P 5 3 1 P P P 10 102 126

19-3 (74-75) 648.24 2 210 42 37 2 8 P P 20 90 1 90 4 P P 15 1 9 3 2 11 180 9 160

19-4 (17-18) 649.17 2 33 21 2 2 7 18 7 1 1 1 5 1 P 160 P 120

20-1 (144-145) 690.94 1 690 2 7 3 P P 12 12 30 2 4 P 2 18 7 21 10 1 4 140 12 2 3 4 4 P 200 P 1 18 P 42 120 33 620

20-2 (6-7) 691.06 10 P 820 5 4 3 P P 1 12 82 3 3 P 1 1 21 1 8 10 8 3 82 P 12 2 2 P P P 330 7 21 90 132 660

20-2 (137-138) 692.37 4 3 470 1 54 10 P 66 1 3 6 48 2 1 P 18 5 P 42 1 1 1 1 112 16 27 2 4 1 240 3 P 2 1 21 112 21 20

20-3 (7-8) 692.57 4 480 6 6 36 6 82 6 P 1 7 1 2 8 18 2 P 66 24 5 3 2 140 27 170 72 120

20-3 (140-141) 693.90 2 630 7 4 1 2 2 5 27 1 2 33 2 1 1 5 1 1 21 5 2 3 1 1 1 150 1 1 6 96 1 66 140

20-4 (92-93) 694.92 1 1 420 20 6 12 P 2 P 45 6 1 P 1 4 5 3 21 1 18 5 102 10 18 4 1 1 1 1 1 24 36 9 30 96

21-1 (74-75) 692.74 3 1 90 1 P 10 4 P P 6 2 110 1 P 2 40 6 P 8 5 4 35 15 7 1 1 1 1 P 10 5 45 55 60

21-2 (95-96) 694.45 2 1 270 11 8 1 5 4 3 66 4 1 2 1 60 1 6 3 6 12 P 4 66 24 3 5 12 P 1 1 2 12 1 10 128 48 230

21-3 (93-94) 695.93 2 180 2 1 7 16 6 2 P 3 8 102 2 1 P P 20 20 P 6 60 P 40 2 40 35 17 1 17 2 2 1 2 11 1 2 16 48 P 25 180

21-4 (50-51) 697.00 P 170 1 66 4 4 1 1 12 3 100 P 2 35 15 3 10 1 25 4 60 1 3 7 4 240 1 3 25 1 60 96 1 78 220

21-5 (66-67) 698.66 3 170 5 8 9 3 P 1 1 30 1 P 1 30 1 P P 2 11 4 126 2 18 8 17 1 1 1 1 2 180 45 230

21-6 (76-77) 700.26 2 230 4 8 7 1 6 2 3 55 1 1 18 60 22 2 2 18 1 P 270 1 16 18 1 11 1 1 4 35 170 30 260

22-1 (130-131) 721.80 P P 1 P 1 P P 1 P 1 1 4 3 2 P P P P 1 42 6

22-2 (18-19) 722.18 2 510 1 35 10 3 1 6 128 34 1 6 1 35 4 5 12 1 1 1 P P 30 2 15 170 1 12 1 21 470 4 30 3 3 15 3 2 35 112 P 25 720

22-3 (46-47) 723.96 P 6 4 P 1 7 1 9 P 1 4 1 P 1 1 P 1 P 7 9 P 3 15 2 1 5 P 2 4 66 10 24

22-4 (55-56) 725.55 1 1 2 1 3 108

22-5 (136-137) 727.86 P 720 9 12 1 5 1 30 6 35 3 2 P 18 1 1 7 20 P 12 1 8 130 160 16 35 20 30 10 1 1 1 3 1 8 40 128 1 3 34 370

22-6 (30-31) 728.30 1 390 1 5 12 2 P 2 1 1 12 P 1 4 1 7 P 1 10 16 P P P 27 5 270 21 3 18 132 5 1 2 8 3 7 36 160 P 12 310

22-6 (44-45) 728.44 1 128 2 1 14 2 1 1 2 1 12 10 1 4 1 2 1 12 1 1 P 1 P 14 12 82 130 16 7 8 16 16 1 P 1 3 3 1 3 3 51 16 102

22-6 (60-61) 728.60 2 380 1 2 1 18 3 24 10 3 P 24 3 1 24 6 2 4 4 4 30 1 9 42 8 36 36 3 4 1 9 24 330 42 330

22-6 (80-81) 728.80 1 2 370 3 6 3 P P 1 115 21 P 1 18 3 5 6 180 2 2 15 2 18 2 5 130 P 27 340

24-1 (141-142) 835.91 BARREN

24-2 (83-84) 836.83 BARREN

24-2 (121-122) 837.21 BARREN

24-3 (10-11) 837.60 BARREN

24-3 (52-53) 838.02 BARREN

24-3 (94-95) 838.44 BARREN

Unassigned

Early

Cenomanian

Late

CenomanianUC5

UC1

NC10a

(upper)Late Albian


130

DSDP Leg 41 Site 367 (Lower Cretaceous)

Ag

e

NF

Zo

ne

De

pth

De

pth

(m

)

As

sip

etr

a i

nfr

ac

reta

ce

a

As

sip

etr

a t

ere

bro

de

nta

riu

s

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op

od

orh

ab

du

s c

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nd

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s

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od

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du

s d

ietz

ma

nn

ii

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cu

tum

co

ns

tan

s

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big

uu

s

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lcic

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thin

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nu

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hra

ph

od

ite

s c

arn

iole

ns

is

Lit

hra

ph

idit

es

aff

. h

ou

gh

ton

ii

La

gu

nc

ula

sp

.

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

cte

n

Mic

ran

tho

lith

us

aff

. b

rev

is

Mic

ran

tho

lith

us

ho

sc

hu

lzii

Mic

ran

tho

lith

us

ob

tus

us

Na

nn

oc

on

us

sp

p (

top

vie

w)

Na

nn

oc

on

us

aff

. c

irc

ula

ris

Na

nn

oc

on

us

aff

. g

lob

ulu

s

Na

nn

oc

on

us

co

rnu

ta

Na

nn

oc

on

us

in

fan

s /

co

mp

res

su

s

Na

nn

oc

on

us

ste

inm

an

nii

Na

nn

oc

on

us

ste

inm

an

nii

min

or

Pe

ris

so

cy

clu

s n

oe

lia

e

Pe

rciv

ali

a f

en

es

tra

ta

Pe

rciv

ali

a f

en

es

tra

ta s

sp

. e

xp

an

su

s

Pic

ke

lha

ub

e f

urt

iva

Po

lyc

os

tell

a b

ec

km

an

nii

Re

tec

ap

sa

sp

p.

Re

tec

ap

sa

an

gu

sti

fora

ta

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

de

ka

en

eli

i

Rh

ag

od

isc

us

in

fin

itu

s

Rh

ag

od

isc

us

ne

bu

los

us

Rh

ag

od

isc

us

ps

eu

do

an

gu

stu

s

Ro

tela

pil

lus

cre

nu

latu

s

Ru

nin

oli

thu

s r

ad

iatu

s

Ru

cin

oli

thu

s "

se

ne

ga

len

sis

" (8

ra

ye

d)

Ru

cin

oli

thu

s w

ise

i

So

lla

sit

es

lo

we

i

Sp

ee

ton

ia c

oll

iga

ta

Sta

uro

lith

ite

s c

rux

Sta

uro

lith

ite

s m

utt

erl

os

ei

Str

ad

ne

rlit

hu

s s

ilv

ara

diu

s

Te

gu

me

ntu

m s

tra

dn

eri

Te

gu

me

ntu

m o

cti

form

is

Tra

no

lith

us

ga

ba

lus

Tri

sc

utu

m b

ea

min

ste

ren

sis

Tri

sc

utu

m a

ff.

be

am

ins

tere

ns

is

Tu

bo

dis

cu

s s

p.

Tu

bo

dis

cu

s j

ura

pe

lag

icu

s

Tu

bo

dis

cu

s f

ran

kia

e

Tu

bo

dis

cu

s v

ere

na

e

Tra

no

lith

us

ga

ba

lus

Um

bri

a g

ran

ulo

sa

ss

p.

gra

nu

los

a

Ve

ks

hin

ell

a s

p.

Wa

tzn

au

eri

a b

arn

es

iae

Wa

tzn

au

eri

a b

rita

nn

ica

Wa

tzn

au

eri

a m

an

ivit

iae

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

rha

bd

otu

s c

f. p

se

do

an

gu

stu

s

Ze

ug

rha

bd

otu

s c

laru

s

Ze

ug

rha

bd

otu

s e

rec

tus

Ze

ug

rha

bd

otu

s f

lux

us

Ze

ug

hrh

ab

do

tus

ho

we

i

Ze

ug

rha

do

tus

mo

ull

ad

ei

Ze

ug

rha

do

tus

sc

utu

la

24-3 (94-95) 838.44 BARREN

25-1 (19-20) 891.69 18 16 P 4 1 1 1 8 16 1 1 1 3 5 P 1 16 4 42 P 4 2 P 1 P 1 330 1 3 1 P

25-1 (41-42) 891,91 96 3 1 1 18 P 18 3 24 7 P P 52 18 102 1 4 16 4 4 460 21 180 3

25-1 (145-146) 892.95 65 2 1 P 6 P 18 1 20 3 P P 1 8 18 7 86 4 1 3 5 1 1 4 340 1 10 2 39 1

25-2 (17-18) 893.17 8 25 1 30 1 2 2 P 5 3 1 1 24 24 60 2 4 1 3 960 3 18 18 1

25-2 (143-144) 894,43 25 78 1 1 P 13 2 2 1 10 3 P P 3 14 20 96 P 2 4 3 360 1 30 3 6

25-3 (4-5) 894.54 35 55 45 P 1 5 2 35 3 P 3 20 22 75 3 1 5 4 660 1 20 2 18 5

25-3 (95-96) 895.45 5 13 1 10 P 3 2 19 4 7 39 3 2 9 5 16 3 2 P P 2 142 9 2 1

25-4 (93-94) 896.93 18 24 2 5 1 22 30 3 6 P 2 21 3 1 7 21 4 1 18 3 45 P 8 P 5 2 1 1 1 1 270 1 5 7 18 4

25-4 (132-133) 897.32 20 25 1 4 1 21 2 2 1 1 4 2 21 2 1 1 P 4 21 18 45 P 3 P 1 3 330 3 20 1 27 3

26-1 (39-40) 910.89 2 96 1 P 1 P 6 12 P 2 7 3 P 2 18 55 2 1 2 2 20 1 42 P P P P 3 440 1 10 1 4 1

26-1 (75-76) 911.25 5 15 P 4 3 1 1 9 1 2 11 1 8 5 18 1 1 160 1 5 2

26-2 (65-66) 912.65 1 3 2 1 2 4 1 4 1 96 2

26-2 (136-137) 913.36 5 30 P 2 21 1 P 4 39 P P 3 3 P 1 36 9 60 1 P 1 P 2 590 2 33 2 13 2

26-3 (62-63) 914.12 12 27 1 P 36 P 15 2 1 15 5 1 1 1 9 12 42 P 1 P 1 1 1 2 660 15 P 1 P

E. Barremian NC5c 26-3 (110-112) 914.60 27 2 P 3 1 P 33 2 P 2 6 4 1 1 4 15 8 2 10 21 21 P 2 1 2 440 P 12 P 16

26-4 (50-51) 915.50 3 1 1 1 P 21 1 27 1 2 1 1 5 3 1 27 66 18 1 1 36 21 33 2 3 5 1 3 P 3 1200 7 1 P

26-4 (137-138) 916.37 8 10 2 4 P 1 P 1 25 1 3 4 3 1 40 4 P 3 1 1 3 25 60 1 1 1 P 1 1 600 18 P 1

27-1 (64-65) 939.64 240 P 30 1 1 16 P 1 5 6 2 ?P P 1 P 1 630 P 46 60

27-1 (130-131) 940.30 132 1 P 15 11 4 1 8 3 1 P 1 6 4 3 4 P 1 P 2 320 3 14 P

27-2 (23-24) 940.73 51 2 1 P 12 5 24 1 5 1 2 1 1 5 1 3 5 4 27 ?P P P P 1 ?P 270 3 7 30

27-2 (85-86) 941.35 120 6 P 8 1 5 2 1 P 2 22 2 1 1 4 3 P 3 14 7 2 4 1 2 3 1 330 8 22

27-2 (106-107) 941.56 90 2 6 P 2 21 4 48 1 1 2 27 1 2 3 2 5 1 P P 9 10 15 P 3 P P 3 P P P ?P 270 15 1 2

27-3 (20-21) 942.20 45 1 1 P 2 2 20 1 P 21 P 5 4 2 4 6 3 3 P 24 1 7 P P 2 P P 3 480 7

28-1 (65-66) 968.15 100 3 1 P 1 6 27 42 1 1 2 15 1 6 2 P 2 18 6 140 4 P 8 2 1 1 P 690 P 21 1 3

28-2 (23-24) 969.23 240 P 4 3 3 1 36 24 2 24 6 3 1 36 15 48 11 1 2 1 760 3 21 1 P

28-2 (70-71) 969.70 4 7 1 3 2 1 1 1 66 1 P 1 1

28-2 (123-124) 970.23 66 P 1 2 72 42 1 12 2 1 1 15 4 1 1 ?P P 1 1 930 P 16 2

28-3 (72-73) 971.22 39 2 P 6 108 5 2 1 27 1 15 6 9 4 2 1 1 P 360 9 1

29-1 (138-139) 997.38 1 1 P 10 4 2 P 5 3 1 60 1 1

29-2 (67-68) 998.17 180 1 P 30 36 2 1 5 2 1 4 6 14 930 P 72 1

29-2 (70-71) 998.20 1 8 3 1 1 1 22

30-1 (25-26) 1024.75 2 5 1 2 2 51 P 2

30-1 (40-41) 1024.90 180 1 2 50 50 1 32 2 ?P 2 P 5 1 7 1 5 3 12 2 1 40 2 1 2 1 5 500 2 17 P P

30-1 (148-149) 1025.96 330 1 2 36 48 150 1 2 3 1 1 18 9 18 2 3 1 66 P P 1 1 720 4 12 1

30-2 (60-61) 1026.60 150 2 P 42 56 18 2 ?P 2 P 1 2 5 1 1 26 P 3 440 7 20

31-1 (33-34) 1053.33 21 24 24 42 81 P 1 1 2 4 3 2 4 2 2 3 2 12 1 3 1 P 390 6 P P

31-1 (70-71) 1053.70 320 6 P 10 P 55 110 1 1 3 1 P 1 P 2 P P 9 2 10 2 5 P P P 1 850 9 11 P

31-2 (37-38) 1054.87 96 P 2 1 P 3 51 42 1 2 4 1 P 1 1 4 10 2 11 ?P 1 P P P P 3 360 3 2 2

31-2 (107-108) 1055.57 270 P 1 25 4 30 72 P 1 P 7 1 1 11 2 7 5 5 2 1 9 180 7 8

32-2 (40-41) 1083.40 102 6 P 12 P 150 33 1 1 7 1 22 1 14 1 5 1 1 1 3 1 1 270 1 18 1 4

32-3 (90-91) 1085.40 36 1 11 1 P 9 4 1 P 48 1 1 1

32-3 (122-123) 1085.72 7 P 4 P 75 11 P 2 11 10 P P 2 1 1 P P P P 1 180 4 P 2 1

32-4 (10-11) 1086.10 2 1 11 1 1 1 2 66 2 1

32-4 (90-91) 1086.90 13 2 2 P 45 11 2 1 3 2 1 P ?P 1 3 5 P 1 P 1 180 1 1 P P P

32-4 (142-143) 1087.42 4 P 1 60 18 5 5 2 1 2 1 P 1 270 2 P

32-5 (20-21) 1087.70 3 P 7 P 2 45 13 1 2 8 P 15 3 3 1 160 2 1

32-5 (57-58) 1088.07 3 3 1 84 6 P 1 5 4 1 P 1 1 1 270 2 1 1

32-5 (69-70) 1088.19 32 P 3 2 220 6 4

32-5 (83-84) 1088.33 1 150 P 1 7 5 7 15 180 4 40 2

32-5 (91-92) 1088.41 P 60 P 7 1 9 10 ?P 270 6 150 1

32-5 (132-133) 1088.82 11 40 1 1 10 15 260 6 10 3

33-1 (71-72) 1106.21 51 3 10 4 120 1 2

33-2 (77-78) 1107.77 54 18 ?1 30 100 3 4 P

33-3 (75-76) 1109.25 3 1 21 33 160 11

34-1 (80-81) 1111.80 1 6 15

34-1 (108-109) 1112.08 5 21 11 17

34-2 (12-13) 1112.62 13 23 6

34-2 (145-146) 1113.95 33 96 6 45

34-3 (21-22) 1114.21 17 300 30 168

34-3 (96-97) 1114.96 16 3 90 3 112

34-4 (10-11) 1115.60 1 1 5

34-4 (105-106) 1116.55 7 72 4 180

37-1 (51-55) 1135.51 33 P 33 24 300 P

37-1 (134-135) 1136.34 8 1 240 4 180

38-1 (140-141) 1143.40 8 120 85 116 P

Early

Kimmeridgian -

?Upper Oxfordian

Earliest

Tithonian -

Kimmeridgian

Middle

Berriasian

Early

Tithonian

Early

Valanginian

UNASSIGNED

Late

Berriasian

Late

BarremianNC5e

NC3

(lower)

Early

Hauterivian -

Late

Valanginian

NC3

(upper)

Late

HauterivianNC5a

NC2

(upper)

NC2

(lower)

NJT16

NJT15

NJT14

(lower)

NJT14

Chapter 3

131

DSDP Leg 41 Site 368

Ag

e

NF

Zo

ne

De

pth

De

pth

(m

)

Ax

op

od

orh

ab

du

s a

lbia

nu

s

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

ga

ult

en

sis

Bro

ins

on

ia e

no

rmis

/sig

na

ta g

p

Bu

kry

lith

us

am

big

uu

s

Co

roll

ith

ion

pro

tos

ign

um

Co

roll

ith

ion

ke

nn

ed

yi

Co

roll

ith

ion

sig

nu

m

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

tu

rris

eif

feli

i

Ep

roli

thu

s f

lora

lis

Fla

be

llit

es

ob

lon

gu

s

Ga

rtn

era

go

co

xa

llia

e

Ga

rtn

era

go

ob

liq

uu

m

Ga

rtn

era

go

pra

eo

bli

qu

um

Ga

rtn

era

go

pra

eo

bli

qu

um

(s

ma

ll v

ar.

)

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Ha

qiu

s c

irc

um

rad

iatu

s

He

mip

od

orh

ab

du

s g

ork

ae

He

lic

oli

thu

s a

ff.

an

ce

ps

He

lic

oli

thu

s c

om

pa

ctu

s

He

lic

oli

thu

s c

om

pa

ctu

s (

sm

all

va

r.)

He

lic

oli

thu

s t

rab

ec

ula

tus

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

mm

ato

ide

a

Pre

dis

co

sp

ha

era

co

lum

na

ta

Pre

dis

co

sp

ha

era

sp

ino

sa

Re

tec

ap

sa

sp

p.

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

in

fin

itu

s

Ro

tela

pil

lus

cre

nu

latu

s

Sta

uro

lith

ite

s c

rux

Sto

ve

riu

s a

ch

ylo

su

s

Tra

no

lith

us

ph

ac

elo

su

s

Wa

tzn

au

eri

a b

arn

es

ae

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

hrh

ab

do

tus

ho

we

i

Ze

ug

rha

do

tus

mo

ull

ad

ei

Ze

ug

rha

bd

otu

s s

cu

tula

ss

p.

turo

nic

us

50-2 (52-53) 704.52 BARREN

50-3 (76-77) 706.26 BARREN

51-2 (38-39) 713.88 BARREN

51-3 (98-99) 715.98 BARREN

52-1 (139-140) 722.89 BARREN

52-2 (26-27) 723.26 BARREN

52-4 (113-114) 727.13 BARREN

57-1 (13-14) 892.63 BARREN

57-2 (134-135) 895.34 BARREN

57-3 (42-43) 895.92 BARREN

57-3 (89-90) 896.39 BARREN

57-4 (80-81) 897.80 BARREN

58-5 (140-141) 928.40 BARREN

60-1 (110-111) 950.60 BARREN

60-2 (24-25) 951.24 BARREN

62-4 (51-52) 973.51 1 8 5 180 1 1 3 1 2 50 P 4 210 55 2

62-4 (69-70) 973.69 1 1 P 96 1 1 P 6 2 126 48 2

63-1 (35-36) 975.35 3 4 3 102 1 1 4 10 160 P 26 1

63-1 (97-98) 975.97 1 54 2 54 1 1 2 6 180 1 3 P 1 1 36 2 1 1 3 102 96 3

63-2 (44-45) 976.94 1 26 3 44 1 2 7 150 4 1 2 3 36 P P 5 210 P 36 3 1

63-2 (106-107) 977.56 1 2 7 3 21 2 P 4 24 P 1 132 3 26 1 1

63-3 (17-18) 978.17 1 48 4 26 1 1 6 1 27 51 6 15 7 P 5 15 1 6 1 1 1 1 180 36 1 2

63-3 (128-129) 979.28 16 2 14 P 2 12 156 P 5 4 3 2 1 2 22 1 1 1 P 2 2 210 26 3 1

63-4 (25-26) 979.75 P 30 33 11 P P P 3 1 30 120 P P 8 P 5 1 8 1 1 P P 66 2 24 1 1 11 4 90 P 24 2 1

63-4 (128-129) 980.78 20 1 30

Unassigned

Late

Cenomanian

Earliest

TuronianUC6

UC5


132

DSDP Leg 76 Site 534A

Table S 3.2 – Distribution charts of calcareous nannofossils from the seven wells studied

Ag

e

NF

Zo

ne

De

pth

De

pth

(m

)

As

sip

etr

a t

ere

bro

de

nta

riu

s

As

sip

etr

a t

ere

bro

de

nta

riu

s y

ou

ng

ii

Ax

op

od

orh

ab

du

s d

ietz

ma

nn

ii

Ax

op

od

orh

ab

du

s c

yli

nd

ratu

s

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

ga

ult

en

sis

Bra

aru

do

sp

ha

era

afr

ica

na

Bra

aru

do

sp

ha

era

afr

ica

na

(s

.v)

Bra

aru

do

sp

ha

era

qu

inq

ue

sti

co

sta

ta

Bro

ins

on

ia g

all

ois

ii

Bu

kry

lith

us

am

big

uu

s

Ca

lcic

ali

thin

a a

lta

Ca

lcio

so

len

ia f

os

sil

is

Ca

lcu

lite

s "

bla

ke

ye

ns

is"

Ca

lcu

lite

s d

isp

ar

Ch

ias

toz

yg

us

lit

tera

riu

s

Co

roll

ith

ion

ex

igu

um

Cre

pid

oli

thu

s b

urw

ell

en

sis

Cre

tarh

ab

du

s c

on

icu

s

Cre

tarh

ab

du

s i

na

eq

ua

lis

Cre

tarh

ab

du

s m

ad

ing

ley

en

sis

Cru

cib

isc

utu

m b

os

un

en

sis

Cru

cib

isc

utu

m n

eu

qu

en

en

sis

Cy

cla

ge

los

ph

ae

ra m

arg

ere

lii

Cy

cla

ge

los

ph

ae

ra r

ota

cly

pe

ata

Cy

lin

dra

lith

us

nu

du

s

Dia

zo

ma

toli

thu

s l

eh

ma

nii

Dil

om

a p

rim

itiv

a

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

pa

rag

og

us

Ep

roli

thu

s f

lora

lis

Fla

be

llit

es

ob

lon

gu

s

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Go

rka

ea

op

eri

o

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

Gra

nta

rha

bd

us

me

dd

ii

Ha

qiu

s c

irc

um

rad

iatu

s

Ha

qiu

s e

llip

tic

us

Ha

ye

sit

es

alb

ien

sis

/ i

rre

gu

lari

s

He

len

ea

ch

ias

tia

He

mip

od

orh

ab

du

s g

ork

ae

He

lic

oli

thu

s t

rab

ec

ula

tus

He

lic

oli

thu

s l

ec

kie

i

Lit

hra

ph

od

ite

s c

arn

iole

ns

is

Lit

hra

ph

idit

es

aff

. h

ou

gh

ton

ii

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

cte

n

Ma

niv

ite

lla

pe

mm

ato

ide

a

Ma

rka

liu

s i

nv

ers

us

Mic

ran

tho

lith

us

ho

sc

hu

lzii

Mic

ran

tho

lith

us

ob

tus

us

Na

nn

oc

on

us

sp

p (

top

vie

w)

Na

nn

oc

on

us

fra

gil

is

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s q

ua

dri

an

gu

lus

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s a

pe

rtu

s

Na

nn

oc

on

us

ste

inm

an

nii

Na

nn

oc

on

us

tru

itti

re

cta

ng

ula

ris

Ora

str

um

pe

rsp

icu

um

Ow

en

ia p

art

itu

m

Pe

ris

so

cy

clu

s n

oe

lia

e

Pre

dis

co

sp

ha

era

co

lum

na

ta

Pre

dis

co

sp

ha

era

sp

ino

sa

Pe

rciv

ali

a f

en

es

tra

ta

Pic

ke

lha

ub

e f

urt

iva

Pic

ke

lha

ub

e "

imp

era

tus

"

Re

pa

gu

lum

pa

rvid

en

tatu

m

Re

tec

ap

sa

sp

p.

Re

tec

ap

sa

an

gu

sti

fora

ta

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Rh

ag

od

isc

us

in

fin

itu

s

Rh

ag

od

isc

us

ps

eu

do

an

gu

stu

s

Rh

ag

od

isc

us

ro

bu

stu

s

Ro

tela

pil

lus

cre

nu

latu

s

So

lla

sit

es

ho

rtic

us

So

lla

sit

es

lo

we

i

Sta

uro

lith

ite

s g

au

so

rhe

thiu

m

Sta

uro

lith

ite

s c

rux

Sta

uro

lith

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27-1 (2-3) 764.52 BARREN

27-3 (123-124) 768.57 BARREN

28-1 (107-108) 775.07 BARREN

34-2 (128-129) 833.34 6 15 17 P P P P 4 P 11 P 1 2 2 P P 1 1 2 P 2 9 P 12 P 1 5 16 P 1 27

35-1 (1-2) 840.51 60 3 5 2 P P P P P 1 P 3 P 1 P 1 P 3 P P P P 2 P P 3 4 3 3 2 1 1 3 3 P P 3 27 P 2 36

35-3 (5-6) 843.55 P 39 P 1 1 2 P 5 8 1 P 6 11 1 6 2 P 1 7 P 4 2 2 P 13 P 1 1 1 6 1 180 5 5 3

37-3 (53-54) 863.03 1 P 1 5 P P P P P 1 P 1 P 1 P P P P P P 4 P PR 4 1 1 3 P 3 P P 3 P P 1 210 1 2 5 2

38-3 (36-37) 872.36

38-3 (66-67) 872.66 12 1 1 3 1 2 1 P 1 2 3 P P 3 2 1 P 18 1 10

38-3 (104-105) 873.04 1 P 48 1 P 3 3 1 6 1 1 1 1 3 P 2 2 7 P P P 2 P 1 4 6 P PR 1 1 1 1 1 2 P P 2 1 4 8 1 1 P 6 3 2 P 1 78 1 3 150

41-4 (91-92) 901.41 BARREN

41-4 (134-135) 901.84 BARREN

43-1 (50-51) 914.50 170 18 36 2 2 1 3 54 P 42 11 8 6 1 33 5 32 5 8 10 33 3 3 84 5 3 20 8 1 5 1 630 3 9 1 340 P

43-1 (128-129) 915.28 112 11 12 1 P 1 60 P 6 P 42 2 1 2 2 410 P 13 1 P

43-2 (2-3) 915.37 90 3 1 22 4 1 P 1 12 1 4 P 3 22 6 12 12 5 4 2 400 2 16 1 3 P

43-2 (89-90) 916.24 9 1 1 2 P 1 1 6 240 2

43-2 (121-122) 916.56 45 5 1 1 1 P 7 6 2 1 P 9 5 9 20 P 2 18 1 1 1 4 2 6 440 1 P 180 4

43-CC (15-16) 917.00 8 1 3 1 1 5 1 P 1 1 1 1 2 1 P P 5 2 30 2 8 ?P P 1 102 2 1 80 1

44-1 (52-53) 923.52 35 2 P 4 3 2 4 P 5 4 8 1 12 1 4 8 1 24 6 65 P 3 45 10 P 3 2 420 3 14 8 330 5

44-1 (144-145) 924.44 110 2 P 33 1 2 14 1 1 1 5 20 5 1 27 2 4 1 1 460 4 5 3 210 1

44-2 (76-77) 925.66 54 3 4 P P 1 5 1 P 10 3 3 1 P 15 12 3 2 P P P 1 8 1 12 5 96 1 33 P 11 1 2 1 P 1 340 1 2 2 320 5

44-3 (129-130) 926.99 33 P 2 P 1 1 1 24 P 2 2 3 P 55 1 2 2 3 3 6 3 102 P 1 16 6 6 1 460 3 4 3 290 12

44-4 (66-67) 927.86 96 1 P 3 7 5 3 102 P 4 1 1 5 27 1 5 1 P 3 4 30 7 160 P 12 5 1 P 1 2 510 3 5 4 200 5

44-CC (10-11) 928.80 82 P 3 5 42 2 2 P 1 14 4 3 36 5 1 1 4 24 3 3 5 6 7 P 24 1 1 8 6 120 4 P 2 20 3 1 1 P 1 660 3 7 1 150 2

45-1 (103-104) 933.03 180 5 P 1 3 8 1 1 1 2 P 8 6 5 7 4 60 1 P 6 1 690 3 13 2 270 1

45-2 (55-56) 934.05 230 4 2 1 4 4 P 48 2 5 1 48 3 1 15 7 1 1 30 9 240 3 P 60 6 2 1 P 5 1 980 54 4 2 360 24

45-3 (74-75) 935.55 112 1 2 8 1 4 6 P P 1 1 52 P 1 3 1 3 P P 7 P P 18 4 210 10 51 3 2 1 P 2 1 820 1 6 8 340 9

45-4 (65-66) 936.96 102 4 3 6 4 1 5 1 1 5 5 P 1 2 P 112 P 48 2 72 4 P 5 20 14 250 12 1 36 18 P 3 2 1 660 3 4 360 9

45-5 (55-56) 938.36 17 1 1 3 2 4 2 18 3 6 P 8 3 4 12 2 4 2 1 3 12 2 120 P 4 1 1 1 1 320 2 P 3 128 2

45-CC (10-11) 938.76 110 4 4 24 2 1 1 1 1 39 7 4 P 1 108 24 6 14 3 10 1 21 14 360 21 80 30 1 5 1 1200 12 24 2 420 4

46-1 (20-21) 941.20 48 4 1 16 1 P 6 1 2 6 12 3 3 P 6 10 6 102 6 5 3 P 1 410 1 9 26 14

46-1 (87-88) 941.87 55 5 1 1 21 1 7 5 P 60 4 1 3 2 P 3 1 4 7 7 132 5 8 5 P 2 3 820 P 9 1 128 10

47-2 (54-55) 952.04 18 2 P 33 P 2 P P 8 2 1 5 1 12 8 12 45 1 4 1 1 P 1 240 12 1 30 5

late Barremian NC5d

Unassigned

NC8AEarly Albian

Unassigned

Earliest Aptian

- latest

Barremian

NC5e -

NC6a

Chapter 3

133

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Withjack, M.O., Olsen, P.E. and Schlische, R.W., 1995. Tectonic evolution of the Fundy rift basin, Canada: evidence of extension and shortening during passive margin development. Tectonics, 14(2), pp.390-405.

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4 Cretaceous continental margin evolution

revealed using quantitative seismic geomorphology, offshore northwest Africa

Max Casson1, Gérôme Calvès2, Jonathan Redfern1, Mads Huuse1, Ben Sayers3





3 TGS, 1 The Crescent Surbiton, Surrey, KT6 4BN, UK

Casson, M., Calvès, G., Huuse, M., Sayers, B. and Redfern, J., 2020. Cretaceous continental margin evolution

revealed using quantitative seismic geomorphology, offshore northwest Africa. Basin Research.

Quantitative seismic geomorphology, The Gambia

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4.1 ABSTRACT

The application of high-resolution seismic geomorphology, integrated with lithological data from the

continental margin offshore The Gambia, northwest Africa, documents a complex tectono-stratigraphic

history and seascape evolution through the Cretaceous. This reveals the spatial-temporal evolution of

submarine canyons by quantifying the related basin depositional elements and providing an estimate of

intra- vs extra-basinal sediment budget. The margin developed from the Jurassic to Aptian as a carbonate

escarpment. Subsequently, an Albian-aged wave-dominated delta system prograded to the paleo-shelf

edge. This is the first major delivery of siliciclastic sediment into the basin during the evolution of the

continental margin, with increased sediment input linked to exhumation events of the hinterland.

Subaqueous channel systems (up to 320 m wide) meandered through the pro-delta region reaching the

paleo-shelf edge, where it is postulated they initiated early submarine canyonisation of the margin. The

canyonisation was long-lived (ca. 28 Myr) dissecting the inherited seascape topography. Thirteen submarine

canyons can be mapped, associated with a Late Cretaceous-aged regional composite unconformity (RCU),

classified as shelf-incised or slope-confined. Major knickpoints within the canyons and the sharp inflection

point along the margin are controlled by the lithological contrast between carbonate and siliciclastic subcrop

lithologies. Analysis of the base-of-slope deposits at the terminus of the canyons identifies two end-member

lobe styles, debris-rich and debris-poor, reflecting the amount of carbonate detritus eroded and redeposited

from the escarpment margin (blocks up to ca. 1 km3). The vast majority of canyon-derived sediment (97%)

in the base-of-slope is interpreted as locally derived intra-basinal material. The average volume of sediment

bypassed through shelf-incised canyons is an order of magnitude higher than the slope-confined systems.

These results document a complex mixed margin evolution, with seascape evolution, sedimentation style

and volume controlled by shelf-margin collapse, far-field tectonic activity and the effects of hinterland

rejuvenation of the siliciclastic source.

Key words: submarine canyons; quantitative seismic geomorphology; Central Atlantic; regional composite

unconformity; continental margin sedimentary processes; mixed siliciclastic-carbonate systems

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4.2 INTRODUCTION

Continental margins through the rift to drift stages of the Wilson cycle are major archives of the stratigraphic

record (Bond & Kominz, 1988; Bradley, 2008). Following a period of initial extension induced by rifting

processes (McKenzie, 1978), continental breakup and related oceanic crust formation (rift to drift transition)

is typically marked by a break-up unconformity (Braun & Beaumont, 1989). Younger post-rift stratigraphy

traditionally ‘passively’ infills the accommodation generated by thermal subsidence of the margin (Steckler

et al., 1988; Bond et al., 1989). The fill of these basins host 35% of known giant hydrocarbon discoveries

(Mann et al., 2003). These extensive basins have been evaluated in deep-sea boreholes, hydrocarbon

exploration wells, exhumed outcrops, seafloor geophysical and seismic reflection data. Since the first

recognition of ‘Atlantic-type’ margins by Suess in 1885 (Bond & Kominz, 1988), findings from these datasets

have been used to pioneer our understanding of continental margins and to develop fundamental

knowledge of earth system processes, i.e. continental drift (Wegener, 1912). New techniques i.e. seismic

stratigraphy (Mitchum & Vail, 1977), seismic geomorphology (Posamentier & Kolla, 2003) and source-to-

sink analysis (Allen, 2008; Clift et al., 2008; Sømme et al., 2009; Martinsen et al, 2010) have been used to

investigate these continental margin sedimentary systems. These observations document the stratigraphic

record to calibrate studies modelling the solid earth (Granjeon and Joseph, 1999; Burgess, 2001; Moucha et

al., 2008).

Study of continental margin sedimentary systems has remained conventionally divided into siliciclastic and

carbonate realms (Chiarella et al., 2017). Moscardelli et al. (2019) highlighted the apparent lack of complete

examples using modern data to document mixed siliciclastic-carbonate systems in the literature. Mixed

siliciclastic-carbonate systems or ‘mixed systems’ are defined by contemporaneous siliciclastic and

carbonate sedimentation in the stratigraphic record. Mixing occurs across the full length of the depositional

system. Shallow marine to shelf settings exhibit a complex interaction between fluvio-deltaic and shallow

marine siliciclastic systems with intervening carbonate factories (e.g. Chiarella & Longhitano, 2012). Deep-

water settings are significantly different, here mixing occurs when siliciclastic and carbonate sediment is re-

deposited by a range of sedimentary gravity flow types (e.g. Payros and Pujalte, 2008; Playton et al., 2010).

The continental margins of the Central Atlantic developed as mixed systems during the Cretaceous,

subsequently deeply dissected by submarine canyon systems (Meyer, 1989; Mourlot et al., 2018a). Canyons

on continental margins act as key pathways for sediment transported from the shelf to deep basin (Normark

& Piper, 1969; Normark, 1974; Davies et al., 2007; Harris & Whiteway, 2011; Fildani, 2017). The seascape

geomorphology is deeply shaped by these long-lived systems (Pratson et al., 2007). Within this complex

depositional and erosional template, fundamental sedimentary processes persist and carve the morphology

of continental margins: sedimentary gravity flows and mass wasting events (gravitational processes),

modified by along-slope oceanographic currents.


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This study examines a high-resolution three-dimensional (3D) seismic dataset offshore The Gambia,

northwest Africa to study continental margin evolution of a mixed system, whilst examining the style and

evolution of buried submarine canyons with associated base-of-slope deposits (Fig. 4.1). The study area is

located in an important position within the source-to-sink system, covering the shelf, through the slope to

the basin floor (Martinsen et al., 2010). Quantitative seismic geomorphology techniques are used

(Posamentier & Kolla, 2003; Wood, 2007), integrated with exploration and scientific well data to reconstruct

sedimentary processes and margin morphology over million-year geological timescales (Fig. 4.2; Pratson et

al., 2007).

Fig. 4.1 (next page) (A) – Shaded bathymetric and topographic map of northwest Africa showing the present-day structure of the continental margin, with major river systems delineated (blue lines). The M25 (154 Ma) magnetic anomaly is shown as a black line and the continent-ocean boundary (COB) as a red dashed line after Labails et al. (2010). 3D seismic reflection dataset in hydrocarbon exploration blocks A1 and A4, offshore The Gambia (WGS 1984 UTM Zone 28N) is tied to Deep Sea Drilling Project (DSDP) sites 367 and 368 by regional 2D seismic reflection data. The study area covers the present-day basin-to-shelf transition. The location of the well correlation in Fig. 4.2 is shown; see Fig. 4.2 inset for a more detailed map naming the exploration wells. Hydrocarbon accumulations along the margin are displayed. The eastern margin of the Mauritania-Senegal-Guinea-Bissau-Conakry (MSGBC) Basin is defined by the Mauritanide front (Labails et al., 2010). The Mesozoic shelf edge (after Purdy, 1989), Late Cretaceous shoreline and erosion (after Mourlot et al., 2018a), and Casamance failed rift arm (after Long, 2016) are mapped. Present-day canyon systems locations from Wynn (2000a). (B) – Regional cross section based on the 2D seismic line. See Fig. 4.1A for location. TB – Top Basement; TJ – Top Jurassic; TAp – Top Aptian; TA – Top Albian; RCU – Regional Composite Unconformity; BTU – Base Tertiary Unconformity; SF – Seafloor.

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The conjugate continental margins of northwest Africa and Eastern America developed following the

formation of the Central Atlantic in the early Mesozoic (Uchupi et al., 1976; Uchupi and Emery, 1991;

Davison, 2005; Labails et al., 2010). The stratigraphy along the northwest African Atlantic Margin (NWAAM)

records rifting in the Late Triassic (Davison, 2005); opening of the Central Atlantic in the Middle Jurassic

(Labails, 2007) and thermal subsidence in the Jurassic to Recent (Latil-Brun & Lucazeau, 1988), from

northern Morocco to the Guinea Fracture Zone. The study area is located at the northernmost tip of the


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Casamance sub-basin (Fig. 4.1A). The margin is structurally segmented by Pan-African structures and later

transform faults (Brownfield & Charpentier, 2003). The sub-basin contains allochthonous salt that forms

pillows and diapirs (Tari et al., 2003). The study area is located outboard of the Casamance failed rift arm,

which is postulated to have controlled the antecedent drainage of the proto-Gambia river (Fig. 4.1; Long and

Cameron, 2016).

The Mesozoic post-rift evolution of the basin fill initiated with the establishment of an extensive Tethyan-

type carbonate platform surrounding the Central Atlantic margins. During the Albian, the platform died out

as siliciclastic sedimentation proceeded to dominate (Martin et al., 2010). At this time, the opening of the

Equatorial Atlantic gateway influenced paleo-circulation in the Central Atlantic (Forster, 1978) influencing

the depositional systems in the deep basin (Mourlot et al., 2018a) and a transpressional tectonic regime was

established along the southern NWAAM and conjugate Demerara Plateau (Reuber et al., 2016).

Subsequently, Albian deltas prograded across the platform, forming the prolific pro-delta hydrocarbon

reservoirs of the SNE field, Senegal (Clayburn, 2017). The Cenomanian transgression and the altered

circulation patterns associated with the opening of the Equatorial Atlantic formed a coastal upwelling zone

of deeper oceanic water masses off the NWAAM (Arthur et al., 1984). This resulted in deposition of ca. 150

m thick organic-rich interval (av. TOC – 10%; Arthur et al., 1984) on the basin floor (encountered at DSDP

Site 367) onlapping onto the wide transgressed shelf and coastal basin.

The Santonian compressional event (84-80 Ma) associated with Africa-Europe convergence caused inversion

of sedimentary basins in North Africa and at this time there was also a change in the pole of rotation in the

opening Central Atlantic (Labails, 2007). Regional uplift of the NWAAM accompanied these tectonic events,

manifesting as a Late Cretaceous regional composite unconformity (RCU) that can be recognised along the

entirety of the margin south of Dakar (ca. 660 km; Fig. 4.1). This feature has previously been termed the

Senonian unconformity (Tari et al., 2003) and pre-Maastrichtian unconformity (Clayburn, 2017). The

tectonism coincided with relatively high sea level and a transgressed onshore basin during the Late

Cretaceous greenhouse period, implying that tectonism was the primary allogenic control (Fig. 4.1; Haq et

al., 2014). Destabilisation of the distal continental margin resulted in tilting and margin collapse, with erosion

focused at the paleo-shelf edge removing up to 1.5 km of sediment (Fig. 4.1; Tari et al., 2003; Mourlot et al.,

2018a). The margin remains heavily canyonised to present-day (Fig. 4.1; Wynn, 2000a). It is postulated that,

despite the high sea level, uplift was such that the platform was subaerially exposed at this time, resulting

in karstification (Tari et al., 2003; Martin et al., 2010). An increase in sedimentary overburden initiated

differential loading and subsequent salt movement at the base of the carbonate escarpment (Tari et al.,

2003). A major Cenozoic magmatic event affected the area surrounding Dakar, Senegal (Goumbo Lo et al.,

1992).

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Historically, the American margin has been a key region for the study of submarine canyons (Miller et al.,

1987; McHugh et al., 1993; Dugan & Flemmings, 2000; Fulthorpe et al., 2000; Mitchell, 2005). Comparatively

less work has documented the African conjugate (Antobreh & Krastel, 2006). However, there is now

increased interest as recent significant hydrocarbon accumulations (e.g. SNE field, Senegal – Clayburn, 2017)

indicate submarine canyons here are an important paleogeomorphic trapping mechanism for oil and gas.

They also spatially control delivery of reservoir sands into the deep basin (e.g. Greater Tortue Ahmeyim field,

Mauritania-Senegal – Kosmos Energy, 2017), and their fill may form attractive hydrocarbon exploration

targets.

4.4. DATASET & METHODS

4.4.1 Data

The subsurface dataset offshore The Gambia consists of a 3D seismic reflection survey covering exploration

blocks A1 and A4, and one regional 2-D seismic tie line linking the 3D survey to DSDP sites 367 and 368

(VER01 MWT). The 3D seismic survey covers an area of 2,566 km2 across the present-day mid to lower slope,

with water depths ranging from 279 to 3524 m. Across all surveys, the seismic data is presented in zero

phase and follows SEG normal polarity convention: where a downward increase in acoustic impedance is

represented by a peak (black) reflection event, and a trough (red) event is associated with the opposite

downward impedance decrease. The bin spacing is 12.5 x 25 m. In the interval of interest (3 – 6.5 s TWT),

the dominant frequency is around 35 Hz. Using an average velocity of 2750 m/s for the overlying Late

Cretaceous to Recent sediments (based on well DKM-2: Fig. 4.2), the vertical resolution (λ/4) is ca. 20 m.

Additionally, wireline data and final well reports from six exploration wells drilled offshore Senegal are

correlated along a 200 km strike profile of the NWAAM (Fig. 4.2; data provided by Petrosen). The gamma

ray log and lithological data for well Jammah-1 offshore The Gambia was published by Clayburn et al., (2017).

4.4.2 Methods

Seismic interpretation of key horizons was performed using the methods of Posamentier (2005; Fig. 4.3).

Age constraints for the key stratigraphic surfaces were attained from nearby exploration wells and

correlated to the 3D seismic dataset using the 2-D regional tie line. The stratigraphy and age model in the

DSDP boreholes have been recently re-evaluated (Mourlot et al., 2018a). Using the available well data, we

have established a correlation between key horizons on the platform, across the escarpment margin, into

the basin.

The RCU (Fig. 4.3; Fig. 4.6A) was manually interpreted and converted to depth using a simple average interval

velocity model (data extrapolated from well DKM-2). We recognise uncertainty is inherent in the depth


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conversion process, however this provides more accurate geometries than a time structure map and was

the best depth conversion method available. The surface was ‘restored’ to depositional geometry by

flattening on the top Aptian horizon (Fig. 4.3). We interpret this horizon to have been a relatively flat

depositional surface at the scale of the study area (horizontal extent of flattened surface and carbonate

platform is 7.5 to 30 km; Fig. 4.6A). This flattened topography is recognised on comparable distal carbonate

platforms (Kenter, 1990). Major structural and tectonic modification of this surface occurred following

canyon incision. The depth-converted surface was exported to ESRI ArcMap v. 10.4.1 and the Arc Hydro

module used to calculate drainage catchments and subsequently flow pathways. This workflow is commonly

used in hydrology to simulate drainage patterns of rivers (Maidment & Morehouse, 2002), and to extract

modern-day submarine drainage (i.e. California margin; Pratson & Ryan, 1996). Flow pathways recording

submarine canyons are labelled from North to South, A1 to M (Fig. 4.6A). From the RCU horizon, there was

further extraction of quantitative seismic geomorphological data to characterise the submarine canyons (Fig.

4.3).

The top Aptian and base Tertiary unconformity were initially interpreted manually. These key surfaces and

the RCU were used to constrain a geo-model in PaleoScan™. Semi-automated seismic interpretation in

PaleoScan™ produced a 200-horizon stack of stratigraphically concordant slices with extracted seismic

attributes such as RMS amplitude (Fig. 4.8) and variance. GeoTeric software was used to perform spectral

decomposition by extracting an amplitude spectrum and assigning each frequency bin, 20-30-40 Hz, with

the colours red, green, blue respectively. These volumes were blended to produce the spectral

decomposition images (Fig. 4.7). Integration of the data from these seismic attributes and acoustic

characteristics was used to identify seismic facies characteristic of deep-water architectural elements

(canyons, channels, lobes, mass transport deposits/MTDs, sediment waves) after Posamentier & Kolla

(2003). These features are associated with specific canyons and plotted against relative time (horizon 1-200)

from the PaleoScan™ model to understand the spatial and temporal evolution of the depositional systems.

A Geobody interpretation in PaleoScan™ was performed to extract quantitative data for the basin deposits

(Table 4.2).

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4.5 RESULTS

Fig. 4.2 – Senegal-Gambia stratigraphy. Regional well correlation, datum the base Tertiary unconformity, along a 200 km strike profile of the NWAAM. Biostratigraphy and formation tops evaluated from well reports. Average interval velocities (m/s) above and below the regional composite unconformity are displayed. Data courtesy of Petrosen. Jammah-1 data from Clayburn (2017). Inset maps shows location of the wells, study area, paleo-shelf edge and hydrocarbon discoveries (green).

4.5.1 Lithological & Stratigraphic Control

The following description of the lithologies and a regional stratigraphic correlation is provided to establish a

framework for the detailed seismic interpretation (Fig. 4.2). The Jurassic to Aptian stratigraphy, as

encountered in wells RF-3, DKM-2, RF-2, Wolof-1, penetrated a thick succession of carbonate lithologies (up

to 3100 m thick in well DKM-2; Fig. 4.2). These generally consist of interbedded micritic limestones, rare

oolitic, sucrosic secondary dolomite, cemented calcareous sandstones and occasional interbedded

mudstones. These heterogenous strata characterise the deposits of the carbonate platform. Outboard of

the platform, well CVM-1 records an Aptian basin stratigraphy that is predominantly composed of mixed


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lithologies; comprising cemented very fine-grained sandstones to sandy micritic limestones, interbedded

with mudstones. At DSDP Site 367 (Core 25 – 32; Lancelot et al., 1978a; Fig. 4.1B) and also exposed on Maio,

Cape Verde islands (Casson et al., 2019), the time-equivalent distal stratigraphy of the carbonate platform

is composed of thin-bedded pelagic limestone interbedded with marls and black shale.

Overlying the carbonate platform, the Albian sequence, as penetrated in the inboard wells, Jammah-1 and

Wolof-1, is principally mudstone dominated with thick units of very fine-grained sandstone. Regionally, the

siliciclastic Albian strata form hydrocarbon reservoirs in the SNE and FAN discoveries deposited within a pro-

delta apron and as basin floor contourites respectively (Fig. 4.2; Clayburn et al., 2017). This corresponds to

a major lithological transition from carbonate- to siliciclastic-dominated stratigraphy recorded across most

of the Central Atlantic in the oceanic domain (Casson et al., 2019). Where present, the Cenomanian-Turonian

interval is characterised by heterogenous assemblage of thin sandstones and limestones within a highly

organic shale-prone interval. TOC values range in the shales attaining up to 36% at DSDP Site 367 (Lancelot

et al., 1978a, 1978b), and decrease onto the shelf (Arthur et al., 1984). Overlying this, the Coniacian to

Maastrichtian interval is a thick succession of non-calcareous silty shale, with an upward increase in sandy

shale beds and sandstone interbeds.

We interpret the top of the main Jurassic to Lower Cretaceous carbonate platform to be top Aptian. Locally

in well Wolof-1, there is evidence for sandstone deposition during the Aptian, and in well GLW-1, the

Cenomanian interval is limestone dominated (Fig. 4.2). This variable spatial and temporal distribution of

carbonate is to be expected on a mixed system margin where carbonate factories exist in areas along strike

where siliciclastic sediment input is absent or limited (i.e. Moscardelli et al., 2019).

The RCU is observed in five of the seven wells studied, variably eroding into the underlying stratigraphy (Fig.

4.2; Fig. 4.6). Erosion is generally greatest in proximity to the paleo-shelf edge, as indicated by well DKM-2,

where the RCU erodes deeply into the Lower Cretaceous carbonate platform. Further inboard, in well Wolof-

1, a more expanded Aptian and younger stratigraphy is preserved. Outboard of the platform edge, there is

no clear record of the RCU in well CVM-1 where Coniacian to Maastrichtian aged sediments overlie the RCU.

Paleo-water depth indicators from foraminiferal analysis of sediments recovered from well GLW-1, located

on the shelf, indicate a deepening in paleo-water depth across the RCU from shallow marine to deep water

slope settings. Seismic evidence (i.e. the first record of canyon-related basin deposits) suggests the onset of

canyon formation and hence establishment of the RCU occurred in the early Late Cretaceous.

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Fig. 4.3 (A) – East-West two-way time seismic section with interpreted key stratigraphic surfaces. The regional composite unconformity (RCU) surface on the adjacent interfluve is projected onto the dip profile (dashed red line) highlighting the amount of erosion in canyon H. Intersections shown in (C). (B) – Inset seismic section focusing on seismic facies identified at the base of the canyon, MTD – mass transport deposit. (C) – North-South two-way time seismic section with canyon axes displayed. See inset map (A) for the line locations. Seismic data courtesy of TGS.

4.5.2 Margin Structure

The large-scale stratal architecture of The Gambian continental margin is very well imaged on the 3D seismic

and characterised as a relict carbonate escarpment (Fig. 4.3A; Mcllreath & James, 1978). Parallel and

continuous seismic reflections stack aggradationally representing the growth of the carbonate platform and

the seismic characteristics and structural geometry of the platform remain consistent throughout deposition

of this unit (Fig. 4.3A). An exception to this seismic character is observed on the most distal ca. 500 m tip of

the interfluve between canyons E and H, where the top Aptian surface has a chaotic, undulating, beaded

response, very similar in seismic expression to structures interpreted as karst in the Tarim Field (Ruizhao et


150

al., 2017). Martin et al. (2010) and Clayburn et al. (2017) found similar features in the top of the carbonate

platform adjacent to the study area. Seismic reflections did not indicate any reef body characteristics.

Only one major NNE-trending post-depositional normal fault is observed in the south of the study area within

the carbonate platform with minor offset (ca. 50 ms TWT). The time-equivalent deposits in the basin are

thinner than the carbonate platform (ca. 1200 vs. 1800 ms TWT maximum thickness, Fig. 4.3A), onlapping

the carbonate platform interfluve. This architecture can be classified as an escarpment bypass margin

considered to be a decoupled sedimentary system, where a bypass surface of non-deposition separates

coeval platform margin and slope-to-basin deposits (Playton et al., 2010).

Stratal evolution can be used for further classification of escarpment margins as inherited or growth (Playton

et al., 2010). Fig. 4.3 shows the progression from an accretionary margin with coupled systems (i.e. Lower

Jurassic, Morocco – Kenter & Campbell, 1991) to escarpment stratal patterns indicating a growth

escarpment margin (Playton et al., 2010). The carbonate platform did not form above high-relief antecedent

topography as indicated by the relatively sub-parallel seismic reflection of the acoustic basement above

extended continental crust (Mourlot et al., 2018a). The subsequent post carbonate platform margin

structure and depositional systems were heavily influenced by this early stratal architecture and the

inflection point in the slope profile.

Fig. 4.4 (A) – Interpreted dip two-way time seismic section of the progradational shelf edge delta shown in Fig. 4.3A. Section flattened on the top Aptian surface shown in Fig. 4.3A to ‘restore’ the depositional geometry. (B) – Interpreted strike two-way time seismic section. Only seismic data between the regional composite unconformity (RCU) and -20 ms TWT below the top Aptian is shown. See inset map (A) and Fig. 4.5C for the line locations. Seismic data courtesy of TGS.

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4.5.3 Shelf-Edge Delta Evolution

Overlying the carbonate platform, within the Albian interval, are a series of oblique to sigmoidal shaped

seismic reflections interpreted as prograding delta-scale clinoforms (242 ms TWT, ca. 330 m height; Fig.

4.3A; Fig. 4.5). On dip sections, mapping the clinoform rollover shows an overall 5.5 km advance that

indicates progradation towards the shelf margin (west) with minor late-stage aggradation (Fig. 4.4A). On

strike sections, the delta has a broad lobate shape extending beyond the eastern edge of the survey. The

erosive surface at the base of the delta is observed truncating parallel continuous seismic reflections (Fig.

4.4A). The top of the delta is expressed as a relatively smooth, sub-horizontal transgressive surface (T1)

identified by onlapping seismic reflections. The internal architecture of the delta is characterised by toplap

and downlap stratal terminations that define a stratigraphic surface separating two smaller-scale delta lobes,

numbered by age chronologically (Lobe 1 & Lobe 2; Fig. 4.4). The term ‘lobe’ is used in this section to refer

to two distinct depositional units of a delta system, not lobes encountered in a deep-marine environment

(see Section 4.5.8). Mapping the bounding surfaces of the two delta lobes and construction of isochore maps

to image the delta evolution (Fig. 4.5).

Fig. 4.5 – Isochore maps (ms TWT) showing the progradation of an Albian-aged shelf-edge delta system across the platform, truncated by RCU erosion at the carbonate escarpment margin. (A) – Isochore map of Lobe 1. See inset map for location of displays in the study area (red box). (B) – Isochore map of Lobe 2 highlighting the progradation of the system. (C) – Total isochore for the shelf-edge delta. See Fig. 4.4 for the seismic horizons mapped for lobe 1 and 2.


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The depocentre of delta lobe 1 is located centrally within the study area, in a more proximal position on the

shelf than delta lobe 2 (Fig. 4.5). Lobe 1 shows significant thinning towards the shelf edge (RCU truncation)

with discrete areas of sediment accumulation scattered across the distal pro-delta, potentially representing

the infill of subaqeous channel systems (Fig. 4.5A). Deposition appears focused at the delta front during the

deposition of both lobes represented by the thickest deposits (Fig. 4.5). Lobe 2 is volumetrically greater than

Lobe 1 and progrades further into the basin. Clinoforms in lobe 2 slightly downstep and show offlap

geometries (Fig. 4.4A) resulting in thinning of Lobe 2 to the east of the lobe 1 clinoform rollover as a result

of compensational stacking (Fig. 4.5B).

The presence of delta-scale clinoforms in close proximity to the shelf edge and the characteristic morphology

is indicative of a shelf-edge delta, comparable to examples from the Gulf of Mexico (i.e. Sylvester et al., 2012.

The delta prograded across the relict carbonate escarpment margin (e.g. Steel et al., 2003). The clinoforms

have a lobate-to-arcuate planform shape, identified in the tripartite classification scheme of Galloway (1975)

as being a likely wave influenced fluvial system (Fig. 4.4; Fig. 4.6A). Further characterisation following the

criteria defined by Patruno et al., (2015) suggests the geometry of the clinoforms is indicative of subaqueous

deposition in a stepped deltaic system. Therefore, the paleo-water depth at the subaqueous clinoform

rollover would not be more than 60 m on the shelf, increasing outboard onto the outer shelf (Patruno et al.,

2015).

Beyond the delta clinoforms, multiple subaqueous channel complexes, with a maximum width of ca. 320 m,

are observed migrating across the remainder of the shelf (Fig. 4.7A), with their infill forming accumulations

in the pro-delta apron (Fig. 4.5). These channels form highly sinuous systems present across the entire shelf,

indicating there was no significant paleo-topography capable of diverting or capturing the channels in this

interval between the delta and paleo-shelf edge. Most channels appear linked to Lobe 2, however earlier

channels in this pro-delta area may have been cannibalised by subsequent channels associated with Lobe 2.

Due to erosion by the RCU, the terminus of the channel systems cannot be observed, although

approximately half are observed to be offset from the canyon axes, indicating these channels did not

contribute to the initial formation of the observed later canyon systems.

Fig. 4.6 (next page) (A) – Depth structure map (contours), draped over a dip magnitude map, showing the regional composite unconformity (RCU) surface and the heavily canyonised carbonate escarpment margin. Arc Hydro™ computed flow pathways are displayed (solid white lines), lettered and cross-referenced in the following figures. (B) – Rose diagram showing the flow direction of each vertices from the flow pathways. (C) – Talweg longitudinal slope profiles of 13 canyons and a interfluve surface shown in (A). A major knickpoint zone exists between -3600 and -4100 m present-day depth (shown in grey shading) corresponding to the change in lithology at the subcrop of the top carbonate, see (A). (D) – Slope angle versus length along talweg longitudinal profile for two major canyons. Fine line sampled every vertices, bold averaged over 10 vertices. (E) – Canyon cross-profiles sampled every 1.5 km along the talweg longitudinal profile, locations displayed on Fig. 4.6A (white dashed lines).

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4.5.4 Canyon Incision

Prior to major canyon incision, the upper part of the continental slope would have had two contrasting

subcropping lithologies separated at the top Aptian subcrop surface (Fig. 4.2; Fig. 4.3A; Fig. 4.6A). Carbonate

sediments would outcrop on the exposed escarpment, however, to the east at the top Aptian subcrop (Fig.

4.6A), siliciclastic sediments introduced by the shelf-edge delta system and overlying transgressive

sediments would be present. Hence, later canyonisation eroded into a variable-lithology paleo-seafloor. The

paleo-topography and margin geometry of the study area in the Aptian can be characterised as a low-relief

platform top/shelf. This extends to the steep carbonate escarpment that has an average dip angle of 18.8°,

with a maximum angle of 83.3° in the canyon walls and a relief from basin floor to shelf of up to ca. 1.5 km

(Fig. 4.6A). Slope gradient increases significantly to the west and downdip of the sub-cropping top Aptian

surface before flattening out on to the basin floor.

4.5.5 Quantitative seismic geomorphology

Analysing the flow pathways over the RCU surface reveal 13 submarine canyons or tributaries (A1 – M) that

are orientated perpendicular to the margin (Fig. 4.6A; Fig. 4.6B). The main flow pathway trend is to the west

(Fig. 4.6B), with a minor WNW trend primarily observed in the north of the dataset. These features variably

erode into the underlying stratigraphy along a ca. 56 km length of the slope with an average spacing of ca.

4 km. This average canyon spacing is significantly smaller than any modern-day canyon system as recorded

by Harris and Whiteway (2011; data resolution 1-2 km), with the average value for modern canyon spacing

on continental margins worldwide being 39 km.

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Table 4.1 – Geomorphological data extracted from the sediment flow pathways (Arc Hydro) and regional composite unconformity (RCU) surface. Shelf-un – shelf-incising ungraded canyons; shelf-gr – shelf-incising graded canyons; slope – slope-confined canyons. Bold values signify the sediment flow pathway extended beyond the study area.

Canyons and associated erosion at this stratigraphic level extend beyond the limit of the study area (Fig.

4.1), as indicated to the north (Martin et al., 2010), and south (Mourlot et al., 2018a). Mounded interfluves

are preserved, with the largest having a maximum area of ca. 75 km2 between canyons E2 and H1 (Fig. 4.6A).

The canyons have relatively straight profiles (average sinuosity – 1.09; Table 4.1 with an average canyon

length of 18.3 km (Fig. 4.6C; Table 4.1). Canyon width was measured every 1 km along the talweg profiles

revealing an average width of 3.1 km and maximum value in canyon H2 of 8.3 km (Table 4.1). Two canyon

profiles are displayed in Fig. 4.6E to illustrate the change from proximal broad low-relief U-shaped profiles

to narrow V- and U-shaped profiles further downslope, as slope angle increases from the low-gradient

platform top to the steeper escarpment (Fig. 4.6D; Fig. 4.6E). Confluences in the canyon tributaries generally

occur on the shelf, where branching tributaries join to form larger conduits (Fig. 4.6A). A zone of major

knickpoints occurs between 3600 m and 4100 m present day depth where the talweg slope profile rapidly

steepens (Fig. 4.6C); overall these profiles are convex in shape. This knickpoint zone is at the maximum limit

of progradation reached by the underlying shelf edge delta. The spatial relationship between the knickpoints

and the top Aptian subcrop illustrates that substrate lithology is one of the primary controls on slope angle

within canyons and their interfluves.

Total Straight Max. Max. DistanceCanyon Length Length Width Incision Eroded Mean

ID Type m m Sinuosity m m m AzimuthA1 Shelf-un 17128 14632 1.2 2172 7239 274.2

A2 Shelf-un 12273 11862 1.0 3718 679 5125 283.8

B Shelf-un 16059 15668 1.0 3845 102 10752 285.2

C1 Shelf-un 17908 17104 1.0 2095 9836 285.0

C2 Shelf-un 12703 12307 1.0 1645 7863 289.5

C3 Shelf-un 11144 9508 1.2 2328 534 12867 301.5

D Slope 12075 11133 1.1 2134 212 4289 305.1

E1 Shelf-gr 25439 21380 1.2 2741 10892 292.6

E2 Shelf-gr 8051 7980 1.0 6308 3976 13086 300.4

F Slope 10534 9999 1.1 2023 199 3896 312.3

G Slope 11287 10949 1.0 2493 298 3920 283.5

H1 Shelf-gr 32979 30348 1.1 1657 17640 269.7

H2 Shelf-gr 11198 10930 1.0 1970 18463 289.8

H3 Shelf-gr 15799 14284 1.1 7030 3561 19735 294.4

I1 Shelf-un 33836 31385 1.1 2050 22947 283.8

I2 Shelf-un 8630 8205 1.1 6138 1974 16872 289.0

J Shelf-un 38158 33626 1.1 5073 1568 28462 270.3

K Slope 11565 10760 1.1 1519 319 1296 238.8

L1 Shelf-un 32915 30172 1.1 3942 21058 257.7

L2 Shelf-un 16603 15150 1.1 1782 936 23985 279.1

M Shelf-un 29658 28057 1.1 2235 1297 19475 263.6

Mean Shelf-un 20585 18973 3085 1013 15540

Shelf-gr 18693 16984 3941 3769 15963

Slope 11365 10710 2042 257 3350

TOTAL 18378 16926 3090 1204 13319


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4.5.6 Canyon Classification

Models for formative processes have been developed following the early identification of submarine

canyons by Shepard (1934). Submarine canyons are typically classified based on the degree of incision into

the shelf and slope (Twichell & Roberts, 1982; Farre et al., 1983; Brothers et al., 2013; e.g. siliciclastic system

– Jobe et al., 2011; mixed system – Puga-Bernabéu et al., 2011; global review – Harris & Whiteway, 2011),

and/or morphological criteria (Tournadour et al., 2017). A geomorphological approach was proposed by

Puga-Bernabéu et al., (2011). Jobe et al., (2011) proposed a more holistic classification incorporating

depositional processes and canyon-fill. In this study these methodologies have been combined to provide a

template for the classification of the canyons offshore The Gambia, the key discriminator being whether the

canyons incise the shelf or not. This allows definition of two primary types; 1. shelf-incised and 2. slope-

confined systems (otherwise known as blind or headless canyons, Amblas et al., 2006). We further subdivide

shelf-incised canyons dependent on the degree of erosion within the canyon long profile, as: 1A. graded

versus 1B. un-graded (Mitchell, 2005). Previous workers have suggested that slope-confined and shelf-

incised canyons represent the primary and secondary stages respectively of canyon evolution, potentially

indicating the relative ages of canyons along the margin (McGregor, 1985; Dingle & Robson, 1985; Nelson &

Maldonado, 1988; Klaus & Taylor, 1991).

Based on this classification, Table 4.1 summarises the main geomorphological parameters extracted from

the canyonised RCU surface (Table 4.1; Fig. 4.6A). Shelf-incised canyons erode into the shelf and extend a

greater distance from the escarpment margin (average distance eroded from paleo-shelf edge 15.7 km),

whereas slope-confined canyons are confined to the escarpment. Only two canyons display the

characteristics of graded shelf-incised canyons based on their relatively smooth long profiles in Fig. 4.6C,

canyons E2 and H1; the remainder have irregular concave upwards profiles. Canyon heads vary from pointed

(slope-confined canyons) to amphitheatre-shaped at the paleo-shelf edge (Fig. 4.6A), however the dataset

does not cover the upper reaches (origin) of these canyons in the north. Canyon width, length and incision

depth commonly decreases from graded to ungraded shelf-incised canyons to slope-confined canyons

(Table 4.1).

4.5.7 Formation Processes

Two models are proposed and well supported by modern day examples for the formation of canyons on

continental margins (summarised in Pratson et al., 2007): downslope erosion (Daly, 1936) and retrogressive

failure (Twichell & Roberts, 1982; Farre et al., 1983). Downslope erosion by sediment gravity flows with a

variety of trigger mechanisms that create incisions in the slope, subsequently enlarged by later flows to

establish a canyon; and retrogressive failure, a result of mass movement due to slope failure that migrates

erosion upslope. These processes propagate in opposite directions, can occur coevally (Pratson & Coakley,

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1996) and vary through time. The type of canyon also controls the amount of potential sediment catchment

at the canyon head and hence the degree of erosion by downslope processes. Shelf-incising canyons are

able to capture sediment from a larger ‘catchment area` compared to slope-confined systems (Jobe et al.,

2011). The architecture of the canyons in this dataset is the final result of these cumulative processes and

as such, each canyon represents various stages of canyon development. To investigate the morphological

evolution and formational processes of each canyon, deposits at the terminus of the canyons have been

studied and are described in the following section.

4.5.8 Base-of-slope to Basin Floor Deposits

Fig. 4.7 – Spectral decomposition at 20, 30 and 40 Hz extracted on two surfaces, Albian-aged T1 (A) and Late Cretaceous-aged T2 (B), see above for the seismic horizons mapped. These images document the two phases of margin evolution. (A) – Inset rose diagram showing the orientation of each vertices from the sediment wave crest polylines. Carbonate escarpment mapped (white line). (B) – Inset zoom in on the basinal area showing glide tracks and carbonate blocks.

T1 – Sediment waves

Surface T1, of Albian to Cenomanian age, is the maximum flooding surface overlying the Albian delta (Fig.

4.4; Fig. 4.7A). Sediment waves (sensu Wynn & Stow, 2002) characterise these deposits in the base-of-slope

to basin floor (Fig. 4.3B; Fig. 4.7A). Three areas of sediment waves are observed; in the north of the dataset

(between canyons A to C; minimum spatial extent – 326 km2); centre (H to I; 255 km2) and to the south (K

to M; 365 km2; Fig. 4.7A). This depositional system is imaged in Fig. 4.3B showing the characteristic

asymmetrical, undulating bedforms, decreasing in wave dimensions basinward. Average wavelength is ca.


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325 m and average trough-to-crest height is ca. 15 m. Orientation data extracted from digitized wave crests

shows a dominant NNE-SSW trend, aligned parallel to the strike of the regional slope (Fig. 4.7A). A 10 km

long moat is present at the base of the escarpment margin (Fig. 4.3B), separating the sediment wave field

from the escarpment. Crest curvature has an upslope convexity, possibly indicating up-current migration

(i.e. antidunes; Wynn et al. 2000b; Fildani et al., 2006; Fildani et al., 2013). Following the classification of

Wynn & Stow (2002), we propose that these sediment waves likely formed by downslope-flowing turbidity

currents originating from subaqueous channel complexes imaged in Fig. 4.7A (Fildani et al., 2013). However,

this classification is based on geomorphological parameters of sediment waves and deducing their formative

processes remains unclear (McCave, 2017). Cretaceous contour-parallel currents have been postulated

along this margin (Mourlot et al., 2018a). Without lithological calibration, we can only postulate based on

the morphology described that the systems are fine-grained (sensu Wynn & Stow, 2002).

T2 – Margin collapse

The T2 surface is Late Cretaceous in age and illustrates a variety of deposits in the basin associated with the

margin collapse (Fig. 4.7B). A total of 58 geobodies at the base-of-slope to basin floor are interpreted

through 200 horizon slices from the top Aptian to the base Tertiary unconformity surface, and

geomorphological data extracted (Table 4.2). The spectral decomposition of surface T2 allows the

visualisation of some of these depositional systems and facies (Fig. 4.7B). Two end-member styles of lobate

deposits are observed originating from canyons (Fig. 4.8). Earlier lobes are predominately debris-poor,

lacking seismically resolvable blocks and have an elongate lobate shape (Fig. 4.8A). Whereas later lobes are

debris-rich containing blocks of the eroded carbonate platform up to 0.92 km2, with some blocks observed

beyond the lobate bodies termed ‘outrunner blocks’ (Fig. 4.8B). In total, three seismic facies dominate in

this region, lobes (debris-poor vs. debris-rich; Fig. 4.8) and mass transport deposits (MTDs).

Table 4.2 (next page) – Geomorphological data extracted from the PaleoScan™ horizon stack and interpreted geobodies. Bold values signify the deposit extended beyond the study area. DP – debris-poor lobes; DR – debris-rich lobes; MTD – mass transport deposit.

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Fig. 4.8 – RMS amplitude maps extracted from a +/- 12 ms window around an intra-Albian horizon (A) and T1 (B), displaying the two end-member types of lobes (debris-poor vs. debris-rich). Location of the maps are shown in Fig. 4.6A.

Based on these observations, we interpret the debris-poor lobes were likely deposited pre-dominantly by

turbidity current processes and the debris-rich lobes by debris flows (McHargue et al., 2020). The degree of

mixing will be difficult to distinguish without lithological data (Talling, 2013). There is an apparent lack of any

base-of-slope or basin floor channel-levee systems that usually characterise the lower courses of canyons in

submarine fan systems in the study area (e.g. Galloway, 1998; Covault, 2011). However, these are present

further north and south of the study area in zones of higher siliciclastic sediment supply (Mourlot et al.,

2018a). The basinal deposits form a strike-discontinuous apron that are interpreted to nearly all originate

from point sourced canyon systems interpreted upslope (Playton et al., 2010). Off-canyon axes, there are

Runout Max. Length: Surface MeanHorizon X Y Depth Length Width Width Area Thickness Volume

ID Start End m m msTWT Facies km km Ratio km2

m km3

A1 108 113 200763 1502457 4723 DP 5.5 1.5 3.6 16.5 79.6 0.5

A Cumulative 0.5

B1 107 111 199452 1500218 4759 DP 9.8 2.6 3.8 53.9 45.7 0.9

B2 116 121 199029 1501318 4734 DP 9.7 3.9 2.5 65.2 82.7 2.1

B3 122 131 188413 1502100 5478 DR 16.6 5.7 2.9 204.5 109.8 7.0

B4 132 141 196302 1501863 4665 DR 17.8 6.6 2.7 222.8 173.1 14.8

B5 142 152 195398 1503254 4663 DP 15.6 1.7 9.4 65.4 56.1 1.5

B6 164 171 199694 1500772 4277 DR 8.6 4.0 2.1 73.2 120.0 2.2

B Cumulative 28.4

C1 108 114 197035 1492787 4925 DP 7.2 1.8 4.0 36.5 110.4 1.4

C2 119 126 196020 1493767 4888 DR 8.8 2.9 3.1 168.3 101.9 3.9

C3 127 129 197031 1492349 4709 DR 20.7 8.5 2.4 237.6 55.0 6.6

C4 130 140 189403 1496527 5242 DR 24.8 9.4 2.6 444.1 137.2 21.4

C5 149 162 192498 1497264 4771 DR 21.5 10.4 2.1 651.9 154.3 24.3

C6 163 172 185669 1496969 5228 MTD 28.2 7.2 3.9 680.7 180.9 42.2

C7 183 195 185450 1498035 4937 DR 33.6 8.7 3.8 744.8 181.2 34.8

C Cumulative 134.6

D1 96 101 199173 1490987 4761 DP 2.7 1.2 2.3 8.2 59.4 0.2

D2 130 136 197446 1491373 4656 DR 5.1 1.5 3.4 26.9 68.2 0.7

D Cumulative 0.9

E1 107 119 188178 1492209 5586 DP 15.4 4.9 3.2 154.3 98.6 5.6

E2 120 122 184646 1492399 5636 DR 19.5 5.6 3.5 129.7 56.2 3.4

E3 123 129 189299 1489058 5264 DP 13.1 2.5 5.3 60.7 57.1 1.5

E4 130 139 181938 1490594 5523 DR 24.3 8.2 3.0 393.3 151.1 22.1

E5 141 166 181245 1498573 5106 DR 26.8 11.9 2.2 504.3 170.2 29.0

E6 171 176 190026 1488398 4762 DR 25.0 6.4 3.9 270.1 91.5 8.7

E7 188 196 188505 1488920 4691 DR 23.3 12.2 1.9 520.4 126.0 16.0

E Cumulative 86.3

F1 113 114 191154 1485262 4968 DP 5.0 2.8 1.8 22.0 27.2 0.2

F Cumulative 0.2

G1 100 101 183938 1485561 5665 MTD 11.7 6.7 1.8 141.1 22.0 1.7

G2 104 104 187064 1482395 5348 MTD 5.5 2.3 2.4 17.2 34.4 0.4

G3 105 106 187254 1482224 5280 DP 6.3 2.6 2.4 32.7 50.8 1.0

G4 112 116 184643 1484928 5440 DR 12.3 6.4 1.9 106.9 60.4 2.7

G5 121 124 182537 1484961 5510 MTD 10.1 4.4 2.3 74.8 51.9 2.2

G6 134 148 182801 1483137 5233 DR 14.3 5.7 2.5 157.6 113.3 5.9

G7 160 168 182748 1483411 5132 DR 15.3 3.6 4.2 170.2 140.0 8.0

G8 182 186 186578 1481605 4685 DR 11.4 3.7 3.1 64.9 77.3 2.3

G Cumulative 24.2

H1 110 119 184875 1474506 5368 DP 13.8 4.8 2.9 135.0 116.2 4.0

H2 121 129 180111 1473824 5518 DR 19.0 6.9 2.7 193.7 83.0 6.4


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abundant polygonal faults in the base-of-slope signifying background apron mud-rich deposits (Fig. 4.8B;

Cartwright & Lonergan, 1996).

The number and volume of debris-poor lobes and run-out distances are minor in comparison to the

contribution to the slope apron by the two other facies (Table 4.2). The average debris-poor lobe run-out

distance is ca. 9.9 km and limited to the most proximal position in the base-of-slope, forming narrow

elongate lobes characterised by high amplitude seismic reflectors (Fig. 4.3B). In Fig. 4.3B, there are multiple

horizons with similar acoustic properties and geometries suggesting vertical lobe stacking over numerous

depositional events.

Throughout the stratigraphy, 8 discrete geobodies are identified with a complex and chaotic internal

character, compressional ridges and imbricate thrusts at their toe, basal scoured shear surfaces that

distinguish them from the debris-rich lobes as MTDs (sensu Moscardelli & Wood, 2016; i.e. Fig. 4.7B). These

are mostly detached from the escarpment margin and occur dispersed throughout the interval. Two types

exist: point-sourced MTDs associated with a local canyon system, and MTDs developed on the basin floor,

both having similar geomorphological features, but different origins. A confined MTD point-sourced from

canyon J is identified with a run-out distance of 23.6 km (Fig. 4.7B), compressional ridges are present in the

distal toe region of the MTD and large blocks are observed proximally. This feature formed basin floor

topography that was capable of deflecting the overlying debris-rich lobe to the north (Fig. 4.7B). Run-out

distances of all MTDs average ca. 14.3 km, with average volumes of 10.1 km3 (Clare et al., 2019; Table 4.2).

These values are comparable to the values reported from a global compilation of MTDs by Moscardelli &

Wood (2016). Clear basal shear surfaces and imbricate thrusts are imaged in Fig. 4.3B. In this example the

MTD appears to be generated by underlying salt pillow inflation increasing the gradient of the sea-floor

topography.

Volumetrically the most significant facies contribution to deposition in the base-of-slope to basin floor are

debris-rich lobes (volume of debris-rich lobes is 573.3 km3 from a total of 669.8 km3, 86%), with run-out

distances commonly beyond the extent of the dataset (Fig. 4.7B; Fig. 4.8B). The lobate planform morphology

is similar in appearance to unconfined submarine fans (Prélat et al., 2010), but the abundance of 100 m-

scale high amplitude blocks suggests these flows are debris-rich (isolated basinal megabreccia sensu Playton

et al., 2010). The blocks are interpreted as eroded blocks of the lithified carbonate platform, based on their

observed glide tracks in the underlying stratigraphy (Fig. 4.7B; Hurd et al., 2016; Bull et al., 2009). These

denser flows, where there is suspension of particles in a viscous matrix, are likely to contribute to more

erosion (Mitchell, 2006). Mapping 36 debris-rich lobes indicates they are exclusively point-sourced from

canyon mouths.

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Fig. 4.9 – Summary of depositional systems active on the platform and in the basin through time, linked to each canyon system displayed in Fig. 4.6A. The line thickness indicates the volume of each geobody/deposit. Canyon K is omitted as this directly feeds the basin system of canyon L and M. Canyon M is also omitted as the majority of the deposits is beyond the dataset. Created through the interpretation of a 200-surface horizon stack generated in PaleoScan™ between the top Aptian and base Tertiary unconformity. The stratigraphic surfaces T1 and T2 are indicated. This is correlated to the geodynamical events effecting the Central Atlantic, with references shown. BTU – Base Tertiary Unconformity; DP – debris-poor lobes; DR – debris-rich lobes; MTD – mass transport deposit; ORI – organic-rich interval; RCU – regional composite unconformity; RSL – relative sea level.

4.5.9 Spatio-temporal evolution

The earliest deposits associated with the initiation of the canyon systems are spatially distinct. In the north

and central areas deposits are dominated by debris-poor lobes for a significant period of time (av. 10 horizon

slices, ca. 1 myr.; Fig. 4.9). The southern sector is dominated by MTDs (Fig. 4.9). This indicates that the

erosional processes responsible for generating canyons varies along strike of the margin. This also suggests

that at this time, the main sediment source input from the shelf was captured by canyons in the north and

central areas. Heterogeneous basinal deposition is strike-discontinuous, with canyons recording

simultaneous deposition of different seismic facies (i.e. debris-rich lobe – canyon E, and MTD – canyon J; Fig.

4.7B). The discontinuous nature of the sedimentation signifies strike-limited points of instability and

subsequent collapse of the margin (Playton et al., 2010). A comparison can be made to the collapse of the

Famennian-aged escarpment margin in the Canning Basin, Australia (George et al., 1995), where a similar 1

to 10s km spacing between collapse deposits is recorded. Offshore The Gambia, canyon deposits evolve

from debris-poor to debris-rich lobes and MTD deposits, as recorded in the evolution of the basin floor

stratigraphy downslope of canyons offshore New Jersey (Pratson & Coakley, 1996).


162

Fig. 4.10 (A) – Volume of deposit (derived from geobody interpretation) plotted with uncertainty against relative time (estimated from the PaleoScan™ horizon stack i.e. horizon 100 to 200 from oldest to youngest), coloured by facies. (B) – Run-out distance plotted against relative time. Trend lines coloured by facies. (C) – Cumulative volumes of sediment transported through each canyon system.

Plotting the volume of each geobody/deposit against relative time shows a weak positive relationship,

suggesting the intensity and scale of margin collapse increased towards the end Cretaceous, supported by

the general increase in runout length through time (Fig. 4.10A; Fig. 4.10B; Table 4.2). This may also reflect

an increase in sediment supply to the margin. These are large volumes that are significant contributors to

base-of-slope sedimentation (Moscardelli & Wood, 2016). Although, the overall frequency of events

decreases through this period. Collapse frequency is higher in the shelf-incised than slope confined canyon

systems (Fig. 4.9); conceivably due to the capture of more shelfal sediment causing further slope erosion

and instability.

The run-out distance increases through time for all facies (Fig. 4.10B), mass wasted deposits (MTDs and

debris-rich lobes) increase to a maximum run-out for a debris-rich lobe of 33.6 km from canyon C, extending

beyond the study area. Slope-confined canyons transport significantly less volume of sediment to the basin

in comparison to shelf-incised canyons; the estimated average volume of sediment transported through

slope-confined canyons is an order of magnitude lower than shelf-incised systems (average volume per

canyon 8.4 to 80.6 km3, respectively; Fig. 4.10C; Table 4.2). If we assume all sediment deposited in debris-

poor lobes is bypassed to the base-of-slope from regional sources i.e. shelf edge deltas, and sediment

deposited in debris-rich lobes to be derived solely from the escarpment margin, a comparison of the total

volume of sediment delivered from regional/extra- and local/intra-basinal sources is 21.8 km3 and 648.0 km3

respectively during the Late Cretaceous.

4.6 DISCUSSION

4.6.1 Mixed System Margin Morphology

The inherited Late Cretaceous slope morphology of The Gambian continental margin is a complex product

of mixed depositional systems that have evolved through the Mesozoic. From carbonate margin growth (top

Aptian), subsequent demise associated with siliciclastic influx from a shelf edge delta system (Albian),

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transgression during the Cenomanian and ultimately Late Cretaceous margin collapse (summarized in Fig.

4.9).

Spatial variability in siliciclastic input is a major control on the location and health of carbonate factories,

which strongly influences continental margin morphology (Moscardelli et al., 2019). The study area is located

in a region that received siliciclastic-dominated sedimentation post-Aptian times, delivered by a shelf-edge

delta, whereas beyond this area we predict margin morphology may have continued to be controlled by

carbonate deposition where siliciclastic sediment input was low. In those areas, there may be other allogenic

controls on the regional demise of the carbonate platform, i.e. climate, nutrient availability, rapid sea-level

rise. Similar spatial heterogeneity of a mixed system recorded on the shelf is documented on the conjugate

US-Canadian margin in the Baltimore Canyon trough (Meyer, 1989) and Shelburne sub-basin, Nova Scotia

(Moscardelli et al., 2019).

The depositional evolution established a significant lithological contrast in the subcrop on the slope prior to

later canyonisation, which had an important regional control on the subsequent inflection in the slope (Hurd

et al., 2016), location of knickpoints within canyons and the nature of the seafloor substrate eroded. This is

comparable to slope morphology observed on the present-day conjugate U.S. Atlantic continental margin,

where steep subcropping Mesozoic limestone escarpments have up to 2 km of relief, and shape the Blake

Escarpment seascape (Jansa, 1981; Land et al., 1999). The lithological properties and seismic character of

the carbonate margin imply heterogeneous carbonate lithologies cropped out on the seabed of the

escarpment during canyon incision, generating rugose seafloor topography. Horizontal limestone benches

form angular ledges in the face of the Blake Escarpment, produced by lateral scarp retreat (Land et al., 1999).

A comparable seafloor is envisaged during the Late Cretaceous in the study area. Knickpoints and the slope

inflection form at the siliciclastic-carbonate contact (top Aptian subcrop – Fig. 4.6A) by simple entrenchment

due to varied competence of the substrate, with similarities to knickpoints in fluvial systems (i.e. Miller et

al., 1991). Substrate lithology is therefore one of the key controls on the slope morphology.

4.6.2 Canyon Incision Evolution

Combining techniques adapted from hydrology with seismic facies analysis and interpretation of the basin

deposits allows interpretation of the possible mechanisms of slope-confined and shelf-incised canyons

initiation during the Late Cretaceous. The spatial variation in the earliest canyon-related deposits recorded

in the basin stratigraphy can be used to interpret the characteristics of the early stages of canyon formation,

i.e. canyons linked with debris-poor lobes are interpreted to be related to downslope eroding sediment

gravity flows (northern canyons), whereas debris-rich lobe- and MTD-related canyons formed due to mass

wasting processes (southern canyons; Fig. 4.9). The relative increase in volume and frequency of gravity flow

and mass wasting events is interpreted to be due to an evolution from ungraded to graded canyons (Fig.


164

4.6C; Fig. 4.9). Pratson & Coakley (1996) show how repeated sediment flows trigger retrogressive failure,

and hence headward migration of canyon erosion by downslope-eroding sediment gravity flows and grading

of the submarine canyon long profile.

The subaqueous channel complexes observed associated with the shelf edge delta are indicative of sediment

transported to the escarpment margin and may have contributed to the early inception of canyons (Fig.

4.7A). This could be another mechanism to initiate canyons that can be tied spatially to channels (Canyons

L and M), however many channels are observed to be spatially-distinct from the overlying younger canyons

(i.e. interfluve between Canyons H and I).

The broad lobate geometry and orientation of the sediment wave deposits in the basin downdip of the

canyons (Fig. 4.7A) suggest sediment gravity flows bypassed and eroded the early escarpment margin,

forming base-of-slope aprons. Nelson et al. (1991) recognise these apron facies on line-sourced mature

continental margins, where deltas feed sediment through a gullied slope. Hence, we postulate some canyons

are likely to have formed from an initial gullied slope during the progradation of the shelf edge delta (in the

Albian), in a similar maturation process documented by Farre et al., (1983) on the U.S. Atlantic continental

margin. This is recorded in many siliciclastic settings (e.g. Jobe et al., 2011; Lonergan et al., 2013; Shumaker

et al., 2017), where the seabed substrate is composed of un-compacted fine-grained sediment. However, in

this study, no gullies have been observed on the RCU surface. To the west of the top Aptian subcrop, i.e.

beyond the shelf edge delta deposits, the Late Cretaceous seabed offshore The Gambia would have been

relatively compact and hard, composed of lithified carbonate lithologies (Fig. 4.6A), potentially preventing

the formation of gullies (e.g. Prélat et al., 2015).

Several canyon evolution models have evolved from the preliminary findings of canyon origins by Daly

(1936), and Twitchell & Roberts (1982). This has been supported by reduced-scale experimental approaches,

such as that of Lai et al. (2016), that develop understanding of how unconfined sediment gravity flows form

and shape submarine canyons, with progressive growth of slope relief. Findings from this model agree with

the results from our analysis for canyons interpreted to have formed by downslope erosion. It would be of

interest to repeat this experiment on a semi-consolidated or consolidated slope to imitate the carbonate

escarpment and understand changes in canyon architecture and long profile grading, and model how basin

deposits temporally evolve. In the study area, there is geomorphological and stratigraphic evidence for

canyons having formed by both processes of downslope erosion and retrogressive failure.

4.6.3 Sediment Transfer from Shelf to Basin

Sediment transfer from the shelf to basin across the carbonate escarpment, and latterly through the

canyonised surface of the RCU, is governed by three principal physical erosional processes: gravity flows,

mass wasting and oceanographic bottom currents, in addition to chemical dissolution of carbonates.

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Ultimately these processes shape the architecture of the continental margin and control sediment

distribution. During the Albian, the location of the main depocentre is linked to the location of the shelf edge

delta. Coarse grained sediment is mainly trapped on the shelf, although some bypass does occur to base-of-

slope aprons down canyons. This regional, extra-basinal, siliciclastic-prone source of sediment and drainage

is postulated to vary laterally and may have also exerted a control on the location and health of the

carbonate factories and accumulation of the platform along this mixed system margin. Mourlot et al. (2018a)

show multiple entry points for similar-aged deltaic systems (see their Fig. 9B), introducing a regional source

of sediment from rivers draining the onshore Senegal Basin and hinterland of NW Africa. This sediment is

likely to be very different in composition to locally derived material associated with the erosion and collapse

of the margin. We postulate the local, intra-basinal sediment to be much more heterogenous, composed of

mixed re-sedimented lithified carbonate facies and siliciclastic material, in comparison to the very-fine

grained, clean sandstones and mudstones derived from the regional fluvio-deltaic input (encountered in

wells Jammah-1 and Wolof-1, Fig. 4.2). As the margin begins to collapse following establishment of the RCU

in the early Late Cretaceous, locally derived sediment, developing debris-rich lobes and MTDs, dominates

over sediments input from extra-basinal drainage. Much of the extra-basinal drainage sediment may have

been trapped further inboard as the onshore Senegal Basin was transgressed.

A quantitative analysis of the different facies distinguishes regional (3% of total sediment transported to the

basin) versus local (97%) provenance signals from the seismic geomorphology. Long-lived (ca. 28 Myr)

sediment bypass is documented by the canyon systems interpreted in this paper (Fig. 4.6A), facilitating

sediment transfer from the shelf to basin floor. The seismic expression of the composite RCU shows

entrenchment of the canyon systems rather than lateral migration, and there is a lack of evidence for

multiple incisions (i.e. slope-channel-levee systems – Deptuck et al., 2003). This forms a deeply incised

surface where we assume the basal surface of the canyons (RCU) records a considerable amount of time

when either complete sediment bypass occurred and/or the canyon was bypass-dominated through time

(sensu Stevenson et al., 2015). The limited vertical resolution (ca. 20 m) of the seismic reflection data and

lack of borehole data within any of the canyons documented in this study inhibits our sedimentological and

stratigraphic interpretation of the deposits associated with these zones. Generally, the stratigraphic

architecture of the canyon-fill has a back-stepping onlapping signature, with a low amplitude acoustic

response throughout the Late Cretaceous sequence (Fig. 4.3). In all the wells where the RCU has been drilled,

the overlying stratigraphy is mudstone-dominated (Fig. 4.2). However, it is conceivable that the canyon fill

directly above the bypass surface may be thin-bedded and sand-prone (i.e. Stevenson et al., 2015 and

references therein), below the resolution of the seismic data. From an applied perspective, the RCU surface

and deposits associated with it, may act as conduits for migrating hydrocarbons from the basin to the shelf,

potential stratigraphic traps and/or act as thief zones in stratigraphic traps of hydrocarbons in the potential

base-of-slope reservoirs (e.g. Ghana – Kelly & Doust, 2016).


166

4.6.4 Regional Controls on Stratigraphic Evolution

High-resolution documentation of the seismic geomorphology related to the collapse and submarine

canyonisation of The Gambian continental margin offers improved understanding of the regional evolution

of this complex ‘passive’ margin. Integrated with the regional geology, we can elude to the possible drivers

behind the stratigraphic evolution (Fig. 4.9). Further work constraining the vertical movements of the

hinterland in Morocco (Charton, 2018) and in Mauritania (Lodhia, 2018; Gouiza et al., 2019) show that the

‘passive’ nature of the margin is punctuated by discrete uplift events (e.g. Leprêtre et al., 2015). The

stratigraphic response in the sink records increased sediment input during these tectonic events as deduced

from backstripping and subsidence analysis (Latil-Brun & Lucazeau, 1988). The Albian shelf edge delta,

recognised in this study, together with others along the margin (Fig. 4.9; Mourlot et al., 2018a), represent

the first major phase of siliciclastic sedimentation into the basin, potentially contributing to the demise of

the Jurassic to Lower Cretaceous carbonate platform. Results from the analysis of neodymium isotope data

delineates the segmented drainage of northwest Africa and the exhumation of Paleozoic cover and

Hercynian belts triggered by the opening of the Equatorial and South Atlantic was most-likely the driver for

delivering the siliciclastic influx during this period (Mourlot et al., 2018b). This is supported by new low-

temperature thermochronology data recording exhumation of the Mauritanides between 180-100 Ma

(Gouiza et al., 2019).

Prior to margin collapse, the Cenomanian-Turonian boundary records maximum transgression of the margin

(Schlanger & Jenkyns, 1976), associated with a flattened peneplained topography (Flicoteaux et al., 1988).

During this period, in the study area there are no collapse features or deposits observed, reflecting the

quiescent geodynamic setting and high eustatic sea-level that resulted in a transgressed margin, where

sedimentation is likely trapped in the onshore Senegal basin and/or drainage reorganisation shifts sediment

input points laterally beyond the study area (Fig. 4.1; Mourlot et al., 2018a; 2018b). Further refinement of

this model would be possible with access to well data located at the base of the carbonate escarpment,

allowing for a more detailed stratigraphic interpretation and lithological control on these deposits.

Margin collapse at the scale and frequency observed through the Late Cretaceous is indicative of a significant

change in accommodation (Playton et al., 2010). Covault et al., (2011) associate convex longitudinal canyon

profiles (i.e. Fig. 4.6C) with continental margin uplift and deformation. Several geodynamic events affecting

the Central Atlantic are likely to manifest in vertical movements of the margin and eventual collapse, i.e.

distal effects of the Santonian-aged early Alpine Orogeny compressional event, a shift in the pole of rotation

of Atlantic spreading due to continental separation between Africa and South America (Guiraud and

Bosworth, 1997; Labails, 2007) and similarly timed rifting episodes in Central Africa (Guiraud, 1998).

Postulated Late Cretaceous volcanic uplift of the Cape Verde islands and associated swell, ca. 500 km from

the continental margin and study area, also affected the oceanic domain architecture (Fig. 4.9; Casson et al.,

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167

2020). Regional uplift associated with this event may have created instability contributing to margin collapse.

Tectonic stress accompanying these far-field events and linked to exhumation onshore was likely localized

along the boundaries of the African plate (Gouiza et al., 2019). The base-of-slope in the study area directly

overlies the continent-ocean boundary (Fig. 4.1B). Further amplification of the base level signal is expected

due to relative changes in sea level (Haq, 2014), where, during lowstands, increased erosion within canyons

is predicted due to canyons capturing more sediment input as depositional systems shift basinward (Pratson

et al., 2007). However, canyon incision can also occur outside of lowstands (e.g. Fulthorpe et al., 2000).

Linking the stratigraphic response to sea-level cyclicity would require a more detailed stratigraphic

framework. Nevertheless, the timing of margin collapse is coeval with the relative first order fall in sea-level

from the Coniacian to Maastrichtian, and expansion of drainage eastwards into the West African Craton (Fig.

4.9; Haq, 2014; Mourlot et al., 2018b).

4.7 CONCLUSIONS

The integration of seismic geomorphology with stratigraphic and lithological data from well data has allowed

a quantitative evaluation of continental margin evolution, recording buried submarine canyons present on

a regional composite unconformity surface (RCU) surface. This has significantly improved the understanding

of the seascape evolution offshore The Gambia during the Cretaceous, developing a workflow and models

applicable to the wider Central Atlantic and other continental margins worldwide within mixed siliciclastic-

carbonate systems. Thirteen submarine canyons are identified from the drainage model and

geomorphological data extracted from these systems has been used to constrain two types of canyons,

slope-confined and shelf-incised. The carbonate subcrop, which would have formed the seabed in the Aptian

(the top Aptian surface), is interpreted to have been the main control on the location of knickpoints within

these canyons and can be correlated with the sharp inflection in the slope profile. Through the Albian, a

progradational shelf-edge delta delivered siliciclastic sediment with an extra-basinal provenance from

hinterland drainage into the margin. It is likely subaqueous channel systems on the paleo-shelf contributed

to the early development of canyons due to erosion by downslope flowing turbidity currents, the

depositional products forming a base-of-slope apron.

By utilising a semi-automated seismic interpretation and a geobody classification workflow we are able to

reconstruct the spatial-temporal evolution of mixed system basin deposits linked to the submarine canyons

and shelfal systems, providing insights into the early stages of canyon incision. Three main seismic facies are

identified in the basin, debris-rich and debris poor lobes, and MTDs. The integration of deposits linked to

feeder canyon morphology reveals distinct types of canyons that originated both by gravity-flow and mass-

wasting processes, with time-equivalent lateral variations along the margin.


168

Following establishment of the RCU, the margin began collapsing and canyonisation was initiated,

intensifying during the Late Cretaceous. It is postulated this collapse was related to regional

tilting/exhumation caused by far-field tectonic stresses, with deformation localized on the margin of the

African plate corresponding to the location of the platform margin study area. Locally derived sediment from

the carbonate escarpment was incorporated and re-deposited in the basin by sediment mass transport

events and sediment gravity flows. Volumetrically, shelf-incised canyons contributed on average an order of

magnitude more sediment to the basin than slope-confined canyons. Large km-scale blocks recognised in

the seismic geomorphology of debris-rich lobes are interpreted to be carbonate detritus. The vast majority

of canyon-derived sediment (97%) in the base-of-slope is observed to comprise of debris-rich lobes and

hence, composed of locally derived material from the degradation of the pre-existing margin.



companies of the North Africa Research Group (NARG) for their continued financial and scientific support.

We are grateful to TGS and Spectrum Geo for the provision of the seismic data, and we appreciate Felicia

Winter’s (TGS) comments on the preparation of figures and manuscript. We are thankful to Petrosen for

permission to access the Senegal exploration wells. Alex Clarke (Cairn Energy) is thanked for his assistance

with the seismic interpretation workflow. Andrew Newton (Queen’s University Belfast) is thanked for the

rose diagram spreadsheet tool. Early discussions of concepts with Keith Maynard (CGG Robertson) and Neil

Mitchell (University of Manchester) helped with original concepts. Schlumberger (Petrel), Eliis (Paleoscan),

ESRI (ArcMap; Arc Hydro) and Geoteric are thanked for academic licenses to the software used herein.

Katherine Maier (National Institute of Water and Atmospheric Research), Zane Jobe (Colorado School of

Mines), Andrea Fildani (Equinor) and Basin Research Editor-in-Chief, Atle Rotevatn, are thanked for their

constructive reviews that improved the direction of this paper.

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5 Evaluating the segmented post-rift

stratigraphic architecture of the Guyanas continental margin

Max Casson1, Jason Jeremiah2, Gérôme Calvès3, Frédéric de Ville de Goyet4, Kyle

Reuber5, Mike Bidgood6, Daniela Reháková7, Luc Bulot8,1, Jonathan Redfern1



2 Golden Spike Geosolutions Ltd., 20 Ten Acres Crescent, Stevenage, Hertfordshire, SG2 9US, UK



4 PetroStrat Ltd. Tan-y-Graig, Parc Caer Seion, Conwy, LL32 8FA, Wales, UK

5 ION GeoVentures, Houston, Texas, USA

6 GSS (Geoscience) Ltd., 2 Meadows Drive, Oldmeldrum, Aberdeenshire, AB51 0GA, UK

7 Comenius University in Bratislava, Faculty of Natural Sciences, Department of Geology and Paleontology,

Mlynská dolina, Ilkovičova 6, 842 15 Bratislava, Slovakia

8 Aix-Marseille Université, CNRS, IRD, Collège de France, INRA, Cerege, Site Saint-Charles, Case 67, 3, Place


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5.1 ABSTRACT

Segmentation of the Guyanas continental margin of South America is inherited from the dual-phase

Mesozoic rifting history controlling the first-order post-rift sedimentary architecture. The margin is divided

into two sectors by a transform marginal plateau (TMP), the Demerara Rise, into the Central and Equatorial

Atlantic domains. This paper investigates the heterogeneities in the post-rift sedimentary systems at a mega-

regional scale (>1000 km). Re-sampling seven key exploration wells and scientific boreholes provides new

data (189 analysed samples) that has been used to build a high-resolution stratigraphic framework using

multiple biostratigraphic techniques integrated with organic geochemistry to refine the timing of 10 key

stratigraphic surfaces and three megasequences. The results have been used to calibrate the interpretation

of a margin-scale two-dimensional seismic reflection dataset and build megasequence isochore maps,

structural restorations and gross depositional environment maps at key time intervals of the margin

evolution.

Our findings revise the dating of the basal succession drilled by the Demerara A2-1 well, indicating that the

oldest post-rift sequence penetrated is late Tithonian age. Early Central Atlantic carbonate platform

sediments passively infilled basement topography controlled by underlying basement structure of thinned

continental crust. Aptian rifting in the Equatorial Atlantic heavily deformed the Demerara Rise resulting in

major uplift, margin collapse, transpressional structures, and peneplanation of up to 1 km of sediment

capped by the regional angular base Albian unconformity. Equatorial Atlantic rifting led to margin

segmentation and the formation of the TMP, where two major unconformities developed during the intra

Late Albian and base Cenomanian. These are time synchronous with oceanic crust accretion offshore French

Guiana and in the Demerara-Guinea transform, respectively. A marine connection between the Central and

Equatorial Atlantic is demonstrated by middle Late Albian times, coinciding with organic-rich sedimentation

(Canje Formation, average TOC 4.21 %). The succession is variably truncated by the middle Campanian

unconformity.

Key words: stratigraphy; post-rift; continental margins; Mesozoic; Demerara Rise; Central Atlantic

Stratigraphic architecture, Guyanas continental margin

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5.2 INTRODUCTION

Continental margins are heterogeneous at various scales, resulting in along strike asymmetry and

segmentation. First-order structural and tectonic diversity is mainly related to pre-existing basement

heterogeneity often separated by long-lived lineaments. Subsequently modified by the rifting process, i.e.

the magnitude and orientation of extension (β-factor; McKenzie, 1978), and breakup magmatism, volcanic

versus non-volcanic margins (Franke, 2013). Post-rift subsidence and sedimentation finally influences the

overall margin architecture, but it is still largely controlled by the pre-existing structure (Clemson et al.,

1997). Old segmented continental margins, and particularly marginal plateaus record multiple rift-to-drift

cycles and/or failed rifts related to the gradual fragmentation of supercontinents (Wilson cycle; Wilson,

1966; Burke & Dewey, 1974). Exemplified in the studied Guyanas continental margin of South America,

caused by the opening of the Central Atlantic and succeeding transform-dominated Equatorial Atlantic, with

oblique opening directions (Fig. 5.1A; Pindell, 1985). Conventional models of lithospheric thinning assume

continuous post-rift subsidence (McKenzie, 1978), yet more studies are revealing the dynamic nature of

continental margins, with major post-rift vertical movements further influencing stratigraphic architecture

(Morocco – Charton, 2018; Mauritania – Gouiza et al., 2019; French Guiana – Derycke et al. 2018). All these

formative processes can invariably lead to a complex structural segmentation of the ‘basement’, i.e. crust

plus syn- and pre-rift strata, that subsequently controls post-rift depositional systems. Limited studies

intrinsically address the margin-scale mega-sequence architecture in this emerging and complex geological

setting.

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Fig. 5.1 (A) – Shaded bathymetric and topographic location map of northeast South America showing the structure of the Guyanas continental margin and subsurface dataset. Exploration wells and scientific boreholes used in this study are shown; orange circles highlight where new stratigraphic analysis has been performed. The ION Geophysical GuyanaSPAN 2D seismic reflection survey, the location of the composite seismic section (Fig. 5.11A), dip section SR1-5400 (Fig. 5.11B) and the isochore maps are shown (Fig. 5.12). Dredge samples recovered basalts and rhyolites zircon-dated at 173.4 ± 1.6 Ma (Basile et al., 2020) from the seabed (white star). Onshore, the limit of sedimentary cover and hence the location of the Archean Guiana Shield is mapped (Cordani et al., 2016). Hydrocarbon discoveries and the limits of Cretaceous source kitchens after Kosmos (2018). DR – Demerara Rise; WA – Waini Arch. (B) – Structural framework of the Guyanas continental margin with a top basement depth structure map interpreted from the ION


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Geophysical GuyanaSPAN 2D seismic reflection survey. The ‘top basement’ map was constructed from a merge between the top oceanic crust and top basement surfaces. The onshore geological map is from the Geological Map of South America (CGMW, CPRM, DNPM, 2003). Structural features are mapped after Gouyet et al. (1994), Yang and Escalona (2011), Reuber et al. (2016), Sapin et al. (2016), crustal thickness modelled from 3D gravity anomaly inversion by Kusznir et al. (2018), predicted Jurassic graben offshore (Griffith, 2017), and volcanics from Gouyet et al. (1994) and Mourlot (2018).

The Demerara Rise is a submarine promontory extending from the continental margin over 200 km into the

Atlantic Ocean (Fig. 5.1A), and has an African conjugate, the Guinea Plateau (Jacobi & Hayes, 1982). Both

features can be classified as transform marginal plateaus covering a combined surface area of 92,000 km2

(TMPs sensu Loncke et al., 2020), due to the presence of a transform margin along one flank. The underlying

basement characteristics have been analysed by documenting and interpreting a compilation of basement

features, which are displayed on the top basement structure map (Fig. 5.1B). This provides a model for the

underlying structural framework to assess how it may have controlled the structural evolution, subsidence

and deposition of the studied overlying post-rift section (Fig. 5.1B).

Surrounding the thinned continental crust of the Demerara Rise (Kusznir et al., 2018), the oceanic crust

displays a diachronous accretion. Within the Guyana-Suriname basin the oceanic crust is inferred to be

Jurassic in age, whereas to the north and east of the Demerara Rise, in the Equatorial Atlantic domain,

oceanic crust is at least 45 Myr younger, accreted during the Upper Cretaceous (Fig. 5.1; Basile et al., 2005;

Reuber et al., 2016). Thus, the dual-phase rifting creates an apparent ocean-ocean boundary northwest of

the Demerara Rise where Jurassic and Upper Cretaceous oceanic crust is juxtaposed across the Demerara-

Guinea transform. This heterogeneity is reflected in the basement morphology, which is more complex than

a typical continental margin (i.e. US Atlantic margin – Bally, 1981), rising from subsurface depths below -

12,000 m (old Jurassic oceanic crust) to -4,000 m depth along the eastern margin of the Demerara Rise (Fig.

5.1B). Additionally, the volcanic nature of the basement below the Demerara Rise is still debated leaving two

plausible models that will only be definitively realised when a well penetrates into the basement.

Investigating how this basement heterogeneity and structural inheritance subsequently controls post-rift

sedimentation provides insights to better characterise the highly prospective world-class petroleum systems

in the post-rift section, reducing uncertainty and risk for future exploration programmes. Our study

integrates geological and geophysical approaches by refining the Mesozoic stratigraphic framework through

resampling and analysis of exploration well data, and cores from the Deep Sea Drilling Project (DSDP) and

Ocean Drilling Project (ODP) boreholes. This provides a template to constrain the timing of key stratigraphic

events during the post-rift history. Results are then extrapolated to a margin-scale seismic reflection dataset

to understand lateral (along strike) heterogeneity and segmentation in depositional systems, which we

believe were influenced by the dual-phase rifting and underlying structural inheritance.

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The Guyanas continental margin of South America extends 1500 km from the Barbados Prism in the west

through the Guyana-Suriname basin and across the Demerara Rise into the Equatorial Atlantic offshore

French Guiana, and the Foz do Amazonas basin, Brazil (Fig. 5.1A). This margin is situated on the north-eastern

rim of the Archean Guiana Shield (Fig. 5.1B). The Demerara Rise, a prominent bathymetric feature, divides

the margin into two tectonic domains, the Central Atlantic passive margin to the west, and the Equatorial

Atlantic transform margin to the east. Consequently, the offshore stratigraphy records the opening of the

Central Atlantic (170 Ma; Labails et al., 2010), and Equatorial Atlantic (105 Ma; Sibuet and Mascle, 1978) as

the African plate rotated anticlockwise and rifted away from South America. Prior to this later rifting and

establishment of the Guinea-Demerara transform, the Demerara Rise formed the southern extension of the

Guinea Plateau and hence the key study area for Atlantic plate reconstructions (Pindell, 1985; Moulin et al.,

2010; Kneller and Johnson, 2011; Heine et al., 2013). Post-rift sedimentation on the sutured south-eastern

margin of the Central Atlantic initiated with the establishment of an extensive, basin-fringing carbonate

platform (Fig. 5.2; Davison, 2005). The south-eastern extension of the Jurassic-Lower Cretaceous Central

Atlantic Ocean formed an arcuate shoreline at the neck of the Equatorial Atlantic across the Demerara Rise

(Gouyet et al., 1994).

Opening of the Equatorial Atlantic punctuated this tectonically-quiescent period which is expressed on the

adjacent transform margin and on the West African conjugate as an Aptian unconformity associated with

the onset of rifting (Sapin et al., 2016; Olyphant et al., 2017). Volcanism linked to Equatorial Atlantic breakup

is locally developed on both margins (Gouyet, 1988; Greenroyd et al., 2008b; Olyphant et al., 2017). The

Equatorial Atlantic basins developed as a series of en-échelon pull-apart basins separated by paleo-dextral

transform faults, now preserved as fracture zones (Pindell, 1985; Greenroyd et al., 2007, 2008a; Basile et

al., 2013). Adjacent to this, on the northern margin of the Demerara Rise, compressional structural features

are observed below a peneplaned Albian-aged angular unconformity (Gouyet, 1988; Mann et al., 1995;

Reuber et al., 2016). Transgression and opening of the Equatorial Atlantic gateway followed (Gasperini et

al., 2001; Friedrich and Erbacher, 2006). Cenomanian to Coniacian organic-rich sediments deposited along

the margin (Canje Formation, Guyana), and in adjacent basins (i.e. Naparima Hill Formation, Trinidad; La

Luna Formation, Venezuela and Colombia). These form prolific hydrocarbon source rocks (Erlich et al., 2003;

Meyers et al., 2006). Thermal subsidence of the continental margin and denudation of the Guiana Shield

resulted in increased sedimentation rates through the Late Cretaceous (Benkhelil et al., 1995; Yang and

Escalona, 2011; Mourlot, 2018). Major uplift of the South American cratons led to the formation of the Purus

Arch induced by Andean tectonism during the Paleogene-Miocene (Sapin et al., 2016). This initiated the

transcontinental Amazon River, debouching significant volumes of sediment in a depocentre along the

margin that persists to present-day (Fig. 5.1A; Figueiredo et al., 2009).


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Fig. 5.2 – Tectono-stratigraphic framework for the Guyanas continental margin, offshore Suriname and Guyana. The major sequence stratigraphic surfaces identified in this study are indicated, linked to key biostratigraphy events. Lithostratigraphy is based on seismic profile SR1-5400 (Fig. 5.11B) and adapted from Nemčok et al. (2016), key in Fig. 5.15. The main seismic markers and megasequences used in this study are highlighted. Calculated sedimentation rates (sedi-rates) displayed in metres per million years (m/Myr). Relative sea level curve after Haq (2014). AF – Albian flooding surface; CAMP – Central Atlantic Magmatic Province; CF – Cenomanian flooding surface; OAE – oceanic anoxic event; SDRs – seaward dipping reflectors; TB – top basement.

5.3.1 Previous Studies

The exploration well A2-1 drilled in 1978 reached total depth (TD) in reported Middle Jurassic-aged

(Callovian) sediments (Fig. 5.1A; Staatsolie, Suriname National Oil Company, 2013), and hence was regarded

as the oldest stratigraphic test. Significantly, as part of this study we have re-dated the basal section of this

well, which actually records a definitive late Tithonian age. Biostratigraphic detail and implications of the

new age dating are provided later in this paper. This key well has been the cornerstone for understanding

the stratigraphic evolution of the margin (i.e. Gouyet, 1988; Gouyet et al., 1994; Erbacher et al. 2004a; Kean

et al., 2007; Reuber et al., 2016; Griffith, 2017). Of note, the ‘Middle Jurassic’ penetration in A2-1 is used by

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Griffith (2017) to propose Jurassic source rock potential. The Deep Sea Drilling Project (DSDP) collected data

from the Cretaceous sequence to investigate the early evolution of the Central Atlantic on Leg 14 at Site 144

(Fig. 5.1A; Hayes et al., 1972). More recently, the Ocean Drilling Project (ODP) studied the opening of the

Equatorial Atlantic Gateway by drilling sites on Leg 207 (Fig. 5.1A; Erbacher et al., 2004a). This provided the

scientific community with core data from the Late Cretaceous to recent sequence, and subsequent studies

have significantly improved the existing stratigraphic framework (Erbacher et al., 2004a; 2004b; Erbacher et

al., 2005; Mosher et al., 2005; Friedrich and Erbacher, 2006; Hardas and Mutterlose, 2006; Kulhanek and

Wise, 2006; Thibault and Gardin, 2006; Krauspenhar et al., 2014). Yang and Escalona (2014) used existing

industry data to propose the tectono-stratigraphic evolution of the Guyana-Suriname basin. Post-Albian

sedimentary evolution of the Demerara Rise is investigated in Tallobre et al. (2016) and Fanget et al. (2020)

focussing on documentation of contourite deposits related to the North Atlantic Deep-Water current. Re-

evaluating and integrating these data along the full extent of the margin provides new stratigraphic insights.

5.4 DATASET & METHODS

5.4.1 Data

Lithological Samples

Re-sampling the DSDP Site 144 and ODP Leg 207 cores took place during 2017-2018, at the IODP Bremen

Core Repository, Germany (request ID: 054376IODP, 065859IODP and 077865IODP). Drill cutting samples

from the exploration wells (A2-1, FG2-1, GM-ES-3) were collected from the CGG Schulenburg facility,

Houston, United-States in 2018, kindly donated by Shell. The remainder of these samples are stored for

reference in the North Africa Research Group collection at the University of Manchester. A sample summary

is provided in the supplementary data (Table S 5.1).

Subsurface Seismic and Well Data

The seismic reflection data used in this study offshore northeast South America consists of 34 two-

dimensional (2D) seismic reflection profiles (total of 7970 line km) from the ION Geophysical GuyanaSPAN

survey (Fig. 5.1A). The survey images the entire continental margin in water depths of 40-3500 m, with a 50

m shot spacing, recording to 40 km depth and was provided as Pre-Stack Depth Migrated (PSDM) SEGY data.

The Suriname – French Guiana data is reprocessed data using WiBand broadband technology, recording to

25 km depth. A comparison is made to the conjugate Guinea Plateau. Wireline logs (gamma ray and sonic)

for the exploration wells were provided by Shell, and downloaded from the IODP data repository for ODP

Leg 207.


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5.4.2 Methods

A multi-disciplinary approach has been adopted to investigate and integrate a large subsurface dataset with

existing studies to document continental margin evolution.

Sedimentology and Organic Geochemistry

Drill cutting samples were set in resin and thin sectioned for petrographic analysis using an optical light

microscope. Descriptive petrographic sandstone classification was performed after Garzanti (2016). Whole-

rock X-Ray diffraction (XRD) was performed at BGS Keyworth on samples from FG2-1 using PANalytical X’Pert

Pro series diffractometer and the quantification methods of Snyder and Bish (1989).

Sixty-five shale samples were selected for organic geochemical analysis using a Shimadzu TOC-V CPN and

Solid Sample Module (SSM), calibrated to sodium carbonate and glucose to measure inorganic and total

carbon respectively. Additional geochemical data for ODP Site 1258C was incorporated from Meyers et al.

(2006). TOC data generated from the analysis of cuttings (exploration wells) is expected to yield lower results

due to the contaminant and mixing with other lithologies, as compared to core data (DSDP Site 144).

Further geochemical characterisation of thirty-four samples yielding greater than 0.5% TOC was completed

using a Rock-Eval 6 instrument at the University of Greenwich. Measurements of TOC are consistently less

than TOC derived from the Rock-Eval, by on average 0.53%. We report the results from the separate TOC

analysis as this is often a more reliable measurement of TOC compared to results from the Rock-Eval 6 (see

Behar et al., 2001). Additionally, a solvent was not used to remove free hydrocarbons prior to the pyrolysis,

whereas in the TOC analysis, free hydrocarbons are generally removed during the process, leading to a

higher value from the Rock-Eval.

Four samples from well A2-1 at levels with reported hydrocarbon shows were sent to GeoMark Research,

Houston for hydrocarbon extract analysis. Extracts were analysed for high resolution gas chromatography

and biomarker geochemical analysis.

Biostratigraphy

Dependent on lithology, various biostratigraphic analyses were performed to provide age constraints on the

stratigraphy. All key biostratigraphic events are shown on Fig. 5.2. Additionally, micro-fossil photographs are

fully documented in the supplementary data for future reference (Fig. S 5.2, Fig. S 5.3). Calcareous

nannofossils (JJ): In total 138 samples (see supplementary data Table S 5.1 for sample overview) were

analysed with standard techniques described by Bown (1998), and the picking brush method of Jeremiah

(1996). Samples were analysed semi-quantitatively, with the first thirty fields of view counted and the

remaining slide scanned for rare specimens. Foraminifera (MB): Thirty-one samples with relatively abundant

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calcareous nannofossil content were chosen for micropaleontological analysis and prepared using the

standard methodology described by Armstrong and Brasier (2013). Palynology (FdVdG): Ten samples for

palynological analyses were subject to the standard palynological preparation technique which involves

removal of all mineral material by hydrofluoric acid digestion and sieving to produce a residue of the 10

micron and above size fraction for each sample. An initial count of 100 in situ palynomorph specimens was

performed and abundance quantitatively assessed using percentage of total palynoflora. Calpionellids (DR):

A total of eight limestone-rich cutting samples from well A2-1 were thin sectioned and petrographically

analysed for the occurrence of calpionellids. Results are amalgamated within the ‘dating’ section of each

well/borehole, therefore the letters (N), (F), (P) and (C) are used to denote the type of fauna, calcareous

nannofossils, foraminifera, palynology, calpionellids respectively, when discussed.

Cuttings samples are (theoretically) composited, representative material from a drilled interval of rock.

Cuttings are susceptible to contamination from material collapsing into the borehole (called “cavings”) from

levels higher in the section and contaminating in situ sample material from near the drill bit. To mitigate

contamination from cavings, multiple picked lithologies per sample were analysed for nannofossils, the

oldest sample being considered representative of the depth, first occurrence (FO’s) and last occurrence

datums (LO’s) were then utilised. This was not possible for the palynology and foraminiferal work where

more rock material is required, here extinction events (or events which become apparent in a downhole

perspective) form the basis for the majority of biostratigraphic determinations i.e. first downhole

occurrence, FDO.

Seismic Interpretation & Structural Evolution

To ensure a robust seismic-well tie and depth calibration, synthetic seismograms for two exploration wells,

A2-1 and FG2-1 (Fig. 5.10), plus the ODP Leg 207 boreholes were produced. This process tied the wireline

log data to the seismic survey following the methodology of Sheriff (1976; 1977). Despiked sonic logs were

converted to give an estimation of the density log using Gardner’s equation. Statistical wavelets were

extracted for A2-1 and FG2-1 from the zones of interest, 2000 – 4000 m and 2000 – 3500 m depth

respectively (Fig. 5.10). Following this, key horizons (Fig. 5.2) identified during the stratigraphic re-evaluation

were interpreted on the 2D seismic dataset using Schlumberger’s Petrel software and the interpretation

methods of Payton (1977). Horizons were gridded and isochore thickness maps calculated (Fig. 5.12).

Flattening of the seismic section (Fig. 5.11A) on key horizons helped improve our understanding of

depositional geometries and structural features at the time of deposition (Fig. 5.14; Bland et al., 2004).

Projecting the uppermost continuous seismic reflector below the base Albian unconformity (BAU) provided

an estimation for the amount of missing section due to erosion.


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5.5 RESULTS

5.5.1 Sedimentological & Stratigraphic Control

Seven wells and scientific boreholes in the study area provide the control on lithologies/facies, age dating

and organic geochemistry. These have been re-examined and the new data used to build depositional

models to constrain and be integrated into the seismic dataset. Sample depths are reported in the original

unit of measurement, a metric conversion is provided for imperial depth measurements.

GM-ES-3

Exploratory drilling offshore French Guiana targeted the Santonian to Maastrichtian-aged Cingulata turbidite

fan system (McCoss, 2017). Through 2011-2013, 5 exploration wells were drilled with the first, GM-ES-1

(Zaedyus), encountering 72 m of net oil pay. Subsequent wells failed to find commercial hydrocarbons in

adjacent prospects. This includes GM-ES-3 (Priodontes), which penetrated a 50 m gross section of oil-stained

sandstone reservoir (Bradypus fan) above the targeted water-wet reservoir (Priodontes fan), well failure as

a result of an invalid trap. The 670 m thick sequence below the reservoir section to TD is mudstone-

dominated with calcareous and organic-rich intervals. At 6036 m, there is a lithology change from shale to

non-calcareous mudstones and at TD, sandstones, considered to be pre-rift strata. The data from this well

provides crucial stratigraphic information of deposits recording the rift-to-drift transition and timing of

breakup in the Equatorial Atlantic (Fig. 5.3).

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Fig. 5.3 – A re-evaluation of the Guiana-Maritime GM-ES-3 well stratigraphy displaying nannofossil events (Table S 5.2), total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Location displayed on Fig. 5.1A.

Dating – The current study investigates the pre-Coniacian/Santonian reservoir section in GM-ES-3 (Fig. 5.3),

all the age dating is based on calcareous nannofossils (N). The interval 5760 m – 5830 m confirms a complete

Turonian sequence. Penetration of the latest Turonian is confirmed at 5760m with the presence of an influx

Marthasterites furcatus below the FO of Micula staurophora. An age no older than Middle Turonian is

confirmed with the FO of Eiffellithus eximius at 5780m. Earliest Turonian sediments characterised by the

quantitative influx of Eprolithus moratus and E. floralis occur between 5800 m – 5830 m, events below the

FO of Quadrum gartneri at 5780 m. The OAE-2 interval is postulated at approximately 5820 m where there

is a subtle peak in the gamma ray log, likely subdued in comparison to other studied wells due to turbidite

input nearby (encountered in GM-ES-1). This occurs within Early Turonian aged sediments, typically latest

Cenomanian with the top at the Cenomanian-Turonian boundary, we postulate this is either due to log to

drillers discrepancy or just rarity of top Cenomanian markers at this point. Penetration of Cenomanian-aged

strata is proven by the LO of Axopodorhabdus albianus at 5850 m. Middle – Lower Cenomanian strata occur

at 5940 m with the LO’s of Gartnerago nanum and G. theta. The LO of consistent Eiffellithus paragogus at

6000 m confirms penetration of the Lower Cenomanian (Burnett, 1998; Ando et. al., 2015; Chin 2016),

Cenomanian sediments are proven as deep as 6020 m – 6040 m with the occurrence of Corollithion kennedyi

and FO’s of common Broinsonia signata.


188

Upper Albian is confirmed at 6060 m, with the consistent LO of Braarudosphaera spp. including B.

stenorhetha. The excellent preservation is reflected in the preservation of B. primula dodecahedra. A marked

decrease in braarudosphaeres was recorded towards top Albian from ODP Leg 171B, Site 1052E off the Blake

Nose plateau by Watkins et al. (2005), a similar top to a Braarudosphaera quinquecostata acme event from

Texas and Oklahoma by Hill (1976) and downhole increase in B. primula often associated with B. stenorhetha

from the offshore Gulf of Mexico (pers. obs.), and offshore Morocco (Chin, 2016). Although Nannoconus

spp. including N. quadriangulus quadriangulus and N. q. apertus are consistently observed the Late Albian

quantitative acme recorded by Watkins et al., (2005) and Hill (1976) is not recorded from offshore Suriname.

GM-ES-3 is unusual in the current study in having a relatively expanded latest Albian section (NC10a upper)

between 6060 m – 6130 m. At 6140 m, the LO of Eiffellithus monechiae is recorded, its co-occurrence with

equal numbers of Eiffellithus turriseiffelii down to 6170 m proving an age no older than the lower part of

NC10 (Jeremiah, 1996; Bown, 2001; Gale et. al., 2011a). Marine Late Albian mudstones rest directly upon

non-marine rift sandstones at TD (palynology results; Shell).

French Guiana 2-1 (FG2-1)

Well FG2-1 was spud in 1978 by ESSO, the main objective being Lower Cretaceous clastics and underlying

carbonates in a structural closure. The well was dry, probably drilled off structure in a hydrocarbon fairway

shadow, source rocks penetrated at the well were immature. Well FG2-1 is unique along the continental

margin as it reaches TD in a 380 m thick succession of basalts previously reported as 125 Ma in age

(Barremian; Fig. 5.1B; Gouyet et al., 1994), 120 ± 6 Ma (ESSO, 1978). Whole rock XRD shows the volcanics

to have a mafic composition, predominantly plagioclase and pyroxene with smectite, chlorite, quartz and

magnetite. Smectite likely originates from weathered basalts. 50 m of oxidised red sands overlie this unit,

suggesting subaerial exposure (Fig. 5.4). About 470 m of very-fine to fine grained litho-quartzose sandstone

with clay matrix is encountered above this. Petrographical investigation reveals the sands are poorly sorted

and matrix supported, with sub-angular quartz grains and additional lithic clasts of reworked sedimentary

material (Fig. S 5.1). These sands were likely deposited in a non-marine/continental environment as no

marine fauna or glauconite were observed in the petrographical analysis. At 3030 m depth, there is a

lithological break recorded as a positive shift in the gamma ray log, sediments above this surface are

calcareous organic-rich mudstones recording the first marine influenced strata.

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Fig. 5.4 – A re-evaluation of the French Guiana 2-1 (FG2-1) well stratigraphy displaying nannofossil events (Table S 5.2), foraminifera and palynology results, total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Location displayed on Fig. 5.1A.

Dating – Nannofossil and foraminifera analysis started at 7600 ft (2316.50 m) within lower Thanetian

sediments, based on the co-occurrence of Heliolithus kleinpellii, Discoaster mohleri (N) and FDO of

Globanomalina pseudomenardii (F). This level is just above the Base Tertiary unconformity (BTU) identified

at 2329.79 m. Lower Paleocene and Upper Maastrichtian deposits appear missing, this sequence is not

encountered in subsequent cavings. A diverse Lower Maastrichtian assemblage is recovered from the

interval 7800 ft – 8000 ft (2377.4 m – 2438.4 m) with Reinhardtites levis (N) recorded, supported by the FDO

of Globotruncana aegyptiaca (F). At 8200 ft (2499.4 m) the LO’s of Marthasterites furcatus, common

Eiffellithus eximius, Lithastrinus grillii and Broinsonia signata (N) indicates basal Campanian deposits.

A relatively complete Santonian to Coniacian sequence is penetrated between 8400 ft – 8980 ft (2560.3 m

– 2737.1 m). At 8400 ft (2560.3 m) Lower Santonian deposits are proven with the LO of Lithastrinus


190

septenarius (N). The LO of Quadrum gartneri and Q. eneabrachium (N) is at 8780 ft (2676.1 m) followed by

the FO of Micula staurophora and LO of Eprolithus floralis (N) at 8980 ft (2737.1 m). This is supported by the

foraminifera analysis where the FDO of Marginotrucana sigmoconcavata (F) indicates an age no younger

than Santonian (intra-Dicarinella asymetrica zone) at 8400 ft (2560.3 m). The presence of common

Marginotruncana spp. (F) in assemblages at and below this depth support the age assignment. This genus is

restricted to the Santonian – Turonian interval.

Turonian sediments are recorded from 9200 ft (2804.2 m), this interval below the FO of Micula staurophora

(N) and supported by the FDO of Praeglobotruncana spp. (F). The base of the Middle Turonian is marked by

both FO’s of Marthasterites furcatus and Eiffellithus eximius (N) at 9400 ft (2865.1 m). The Upper

Cenomanian is penetrated at 9790 ft (2984.0 m) characterised by the LO of Axopodorhabdus albianus and

Gartnerago praeobliquum (N). Between 9820 ft (2993.1 m) and 9890 ft (3014.5 m) the cuttings are

dominated by Upper Turonian cavings, no in-situ assemblages are recovered. Penetration of Middle to Lower

Cenomanian is confirmed by the LO’s of Gartnerago theta and G. nanum (N) at 9920 ft (3023.6 m). The

oldest sample from 9950 ft (3032.5 m) yields Corollithion kennedyi, abundant Broinsonia enormis and G.

nanum (N) confirming Cenomanian sediments, Upper Albian deposits absent.

Three samples from the sandstones overlying the volcanics were analysed for palynology (3072.4 to 3288.8

m; Fig. 5.4), however, the samples were dominated by Late Cenomanian cavings.

Demerara A2-1

Demerara A2-1 was spudded by Esso in 1977 in 3937 ft (1200 m) water depth to appraise a large anticlinal

structure over the Demerara Rise, offshore Suriname. The well was drilled to a total measured depth of

16207 ft (4940.0 m) within previously reported Middle Jurassic (Callovian) platform carbonates and

abandoned as a dry well. The lowermost ca. 2350 m of stratigraphy in A2-1 is composed mainly of an

alternating limestone/mudstone sequence (Fig. 5.5). Limestone-dominated strata sharply decrease the

gamma ray log forming distinctive blocky responses (Fig. 5.5; Fig. 5.10), these sequences are up to 450 m

thick. Petrographic analysis of these limestones reveals a mixture of microfacies within the cuttings;

biomicritic, bioclastic, sandy, silty limestones are observed with a mudstone to grainstone texture,

occasionally dolomitised. Limestones rich in bioclastic material contain fragments of ostracods, crinoids,

spores, echinoid spines, recrystalised bivalve shells, framboidal pyrite, representative of platform

carbonates. The micro-fauna includes planktonic foraminifera observed in most limestone cuttings, with

common cysts and spores, and occasional calpionellids (discussed below). Two samples from near TD of the

well contain more argillaceous and siliciclastic material with minor organic matter. Sedimentation rates are

relatively high averaging 65.8 m/Myr throughout this interval (Fig. 5.2). This sequence is more mudstone-

dominated towards the top, becoming increasingly organic (max. TOC – 1.09%).

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A 40 m thick sandstone unit with remarkably similar lithological characteristics to the fine-grained sands in

FG2-1 overlies this package and is interpreted as part of the Starbroek Formation (Fig. S 5.1). Of note, the

presence of glauconite is indicative of deposition in shallow marine conditions (e.g. Stonecipher, 1999; Fig.

S 5.1) and sedimentation rates. Limestones (Potoco Formation), 80 m thick, overlie these sands and are the

first transgressive deposits above the BAU. The overlying unit is marked by a sharp increase in the gamma

ray log. A thick interval of calcareous mudstone is encountered with high organic content and is eventually

truncated by the BTU.

Fig. 5.5 (next page) – A re-evaluation of the Demerara A2-1 well stratigraphy displaying nannofossil events (Table S 5.2), foraminifera and palynology results, total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Oil shows indicated on lithology column as green stars. Palynology abbreviations: CMN – common, FDCO – first downhole common occurrence. Location displayed on Fig. 5.1A.


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193

Dating – The youngest samples analysed at 7020 ft (2139.7 m) yielded a middle Campanian assemblage

characterised by Eiffelithus eximius, Uniplanarius sissinghi and Arkhangelskiellla cymbiformis (N), and FDOs

of Contusotruncana fornicata, C. ?contusa and Rugotruncana subcircumnodifer (F). The middle Campanian

unconformity (MCU) is recognised in this well at 2156.65 m, with the underlying sediments recorded from

7110 ft (2167.1 m) yielding Santonian fauna characterised by Marthasterites furcatus, Lithastrinus grillii (N)

below FO’s of the Broinsonia parca group and A. cymbiformis (N). Organic mudstones of Coniacian to ?Upper

Turonian age are recovered over the interval 7260 ft – 7290 ft (2212.8 m – 2222.0 m). The assemblages are

characterised by Quadrum gartneri, Eprolithus floralis and Lithastrinus septenarius (N). The FO of Micula

staurophora (N) at 7290 ft (2212.8 m; if in-situ) would indicate an age no older than Coniacian. The

occurrence of abundant M. furcatus (N) also at 7290 ft (2212.8 m) confirms an age no older than uppermost

Turonian.

A relatively expanded Lower Turonian succession between 7410 ft – 7650 ft (2258.6 m – 2331.7 m) is

characterised by the HRA of Eprolithus spp. (N) including quantitative influxes of Eprolithus moratus and E.

floralis (N) below the FO of Eiffelithus eximius (N). The LO of Zeugrhabdotus scutula ssp. turonicus (N) is at

7500 ft (2286.0 m), whilst the FO of Quadrum gartneri (N) is at 7590 ft (2313.4 m). The age assignment is

supported by FDOs of Whiteinella aprica and ?W. inornata (F). Penetration of Upper Cenomanian strata is

confirmed by the LO’s of Axopodorhabdus albianus, Gartnerago praeobliquum and Helenea chiastia co-

occurring with Gartnerago obliquum (N) at 7710 ft (2350.0 m). Lower Cenomanian age is penetrated at 7800

ft (2377.4 m) with the LO’s of Gartnerago nanum and G. theta (N), the age assignment supported by the LO

of consistent Eiffellithus paragogus at 7840ft (2389.63m). The basal Cenomanian is characterised by the

Broinsonia plexus including B. cenomanicus, B. signata and B. enormis (N). Other characteristic nannofloral

events of the basal Cenomanian is the HRA of Helicolithus compactus, H. compactus (small var.) and

Gartnerago praeobliquum (small var.). At well A2-1 the base Cenomanian unconformity (BCU) lies directly

upon a ?Lower Albian Potoco carbonate succession, no Upper to Middle Albian preserved as at ODP Leg 207

(Erbacher et al., 2004a).

The mudstone-dominated sequence below the BAU at 2496.4 m yields an intra-early Aptian to ?Barremian

marine dinocyst assemblage due to the presence of Pseudoceratium pelliferum (Duxbury, 1983),

Achomosphaera verdierii (Below, 1982) and Afropollis zonatus (Doyle et al., 1982; P). The co-occurrence of

common Dicheiropollis etruscus, is a sporomorph event which has been recorded from unpublished data of

Atlantic offshore Morocco within Hauterivian dated sediments. It is widely recorded from undifferentiated

Neocomian sediments offshore West Africa) and Muderongia simplex microperforata (Davey, 1982; Costa

et al., 1992; P).

Between 10840 ft (3307.1 m) and 11790 ft (3593.6 m) rich nannofloras yielding Eiffellithus windii, E. striatus,

Stradnerlithus silvaradius, Rhagodiscus dekaenelii, R. manifestus, Speetonia colligata, Cruciellipsis cuvillieri,


194

abundant Cyclagelosphaera margerelii, C. brezae, Tubodiscus verenae and Tripinnalithus surinamensis (N)

are encountered indicating penetration of late Valanginian sediments. Sporadic occurrences of

Calcicalathina oblongata and Diadorhombus rectus (N) are also recorded. Nannoconids are dominated by

the wide canal species N. kamptneri, N. wassalii and N. cornuta (N). The late Valanginian appears to record

the Lower Cretaceous maximum sea level pre-Albian and associated increase in nannofloral diversity. This

level is calibrated to the Upper Valanginian MFS (VF), an event recorded in this study from the Gulf of Mexico

(Loucks et al., 2017; Jeremiah, pers. obs.).

Below 11790 ft (3593.6 m), nannofossil diversity decreases with the increased frequency of platform

limestones. A brief flooding event is recorded between 12850 ft (3916.7 m) and 13090 ft (3989.8 m), where

calcareous mudstones are encountered again. The nannoflora is characterised by Crucibiscutum salebrosum,

Nannoconus steinmannii minor, Diadorhombus rectus, Eiffellithus primus and Tubodiscus verenae below the

FO of Calcicalithina oblongata (N), an indication that late Berriasian sediments have been penetrated.

The current biostratigraphy study confirms the age at TD of this well as no older than late Tithonian based

on calpionellid occurrences, much younger than previous studies that indicate an age as old as Callovian

(Griffith, 2017). The majority of the carbonate succession is Early Cretaceous aged. At 14100 ft (4297.7 m)

the top occurrence of Crassicollaria intermedia (C) is recorded, indicating the late Tithonian has been

penetrated, specifically the Crassicollaria Zone (Rename, 1985; Blau & Grün, 1997). Below this, the top

occurrence of Calpionella alpina and Crassicollaria parvula (C) occur at 15100 ft (4602.5 m), as well as

occurrences of Calpionella alpina, Crassicollaria intermedia and Tintinnopsella carpathica (C) at 15590 ft

(4751.8 m) are again characteristic of the late Tithonian Crassicollaria Zone. The acme of Calpionella alpina,

diagnostic of the Jurassic-Cretaceous boundary (Michalík & Reháková, 2011; Wimbledon et al., 2011), is not

recorded likely due to the studied sampling interval and therefore a tentative top Jurassic is placed at 4277.1

m. Three samples from the interval 15330 ft – 16070 ft (4672.6 m – 4898.1 m) yield a low diversity dinocyst

assemblage of Amphorula metaelliptica (Dodekova, 1969; Monteil, 1992; Habib & Drugg, 1983; van Helden,

1986), Oligosphaeridium diluculum (Davey, 1982) and Pseudoceratium pelliferum (P), indicating an age no

older than Berriasian, the assemblage considered caved.

ODP Leg 207

The following lithological summary is provided for the Cretaceous sediments of Site 1258C (the main focus

of the study), however a more complete description of the stratigraphy penetrated on Leg 207 and

specifically Site 1258 is presented in Erbacher et al. (2004a; 2004b; Fig. 5.6). Additional data is presented

from sites 1257A and 1260A. Cores from three Cretaceous units were recovered (Fig. 5.7): Unit 3 –

calcareous nannofossil clay (139 m); Unit 4 – laminated black shale and limestone (55 m); Unit 5 –

phosphoritic calcareous clay with organic matter (thickness – 37 m). The top of Unit 3 is marked by 2 cm

thick layer of graded medium to fine-sized green spherules representing the ejecta layer of the Cretaceous-

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195

Tertiary (K/T) boundary (Erbacher et al., 2004a; 2004b). The uppermost section of Unit 5, Core 27 (Fig. 5.7)

is calcified and indurated interpreted to be indicative of multiple unconformities, hiatus and condensation,

supported by low sedimentation rates (<5 m / Myr; Fig. 5.2).

Fig. 5.6 – A re-evaluation of the ODP Leg 207 Site 1258C stratigraphy displaying nannofossil events (Table S 5.2), total organic carbon (TOC; Table S 5.1) data compiled from Meyers et al. (2006) and key stratigraphic surfaces. A 12 m correction has been applied to the gamma ray log, where LD is logger’s depth and DD is driller’s depth. Early Late Albian ammonites identified in cores 30 and 31 by Owen & Mutterlose (2006) are annotated, as well as the cores displayed in Fig. 5.7. Location displayed on Fig. 5.1A.


196

Fig. 5.7 – Photographs of two cores, 15 and 27 from ODP Leg 207 Site 1258C with analysed samples and interpreted ages displayed by red arrows, highlighting the Cretaceous stratigraphy and unconformities present in the borehole (Erbacher et al., 2004a). Inset – zoom in on the sharp contact between the calcareous nannofossil clay of Unit 3 and black shale of Unit 4 representing the middle Campanian unconformity (MCU) and a ca. 12 Myr hiatus (Erbacher et al., 2004b). Ceno. – Cenomanian; Camp. – Campanian. Scale in cm.

Dating – All dates have been determined from calcareous nannofossil analysis (N). At Site 1258C, Erbacher

et al. (2004b) described a Campanian unconformity, with the early Campanian to Santonian absent. This

MCU is confirmed at the base of Core 15 -3 (Fig. 5.7), middle Campanian chalks yielding Eiffelithus eximius,

Broinsonia enormis, Broinsonia parca constricta and Arkhangelskilella cymbiformis immediately above a

condensed Middle Turonian organic shale succession with Quadrum gartneri and Lithastrinus septenarius

recorded at 393.77 m. Erbacher et al. (2004a) documented younger Coniacian organic mudstones preserved

beneath the unconformity south-eastwards at Site 1260. This is supported by sediments as young as

Santonian age preserved beneath the MCU at well A2-1 (Fig. 5.5).

Hardas and Mutterlose (2006) investigated the Cenomanian-Turonian boundary from Site 1258C and

recorded the LO of the Cenomanian marker, Axopodorhabdus albianus at 400.55 m. Due to a sample gap,

penetration of Cenomanian strata is confirmed slightly lower in the current study at 404.30 m, the LO’s of

Axopodorhabdus albianus and Gartnerago praeobliquum recorded.

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Lower Cenomanian sediments are proven at 428.95m with the occurrence of common Gartnerago theta,

the age assignment supported by the LO of consistent Eiffellithus paragogus at 438.32m. Cenomanian strata

are confirmed down to 447.58 m at Site 1258C with the FO of Corollithion kennedyi. Erbacher et al. (2004b)

documented a major hiatus at the base Cenomanian with no support for the preservation of Upper Albian

sediments. The current study supports the identification of the BCU, with latest Albian sediments missing.

The upper part of Zone NC10 is not recorded. Intra Late Albian aged sediment is however recorded

immediately below at 449.74m with the LO of an increase in Eiffellithus monechiae, E. turriseiffelii, however

still quantitatively dominant over E. monechiae, down to 450.06m.

The FO of E. turriseiffelii and associated E. monechiae acme and earlier FO is not preserved in 1258C. Another

hiatus, an intra Late Albian unconformity is recorded from the base of Core 27-2 at 450.16m, sediments

occurring below characterised by Staurolithites angustus at 450.45m. The LO’s of Watznaueria britannica

and Hayesites albiensis are both recorded from 450.45m, these forms utilised as alternative top Albian

markers (Watkins and Bowdler, 1984; Burnett, 1998); their occurrences here depressed stratigraphically but

of potential local correlative significance. Another major change in nannoflora at this stratigraphical level is

the increase downhole of cold-water nannofossils such as the HRA of Repagulum parvidentatum below

450.45 m and consistent Seribiscutum primitivum below 451.85 m, events also recorded by Kulhanek and

Wise (2006).

The oldest definitive Late Albian sediments at Site 1258C are confirmed by the FO of Staurolithites angustus

and consistent Cribrosphaerella ehrenbergii (Jeremiah, 1996; 2001; Bown, 2001) at 456.84 m (Core 29-1).

Additionally, an assemblage of ammonites collected and examined by Owen and Mutterlose (2006) from

cores 30 and 31, Site 1258C refine this age assignment to early Late Albian within the Hysteroceras varicosum

Zone. Late Albian sediments are potentially confirmed as deep as 467.94 m with the FO of Crucibiscutum

hayi (Jeremiah, 1996; Bown, 2001; Gale et. al., 2011); similar forms though are known to range down into

the Middle Albian (Jeremiah, 1996). Hence in the current paper are assigned the ranged Middle-Late Albian

age.

Kulhanek and Wise (2006) also recorded Eiffelithus monechiae consistently down to Core 33-2,

Cribrosphaerella eherenbergii almost to the base of the cored section at Core 34-2 and the boreal Upper

Albian marker Tegulalithus tessellatus between Cores 33-2 and 34-2. All these markers are Upper Albian

restricted but could not be corroborated in the current study at these deeper levels within the core. The

interval 459.85 m – 484.82 m yields an early Late Albian through late Middle Albian nannoflora. Boreal

markers that would enable further subdivision of the early Late Albian through Middle Albian succession

such as Tegulalithus tessellatus, the Ceratolithina plexus and Braloweria boletiformis are all absent. The

consistent occurrence of Axopodorhabdus albianus to the base of the cored section at 484.82 m, however,

confirms an age no older than late Middle Albian.


198

Sporadic records of Axopodorhabdus albianus are recorded from the lower Middle Albian (Jeremiah, 1996,

2001; Bown, 2001; this study DSDP144; 299.28 m). Base consistent A. albianus from the upper Middle Albian

was preferred by Jeremiah (1996, 2001; Bown, 2001) as a cosmopolitan event and supported by

observations from Texas by Hill (1976) and Bralower et al., 1993.

The oldest cored sediments investigated from the Demerara Rise on ODP Leg 207 were found at sites 1257A

and 1260A. Here, early Middle Albian nannofloral assemblages were recovered similar to that recorded from

DSDP Leg 14, Site 144 (Table S 5.2).


The objective of DSDP Leg 14 Site 144 was to recover the oldest marine sediments of the proto-Atlantic

(Hayes et al., 1972). Three boreholes (A, B, Z) were drilled to a TD of 327 m recovering 10 cores, totalling

31.9 m in length, from four Cretaceous-aged units (Fig. 5.8): Unit 2 – zeolitic greenish-grey marl; Unit 3 –

black and olive zeolitic marl; Unit 4 – olive green marl; Unit 5 – silty quartzose marl with shelly limestones

and background organics. These units differ from the lithostratigraphic units of ODP Leg 207 (Fig. 5.6; Fig.

5.7).

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Fig. 5.8 – A re-evaluation of the DSDP Leg 14 Site 144 stratigraphy displaying nannofossil events (Table S 5.2), total organic carbon (TOC; Table S 5.1) measurements and key stratigraphic surfaces. Location displayed on Fig. 5.1A.

Dating – All the age datings are determined from calcareous nannofossil analysis (N). The hiatus associated

with the MCU is also recorded at DSDP 144 where late Campanian sediments from the base of Core 4-2

(173.96 m) are recorded only 7 m above Upper to -Middle Turonian sediments at the top of Core 5-1 (Fig.

5.8). The sample at 181.05 m yields Eiffellithus eximius and Quadrum gartneri below the FO of Micula

staurophora. Upper Cenomanian-aged sediments yielding Gartnerago obliquum, G. praeobliquum and

Axopodorhabdus albianus are recorded from Cores 4-2 to 4-3 (Fig. 5.8), equivalent to Core 19-1 at ODP Site

1258C (Fig. 5.6). An early Middle Albian succession is preserved in the interval 264.14 m – 328.35 m (TD).

The base Middle Albian age assignment is supported by the FO of Tranolithus phacelosus at 264.14m and

absence of consistent Axopodorhabdus albianus. A Middle Albian age to the base of the cored section is

supported by the presence of Crucicribrum anglicum down to 328.35 m. Braarudosphaera spp. are

recovered including B. stenorhetha in association with nannoconids including Nannoconus quadriangulus

quadriangulus and N. q. apertus.


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5.5.2 Organic Geochemistry

Combined with re-dating of sediments from the seven wells and scientific boreholes studied, further organic

geochemical analysis was undertaken to improve characterisation of the prolific Upper Cretaceous organic-

rich interval (Canje Formation) encountered along the continental margin. This source rock in the basin

kitchens either side of the Demerara Rise (Fig. 5.1A) has been generating hydrocarbons from Late Miocene

to present-day (James et al., 2020). Hydrocarbons charge turbidite reservoirs in the base-of-slope to basin

floor setting in the Guyana-Suriname basin (Cedeño et al., 2019) and offshore French Guiana observed in

the GM-ES-1 well, and through long-distance migration to the onshore Tambaredjo heavy oil field, Suriname

(Fig. 5.1A; Dronkert & Wong, 1993). Additionally, the new dataset improves our understanding of older

source potential (i.e. Jurassic).

The new data generated from DSDP Site 144 and ODP Site 1258C refines the onset of organic-rich

sedimentation on the Demerara Rise to occur during the late Middle Albian. Early Middle Albian olive green

marls from DSDP Site 144 (and ODP Sites 1257A and 1260A) are organic-lean, with average TOC from cores

5 to 8 at 0.65% (Fig. 5.8). Whereas, late Middle Albian black shales recovered from ODP Site 1258C average

4.23% TOC (Fig. 5.6; Fig. 5.7). Pyrolysis reveals the organic matter is Type II algal material (Unit 4) and mixed

Type II/III (Unit 5; Erbacher et al., 2004b).

Throughout the wells, TOC values peak around the Cenomanian-Turonian boundary (~OAE-2), reaching a

maximum value at ODP Site 1258C of 28.13% TOC, as recorded globally (Schlanger et al., 1987). This peak is

observed in additional exploration wells on the Guyana shelf (AR-1, ESS-2; Fig. 5.15; Mourlot, 2018), and is

commonly associated with a significant peak in the gamma ray log (Fig. 5.4; Fig. 5.5). This peak is subdued in

GM-ES-3 (Fig. 5.3), likely due to the proximity of sand dominated turbidite systems suppressing the signature

(Fig. 5.16). In all the wells studied on the Demerara Rise, the Upper Cretaceous organic-rich interval is

truncated by the MCU. Campanian organic content is present in FG2-1, documented to be terrestrially-

derived (Fig. 5.9). Average TOC values for the Canje Formation vary along the margin; on the Demerara Rise

the highest average TOC values are recorded on the north-western distal margin at DSDP Site 144 (7.22%)

and ODP Site 1258C (7.67%). The TOC decreases towards the paleo-coastline in A2-1 to 3.96%, and again at

FG2-1 to 2.09% (Fig. 5.16). In the Equatorial Atlantic domain at GM-ES-3 TOC averages 4.28%.

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Fig. 5.9 – Classification of kerogen types using hydrogen and oxygen indices plotted on a modified van Krevelen diagram displaying the results of the Rock-Eval pyrolysis. The symbology reflects the age of each sample analysed. New data generated in this study from four of the revised wells (A2-1, DSDP Site 144, FG2-1 and GM-ES-3) is amalgamated with data presented in Meyers et al. (2006) from ODP Site 1258C, the ages are updated following the new biostratigraphy results. The tabulated data is presented in the supplementary material (Table S 5.1).

Source rock maturity indicated by Tmax values range from 346 to 430 °C, averaging 418 °C indicating all

samples are immature (Table S 5.1). To compare source rock quality and kerogen type, hydrogen and oxygen

indices were plotted on a modified van Krevelen diagram (Fig. 5.9). Raw data is presented in Table S 5.1. To

understand temporal changes in kerogen type the symbology reflects the age of the sample. The majority

of samples have high hydrogen index (HI; 475 to 600+ mg hydrocarbons/g organic carbon) and low oxygen

index (OI; 20 to 65 mg CO₂/g organic carbon) indicating Type II marine kerogen with oil generating potential.

Outliers from this group with low HI and high OI values are all early Middle Albian in age from DSDP Site 144

(cores 5 to 8) indicative of gas-prone Type III terrestrial kerogen. Younger Albian samples show a progressive

increase in HI and decrease in OI towards the Type II group, indicating the gradual increase in marine-type

organic matter through this interval. Cenomanian to Coniacian samples from FG2-1 have lower HI and higher

OI values (average HI – 251 mg hydrocarbons/g organic carbon; average OI – 76 mg CO₂/g organic carbon)

showing a mixing between Type II/III. This reflects the relative position of FG2-1 closer to the paleo-shoreline

and sediment input from river systems (Fig. 5.16) and therefore likely receiving more terrestrial input as

indicated by the higher sedimentation rates compared to the time-equivalent interval in A2-1 (Fig. 5.2).

Pyrolysis results from GM-ES-3 fall within a tight grouping away from main Type II signature with low OI (20


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to 30 mg CO₂/g organic carbon) and moderate HI (200 to 450 mg hydrocarbons/g organic carbon) values,

suggesting a mixing of kerogen types. S1 peaks are representative of hydrocarbons generated at low

temperatures during the pyrolysis and indicate free or absorbed hydrocarbons (Allen & Allen, 2013). Average

S1 values for GM-ES-3 samples are 21.4 mg/g, compared to an average of 1.0 mg/g for all remaining samples,

indicating free hydrocarbons throughout the interval analysed in GM-ES-3. Alongside the low Tmax values

(immature), this suggests the free hydrocarbons are migratory.

Geochemical analysis of samples below the BAU in A2-1, i.e. Aptian to Berriasian, all yield low TOC values

(average 0.37%). Higher values 1.1 to 1.5% TOC were previously reported by Griffith (2017) from this interval

as indicative of a Middle Jurassic (Callovian) syn-rift source rock based on the original biostratigraphy. Our

new age dating proves no Callovian sediments were encountered in A2-1, meaning the well did not

penetrate a syn-rift source rock below the Demerara Rise. However, this new evidence does not rule out the

potential for a Jurassic source rock along the margin. Seismic evidence from this study supports the

interpretation of additional older Jurassic sediments below the well TD of A2-1 (Fig. 5.11), distributed deeper

across the Demerara Rise (see Margin Architecture, Fig. 5.12A – MS1), and onto the Guinea Plateau (Fig.

5.16A). Oil and gas shows within the Lower Cretaceous interval are reported suggesting deeper source rock

potential as the main organic-rich interval sits above the BAU (Fig. 5.5). Additional support for a potential

Jurassic source rock is evidenced by proven Jurassic-aged lacustrine shales with 2.5% TOC within the Takutu

Graben onshore (Webster, 2004), and predicted in two grabens (Nickerie, Commeqijine; Fig. 5.1B) offshore

from gravity data (Griffith, 2017). Further geochemical work by Cedeño et al. (2019) of oil recovered from

wells onshore Suriname (Tambaredjo field) revealed two hydrocarbon groups, one typed to the proven

Upper Cretaceous source rock and another group from a source that generated hydrocarbons from

terrestrial organic matter in marly sediments interpreted as Jurassic or Lower Cretaceous in age. These

hydrocarbons are postulated to be generated from the Lower Cretaceous interval penetrated by A2-1.

The hydrocarbons at the Liza and Tambaredjo fields have migrated out of the deep Guyana-Suriname basin

from the Canje Formation, sitting on oceanic crust (Fig. 5.1B; Cedeño et al., 2019). We postulate that an

unpenetrated early Aptian source rock (OAE-1A-equivalent) may be present in the deep marine basin

(Bihariesingh, 2014), and absent across the Demerara Rise and basin margins. Additionally, along the French

Guiana margin, Aptian lacustrine syn-rift deposits may be potential source rock candidates.

Hydrocarbons were extracted from four Lower Cretaceous – Upper Jurassic samples (well A2-1) with very

low organic richness (0.11 to 0.43%) yielding very low quantities. It is difficult to determine for certain if the

extracts are a naturally occurring product or a drilling introduced contaminant. If the former then their

geochemical characteristics are very consistent and would most likely represent the residual product of

migratory hydrocarbons rather than in-situ generation. Overall the extracted hydrocarbons are from an

aquatic (possibly marine) environment, but with significant terrestrial input (Fig. 5.9).

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To summarise, further geochemical characterisation of the main source rock (Canje Formation) reveals the

heterogeneities in age of organic-rich sedimentation, organic richness and kerogen type. Highest TOC with

marine Type II kerogen occurs at the Cenomanian-Turonian boundary (OAE-2), typically recognised as a spike

in the gamma ray log profile. Free hydrocarbons are recorded throughout all samples analysed in GM-ES-3.

Jurassic source potential is not encountered in A2-1, further evidence for its occurrence is postulated. Aptian

source rock potential is hypothesised.

5.5.3 Margin Architecture

Mapping of the deep-penetrating GuyanaSPAN seismic data tied to the re-evaluated wells (Fig. 5.10) reveals

the seismic-stratigraphic architecture of the Guyanas continental margin (Fig. 5.11; Fig. 5.12; Fig. 5.13).

Three Mesozoic megasequences are defined and discussed based on our new data (Fig. 5.2).


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Fig. 5.10 – Synthetic seismogram calculated for two exploration wells, Demerara A2-1 (Fig. 5.5) and French Guiana FG2-1 (Fig. 5.4), providing the well to seismic correlation of key horizons and megasequences identified in this new stratigraphic study. Extracted statistical wavelets presented. Location of the two wells displayed on Fig. 5.1A.

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Fig. 5.11 (A) – Composite seismic section in depth displaying megasequence architecture along a >1000 km length of the Guyanas continental margin. Location displayed on Fig. 5.1A. Erosional truncation (red arrows) and onlap (black arrows) marked. BFF – basin floor fan; MFS – maximum flooding surface. (B) – Conjugate dip-orientated seismic depth sections from the Demerara Rise (2D line – SR1-5400, clipped at 20 km depth) and Guinea Plateau (after Edge, 2014) displaying megasequence architecture. Location displayed on Fig. 5.1A and reconstructed location on Fig. 5.16A. Note change of horizontal and vertical scale from (A). COB – continent-ocean boundary. Seismic data courtesy of ION Geophysical.

Fig. 5.12 (left) – Isochore thickness maps for three megasequences, MS1 – top basement (seaward dipping reflectors, continental and oceanic crust) to upper Valanginian maximum flooding surface (VF); MS2 – VF to base Albian unconformity (BAU); MS3 – BAU to base Tertiary unconformity (BTU). Cont. – continental; GP – Guinea Plateau; TJ – top Jurassic.

Fig. 5.13 (right) – A fence diagram constructed from 7 dip-orientated (N-S) seismic depth sections across the Demerara Rise, interpreted with the megasequences, structural domains and underlying basement structure. BAU – Base Albian unconformity; COB – continent-ocean boundary. Seismic data courtesy of ION Geophysical. Location inset.


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Basement

As introduced earlier, the ‘basement’ in this study is defined as the crust plus pre- and syn-rift sediments,

that exist below the Central Atlantic post-rift succession. Previous studies (Mercier de Lépinay et al., 2016;

Reuber et al., 2016; Kusznir et al., 2018) have characterised this interval, which is beyond the scope of this

paper. However, a brief overview is provided summarising the evidence for the two models of basement

composition. Despite the nature of the basement, the top surface is defined by a major unconformity,

interpreted as the top basement (TB), with MS1 strata successively onlapping this surface towards to the

southeast (Fig. 5.12; Fig. 5.13).

The main evidence for the volcanic nature of the basement below the Demerara Rise is the interpretation

of seaward dipping reflectors (SDRs) based on deep-penetrating seismic data (Mercier de Lépinay et al.,

2016; Reuber et al., 2016). Clearly on Fig. 5.11A, the basement comprises a series of high-amplitude

reflections forming a thick package (up to 21 km), dipping towards the Guyana-Suriname basin to the

northwest, i.e. seaward dipping. The interpreted basaltic flows have either been associated with the

migrating Bahamas hotspot (Morgan, 1983) during early opening of the Central Atlantic (~158 Ma; Reuber

et al., 2016), or related to the Central Atlantic Magmatic Province (CAMP) volcanism (~200 Ma; Loncke et

al., 2019). Volcanism is further supported by recovered dredge samples of Jurassic-aged (173.4 ± 1.6 Ma)

rhyolites and basalts from the Demerara Rise (white star – Fig. 5.1A; Basile et al., 2020).

Alternatively, a model for the non-volcanic origin of the basement is also conceivable where the basement

is composed of heavily deformed Paleozoic strata (Geognostics, 2020), as the acoustic properties and

thickness of the interpreted SDR sequence do not show close affinity to other volcanic sequences (Franke,

2013). This possible layered sedimentary sequence thins to the east, onlaps the basement, is broadly folded

and truncated at the TB (Fig. 5.11A). These postulated Paleozoic sediments are interpreted as marine

sediments deposited on top of stranded Neoproterozoic oceanic crust and distal Appalachian-related

foredeep sediments, initially deformed during the early Appalachian orogeny (Hercynian), and latterly by

Equatorial Atlantic-associated tectonism (Fig. 5.13).

Megasequence 1 – MS1

Well A2-1 penetrated the deepest and oldest stratigraphy on the Demerara Rise, re-dated as late Tithonian.

This succession (up to 7 km thick) of alternating limestone and mudstone forms parallel, high-amplitude

reflections (limestones) interspersed with low amplitude, transparent acoustic facies (mudstones) that are

extremely laterally continuous (>200 km; Fig. 5.11A). MS1 and MS2 both prograde basinward towards the

northwest. The upper Valanginian MFS (VF) encountered in A2-1 onlaps the TB in a more proximal position

(near FG2-1) defining the south-eastern limit of Central Atlantic Ocean during the Lower Cretaceous (Fig.

5.16A). The MS1 interval is thickest below A2-1, extending below ODP Leg 207 sites (Fig. 5.12), and

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temporally records the highest sedimentation rates from the studied wells (Fig. 5.2). Sediments thin over a

series of northeast-trending basement highs and thicken inboard to form an elongate depocentre aligned

along the paleo-shelf edge. MS1 sediment is absent northeast of the Guinea-Demerara transform on this

map due to succeeding Equatorial Atlantic rifting (now located below the Guinea Plateau) and is notably thin

to absent above Jurassic-aged oceanic crust in the Guyana-Suriname basin (Fig. 5.11A; Fig. 5.12; Fig. 5.13).


The Valanginian flooding surface (VF) defines the base of MS2, which comprises of a Hauterivian to Aptian-

aged mudstone-dominated package, with the top truncated by the BAU across the distal area of the

Demerara Rise (Fig. 5.13). MS2 shows gradual progradation (Fig. 5.11B) culminating in the major fluvio-

deltaic system (Stabroek Formation). Mapping MS2 thickness shows the sequence is completely eroded and

peneplaned by the BAU to the north and east against the arcuate-shaped bounding faults of the Demerara

Rise (Fig. 5.12). The northeast-trending anticlinal folds appear to control the amount of erosion, suggesting

MS2 was deformed first, followed by peneplanation (Fig. 5.12). BAU erosion decreases towards the

southwest, highlighted along the dip profile (Fig. 5.11B) and fence diagram (Fig. 5.13). Towards the present-

day South American coastline the sequences below the unconformity are less deformed and no truncation

is observed, suggesting a more complete section and the BAU becoming a correlative conformity (Fig. 5.11B;

Mitchum & Vail, 1977). On the north-western margin of the Demerara Rise below the ODP Leg 207 sites, the

pre-Albian sediments are rotated by extensional listric normal faults, and thin over a basement high showing

compressional features (thrust faults) 100 km downdip in the Guyana-Suriname Basin (Fig. 5.11A). The

extensional domain is divided from the remainder of the Demerara Rise by an arcuate fault zone defining

the headwall, positioned above continental crust; the compressional domain is emplaced on Jurassic oceanic

crust (Fig. 5.11A). This feature is interpreted as a major margin collapse and forms two thick northwest-

trending lobes with a spatial extent of over 1000 km2 emplaced around the basement high (Fig. 5.13). These

lobes (A, B) are observed in strike profile through Fig. 5.13 separated by a thrusted basement high.

The BAU can be followed through the Guyana-Suriname Basin where overlying sediments onlap this surface.

MS2-aged sediments of the French Guiana margin show growth strata into a major basin-bounding

eastward-dipping normal fault (Fig. 5.11A). The thickest MS2 deposits occur along this section of the margin,

controlled by accommodation generated in a series of en-échelon normal faults recording the syn-rift non-

marine sediments of the proto-Equatorial Atlantic encountered at TD in GM-ES-3 (Fig. 5.12). These MS2

sequence syn-rift sediments attain maximum thickness in the Brazilian Cacipore grabens (Fig. 5.15), wells

here penetrate >3000 m of non-marine clastics, seismic indicating these rifts attain >6000m thickness (pers.

obs). At FG2-1, the basaltic lavas encountered at TD of the well are expressed in the seismic data as a chaotic

high amplitude package interpreted to pinch out to the northeast and onlap the basement to the southeast

(Fig. 5.11A). Their distribution forms a north-trending elongate ribbon (Fig. 5.1B; Gouyet et al., 1994)


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emplaced above thinned continental crust (Fig. 5.11A). These breakup volcanics within MS2 are interpreted

to be emplaced during Equatorial Atlantic rifting.


The Late Albian to Maastrichtian MS3 sequence is highly condensed on the northwest of the Demerara Rise,

thickening inboard and outboard into the surrounding basins (Fig. 5.12). These sediments onlap the BAU

and margin collapse, and passively infill the oceanic crust topography beyond the Demerara-Guinea

transform in the Equatorial Atlantic (Fig. 5.12). The remnant topography generated by the margin collapse

is the primary control for MS3 distribution in this area, forming a long-lived sediment depocentre between

the two lobes of the collapse (Fig. 5.13). A thick depocentre is observed orientated east-west located in the

south of the study area, related to the location of the palaeo-shelf edge and major sediment input (20.5

Mt/year; Ugwu Oju, 2018) through the shelf-incised Berbice canyon.

An unconformity truncates the stratigraphy in the middle of MS3 (MCU; Fig. 5.11). In the surrounding basins,

erosive incisions at the MCU, hundreds of metres deep, cut into the underlying stratigraphy containing low

amplitude fill (Fig. 5.11A). These are interpreted as the laterally equivalent channel-lobe systems supplying

reservoir sands to the recent hydrocarbon discoveries within the Late Cretaceous succession of the Guyana-

Suriname Basin, and the Cingulata turbidite fan system in French Guiana. In contrast to the broad

topographic relief of the Demerara Rise, the French Guiana margin is much steeper where sediment input

is point-sourced at relay zones related to the underlying normal fault array (Fig. 5.12). The top of the

Cretaceous (top MS3) is defined by the BTU across the study area. All these unconformities are more

pronounced on the distal area of the Demerara Rise (Fig. 5.11).

5.5.4 Structural Evolution

Although the structural evolution of the Demerara Rise has been studied before (Gouyet, 1988; Basile et al.,

2013; Reuber et al; 2016), important new insights can be developed by employing the new stratigraphic

results with deep-penetrating seismic sections, to examine the deformation and basement structure along

strike (Fig. 5.13). Sequential restoration by horizon flattening reveals the structural evolution of the

continental margin (Fig. 5.14).

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Fig. 5.14 – Sequential restoration by horizon flattening for a segment of the strike seismic profile displayed in Fig 11A, at three key time stages, (D) Valanginian, (C) Aptian and (B) Albian revealing the structural evolution of the continental margin to (A) present day. A zoom in on the seismic around Demerara A2-1 with a projection of the uppermost truncated seismic reflection (black dashed line) revealing approximately a kilometre of erosion at the well location is shown. MFS – maximum flooding surface. Fig. 5.1A for location of the section.


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Angular onlap of the MS1 sequence onto the TB is apparent (Fig. 5.14D), suggesting significant topography

was present prior to deposition of MS1. Flattening on the TB shows the basement was broadly folded prior

to deposition of Central Atlantic carbonates (Fig. 5.14D). Eventual flooding of the paleo-topography occurred

in the upper Valanginian (Fig. 5.14D). A major depocentre is mapped in MS1 (Fig. 5.12) positioned above the

youngest SDR sequence (syn-6 sensu Reuber et al., 2016) that is located between the Jurassic oceanic crust

and thinned continental crust, indicating the area of maximum subsidence. MS1 is therefore interpreted to

represent the early sag phase following opening of the Central Atlantic.

The Aptian (125 – 113 Ma) onset of Equatorial Atlantic extension generated syn-rift en-échelon half grabens

along the divergent margin east of the Demerara Rise (Fig. 5.14C; Pindell, 1985; Greenroyd et al., 2007,

2008a; Basile et al., 2013). On the Demerara Rise, the Equatorial Atlantic rifting induced a transpressional

tectonic regime across the northern margin due to movement on the Demerara-Guinea transform. This

induced compression buckling of the MS1 and MS2 stratigraphy into tight (wavelength 30-50 km) anticlinal

folds trending ENE (Fig. 5.12). Major imbricate thrust fault systems with hundreds of metres of displacement

contain associated roll-overs and basement pop-up structures (Fig. 5.13). The orientation of these features

indicates a maximum paleo-stress direction orientated northwest-southeast suggesting there was significant

compression associated with the transpressional Equatorial Atlantic breakup. Faulting also affects the

underlying basement sequence and is pervasive in the rheologically-competent carbonate lithologies. An

approximate estimation of shortening by measuring the most continuous stratigraphic surface (VF) suggests

8.3 km of shortening along the profile orientated in the direction of maximum compression (Fig. 5.14C).

Maximum deformation and basin inversion occur localised above the thickest MS1 and MS2 deposits.

Deformation continues outboard onto Jurassic oceanic crust (Fig. 5.13). At this time, there is evidence for

margin collapse to the northwest into the Guyana-Suriname basin induced by uplift-related instability. The

north-westward collapse indicates the asymmetric instability of the Demerara Rise. The compressional

features, inversion and collapse of the margin are all related to transpressional deformation along the

sheared northern margin of the Demerara Rise (Gouyet, 1988).

The compression-related paleo-topography was subsequently peneplaned by the BAU across the full width

of the Demerara Rise, truncating up to 1 km of section at the A2-1 well location (Fig. 5.14B), comparable to

the amount of erosion observed in the megasequence isochore mapping (Fig. 5.12). There is a lack of any

major incisional features on the peneplaned surface that would be indicative of canyon systems at the

resolution of our dataset. The recognition of red oxidised sands in FG2-1 indicates subaerial exposure at this

time. Erosion by a combination of subaerial (denudation) and shallow marine submarine processes (wave

action) created the peneplain architecture. Eroded sediments are postulated to have filled depocentres

adjacent to the Demerara Rise. Accommodation generated by the major bounding fault on the eastern

margin of the Demerara Rise forms a significant syn-rift wedge capped by the BAU (Fig. 5.11A), likely

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receiving some of the eroded material. Further deformation of the BAU results in the surface subtly tilted

east and west (Fig. 5.14A). This deformation is related to the loading of adjacent oceanic crust by the

initiation of the Amazon, Essequibo and Orinoco river systems in the Cenozoic depositing excessively thick

deep-sea fans, loading the crust and causing subsequent flexure of the Demerara Rise (Watts et al., 2005;

Basile et al., 2013).

5.5.5 Chronostratigraphic Analysis

Visualisation in the geological time domain of the stratigraphic architecture can be enhanced through the

construction of a Wheeler diagram or chronostratigraphic chart, building a spatiotemporal stratigraphic

framework (Wheeler, 1958; Fig. 5.15). Key stratigraphic surfaces and sequences, re-dated from the samples

analysed from seven key wells and scientific boreholes were used as the framework, and later extended to

an additional thirteen exploration wells. The Wheeler diagram (Fig. 5.15) highlights the variability in the age

and composition of the basement template as documented earlier. Several wells penetrate continental crust

along the margin, with Arapaima-1 (AR-1) recovering phyllitic schists. The Jurassic to Barremian stratigraphy

is restricted to below the Demerara Rise based on seismic interpretation (MS1 mapping – Fig. 5.12) and is

only penetrated by A2-1. However, it is conceivable that a condensed equivalent extends out onto the

oceanic crust in the Guyana-Suriname basin. Defining the exact age of the Jurassic oceanic crust in the

Guyana-Suriname basin is problematic due to the lack of basement penetrations and magnetic anomalies

(Nemčok et al., 2017). Based on the east-west spreading axis of the Central Atlantic, it can be assumed

oceanic crust becomes younger into the basin towards the northwest.

Fig. 5.15 (next page) – A Wheeler diagram constructed along strike from Guyana (left) to Brazil (right) detailing the stratigraphic evolution of the segmented Guyanas continental margin. Pin stripe vertical lines indicate hiatus’ corresponding to various regional unconformities dated in the stratigraphic analysis. Dash black and white lines indicate revised wells in this study. The geological time scale (GTS 2018) is non-linear. Hydrocarbon occurrences are shown. Average TOC values for the Canje Formation displayed, AR-1 data from Mourlot (2018).


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Further heterogeneity along strike is apparent at the Aptian unconformity. In the Equatorial Atlantic domain,

as penetrated by the 1-APS wells, the first deposits within the syn-rift half-grabens are non-marine

mudstones, with postulated lacustrine-sourced organic material encountered further along the Equatorial

margin (Pasley et al. 2005; Dickson et al., 2016), followed by coarser siliciclastics deposited in fluvial channel

and alluvial fan systems of the Cacipore Formation. Contiguous, time-equivalent deposits in the Central

Atlantic domain belong to the Stabroek Formation, a unit of progradational fluvio-deltaic sands. We assume

an Aptian age for the oil-bearing carbonate reservoir encountered in Ranger-1, that built-up above a volcanic

seamount in the deep basin. Early Albian Potoco Formation shallow marine limestones, as described from

A2-1, are the transgressive deposits that were deposited above the regional BAU. These deposits are

restricted to the shallow water areas of the Demerara Rise and Guyana shelf. Time-equivalent shelfal sands

are located more proximally (GLO-1 and FG2-1; Fig. 5.15).

The onset of organic-rich sedimentation is well calibrated at ODP Site 1258C to commence during the late

Middle Albian (Fig. 5.6). Deep-water Late Albian deposition was established in the adjacent French Guiana

basin associated with localised turbidites. Marine flooding of this basin and creation of oceanic crust

outboard of the GM-ES wells is coincident with the intra Late Albian unconformity recognised across the

Demerara Rise (Fig. 5.6; Fig. 5.7). The BCU truncates the Late Albian stratigraphy along the Guyana shelf and

Demerara Rise, coeval with the final continental breakup (unlocking) of the African and South American

plates (Geognostics, 2020) at the Demerara Rise-Guinea Plateau. At this time, a short-lived compressional

phrase is recognised along the Romanche Fracture Zone within the Equatorial Atlantic (Davison et al., 2016).

By earliest Cenomanian times oceanic crust is contiguous between the Central Atlantic and Equatorial

Atlantic. Organic-rich sedimentation persists into the Coniacian within the Guyana-Suriname basin and onto

the Demerara Rise, forming the prolific source rock of the Canje Formation, and continues even younger

into the Upper Santonian further northwest in Venezuela (La Luna facies). Cessation of organic-rich

sedimentation is diachronous along the margin, organic levels in FG2-1 decrease during the late Turonian,

and even earlier in the early Turonian within the Equatorial Atlantic domain. Subsequent establishment of

deep-water turbidite depositional systems, i.e. submarine channel-lobe-fan systems, characterise the Late

Cretaceous succession hosting significant oil discoveries within the New Amsterdam Formation.

Deep-water sands overlie the MCU, related to a significant hiatus observed across the Demerara Rise.

Although not re-evaluated in this study, several significant unconformities through the Cenozoic are

regionally distinguished, often linked to sandstone reservoir development within the overlying sequence (i.e.

George Town and Corentyne Formations). Throughout the Cenozoic, shelfal carbonates replace previously

siliciclastic-dominated systems, and shallow marine chalks are present over the Demerara Rise.


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5.5.6 Palaeogeographical Reconstructions

A series of gross depositional environment (GDE) maps (Fig. 5.16) have been constructed at four key time

intervals during the Cretaceous recognised in the stratigraphic analysis (Fig. 5.2). These events are either

major sequence boundaries or maximum flooding surfaces, representing the environment of deposition

during maximum regression or transgression, respectively. Four types of environment are described in this

study: terrestrial, transitional, slope, and deep basin with their sand fairways (submarine canyon, channel to

fan systems). These environmental interpretations are primarily based on the well data and seismic evidence

presented in this study, as well as the incorporation of additional published data. Facies distributions (pies)

for wells that penetrate sediments of each age interval are added as control points, however there may be

additional penetrations of the stratigraphy unavailable in this study. As the individual depositional systems

have been described earlier, a more holistic review of the regional geology is discussed below.

Fig. 5.16 (next page)– Gross depositional environment (GDE) maps for four key time stages, defined by the stratigraphic analysis, in the evolution of the Guyanas continental margin. (A) Upper Valanginian (135 Ma); (B) Aptian (115 Ma); (C) Latest Albian (101 Ma) and (D) Santonian (85 Ma). The reconstructed location of the conjugate seismic sections (Fig. 5.11B) are displayed in (A). Facies distribution (%) for the interval encountered in each well is shown. Geometries were reconstructed following the Geognostics Earth Model (GEM™). BFF – basin floor fan; DR – Demerara Rise; FZ – fracture zone; GP – Guinea Plateau.

Chapter 5

215


216

Upper Valanginian

The conjugate Demerara Rise and Guinea Plateau formed a carbonate-dominated shallow marine

embayment extending ca. 300 km from the paleo-coastline to the shelf margin. The maximum extent of the

south-eastern proto-Central Atlantic Ocean prior to Equatorial Atlantic opening and breakthrough is defined

by the coastline shown in Fig. 5.16A. Due to the margin collapse, an interpretation of the carbonate shelf

margin architecture is restricted, however a carbonate escarpment geometry is documented to the north in

The Gambia and to the west in Guyana (Mourlot, 2018; Mourlot et al., 2018; Casson et al., 2020). The

extension of the major depocentre below the majority of the Guinea Plateau (Fig. 5.16A; Zinecker et al.,

2018) indicates continuous and synchronous deposition linking the conjugate margins, challenging the

interpretation by Gouyet et al. (1994) that a local high was present between the Demerara Rise and Guinea

Plateau. Lower Cretaceous strata are absent due to post-depositional erosion across the Guyana shelf.

Late Aptian

Rift initiation to the east in the Equatorial Atlantic created an oblique-slip stress regime that exerted

transpression-related compression along the Demerara-Guinea transform, leading to the north-westward

collapse of the Demerara Rise margin. A similar margin collapse feature is recognised from seismic data on

the Guinea Plateau (Casson et al. in prep). The topography generated by this feature on the Guinea Plateau

remains reflected in the present-day bathymetry, forming an ‘outer high’ (Long et al., 2018). Progressive

anti-clockwise rotation of Africa away from South America continued to deform the transform margins of

the Demerara Rise and Guinea Plateau (Pindell, 1985; Greenroyd et al., 2007, 2008a; Basile et al., 2013).

Equatorial Atlantic rifting likely rejuvenated sediment supply from the Guiana Shield resulting in

progradation of the fluvio-deltaic systems of the Stabroek Formation (MS2) into the Guyana-Suriname basin.

This system was likely fed by a major axial fluvial system interpreted running through the Cacipore Graben

north-westwards into French Guiana, with associated non-marine and fluvial sediments preserved within

the rifting-induced accommodation. Coastal plain strata are not preserved due to no or low accommodation

as recorded in wells I23/-1X, SNY-1 and Tambaredjo (Dronkert & Wong, 1993). Associated exhumation of

the hinterland is supported by low-temperature thermochronological data from the northern rim of the

Guiana Shield in French Guiana, where Derycke et al. (2018) record a major cooling event suggesting

exhumation occurred from 140-100 Ma.

Latest Albian

During this time, elevated organic levels were established in sediments deposited across the shelf to slope

environment, evidenced in the scientific boreholes. A stepped slope was established along the Guyana-

Suriname margin. Deposition of a major submarine channel-fan system was controlled by the antecedent

topography generated by the collapsed margin. Rift volcanics observed on seismic are also interpreted

Chapter 5

217

throughout the opening Demerara – Guinea oceanic domain segment (Olyphant et al., 2017, Fig. 5.16C).

Adjacent continental margins are narrow and fault controlled within the extensional basin.

At this time, models of magnetic anomalies in the oceanic crust (Müller et al., 2008) predict seafloor

spreading initiated in the extensional segment offshore French Guiana between 105 and 110 Ma (Albian).

The relatively thick (ca. 200 m) latest Albian (NC10a oldest) deep marine section documented in GM-ES-3

(Fig. 5.11A) unconformably, based on seismic interpretation, overlies undated non-marine syn-rift strata.

The well is located above thinned continental crust (Fig. 5.11A). This interval (NC10a) is highly condensed,

only 0.55 m thick, on the Demerara Rise above an intra Late Albian unconformity (Fig. 5.7). We suggest that

the creation of accommodation offshore French Guiana and subsequent filling with latest Albian deep

marine deposits indicates an early Late Albian age (i.e. pre-intra Late Albian unconformity) for the onset of

seafloor spreading and oceanic crust formation. It remains to be understood whether the late Albian marine

connection between the Central and Equatorial Atlantic occurred over a flooded Demerara Rise or through

an open Demerara-Guinea transform. The conjugated Demerara Rise and Guinea Plateau was likely the final

buttress (thinned continental crust) preventing the establishment of a deep-water connection between the

Equatorial and Central Atlantic, this deep-water connection only established with the final phase of oceanic

crust formation at the beginning of the Cenomanian, this event is represented by the BCU across the

Demerara Rise (Fig. 5.15).

Santonian

By Santonian times (Fig. 5.16D), Africa has drifted away from South America forming a deep-water

connection between North and South Atlantic Oceans. The Late Cretaceous sequence is highly condensed

and the MCU is observed in wells across the distal Demerara Rise, due to this area likely being a paleo-high.

This period is associated with deposition of extensive submarine fan-channel systems in the basin. These

systems offshore French Guiana are relatively short (distance from shelf margin to fan) in comparison to

their Suriname-Guyana counterparts, likely due to the narrow and steep nature of the margin, and perhaps

corresponding to the length and volume of the onshore drainage system (Sømme et al., 2009). Entry points

for these systems breach relay zones between rift faults along the Equatorial Atlantic margin. The channels

of these short systems erode and remove the underlying organic-rich interval as observed in GM-ES-3. The

deep-water systems in Suriname-Guyana form the prolific hydrocarbon reservoirs encountered in the

Stabroek block. Up-dip these systems are fed through the Berbice and Essequibo canyons, depositing sand

in submarine channel complexes across the slope to basin floor fans. A re-orientation and retrogression of

this fairway axis is observed through the Late Cretaceous, postulated to be related to a decrease in sediment

supply through the Berbice canyon and compensational stacking (T3 – Albian to Turonian; T4 – Coniacian to

Maastrichtian; Mourlot, 2018).


218

5.6 DISCUSSION

5.6.1 Comparison to the Conjugate Margin – Guinea Plateau

Although seismic reflection or well data from the Guinea Plateau was not available for this study, a review

of material previously published allows both the conjugate margins to be examined in light of our new

findings. Analysis of seismic lines (Fig. 5.11) on the Demerara Rise, SR1-5400 (GuyanaSPAN), and lines from

the Guinea Plateau presented in Edge (2014), reconstructed to their position at pre-Equatorial Atlantic rifting

times, i.e. pre-Aptian, reveals that these lines align as ‘conjugates’ (Fig. 5.16A). This has been used to

supplement the GDE mapping of the Guinea Plateau (Fig. 5.16). Although seismic imaging quality of the deep

basement structure below the Guinea Plateau is poor, preventing detailed analysis, exploration wells on the

southern margin of the Guinea Plateau (GU-2B-1, Sabu-1, Fatala-1; Fig. 5.16C) targeted the post-rift

sequence. Calibration of the oldest strata is extrapolated from wells PGO-2 and PGO-6, reaching TD in

Jurassic micritic limestones and shale (Zinecker et al., 2018). Notably, both Long et al. (2018) and Zinecker

et al. (2018) during their regional seismic interpretation of 2D seismic data across the Guinea Plateau

identified northwest-ward orientated SDR sequences underlying the Jurassic carbonate sequence (~MS1),

consistent with the dip orientation of the basement sequence below the Demerara Rise (Reuber et al., 2016).

Several major southwest-ward dipping listric faults (i.e. Baraka fault; Fig. 5.16B) are observed on the

southern rifted margin of the Guinea Plateau; Olyphant et al. (2017) interpreted these faults to sole out into

basement. The geometry of the Demerara-Guinea transform faults and narrow conjugate continental

margins appear similar, however the first major faults that develop at the continental/oceanic transition

have reverse polarities, i.e. the faults near the Guinea Plateau COB dip landward, whereas on the Demerara

Rise they dip towards the oceanic basin, highlighting the margin asymmetry (Fig. 5.11B).

Our interpretation is that the mapped Top Neocomian horizon of Edge (2004) represents the VF, based on

the correlation of seismic facies and architecture (Fig. 5.11B). Below the BAU, the Aptian unconformity and

overlying syn-rift wedge is penetrated in well GU-2B-1 on the Guinea Plateau (Fig. 5.11B). These syn-rift

strata are only preserved basinward of the east-west trending Baraka fault (see Fig. 3 in Olyphant et al.,

2017), likely analogous to the syn-rift strata offshore French Guiana (Fig. 5.11A) and correlating with the

Cacipore Formation in the Foz do Amazonas basin (Fig. 5.15). Within this sequence, breakup related basalts

and volcaniclastics are penetrated in wells GU-2B-1 and Sabu-1 (Olyphant et al., 2017), distributed along the

southern margin of the Guinea Plateau (Fig. 5.16C; Benkhelil et al., 1994; Gouyet et al., 1994). The apparent

lack of any Aptian compressional deformation on the conjugate margin seismic profile (Fig. 5.11B) is

probably due to its position, as the majority of the deformation is located on the southwest nose of the

Guinea Plateau (Fig. 5.16B; Benkhelil et al., 1994; Basile et al., 2013). There is a considerable difference in

the Cenozoic sediment thickness (Fig. 5.11B); progradational sigmoidal seismic reflections (clinoforms) on

Chapter 5

219

the Demerara Rise indicate the deposition of a major shelfal siliciclastic system penetrated in well GLO-1

leading to the deeper burial of pre-Cenozoic stratigraphy.

5.6.2 Margin Heterogeneity Influenced by Structural Inheritance

Evaluating the margin architecture at a super-regional scale, i.e. >1000 km along strike, highlights the

heterogeneities that result in the segmentation of continental margins (e.g. Watts & Stewart, 1998; Franke

et al., 2007; Faleide et al., 2008). From this study, spatial variabilities are recorded in the depositional

systems, associated drainage systems onshore, structural style and organic matter distribution. Further

studies show segmentation causes additional variations in subsidence history (Pereira & Alves, 2011; Tsikalas

et al. 2001). Sedimentation over the Demerara Rise, particularly the more distal section, is heavily condensed

with low sedimentation rates (Fig. 5.2), and many Cretaceous to recent post-rift unconformities are recorded

(Fig. 5.11). These re-dated surfaces are interpreted to be sequence boundaries developed at lowstands that

can be correlated with increased siliciclastic delivery into the adjacent deep-water basins (Vail et al., 1980).

Additionally, the margins of the Demerara Rise were the focus of repeated tectonic deformation, developing

both transpressional and extensional fault systems, during Equatorial Atlantic breakup. Internal deformation

of the Demerara Rise is diverse, ranging from broad long-wavelength folding to tight imbricate thrust fault

systems. Fundamentally the heterogeneities discussed are consequential of the pre-rift structural

inheritance, eventually modified by the dual-phase rifting history.

The Demerara Rise and its conjugate, the Guinea Plateau, is thought to have formed a focal point for hot

spot magmatism (CAMP or Bahamas hotspot related) during the early stages of the Central Atlantic opening,

potentially creating a volcanic accumulation up to 21 km thick (Reuber et al., 2016; Long et al., 2018; Zinecker

et al., 2018). These submarine plateaus are clearly identifiable in present-day bathymetric maps, being a

testament to the longstanding influence this basement configuration had on the bathymetry and ultimately,

the segmentation of the continental margin, as observed on other TMPs worldwide (Loncke et al., 2019).

The location of the volcanism in the south-eastern Central Atlantic has been interpreted as creating a

‘pinning point’ for the final fragmentation of Gondwana and the breakup of the Equatorial Atlantic segment

(Pindell, 1985; Greenroyd et al., 2007, 2008a; Basile et al., 2013). It is conceivable the volcanism was

associated with a crustal weakness exploited during the second Equatorial phase of rifting. Similar

segmentation of continental margins and its effects on post-rift deposition are documented globally from

the rifted Norwegian (Tsikalas et al. 2001), western India (Calvès et al., 2011), Levant (Ben‐Avraham et al.,

2006) and Uruguayan margins (Soto et al., 2001).


220

5.7 CONCLUSIONS

New stratigraphic data acquired by re-sampling seven exploration wells and scientific boreholes located

along the Guyanas continental margin of South America has been used to refine a high-resolution

stratigraphic framework, applicable to the Central Atlantic. This framework is applied to the interpretation

of a margin-scale two-dimensional deep seismic reflection survey to produce a new megasequence

architecture model, create updated paleogeographic reconstructions for four key geological intervals and

reconstruct the structural evolution through the two divergent phases of breakup.

Our findings highlight deposition during the early Central Atlantic post-rift sequence (Jurassic-Lower

Cretaceous i.e. MS1) was influenced by the underlying heterogenous basement structure. The major MS1

depocentre below the Demerara Rise passively infilled pre-existing basement topography, continuing below

the conjugate Guinea Plateau. The only well on the South American margin to penetrate this sequence is

the Demerara A2-1 well. New multi-proxy biostratigraphy data conclusively reveals the well reached total

depth in late Tithonian organic-lean (average TOC 0.37%) shales and limestones. Previous work that suggests

A2-1 penetrated a Jurassic-aged source rock is questioned by this new integrated dataset. MS1 is capped by

a super-regional maximum flooding surface (MFS) during the upper Valanginian (VF) recognised elsewhere

around the Central Atlantic and Gulf of Mexico. The landward limit of the MFS reveals the south-eastern

extension of the early Central Atlantic.

Rifting in the Equatorial Atlantic during Barremian to Aptian times modified the continental margin

architecture, the structure and succeeding depositional systems. Deep grabens formed along the proto-

Equatorial margins receiving continental sedimentation. Further associated breakup volcanism is evidenced

by basalts recovered in the French Guiana FG2-1 well. The progressive anti-clockwise rotation of Africa from

South America during the Aptian induced a transpressional regime causing an estimated 8.3 km of

shortening across the distal Demerara Rise. This tectonism resulted in short-wavelength folding and

thrusting, major margin collapse into adjacent basins and the formation of a progradational shelfal

siliciclastic system (Stabroek Formation). This sequence (MS2) is truncated by a super-regional angular

unconformity re-dated as basal Albian (BAU), peneplaning up to 1 km of sediment from the Demerara Rise.

Late Albian deep marine sediments from GM-ES-3 prove oceanic crust had formed by this time in the

extensional segment of the opening Equatorial Atlantic offshore French Guiana, represented by the time

synchronous intra Late Albian unconformity recognised on the Demerara Rise. Our model suggests final

breakup of the Demerara Rise and Guinea Plateau, and deep marine connection between the Equatorial and

Central Atlantic occurred during the earliest Cenomanian.

The distal Demerara Rise sedimentary sequence is highly condensed and contains multiple unconformities

dated as middle Campanian (MCU), base Tertiary (BTU) and middle Miocene (MMU), suggesting this area

Chapter 5

221

remained an area of low accommodation and a relative high. Onset of organic-rich sedimentation (Canje

Formation) co-occurred with the flooding of the Equatorial Atlantic (pre-oceanic crust formation), during

the late Middle Albian. Geochemical characterisation of these primarily marine Type II organic-rich strata

(average TOC 4.21%) shows heterogeneity along strike, reflecting sediment dilution and terrestrial organic

matter input.

The topography generated by the margin collapse is interpreted to have been a major control on the entry

point of siliciclastic delivery, funnelling sediment from the shallow Demerara Rise into the deep-water

sedimentary systems of the Guyana-Suriname basin. The Berbice canyon has already been described from

previous studies as another major sediment input point throughout the Late Cretaceous, delivering

sediment to the world-class hydrocarbon reservoirs in the Guyana-Suriname basin. Coeval siliciclastic input

occurred along the Equatorial margin, and the depositional systems display relatively short runout lengths,

related to the steep, narrow margin geometry.

Examining the sedimentary systems using this integrated approach at a margin-scale, reveals the important

control of inherited pre-rift structural and basement heterogeneity, and later structural evolution associated

with the second phase of breakup, on the post-rift depositional system distribution and overall margin

heterogeneity.



companies of the North Africa Research Group (NARG) for their continued financial and scientific support.

The sampling and subsequent analysis of DSDP/ODP cores was partially supported by a European

Consortium for Ocean Research Drilling (ECORD) research grant awarded to the lead author. Holger

Kuhlmann provided excellent support during our visits to the Bremen Core Repository and subsequent

requests for additional samples. Shell is thanked for the access to hydrocarbon exploration well data,

particularly Tyrone Sigur at the CGG storage facility, Schulenburg, Texas. Iain Prince and Peter Osterloff

(Shell) are thanked for their attentive support and additionally David Owen and Robert Campbell (Shell)

helped improve the manuscript. The seismic data presented is courtesy of ION Geophysical. Ian Mounteney

is acknowledged for his assistance in performing the XRD analysis at the British Geological Survey, Keyworth.

Alastair Bewsher at the University of Manchester is thanked for use of the organic geochemistry laboratory.

Discussion with Jon Teasdale and academic access to the Geognostics Earth Model (GEM™) were particularly

useful in understanding the regional geology, plate tectonics and structure. Frédéric de Ville de Goyet thanks

Nick Miles, Petrostrat for assistance in the Lower Cretaceous palynology. Prof. David Wray, Greenwich

University is acknowledged for his assistance running the pyrolysis. Cairn Energy are thanked for funding the


222

hydrocarbon extractions at GeoMark Research. Jim Armstrong is acknowledged for his assistance

interpreting the organic geochemistry results.

Chapter 5

223


Fig. S 5.1 – Thin section photographs documenting the sandstone petrography of six drill cutting samples from wells Demerara A2-1 (A – 251.6 m) and French Guiana FG2-1 (B – 3104.4 m; C – 3232.4 m; D – 3287.3 m; E – 3351.3 m; F – 3418.3 m). Gl. – glauconite, PPL – plane polarised light, Qz. – quartz, XPL – cross polarised light. Scale displayed in A


224

Fig. S 5.2 – Calcareous nannofossil photographic plate of the key specimens identified during this study.

Scale bar in all photos is 5 m.

Chapter 5

225

Demerara A2-1Demerara A2-1 (Expl. Well A): Palynological Distribution Chart

Compiled by Frédéric de Ville de GoyetChart date: 16-Jun-2020Scale: 1:4500



SP

FT

DC

ALPR

ALBO

AL

AC

1002500

2600

2700

2800

2900

3000

3100

3200

3300

3400

3500

3600

3700

3800

3900

4000

4100

4200

4300

4400

4500

4600

4700

4800

4900

Me

asu

red

de

pth

(m

)

Early Cretaceous

Early Cretaceous - ?Late Jurassic

Pe

riod

/Ep

och

Hauterivian

?Late Albian - ?Middle Albian

?intra-Early Aptian

?Early Valanginian - ?Late Berriasian

Late Berriasian

Late Berriasian - ?Tithonian

Ag

e

FSE (P): PRES (RARE) Chichaoudinium arabicum, Subtilisphaera terrula; PRES (FREQ) Elaterosporites protensus; PRES (CMN) Classopollis spp. (small, <30microns)

FDO (RARE) Pseudoceratium pelliferum, Achomosphaera verdierii, Afropollis zonatus, Callialasporites dampieri; FDCO Callialasporites trilobatus; PRES questionable Sergipea naviformis

FDCO Dicheiropollis etruscus; FDO (RARE) Muderongia simplex microperforata, Cymososphaeridium validum

PRES (CMN) Dicheiropollis etruscus

FDCO (consistent) Amphorula metaelliptica

FDO (RARE) Oligosphaeridium diluculum; PRES (RARE) Pseudoceratium pelliferum

LSE: PRES (SABN) Dicheiropollis etruscus


3 + 1 + 6 1 10

2

1

3

4

20

7

3

1

1

13

19

7

11

9

8

22

2

7

8

2

7

8

2

7

15

4

8

6

3

3

4

5

3

3

1

12

5

13

11

6

3

6

+ 1 ? 1 + + 1 ? 2 ? 9

7

3

+

5

1

5

5

1

1

+

2

5

11

17

5

24

19

1

8

4

1

5

2

6

15

25

1

14

3

4

+

1

5

+ + 1 +

+

+

+

2

+

1

21

2

+

1

1

1

+

1

2

1

2

4

1

2

1

3

3

+

1 1 1 + 1 1 + 1 +

+

+

+

7

5

5

2

7

6 4 2 1 + 1 1 11 1 2

1 + 1 + + 1 1

*2

1

1

2

1

*2

4

1

2

1

1

10

1

4

3

12

8

5

30

2

3

1

1

1

*2

3 12 1 3

1

3

3

1

1

2

*2

1

1

1

*2

3

2

2500

2600

2700

2800

2900

3000

3100

3200

3300

3400

3500

3600

3700

3800

3900

4000

4100

4200

4300

4400

4500

4600

4700

4800

4900

Me

asu

red

de

pth

(m

)


4 1 1 1

1

1

2

1

1

1

3

3

1

2

1

1

1

+

1

1

2

11

13

18

6

5

11

8

1

1

5

1

1

2

1

1

2

2

35

37

28

22

11

20

24

37

24

31

41

27

20

21

1

2

2

2

1

2

1

+ 5 1 1 + ? + 3

1

+

+

2

3

1

+

1

+

1

+

2

1

1

7

2

+

1

3

1

4

1

2

1

+

+

+

4

11

13

25

36

36

2 ? + + 1

1

+

1

1 1

1

1

(Rw, Cv excluded)

WA

- T

richodin

ium

ca

sta

ne

a (

tota

l co

un

t)

80

3

+

5

1

5

(Rw, Cv excluded)

WA

- S

ubtilis

ph

aera

spe

cie

s (

tota

l co

unt)

80

22

7

14

11

6

3

6

(Rw, Cv excluded)

WA

- O

ligo

sphae

ridiu

m s

pecie

s (

tota

l cou

nt)

80

5

22

61

56

17

33

36

(Rw, Cv excluded)

WA

- C

lassop

olli

s s

pecie

s (

tota

l cou

nt)

80

11

14

18

8 ?

5

11

8

(Rw, Cv excluded)

WA

- E

phedrip

ite

s s

pe

cie

s (

tota

l co

unt)

80

7

1

1

1

(Rw, Cv excluded)

WA

- A

lgal cysts

(excl. s

pin

o (

tota

l co

unt)

80

40

1

6

6

13

9

6

(Rw, Cv excluded)

WA

- A

lga

l cysts

(spin

ose)

(tota

l co

unt)

80

4

1

2

1

1

(Rw, Cv excluded)

Pra

sin

oph

yce

a (

tota

l co

unt)

80

19

1

3

3

1

1

2

(Rw, Cv excluded)

Bo

tryo

coccus &

Pe

dia

str

um

spp (

tota

l coun

t)

80

1

1

(Rw, Cv excluded)

Din

ocyst

Coun

t 1

(A

M)

(tota

l count)

80

23

68

47

46

45

57

(Rw, Cv excluded)

spore

s a

nd p

olle

n (

co

unt

1)

AM

(to

tal cou

nt)

80

43

24

42

39

43

36

(Rw, Cv excluded)

Din

oflag

ella

te c

ysts

(spe

cie

s r

ichne

ss)

80

14

21 ?

20

19

28

27

23

(Rw, Cv excluded)

Sp

ore

s a

nd p

olle

n (

specie

s r

ichness)

80

14

21 ?

15

21 ?

13

12

14

2500

2600

2700

2800

2900

3000

3100

3200

3300

3400

3500

3600

3700

3800

3900

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4300

4400

4500

4600

4700

4800

4900

Me

asu

red

de

pth

(m

)

Me

asu

red

de

pth

(m

)

Chronostratigraphy

Palynology Comments

Dinoflagellate cysts A-...

Algae Prasinoph-ycea

Bot-ry......

T-......

Me

asu

red

de

pth

(m

)


WA -Subtilisphaera...


WA -Classopollis sp...





DinoflagellateCysts

Spores andPollen




Me

asu

red

de

pth

(m

)

Text Keys



Boundary Types

Confident

Sampling

Cutting

Core

Sidewall Core

Taxon Categories

AC - Acritarchs

AL - Algae




FT - Foram test linings



226

Fig. S 5.3 – Palynology distribution charts from wells Demerara A2-1 and French Guiana FG2-1.

French Guiana 2-1 (FG2-1)French Guiana 2-1 (FG2-1) (Expl. Well B): Palynological distribution Chart

Compiled by Frédéric de Ville de GoyetChart date: 16-Jun-2020Scale: 1:3000



SP

FU

DC

ALPR

ALBO

AL

1003075

3100

3125

3150

3175

3200

3225

3250

3275

3300

Mea

sure

d d

epth

(m

)

Late Cretaceous

Pe

rio

d/E

po

ch

Late Cenomanian

Ag

e

FSE: PRES (RARE) Pemphixipollenites inequiexinius, Galeacornea causea; PRES (FREQ) Triorites africaensis, Classopollis brasiliensis/major, Oligosphaeridium complex ; PRES (SABN) Subtilisphaera cheit

FDCO Classopollis brasiliensis / major; FDO Classopollis spp. (small, <30microns), Elateroplicites africaensis (2 elaters); PRES (reworked) Afropollis jardinus

LSE: FDO (RARE) Pemphixipollenites inequiexinius, Gnetaceaepollenites diversus; PRES (FREQ) Triorites africaensis; PRES (CMN) Classopollis brasiliensis/major


1 1 1 1 2 1 1

1

2

3

1

1

+

6

2

5

1

3

21

1

19

18

14

41

25

34

25

23

27

1 1 1 + 2 3

4 2 4 1 1 1 1 4


1 23

12

14

31

39

24

19

6

2 1

*2

3

1

5

6

14

12

10

16

+

1 1

*2

1

2 2 1

*2

1

3075

3100

3125

3150

3175

3200

3225

3250

3275

3300

Mea

sure

d d

epth

(m

)


2

6

1

1

1

5

7

9

1

1

3

1

2

1

2

1

3

1

1 ?

1

1

2

1

4 ?

1 2 1 2 1 1 ? 4

1

1

1 1 3 1 ? 1 1 1 5 1

2 Rw ?

(Rw, Cv excluded)

WA

- T

rich

od

iniu

m c

asta

ne

a (

tota

l cou

nt)

80

1

(Rw, Cv excluded)

WA

- S

ubtilis

phae

ra s

pecie

s (

tota

l cou

nt)

80

66

48

61

(Rw, Cv excluded)

WA

- O

ligo

sp

ha

eri

diu

m s

pecie

s (

tota

l cou

nt)

80

2

+

1

(Rw, Cv excluded)

WA

- C

lass

opo

llis s

pecie

s (

tota

l cou

nt)

80

5

11

10

(Rw, Cv excluded)

WA

- E

phe

dripites s

pecie

s (

tota

l co

un

t)

80

2

1

7 ?

(Rw, Cv excluded)

WA

- A

lga

l cysts

(e

xcl. s

pin

o (

tota

l cou

nt)

80

54

51

38

(Rw, Cv excluded)

WA

- A

lga

l cysts

(spin

ose

) (t

ota

l co

un

t)

80

20

6

2

(Rw, Cv excluded)

Pra

sin

oph

ycea

(to

tal co

un

t)

80

20

17

32

(Rw, Cv excluded)

Bo

tryococcus &

Pe

dia

str

um

spp

(to

tal coun

t)

80

1

5

(Rw, Cv excluded)

Din

ocyst C

ou

nt

1 (

AM

) (t

ota

l cou

nt)

80

49

51

47

(Rw, Cv excluded)

spo

res a

nd p

olle

n (

cou

nt 1)

AM

(to

tal co

unt)

80

8

8

16

(Rw, Cv excluded)

Din

oflag

ella

te c

ysts

(spe

cie

s r

ich

ness

)

80

14

14

15

(Rw, Cv excluded)

Sp

ore

s a

nd

po

llen (

sp

ecie

s r

ichn

ess

)

80

9

15 ?

18 ?

3075

3100

3125

3150

3175

3200

3225

3250

3275

3300

Mea

sure

d d

epth

(m

)

Mea

sure

d d

epth

(m

)

Chronostratigraphy

Palynology Comments

Dinoflagellate cysts Algae Prasinophycea Botry-oco......

F-......

Mea

sure

d d

epth

(m

)


WA -Subtilisphaera...


WA -Classopollis sp...





DinoflagellateCysts

Spores andPollen




Mea

sure

d d

epth

(m

)

Text Keys



Boundary Types

Confident

Sampling

Cutting

Core

Sidewall Core

Taxon Categories

AL - Algae




FU - Fungi


Chapter 5

227

GM-ES-3

Top Base Top Base Nan

no

s

Pal

yno

logy

Fora

ms

Cal

pio

nel

lid

s

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

TOC

(%)

HC

Ext

ract

ion

SST

Pet

rogr

aph

y

Vit

rnit

ie R

efle

cten

ce

5750 5755 3.96 23.6 15.2 0.73 425 333 16 4.57

5755 5760

5760 5765

5765 5770

5770 5775

5775 5780

5780 5785

5785 5790

5790 5795

5795 5800

5800 5805 3.80 22.7 20.4 0.93 425 426 19 4.79

5805 5810

5810 5815

5815 5820

5820 5825

5825 5830

5830 5832

5832 5835

5835 5840

5840 5845

5845 5850

5850 5855 3.16

5855 5860

5860 5865

5865 5870

5870 5875

5875 5880

5880 5885

5885 5890

5890 5895

5895 5900

5900 5905 3.75 23.9 19.1 0.77 428 386 16 4.94

5905 5910

5910 5915

5915 5920

5920 5925

5925 5930

5930 5935

5935 5940

5940 5945

5945 5950

5950 5955 4.69 18.4 20.1 0.89 429 380 17 5.28

5955 5960

5960 5965

5965 5970

5970 5975

5975 5980

5980 5985

5985 5990

5990 5995

5995 6000

6000 6005 4.32 20.5 20.1 1.15 430 382 22 5.26

6005 6010

6010 6015

6015 6020

6020 6025

6025 6030

6030 6035 5.09 23.8 23.6 1.05 429 382 17 6.17

6035 6040

6040 6045

6045 6050

6050 6055 3.90

6055 6060

6060 6065

6065 6070

6070 6075

6075 6080

6080 6085

6085 6090

6090 6095

6095 6100

6100 6105 4.79 21.3 15.9 0.94 430 284 17 5.58

6105 6110

6110 6115

6115 6120

6120 6125 5.29 21.3 14.4 0.87 427 243 15 5.92

6125 6130

6130 6135

6135 6140

6140 6145

6145 6150

6150 6155 5.45

6155 6160

6160 6165

6165 6170

6170 6175

6175 6180

6180 6185

6185 6190

6190 6195

6195 6200

6200 6205 4.28 21.6 15.5 1.09 428 333 23 4.65

6205 6210

6210 6215

6215 6220

6220 6225

6225 6230

6230 6235

6235 6240

6240 6245

6245 6250

6250 6255 3.15 17.7 12.9 1.23 426 364 35 3.54

6255 6260

6260 6265

6265 6270

6270 6275

6275 6280

6280 6285

6285 6290

6290 6295

6295 6300

6300 6305

6305 6310

6310 6315

6315 6318

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

unused

Pyrolysis

Sample Depth (ft) Sample Depth (m) Analysis

unused


228

French Guiana – FG2-1


no

s

Pal

yno

logy

Fora

ms

Cal

pio

nel

lid

s

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

TOC

(%)

HC

Ext

ract

ion

SST

Pet

rogr

aph

y

Vit

rnit

ie R

efle

cten

ce

7600 7620 2316.5 2322.6 0.85

7800 7820 2377.4 2383.5 0.71

8000 8020 2438.4 2444.5 0.94

8200 8220 2499.4 2505.5 2.08 2.18 10.4 1.19 413 471 54 2.21

8400 8420 2560.3 2566.4 1.62

8580 8600 2615.2 2621.3 1.2 0.47 3.22 1.11 425 218 75 1.48

8780 8800 2676.1 2682.2 1.42

8980 9000 2737.1 2743.2 1.89 0.54 4.51 1.24 423 265 73 1.7

9200 9220 2804.2 2810.3 1.37

9400 9420 2865.1 2871.2 3.28 0.74 3.54 1.79 423 217 110 1.63

9580 9590 2920.0 2923.0 2.24

9790 9800 2984.0 2987.0 1.48 0.52 4.74 1.33 422 269 76 1.76

9810 9820 2990.1 2993.1

9820 9830 2993.1 2996.2

9830 9840 2996.2 2999.2

9840 9850 2999.2 3002.3

9850 9860 3002.3 3005.3

9860 9870 3005.3 3008.4

9870 9880 3008.4 3011.4

9880 9890 3011.4 3014.5

9890 9900 3014.5 3017.5

9900 9910 3017.5 3020.6 2.35 0.95 6.91 1.57 424 284 65 2.43

9910 9920 3020.6 3023.6

9920 9930 3023.6 3026.7

9930 9940 3026.7 3029.7

9940 9950 3029.7 3032.8

9950 9960 3032.8 3035.8 1.79 1.03 4.92 1.06 422 258 55 1.91

10070 10080 3069.3 3072.4

10180 10190 3102.9 3105.9 B

10400 10410 3169.9 3173.0

10600 10610 3230.9 3233.9 C

10780 10790 3285.7 3288.8 D

10990 11000 3349.8 3352.8 E

11210 11220 3416.8 3419.9 F

11640 11650 3547.9 3550.9

12030 12040 3666.7 3669.8

XRD

XRD

unused

unused

unused

unused

unused

unused

unused

unused

Sample Depth (ft) Sample Depth (m)

Am.

Am.

Analysis

Pyrolysis

Chapter 5

229

Demerara A2-1


no

s

Pal

yno

logy

Fora

ms

Cal

pio

nel

lid

s

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

TOC

(%)

HC

Ext

ract

ion

SST

Pet

rogr

aph

y

Vit

rnit

ie R

efle

cten

ce

7020 7050 2139.7 2148.8 0.85

7110 7140 2167.1 2176.3 1.95 0.59 9.33 1.58 419 366 62 2.55

7260 7290 2212.8 2222.0 2.32

7290 7320 2222.0 2231.1 4.57 1.51 29.7 2.34 415 609 48 4.88

7410 7440 2258.6 2267.7 3.22

7500 7530 2286.0 2295.1 3.33 2.06 21.8 2.01 417 488 45 4.47

7590 7620 2313.4 2322.6 3.44

7650 7680 2331.7 2340.9 4.7

7710 7740 2350.0 2359.2 5.94 1.39 34.1 2.7 413 538 43 6.33

7740 7770 2359.2 2368.3 8.17 2.3 53.7 3.44 409 617 40 8.7

7770 7800 2368.3 2377.4 4.83 1.53 32.5 2.43 416 586 44 5.55

7790 7800 2374.4 2377.4 2.76

7800 7810 2377.4 2380.5 4.28

7810 7820 2380.5 2383.5 4.62 1.17 27.2 2.58 413 519 49 5.23

7820 7830 2383.5 2386.6 3.58

7840 7850 2389.6 2392.7 3.35 0.78 20.3 2.38 414 483 57 4.21

7860 7870 2395.7 2398.8

7870 7880 2398.8 2401.8 5.58 1.94 28.2 2.76 412 500 49 5.64

7880 7890 2401.8 2404.9

7890 7900 2404.9 2407.9 3.96

7900 7910 2407.9 2411.0

7910 7920 2411.0 2414.0

7920 7930 2414.0 2417.1

7920 7930 2414.0 2417.1 1.08 0.35 8.33 1.49 422 380 68 2.19

7930 7940 2417.1 2420.1

7940 7950 2420.1 2423.2

7950 7960 2423.2 2426.2

7960 7970 2426.2 2429.3

7970 7980 2429.3 2429.3

7970 7980 2429.3 2432.3

7980 7990 2432.3 2432.3

7990 8000 2435.4 2435.4

8000 8010 2438.4 2438.4

8010 8020 2441.4 2441.4

8020 8030 2444.5 2444.5

8030 8040 2447.5 2447.5

8040 8050 2450.6 2450.6

8050 8060 2453.6 2453.6

8060 8070 2456.7 2456.7

8070 8080 2459.7 2459.7

8080 8090 2462.8 2462.8

8090 8100 2465.8 2468.9

8100 8110 2468.9 2471.9

8110 8120 2471.9 2475.0

8150 8160 2484.1 2487.2

8220 8230 2505.5 2508.5

8250 8260 2514.6 2517.6 A

8300 8310 2529.8 2532.9

8350 8360 2545.1 2548.1

8360 8370 2548.1 2551.2

8410 8420 2563.4 2566.4

8980 8990 2737.1 2740.2

9200 9210 2804.2 2807.2

9450 9460 2880.4 2883.4

9760 9770 2974.8 2977.9 0.54

9980 9990 3041.9 3045.0

10270 10280 3130.3 3133.3 0.39

10420 10430 3176.0 3179.1 0.44

11010 11020 3355.8 3358.9 1

10810 10820 3294.9 3297.9

10840 10850 3304.0 3307.1

10870 10880 3313.2 3316.2

11150 11160 3398.5 3401.6 2 0.00

11180 11190 3407.7 3410.7

11240 11250 3426.0 3429.0

11280 11290 3438.1 3441.2

11340 11350 3456.4 3459.5

11380 11390 3468.6 3471.7

11440 11450 3486.9 3490.0

11480 11490 3499.1 3502.2

11540 11550 3517.4 3520.4

11580 11590 3529.6 3532.6

11680 11690 3560.1 3563.1

11740 11750 3578.4 3581.4

11780 11790 3590.5 3593.6

12840 12850 3913.6 3916.7

12890 12900 3928.9 3931.9

12980 12990 3956.3 3959.4

13080 13090 3986.8 3989.8

13450 13460 4099.6 4102.6 3

14100 14110 4297.7 4300.7 4

14600 14610 4450.1 4453.1 5

14850 14860 4526.3 4529.3 6 0.05

15100 15110 4602.5 4605.5 7

15330 15340 4672.6 4675.6 0.43

15590 15600 4751.8 4754.9 8

15780 15790 4809.7 4812.8 0.00

16070 16080 4898.1 4901.2

unused

unused

unused

unused

unused

Am.

AnalysisSample Depth (ft) Sample Depth (m)

Am.

Am.

Pyrolysis

unused

unused

unused

unused

unused

unused

unused

unused

unused


230

ODP Leg 207 Site 1257

ODP Leg 207 Site 1258C

ODP Leg 207 1260

EXP SITE HOLE CORE SECT TOP BOT MBSF_TOP MCD_TOP Sample ID Nan

no

s

Pal

yno

logy

Fora

ms

Cal

pio

nel

lid

s

TOC

(%)

Pyr

oly

sis

HC

Ext

ract

ion

SST

Pet

rogr

aph

y

Vit

rnit

ie R

efle

cten

ce

207 1257 31 1 45 46 275.55 281.35 5046758

207 1257 31 2 51 52 276.42 282.22 5046759



no

s

Pal

yno

logy

Fora

ms

Cal

pio

nel

lid

s

TOC

(%)

Pyr

oly

sis

HC

Ext

ract

ion

SST

Pet

rogr

aph

y

Vit

rnit

ie R

efle

cten

ce

207 1258 C 14 1 22 24 385.02 396.91 5103479

207 1258 C 15 1 56 59 390.36 411.29 5103480

207 1258 C 15 3 90 91 393.67 414.6 5200841

207 1258 C 15 3 100 102 393.77 414.7 5200842

207 1258 C 16 1 13 14 394.53 418.86 5103468

207 1258 C 17 1 38 42 399.78 425.17 5103469

207 1258 C 18 1 20 22 404.3 428.41 5103470

207 1258 C 19 1 66 68 409.76 433.87 5103471

207 1258 C 20 1 70 72 414.4 438.51 5103472

207 1258 C 21 1 102 104 419.72 443.83 5103473

207 1258 C 22 1 61 63 423.91 448.47 5103474

207 1258 C 23 1 65 66 428.95 454.91 5103475

207 1258 C 24 1 33 36 433.23 459.97 5103476

207 1258 C 25 1 42 44 438.32 466.34 5103477

207 1258 C 26 1 20 22 442.7 471.13 5103478

207 1258 C 27 1 8 9 447.58 478.96 5054740

207 1258 C 27 2 15 16 449.06 480.44 5054741

207 1258 C 27 2 42 43 449.33 480.71 5200603

207 1258 C 27 2 59 60 449.5 480.88 5200604

207 1258 C 27 2 83 84 449.74 481.12 5200605

207 1258 C 27 2 115 116 450.06 481.44 5200606

207 1258 C 27 3 4 5 450.45 481.83 5054742

207 1258 C 28 1 5 6 451.85 484.35 5054743

207 1258 C 28 2 12 13 453.42 485.92 5054744

207 1258 C 28 3 2 3 454.2 486.7 5054745

207 1258 C 29 1 4 5 456.84 489.34 5054748

207 1258 C 29 2 5 6 458.35 490.85 5054749

207 1258 C 29 3 5 6 459.85 492.35 5054750

207 1258 C 30 1 5 6 461.45 493.95 5054751

207 1258 C 30 2 5 6 462.67 495.17 5054752

207 1258 C 30 3 4 5 464.16 496.66 5054753

207 1258 C 31 1 4 5 466.44 498.94 5054754

207 1258 C 31 2 4 5 467.94 500.44 5054755

207 1258 C 31 3 4 5 469.44 501.94 5054756

207 1258 C 32 1 132 133 472.32 504.82 5046745

207 1258 C 32 2 82 83 473.19 505.69 5046746

207 1258 C 33 1 142 143 477.42 509.92 5046747

207 1258 C 33 2 138 139 478.88 511.38 5046748

207 1258 C 33 3 58 59 479.58 512.08 5046749

207 1258 C 34 1 122 123 481.92 514.42 5046750

207 1258 C 34 2 132 133 483.52 516.02 5046751

207 1258 C 34 3 45 46 484.15 516.65 5046752

207 1258 C 34 3 112 113 484.82 517.32 5046753

AnalysisSample Depths (m)

unused

unused

unused


no

s

Pal

yno

logy

Fora

ms

Cal

pio

nel

lid

s

TOC

(%)

Pyr

oly

sis

HC

Ext

ract

ion

SST

Pet

rogr

aph

y

Vit

rnit

ie R

efle

cten

ce

207 1260 A 54 3 70 70 491.3 493.78 5046754

207 1260 A 54 4 2 3 491.32 493.8 5046755


Chapter 5

231


Table S 5.1 – Sample table detailing the analysis performed on each sample, and organic geochemistry data generated. Am. – amalgamated sample.

GM-ES-3

French Guiana – FG2-1


no

s

Pal

yno

logy

Fora

ms

Cal

pio

nel

lid

s

TOC

(%)

S1 (m

g/g)

S2 (m

g/g)

S3 (m

g/g)

Tmax

(°C

)

HI

OI

TOC

(%)

HC

Ext

ract

ion

SST

Pet

rogr

aph

y

Vit

rnit

ie R

efle

cten

ce

14 144 A 4 1 120 121 172.2 172.2 5200836

14 144 A 4 2 30 32 172.8 172.8 5200837

14 144 A 4 2 146 148 173.96 173.96 5200838 0.98

14 144 A 5 1 105 106 181.05 181.05 5200839 1.31 0.57 7.76 0.78 409 575 58 1.35

14 144 Z 3 1 125 126 163.25 163.25 5200823

14 144 Z 3 2 91 93 164.41 164.41 5200824

14 144 Z 4 2 96 98 215.46 215.46 5200825 6.93 2.47 38.2 3.47 409 499 45 7.66

14 144 Z 4 3 36 38 216.36 216.36 5200826 7.51 1.3 40.4 3.58 414 513 45 7.87

14 144 Z 5 1 14 16 264.14 264.14 5200827 1.00 0.11 1.34 1.48 425 137 151 0.98

14 144 Z 5 1 125 127 265.25 265.25 5200829 0.80 0.07 1.03 1.23 426 121 145 0.85

14 144 Z 6 1 126 128 296.26 296.26 5200830 0.26

14 144 Z 7 1 73 75 298.73 298.73 5200831 0.66 0.16 2.01 2.18 346 188 204 1.07

14 144 Z 7 1 128 130 299.28 299.28 5200832 0.51

14 144 Z 8 2 15 17 325.65 325.65 5200833 0.21

14 144 Z 8 3 103 105 328.03 328.03 5200834 0.53

14 144 Z 8 3 135 137 328.35 328.35 5200835 0.56 0.07 0.3 1.23 416 60 246 0.5

unused


Pyrolysis

unused

unused

Ag

e

NF

Zo

ne

De

pth

(M

)

An

fra

ctu

s "

sh

ilo

he

ns

is"

Ax

op

od

orh

ab

du

s a

lbia

nu

s

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

ga

ult

en

sis

Bra

aru

do

sp

ha

era

pri

mu

la

Bra

aru

do

sp

ha

era

qu

inq

ue

co

sta

ta

Bra

aru

do

sp

ha

era

ste

no

rhe

tha

Bra

aru

do

sp

ha

era

do

de

ka

he

dro

n

Bro

ins

on

ia c

en

om

an

ica

Bro

ins

on

ia e

no

rmis

Bro

ins

on

ia g

all

ois

ii

Bro

ins

on

ia s

ign

ata

Bu

kry

lith

us

am

big

uu

s

Ca

lcic

ala

thin

a a

lta

Ca

lcu

lite

s s

p.

Ch

ias

toz

yg

us

lit

tera

riu

s

Co

roll

ith

ion

ke

nn

ed

yi

Co

roll

ith

ion

sig

nu

m

Cri

bro

sp

ha

ere

lla

eh

ren

be

rgii

Cru

cic

rib

rum

an

gli

cu

m

Cy

lin

dra

lith

us

co

ron

atu

s

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

ex

imiu

s

Eif

fell

ith

us

pa

rag

og

us

Eif

fell

ith

us

tu

rris

eif

feli

i

Eif

fell

ith

us

mo

ne

ch

iae

Eif

fell

ith

us

vo

ns

ali

sia

e

Ep

roli

thu

s f

lora

lis

Ep

roli

thu

s m

ora

tus

Ep

roli

thu

s s

ide

vie

w

Fla

be

llit

es

ob

lon

gu

s

Ga

rtn

era

go

co

xa

llia

e

Ga

rtn

era

go

na

nu

m

Ga

rtn

era

go

ob

liq

uu

m

Ga

rtn

era

go

pra

eo

bli

qu

um

Ga

rtn

era

go

pra

eo

bli

qu

um

(s

ma

ll v

ar.

)

Ga

rtn

era

go

th

eta

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Go

rka

e o

pe

rio

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

He

len

ea

ch

ias

tia

He

mip

od

orh

ab

du

s g

ork

ae

He

lic

oli

thu

s a

nc

ep

s

He

lic

oli

thu

s c

om

pa

ctu

s

He

lic

oli

thu

s c

om

pa

ctu

s (

sm

all

va

r.)

He

lic

oli

thu

s t

rab

ec

ula

tus

He

lic

oli

thu

s t

rab

ec

ula

tus

(s

ma

ll v

ar.

)

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

mm

ato

ide

a

Ma

rth

as

teri

tes

fu

rca

tus

Na

nn

oc

on

us

sp

(to

p v

iew

)

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s a

pe

rtu

s

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s q

ua

dri

an

gu

lus

Na

nn

oc

on

us

tru

itti

Oc

toc

yc

lus

re

inh

ard

tii

Ora

str

um

pe

rsp

icu

um

Ow

en

ia p

art

itu

m

Pre

dis

co

sp

ha

era

co

lum

na

ta

Pre

dis

co

sp

ha

era

cre

tac

ea

Pre

dis

co

sp

ha

era

sp

ino

sa

Qu

ad

rum

en

ea

bra

ch

ium

Qu

ad

rum

ga

rtn

eri

Re

tec

ap

sa

sp

p.

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Ro

tela

pil

lus

cre

nu

latu

s

Sto

ve

riu

s p

roto

sig

nu

m

Sto

ve

riu

s a

ch

ylo

su

s

Te

gu

me

ntu

m s

tra

dn

eri

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

ph

ac

elo

su

s

Ve

ks

hin

ell

a s

p.

Wa

tzn

au

eri

a b

arn

es

ae

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

rha

bd

otu

s h

ow

ei

Ze

ug

rha

bd

otu

s m

ou

lla

de

i

Ze

ug

rha

bd

otu

s s

cu

tula

ss

p.

turo

nic

us

5750 BARREN

late Turonian UC9b 5760 P/L 1 1 3 3 3 P 2 3 1 P 2 50 3 P P 1 102 3

middle Turonian UC8 5780 P/L 4 P 4 1 18 6 3 8 1 5 5 1 1 1 5 3 1 3 26 110 2 2

5800 P/L P 1 7 13 1 1 9 P

5830 P/L 1 1 1 2 17 30 1 45 P 3 5

5850 P/L P 2 1 1 2 P 2 3 P P P 1 90 3

5870 P/L 1 P 1 1 1 5 P 1 1 P 1 1 1 15 180 1 2 P

5900 P/L 4 1 1 4 2 3 2 1 3 1 P 1 1 7 96 1 P

5930 P/L 8 1 1 1 42

5940 P/L P 33 3 2 1 3 2 P P 3 4 1 1 1 1 P 2 P 1 4 1 P 4 8 240 1 21 20

5950 P/L P 8 2 1 P 1 1 4 1 2 1 1 P 2 1 1 2 2 138 1 36

6000 P/L P 33 P P P P 4 3 22 1 P P P 1 P 2 1 P 1 P 16 P 45 2

6020 P/L P 25 P P P 10 1 45 P 12 1 2 1 10 P P 1 P 3 7 P 12 P P 8 16 30 3

6040 P/L 1 14 3 1 1 1 13 1 1 1 P 1 1 P P 3 3 2 P P 4 4 2 210 11 21

6060 P/L 4 1 1 1 1 1 1 3 8 P 1 4 1 1 2 3 14 2

6070 P/L 60 1 2 1 1 P 3 P P P 12 1 2 1 P P 1 7 3 4 P 3 P 16 P 96 4 4

6080 P/L 30 2 1 3 2 P P P P P 1 P P P P 2 P 1 1 2 P 4 P 12 6 15

6100 P/L 3 P P 1 1 1 3 1 1 2 3

6120 P/L 2 2 1 1 1 5

6130 P/L 3 8 P 1 3 1 1 2 2 1 2 1

6140 P/L P 2 1 2 P P P P P P P 1 1 P P 4 7

6150 P/L 1 10 P 2 1 P 1 1 P 1 P 1 1 P 1 P 1 P P 2 4 2

6160 P/L P 1 P P 1 9 1

6170 P/L 1 1 P P P 1 P 1 P P P 1 P 1 1 P 2 1 6 4

6190 BARREN

6200 BARREN

6300 BARREN

NOT ASSIGNED

UC5

UC2 -

UC3

middle Cenomanian -

early Cenomanian

late Cenomanian

NOT ASSIGNED

late Albian

UC1early Cenomanian

UC6early Turonian

NC10a

(upper)

NC10a

(lower)

Ag

e

NF

Zo

ne

De

pth

(ft

)

Ah

mu

ell

ere

lla

oc

tora

dia

ta

Ark

ha

ng

els

kie

lla

cy

mif

orm

is

Ark

ha

ng

els

kie

lla

ma

as

tric

hti

en

sis

Ax

op

od

orh

ab

du

s a

lbia

nu

s

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

ga

ult

en

sis

Bro

ins

on

ia e

no

rmis

Bri

on

so

nia

sig

na

ta

Bu

kry

lith

us

am

big

uu

s

Ca

lcic

ala

thin

a a

lta

Ca

lcio

so

len

ia f

os

sil

is

Ca

lcu

lite

s p

erc

ern

is

Ce

rato

lith

oid

es

ac

ule

us

Ch

ias

mo

lith

us

ed

en

tulu

s

Ch

ias

mo

lith

us

so

litu

s

Ch

ias

toz

yg

us

am

pip

ho

ns

Ch

ias

toz

yg

us

lit

tera

riu

s

Co

cc

oli

thu

s p

ela

gic

us

Co

roll

ith

ion

ke

nn

ed

yi

Co

roll

ith

ion

sig

nu

m

Cru

cip

lac

oli

thu

s t

en

uis

Cri

bro

sp

ha

ere

lla

eh

ren

be

rgii

Cy

lin

dra

lith

us

bia

rcu

s

Cy

lin

dra

lith

us

sc

ulp

tus

Cy

lin

dra

lith

us

se

rra

tus

Dis

co

as

ter

mo

hle

ri

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

ex

imiu

s

Eif

fell

ith

us

tu

rris

eif

feli

i

Ell

ips

oli

thu

s m

ac

ell

us

Ep

roli

thu

s s

.v

Ep

roli

thu

s f

lora

lis

Ep

roli

thu

s m

ora

tus

Fa

sc

icu

lith

us

to

nii

Fa

sc

icu

lith

us

ty

mp

an

ifo

rmis

Ga

rtn

era

go

co

xa

llia

e

Ga

rtn

era

go

na

nu

m

Ga

rtn

era

go

ob

liq

uu

m

Ga

rtn

era

go

pra

eo

bli

qu

um

Ga

rtn

era

go

pra

eo

bli

qu

um

(s

ma

ll v

ar.

)

Ga

rtn

era

go

th

eta

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

He

lic

oli

thu

s a

nc

ep

s

He

lic

oli

thu

s c

om

pa

ctu

s

He

lic

oli

thu

s c

om

pa

ctu

s (

sm

all

va

r.)

He

lic

oli

thu

s t

rab

ec

ula

tus

He

lio

lith

us

kle

inp

ell

ii

Ka

mp

tne

riu

s m

ag

nif

icu

s

Lit

ha

str

un

us

gri

llii

Lit

ha

str

un

us

se

pte

na

riu

s

Lit

hra

ph

idit

es

qu

ad

ratu

s

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

mm

ato

ide

a

Ma

rth

as

teri

tes

fu

rca

tus

Mic

ula

sta

uro

ph

ora

Mic

rorh

ab

du

lus

de

co

ratu

s

Na

nn

oc

on

us

sp

p.

(to

p v

iew

)

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s q

ua

dri

an

gu

lus

Na

nn

oc

on

us

tru

itti

i

Ne

oc

hia

sto

zy

gu

s c

on

cin

nu

s

Ne

oc

hia

sto

zy

gu

s p

erf

ec

tus

Ora

str

um

pe

rsp

icu

um

Ow

en

ia p

art

itu

m

Pla

co

zy

gu

s s

pir

ali

s

Pre

dis

co

sp

ha

era

co

lum

na

ta

Pre

dis

co

sp

ha

era

cre

tac

ea

Qu

ad

rum

en

ea

bra

ch

ium

Qu

ad

rum

ga

rtn

eri

Qu

ad

rum

oc

tob

rac

hiu

m

Re

inh

ard

tite

s a

nth

op

ho

rus

Re

inh

ard

tite

s l

ev

is

Re

tec

ap

sa

sp

p.

Re

tec

ap

sa

su

rire

lla

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

sp

len

de

ns

Ro

tela

pil

lus

cre

nu

latu

s

So

lla

sit

es

ho

rtic

us

Sp

he

no

lith

us

an

arr

ho

pu

s

Sta

uro

lith

ite

s g

au

so

rhe

thiu

m

Sta

uro

lith

ite

s i

mb

ric

atu

s

Sto

ve

riu

s a

ch

ylo

su

s

Sto

ve

riu

s p

roto

sig

nu

m

Str

ad

ne

rlit

hu

s f

rac

tus

Te

gu

me

ntu

m s

tra

dn

eri

Te

tra

po

do

rha

bd

us

de

co

rus

To

we

ius

pe

rtu

su

s

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

min

imu

s

Tra

no

lith

us

ph

ac

elo

su

s

Ve

ks

hin

ell

a

Wa

tzn

au

eri

a b

arn

es

ae

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

rha

bd

otu

s h

ow

ei

Ze

ug

rha

bd

otu

s a

ff.

sc

utu

la

Ze

ug

rha

bd

otu

s m

ou

lla

de

i

Ze

ug

rha

bd

otu

s s

igm

oid

es

Thanetian NP7 7600 16 8 150 1 4 24 1 30 4 18 1 4 210 1

7800 5 10 78 P 21 1 18 45 P 15 35 2 9 3 3 3 180 P

8000 12 12 1 30 4 2 10 12 72 30 4 5 36 P 36 3 8 P 1 240 P

early Campanian UC13 8200 5 24 P P 24 1 4 18 1 P 48 P 36 P 1 1 55 1 3 24 1 P 2 2 P P 3 210 P

8400 4 3 1 1 54 2 3 10 6 16 1 54 1 P P 5 200 2 8 32 P 10 4 4 3 P 3 2 1 240 1

8580 P/L 2 2 P 3 1 36 4 3 P 1 8 4 1 16 6 1 30 3 1 2 10 72

8780 1 1 1 2 7 1 48 7 1 1 3 1 8 1 1 1 1 10 54 1 30 1 1 3 2 1 P 2 1 8 160 P

8980 P/L 1 1 P 2 45 P 5 1 36 1 1 P 1 1 1 3 7 1 1 P 1 1 45 210

9200 P/L 2 1 10 14 10 16 P 14 5 P 1 60 1 P 1 P 36 120 2 90

9400 P/L P 2 2 P 1 1 26 P 1 P 2 P 20 2 2 3 40 10

early Turonian UC6 - UC7 9580 P/L 1 1 1 2 1 3 1 27 1 P 1 5 21 1 1 P 1 P 2 21 2 1 12

late Cenomanian UC 5 9790 P/L 1 15 15 13 1 2 P 7 P 21 2 2 8 P 2 P 3 1 P 2 P 5 30 33 15

9920 P/L 1 370 6 1 P 3 8 1 P P 1 4 1 1 8 2 P 1 P 1 4 4 P 1 3 1 4 96 30 95

9950 P/L 1 480 14 1 1 1 1 1 1 1 14 P 1 2 2 1 1 16 3 2 1 6 4 1 8 3 P 1 3 10 5 108 18 24mid - early Cenomanian UC2- UC3a

early Santonian -

Coniacian

late - middle Turonian

early Maastrichtian

UC8-UC9

UC10- UC11

UC18

Ag

e

NF

Zo

ne

De

pth

(ft

)

Ah

mu

ere

lla

oc

tora

dia

ta

Ark

ha

ng

els

kie

lla

cy

mb

ifo

rmis

Ax

op

od

orh

ab

du

s a

lbia

nu

s

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

ga

ult

en

sis

Bro

ins

on

ia c

en

om

an

ica

Bro

ins

on

ia e

no

rmis

Bro

ins

on

ia p

arc

a c

on

str

icta

Bro

ins

on

ia s

ign

ata

Bu

kry

lith

us

am

big

uu

s

Ch

ias

toz

yg

us

aff

. a

mp

hip

on

s

Ch

ias

toz

yg

us

lit

tera

riu

s

Co

roll

ith

ion

sig

nu

m

Cri

bro

sp

ha

ere

lla

eh

ren

be

rgii

Cy

lin

dra

lith

us

bia

rcu

s

Cy

lin

dra

lith

us

sc

ulp

tus

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

ex

imiu

s

Eif

fell

ith

us

pa

rag

og

us

Eif

fell

ith

us

tu

rris

eif

feli

i

Eif

fell

ith

us

vo

ns

ali

sia

e

Ep

roli

thu

s f

lora

lis

Ep

roli

thu

s m

ora

tus

Ep

roli

thu

s s

ide

vie

w

Fa

rha

nia

sp

.

Fla

be

llit

es

ob

lon

gu

s

Ga

rtn

era

go

co

xa

llia

e

Ga

rtn

era

go

na

nu

m

Ga

rtn

era

go

ob

liq

uu

m

Ga

rtn

era

go

pra

eo

bli

qu

um

Ga

rtn

era

go

pra

eo

bli

qu

um

(s

ma

ll v

ar.

)

Ga

rtn

era

go

th

eta

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Go

rka

e o

pe

rio

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

He

len

ea

ch

ias

tia

He

mip

od

orh

ab

du

s g

ork

ae

He

lic

oli

thu

s a

nc

ep

s

He

lic

oli

thu

s c

om

pa

ctu

s

He

lic

oli

thu

s c

om

pa

ctu

s (

sm

all

va

r.)

He

lic

oli

thu

s t

rab

ec

ula

tus

He

lic

oli

thu

s t

rab

ec

ula

tus

(s

ma

ll v

ar.

)

He

lic

oli

thu

s l

ec

kie

i

Ka

mp

tne

riu

s m

ag

nif

icu

s

La

pid

ea

ca

ss

is c

orn

uta

Lit

ha

str

inu

s g

rill

ii

Lit

ha

str

inu

s p

en

tab

rac

hiu

s

Lit

ha

str

inu

s s

ep

ten

ari

us

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

mm

ato

ide

a

Ma

rth

as

teri

tes

fu

rca

tus

Mic

rorh

ab

du

lus

de

co

ratu

s

Mic

ula

sta

uro

ph

ora

Na

nn

oc

on

us

sp

(to

p v

iew

)

Ora

str

um

pe

rsp

icu

um

Ow

en

ia p

art

itu

m

Pla

co

zy

gu

s s

pir

ali

s

Pre

dis

co

sp

ha

era

co

lum

na

ta

Pre

dis

co

sp

ha

era

cre

tac

ea

Pre

dis

co

sp

ha

era

sp

ino

sa

Qu

ad

rum

en

ea

bra

ch

ium

Qu

ad

rum

ga

rtn

eri

Re

inh

ard

tite

s a

nth

op

ho

rus

Re

pa

gu

lum

pa

rvid

en

tatu

m

Re

tec

ap

sa

sp

p.

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Rh

ag

od

isc

us

sp

len

de

ns

Ro

tela

pil

lus

cre

nu

latu

s

Sa

ep

iov

irg

ata

bif

eru

la

So

lla

sit

es

ho

rtic

us

Sto

ve

riu

s a

ch

ylo

su

s

Str

ad

ne

rlit

hu

s f

rac

tus

Te

gu

me

ntu

m s

tra

dn

eri

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

ph

ac

elo

su

s

Un

ipla

na

riu

s s

iss

ing

hii

Ve

ks

hin

ell

a s

p.

Wa

tzn

au

eri

a b

arn

es

ae

Wa

tzn

au

eri

a b

rita

nn

ica

Ze

ug

rha

bd

otu

s b

icre

sc

en

tic

us

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

rha

bd

otu

s h

ow

ei

Ze

ug

rha

bd

otu

s m

ou

lla

de

i

Ze

ug

rha

bd

otu

s s

cu

tula

ss

p.

turo

nic

us

middle Campanian UC15c-d 7020 3 P 24 3 2 3 12 1 24 1 2 140 3 36 6 P P 260 48 1

Santonian UC12 7110 4 4 6 1 9 18 1 18 1 2 2 2 3 4 1 180 39 24 P 16 1 3 15 240 3 P

7260 2 1 1 P 1 2 66 3 3 5 42 3 1 5 2 66 1 P 17 4 5 2 2 2 P 2 16 180 P 2

7290 P 1 2 1 3 2 3 5 5 2 18 5 4 3 1 30 P 3 1 1 6 5 P 9 720 P 5

7410 1 1 1 2 6 35 5 42 1 1 P 1 2 2 8 P 1 3 1 P 1 124 4

7500 P 2 1 39 14 82 96 16 5 2 1 1 2 18 6 1 1 2 P 10 45 2 1 2 P

7590 10 2 3 4 27 21 36 48 1 3 12 27 P 2 P 1 P 36 1 2 2 1 P 30 320 4 82 9

7650 5 3 P 4 4 P 50 4 5 21 1 7 40 1 5 P 3 P 24 2 1 1 P P 40 51 152 3

7710 P 1 2 P 1 1 7 1 1 39 30 12 96 2 P 4 P 5 8 1 P 21 10 P P 12 190 18 120 5

7740 P 1 1 1 4 1 4 3 P 30 42 6 60 5 21 42 1 P 4 6 1 12 2 160 2 1 4 1 2 2 3 6 180 2 33 120 5

7770 3 2 1 4 1 1 P 1 P 4 90 92 2 1 3 P 30 160 P 94 8

UC3 -UC4 7790 6 660 15 1 1 1 3 P 1 P 40 P 1 1 25 P P 1 1 4 1 1 1 3 6 15 5 3 1 3 47 330 1 3 35 630

UC2 7800 P 640 30 2 1 P 3 54 2 P 3 1 25 3 60 1 P 12 3 20 2 3 1 1 1 2 1 24 24 270 35 580

7840 30 690 20 3 1 1 50 2 1 6 1 25 1 3 4 1 1 35 5 3 3 40 2 1 1 1 2 30 160 210 42 450

7860 10 620 2 2 25 P 14 3 160 2 P 2 12 20 1 3 1 5 1 6 1 1 2 20 10 55 8 P 1 1 P 40 2 102 78 180

7880 9 720 2 2 2 4 2 9 3 125 P P 20 3 1 1 1 1 2 35 30 45 1 8 3 1 35 6 190 50

7900 8 660 2 2 5 14 1 4 1 2 160 8 2 14 10 2 2 18 1 1 120 7 8 2 1 8 45 6 180 1 55 160

7910 P 630 16 6 3 1 P P 30 1 P P 15 P 1 P 4 2 1 18 4 18 2 3 1 1 33 80 210 1 180 54

7940 BARREN

8040 BARREN

8090 BARREN

early Cenomanian

late CenomanianUC5

UC1

UNASSIGNED

early Turonian

Coniacian - ?late

Turonian

UC10-

?UC9C

UC6

UC7


232

Demerara A2-1 (Upper Cretaceous)

Demerara A2-1 (Lower Cretaceous)

ODP Leg 207 Site 1257

ODP Leg 207 Site 1258C

ODP Leg 207 1260

Age NF ZoneDepth

(ft)

An

fra

ctu

s c

f. s

hil

oh

en

sis

Ax

op

od

orh

ab

du

s d

ietz

ma

nn

ii

Bis

cu

tum

co

ns

tan

s

Bu

kry

lith

us

am

big

uu

s

Ca

lcic

ala

thin

a o

blo

ng

ata

Ca

lcu

lite

s s

p.

Ca

lcu

lite

s p

erc

ern

is

Co

nu

sp

ha

era

ro

thii

Cre

tarh

ab

du

s c

on

icu

s

Cru

cib

isc

utu

m s

ale

bro

su

m

Cru

cie

llip

sis

cu

vil

lie

ri

Cy

cla

ge

los

ph

ae

ra b

rez

ae

Cy

cla

ge

lop

sh

ae

ra m

arg

ere

lii

Dia

do

rho

mb

us

re

ctu

s

Dia

zo

ma

toli

thu

s l

eh

ma

nii

Dil

om

a p

rim

itiv

a

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

str

iatu

s

Eif

fell

ith

us

pri

mu

s

Eif

fell

ith

us

win

dii

Eth

mo

rha

bd

us

ha

ute

riv

ian

us

Gra

nta

rha

bd

us

me

dd

ii

Ha

qiu

s e

llip

tic

us

Ha

qiu

s c

irc

um

rad

iatu

s

He

len

ea

ch

isti

a

He

len

ia q

ua

dra

ta

He

len

ia s

tau

roli

thin

a

He

mip

od

orh

ab

du

s g

ork

ae

La

gu

nc

ula

do

roth

ea

e

Lit

hra

ph

idit

es

ca

rnio

len

sis

Lit

hra

ph

idit

es

aff

. b

oll

ii

Lit

hra

ph

idit

es

cf.

ho

ug

hto

nii

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

cte

n

Mic

ran

tho

lith

us

?b

rev

is

Mic

ran

tho

lith

us

ho

sc

hu

lzii

Mic

ran

tho

lith

us

ob

tus

us

Me

tad

og

a m

erc

uri

us

Na

nn

oc

on

us

sp

p (

top

vie

w)

Na

nn

oc

on

us

sp

p.

Na

nn

oc

on

us

cir

cu

lari

s

Na

nn

oc

on

us

co

rnu

ta

Na

nn

oc

on

us

fra

gil

is

Na

nn

oc

on

us

ka

mp

tne

ri

Na

nn

oc

on

us

ka

mp

tne

ri m

ino

r

Na

nn

oc

on

us

glo

bu

lus

gp

.

Na

nn

oc

on

us

pa

ks

en

tae

ns

is

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s

Na

nn

oc

on

us

ste

inm

an

nii

Na

nn

oc

on

us

ste

inm

an

nii

min

or

Na

nn

oc

on

us

vo

co

nti

en

sis

Na

nn

oc

on

us

wa

ss

all

ii

Ow

en

ia p

art

itu

m

Pe

rciv

ali

a f

en

es

tra

ta

Pe

ris

so

cy

clu

s p

leth

otr

etu

s

Pic

ke

lha

ub

e f

urt

iva

Re

tec

ap

sa

sp

p.

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

in

fin

itu

s

Rh

ag

od

isc

us

ps

eu

do

an

gu

stu

s

Rh

ag

od

isc

us

ma

nif

es

tus

Rh

ag

od

isc

us

de

ka

en

eli

i

Ro

tela

pil

lus

cre

nu

latu

s

So

lla

sit

es

ho

rtic

us

So

lla

sit

es

lo

we

i

Sp

ee

ton

ia c

oll

iga

ta

Sta

uro

lith

ite

s c

rux

Sta

uro

lith

ite

s m

utt

erl

os

ei

Str

ad

ne

rlit

hu

s f

rac

tus

Str

ad

ne

rlit

hu

s s

ilv

ara

diu

s

Tra

no

lith

us

ga

ba

lus

Tri

pin

na

lith

us

sh

etl

an

de

ns

is

Tri

pin

na

lith

us

su

rin

am

en

sis

Tu

bo

dis

cu

s s

p.

Tu

bo

dis

cu

s v

ere

na

e

Wa

tzn

au

eri

a b

arn

es

iae

Wa

tzn

au

eri

a b

rita

nn

ica

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

rha

bd

otu

s e

rec

tus

Ze

ug

rha

bd

otu

s f

lux

us

Ze

ug

rha

bd

otu

s f

iss

us

Ze

ug

rha

bd

otu

s m

ou

lla

de

i

10820 Barren

10850 P P 7 2 1 1 P 1 P 1 2 24 5 4 6 P P 1 6 1 P P 13 P

10880 1 1 P P 2 8 2 P P P P P 1 P 8 P 20 1 2 2 P 8 2 P P 10 1 P P P P 2 1 P 2 1 P 36 P P

11190 2 P 1 1 7 3 2 P 10 2 7 1 1 P 24 1 1 1 1 P 2 P P 24 1

11250 P P P P 2 P 13 P 8 5 P P P 1 P 1 P P 3 5 33 6 10 6 1 5 3 1 18 3 P 30 1 P 1 P P 2 72 P 33

11290 1 P P P 30 5 1 P P 5 P 1 6 P P 10 1 14 10 9 1 P 14 5 2 2 1 P 24 P 1

11350 1 2 2 1 1 1 P P 4 90 24 9 P 1 P 3 1 1 P 2 12 1 54 3 3 18 4 2 2 P 8 3 4 6 1 P 21 p P P 1 P 180 P P 6 24

11390 P 1 P 1 P P P 10 13 P 22 P 1 P 1 P 2 P P 3 6 36 1 18 21 1 21 P 7 4 P 22 P P 1 P 1 33 P P

11450 1 P P P 2 6 1 1 P P 1 P 1 5 4 21 P 21 1 1 1 1 P P 11 P P 3 1 P 30 P 1 21

11490 3 2 P P P 2 6 7 1 P P 2 P 10 2 2 3 8 1 8 18 2 6 P 2 P 8 P 1 P 3 1 P 2 P 1 P 33 2 8

11550 P P 5 1 1 P 1 P 1 24 1 11 6 3 2 P P 1 P P 14 2

11590 P P 1 1 1 P 1 P 2 51 P 8 P P P 2 P 2 4 24 39 3 2 6 3 P 1 27 4 1 1 1 P P 22 2 P 1 P 1 2 2 60 1 2

11690 P P 4 7 1 P 1 P 4 2 P 1 1 P P P 3 3

11750 2 2 2 P P P 4 21 12 4 P P P 1 P 1 2 3 21 P 4 21 4 P 1 2 2 P P P 24 2 P 2 1 1 39 P 2 1

11790 P 1 1 P 1 1 1 4 8 1 P 1 2 2 1 20 15 30 P 1 3 4 1 18 P 2 P P P P 15

12850 1 1 2 1 4 P 1 1 1 P P 2 3 P 7 1 P

12900 2 1 P 1 P 1 P P 3 P

12990 1 P 1 10 P 60 P P P 2 1 5 2 1 14 1 2 2 3 2 3 10 52 4 P 1 P P P 160 3 2 30

13090 P 1 P 5 1 21 P 3 1 12 P 3 1 P 3 4 1 42 P 1 24

late

Valanginian

late

Berriasian

NC3

(late)

NC2

(late)

Ag

e

NF

Zo

ne

CO

RE

SA

MP

LE

De

pth

(m

)

Ax

op

od

orh

ab

du

s d

ietz

ma

nn

ii

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

ga

ult

en

sis

Bra

aru

do

sp

ha

era

afr

ica

na

Bra

aru

do

sp

ha

era

pri

mu

la

Bra

aru

do

sp

ha

era

qu

inq

ue

sti

co

sta

ta

Bro

ins

on

ia g

all

ois

ii

Bu

kry

lith

us

am

big

uu

s

Ca

lcic

ali

thin

a a

lta

Ca

lcio

so

len

ia f

os

sil

is

Ca

lcu

lite

s d

isp

ar

Ch

ias

toz

yg

us

lit

tera

riu

s

Cru

cib

isc

utu

m n

eu

qu

en

en

sis

Cru

cic

rib

rum

an

gli

cu

m

Dis

co

rha

bd

us

ig

no

tus

Ep

roli

thu

s f

lora

lis

Fa

rha

nia

sp

.

Fla

be

llit

es

ob

lon

gu

s

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Go

rka

ea

op

eri

o

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

Ha

ye

sit

es

alb

ien

sis

He

len

ea

ch

ias

tia

He

mip

od

orh

ab

du

s g

ork

ae

He

lic

oli

thu

s l

ec

kie

i

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

cte

n

Ma

niv

ite

lla

pe

mm

ato

ide

a

Ma

rka

liu

s i

nv

ers

us

Na

nn

oc

on

us

sp

p (

top

vie

w)

Ora

str

um

pe

rsp

icu

um

Ow

en

ia p

art

itu

m

Pre

dis

co

sp

ha

era

co

lum

na

ta

Re

pa

gu

lum

pa

rvid

en

tatu

m

Re

tec

ap

sa

sp

p.

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Ro

tela

pil

lus

cre

nu

latu

s

So

lla

sit

es

ho

rtic

us

Sta

uro

lith

ite

s s

p.

Sta

uro

lith

ite

s

gla

be

r

Sto

ve

riu

s a

ch

ylo

su

s

Te

gu

me

ntu

m s

tra

dn

eri

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

ph

ac

elo

su

s

Wa

tzn

au

eri

a b

arn

es

ae

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

hrh

ab

do

tus

ho

we

i

Ze

ug

rha

do

tus

mo

ull

ad

ei

31-1 (45-46) 275.55 P 72 15 6 P 5 1 1 2 2 2 2 1 1 1 2 4 P P 1 1 30 P 42 5 2 13 12 9 3 5 3 1 1 P 2 4 4 1 90 P 15 140

31-1 CC (51-52) 276.42 1 14 P 1 P 4 1 1 P P P P P 5 1 1 1 P 3 14 2 P 2 P 1 8 12 8 5 4 1 4 P 2 1 90 12 81

early Middle

Albian NC8C

Ag

e

NF

Zo

ne

CO

RE

SA

MP

LE

De

pth

(m

)

Ah

mu

ell

ere

lla

oc

tora

dia

ta

Am

ph

izy

gu

s b

roo

ks

ei

Ark

ha

ng

els

kie

lla

cy

mb

ifo

rmis

As

sip

etr

a t

ere

bro

de

nta

riu

s

Ax

op

od

orh

ab

du

s a

lbia

nu

s

Ax

op

od

orh

ab

du

s d

ietz

ma

nn

ii

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

co

ron

um

Bis

cu

tum

ga

ult

en

sis

Bra

aru

do

sp

ha

era

afr

ica

na

Bra

aru

do

sp

ha

era

big

elo

wi

Bra

aru

do

sp

ha

era

pri

mu

la

Bra

aru

do

sp

ha

era

qu

inq

ue

sti

co

sta

ta

Bro

ins

on

ia c

en

om

an

icu

s

Bro

ins

on

ia e

no

rmis

Bro

ins

on

ia p

arc

a c

on

str

icta

Bro

ins

on

ia s

ign

ata

Bro

ins

on

ia g

all

ois

ii

Bro

ins

on

ia s

ten

os

tau

rio

n

Bu

kry

lith

us

am

big

uu

s

Ca

lcic

ali

thin

a a

lta

Ca

lcio

so

len

ia f

os

sil

is

Ca

lcu

lite

s d

isp

ar

Ca

lcu

lite

s p

erc

ern

is

Ch

ias

toz

yg

us

lit

tera

riu

s

Ch

ias

toz

yg

us

pla

tyrh

eth

us

Co

roll

ith

ion

ex

igu

um

Co

roll

ith

ion

ke

nn

ed

yi

Co

roll

ith

ion

sig

nu

m

Cre

pid

oli

thu

s b

urw

ell

en

sis

Cre

tarh

ab

du

s c

on

icu

s

Cre

tarh

ab

du

s i

na

eq

ua

lis

Cre

tarh

ab

du

s l

ori

ei

Cri

bro

sp

ha

ere

lla

eh

ren

be

rgii

Cru

cib

isc

utu

m h

ay

i

Cru

cib

isc

utu

m n

eu

qu

en

en

sis

Cru

cic

rib

rum

an

gli

cu

m

Cy

cla

ge

los

ph

ae

ra m

arg

ere

lii

Cy

cla

ge

los

ph

ae

ra r

ota

cly

pe

ata

Cy

lin

dra

lith

us

co

ron

atu

s

Cy

lin

dra

lith

us

nu

du

s

Cy

lin

dra

lith

us

sc

ulp

tus

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

ex

imiu

s

Eif

fell

ith

us

ha

nc

oc

kii

Eif

feli

thu

s m

on

ec

hia

e

Eif

feli

thu

s p

ara

go

gu

s

Eif

fell

ith

us

tu

rris

eif

feli

i

Ep

roli

thu

s f

lora

lis

Fa

rha

nia

sp

.

Fla

be

llit

es

ob

lon

gu

s

Ga

ard

ere

lla

gra

nu

life

ra

Ga

rtn

era

go

co

xa

llia

e

Ga

rtn

era

go

na

nu

m

Ga

rtn

era

go

ob

liq

uu

m

Ga

rtn

era

go

pra

eo

bli

qu

um

Ga

rtn

era

go

pra

eo

bli

qu

um

(s

ma

ll v

ar.

)

Ga

rtn

era

go

th

eta

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Go

rka

ea

op

eri

o

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

Ha

qiu

s c

irc

um

rad

iatu

s

Ha

qiu

s e

llip

tic

us

Ha

ye

sit

es

alb

ien

sis

He

len

ea

ch

ias

tia

He

mip

od

orh

ab

du

s g

ork

ae

He

lic

oli

thu

s a

nc

ep

s

He

lic

oli

thu

s c

om

pa

ctu

s

He

lic

oli

thu

s c

om

pa

ctu

s (

sm

all

va

r.)

He

lic

oli

thu

s t

rab

ec

ula

tus

He

lic

oli

thu

s l

ec

kie

i

Ka

mp

tne

riu

s m

ag

nif

icu

s

La

pid

ea

ca

ss

is c

orn

uta

Lit

hra

ph

od

ite

s c

arn

iole

ns

is

Lit

ha

str

inu

s s

ep

ten

ari

us

Lit

hra

ph

idit

es

aff

. h

ou

gh

ton

ii

La

gu

nc

ula

do

roth

ea

e

Lo

rdia

xe

no

ta

Lu

cia

no

rha

bd

us

ma

lefo

rmis

Ma

niv

ite

lla

pe

cte

n

Ma

niv

ite

lla

pe

mm

ato

ide

a

Ma

rka

liu

s i

nv

ers

us

Mic

rorh

ab

du

lus

de

co

ratu

s

Mic

ula

sta

uro

ph

ora

Na

nn

oc

on

us

sp

p (

top

vie

w)

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s q

ua

dri

an

gu

lus

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s a

pe

rtu

s

Na

nn

oc

on

us

tru

itti

fre

qu

en

s

Na

nn

oc

on

us

tru

itti

re

cta

ng

ula

ris

Ora

str

um

pe

rsp

icu

um

Ow

en

ia p

art

itu

m

Pic

ke

lha

ub

e f

urt

iva

Pre

dis

co

sp

ha

era

co

lum

na

ta

Pre

dis

co

sp

ha

era

cre

tac

ea

Pre

dis

co

sp

ha

era

sp

ino

sa

Pe

rciv

ali

a f

en

es

tra

ta

Qu

ad

rum

ga

rtn

eri

Qu

ad

rum

in

term

ed

ium

Re

inh

ard

tite

s a

nth

op

ho

rus

Re

inh

ard

tite

s l

ev

is

Re

pa

gu

lum

pa

rvid

en

tatu

m

Re

tec

ap

sa

sp

p.

Re

tec

ap

sa

an

gu

sti

fora

ta

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Rh

ag

od

isc

us

re

nif

orm

is

Rh

ag

od

isc

us

sp

len

de

ns

Ro

tela

pil

lus

cre

nu

latu

s

Sc

am

pa

ne

lla

sp

p.

Se

rib

isc

utu

m p

rim

itiv

um

So

lla

sit

es

ho

rtic

us

Sta

uro

lith

ite

s s

p.

Sta

uro

lith

ite

s a

ng

us

tus

(s

ma

ll v

ar.

)

Sta

uro

lith

ite

s a

ng

us

tus

Sta

uro

lith

ite

s g

au

so

rhe

thiu

m

Sta

uro

lith

ite

s c

rux

Sta

uro

lith

ite

s m

itc

he

ne

ri

Sta

uro

lith

ite

s m

utt

erl

os

ei

Sta

uro

lith

ite

s r

ota

tus

Sta

uro

lith

ite

s r

ota

tus

(sm

all

va

r.)

Str

ad

ne

rlit

hu

s f

rac

tus

Sto

ve

riu

s a

ch

ylo

su

s

Sto

ve

riu

s p

roto

sig

nu

m

Te

gu

me

ntu

m s

tra

dn

eri

Te

tra

po

do

rha

bd

us

de

co

rus

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

min

imu

s

Tra

no

lith

us

ph

ac

elo

su

s

Un

ipla

na

riu

s g

oth

icu

s

Un

ipla

na

riu

s t

rifi

du

m

Ve

ks

hin

ell

a s

p.

Wa

tzn

au

eri

a b

arn

es

ae

Wa

tzn

au

eri

a b

rita

nn

ica

Ze

ug

rha

bd

otu

s b

icre

sc

en

tic

us

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

hrh

ab

do

tus

ho

we

i

Ze

ug

rha

do

tus

mo

ull

ad

ei

Ze

ug

rha

bd

otu

s s

cu

tula

ss

p.

turo

nic

us

Ze

ug

rha

bd

otu

s s

igm

oid

es

Ze

ug

rha

bd

otu

s t

riv

ec

tis

14-1 (22-24) 385.02 1 P 1 27 1 2 P 6 1 120 15 7 6 36 P 6 3 240 24 6 1

15-1 (56-59) 390.36 2 2 1 5 16 2 2 3 1 P 2 1 32 20 11 22 P P 1 2 320 6 2 P

Mid Campanian UC15 15-3 (90-91) 393.67 2 4 P 2 2 P 2 6 4 1 1 P 60 33 3 12 1 6 360 P 1 1

UC9a 15-3 (100-102) 393.77 3 P 2 3 P P P 4 5 P 7 2 1 5 P P 2 27 4 1 3 1 1 1 1 8 39 1 9 2

UC8 16-1 (13-14) 394.53 2 22 3 6 P 21 11 54 1 21 8 6 1 P 4 P 95 160 21 P 1 3 P 2 P 1 33 6 4 72 1 1

early Turonian UC6 17-1 (38-42) 399.78 3 P 5 7 1 2 3 60 72 2 1 1 3 1 240

18-1 (20-22) 404.3 P 3 4 5 P 1 7 150 5 1 6 1 P 2 1 1 1 1 P P P 3 108 P 120 1

19-1 (66-68) 409.76 5 4 35 7 P 1 P 40 12 1 4 2 7 12 2 1 P 1 1 1 3 1 60 16 15 2 2 2

20-1 (70-72) 414.2 3 120 120 35 2 2 72 8 2 18 12 1 1 1 16 2 1 12 30 1 4 1 240 1 12 7 12

21-1 (102-104) 419.72 2 560 180 4 3 1 1 6 96 21 P 3 15 1 12 7 P 4 5 P 5 8 180 P 9 3 P 1 1 1 12 78 380 30 78 P

22-1 (61-63) 423.91 55 P 720 30 2 14 P P 2 13 2 18 18 P 55 4 55 P 1 1 1 2 P 25 4 4 1 P 30 78 270 25 1 40

23-1 (65-66) 428.95 P 810 24 21 1 3 P 3 1 24 72 7 P 3 1 1 8 24 2 2 2 2 4 15 1 15 1 P 5 P 24 28 280 P 84 220

24-1 (33-36) 433.23 2 660 12 4 10 4 1 12 3 60 4 P 1 12 3 3 10 4 3 10 4 2 24 1 18 60 3 18 4 4 P 1 1 36 27 210 1 108 30

25-1 (42-44) 438.32 3 900 P 27 6 15 P 6 P 4 P 60 1 1 P P 1 12 1 2 7 5 P 7 12 P 5 30 3 35 1 P 2 15 310 P 110 180

26-1 (20-22) 442.7 1 P 630 P 1 3 1 P 18 P P P 4 1 P 27 126 10 P 1 2 14 P 1 8 15 1 3 P P 60 P 10 24 4 18 P 1 15 1 1 16 210 P 66 460

27-1 (8-9) 447.58 6 320 1 5 2 2 1 ?P P 7 P 20 P 2 1 14 2 2 1 3 3 1 P 102 3 P 2 10 14 P 4 2 P ?P 2 12 3 P 6 330 P 30 190

?early Cenomanian ?UC1 27-2 (15-16) 449.06 54 P 1 1 2 3 P P 30 1 P 5 1 4 3 5 1 3 12 P P 24 1 33 P P 2 P 3 120 P 21 10

27-2 (83-84) 449.74 3 180 24 1 16 1 21 P 6 1 1 P 60 2 36 1 1 ?P 1 14 2 16 1 2 5 10 P 8 1 78 3 4 18 12 P 1 3 1 1 7 2 3 102 24 230 24 390

27-2 (115-116) 450.06 2 4 210 4 1 4 1 14 P 18 1 16 5 2 45 2 P P 14 4 P 4 1 6 5 27 P 2 24 4 10 7 P P 2 1 P 4 1 16 33 240 P 60 330

27-3 (4-5) 450.45 P P 2 1 4 2 1 1 P P P 1 P 5 P 26 10 P P 3 P 10 20 10 P 36 4 1 4 48 2 4 P P 600 P 6 50 96

28-1 (5-6) 451.85 P 210 24 4 1 P 1 P 1 P 1 3 2 P P 1 P 9 15 P 9 4 8 7 70 3 5 8 P 1 P 2 84 P 48 112

28-2 (12-13) 453.42 P 14 1 P P 10 2 P P P P 1 P 390 P P 14 3 2 2 P 1 7 P 10 P 20 5 10 2 30 2 P 1 P 1 P 22 140 P 1 14 160

28-CC (2-3) 454.2 P 180 P 4 1 3 1 P P P 3 55 P 1 P 5 1 P 4 1 12 14 1 18 8 20 5 30 P 5 P P P P 1 P P 1 4 240 1 2 112 90

29-1 (4-5) 456.84 1 42 5 16 1 1 1 1 1 P 2 P 5 p 3 3 P 5 1 10 2 P 5 P 36 18 5 5 120 6 22 P P P P 2 2 330 P 5 36 180

29-3 (5-6) 459.85 P P 1 P 5 4 2 1 P 1 1 3 P 4 P 8 1 P 1 3 8 5 1 10 10 14 4 54 20 1 2 4 P P 12 96 P P 16 220

30-1 (5-6) 461.45 6 5 1 1 4 2 1 1 96 P 10 1 3 10 4 2 5 10 2 4 2 4 P 1 P P 12 144 P 16 180

30-2 (5-6) 462.67 P P 24 2 8 P P 1 1 15 P 1 P 1 1 1 P 2 15 P 6 15 1 90 1 P 1 1 12 360 P 2 27 230

30-3(4-5) 464.16 4 2 P P P 1 1 2 P P P 1 30 1 1 8 1 3 4 1 10 P 1 1 2 96 2 54 72

31-1 (4-5) 466.44 P P 42 1 P 1 7 4 P P 1 1 P 42 P P 1 2 P 3 1 1 1 P 25 4 6 30 2 24 P 42 1 P 1 P P 24 160 P 60 114

31-2 (4-5) 467.94 3 P 84 P P 20 3 2 1 2 1 2 15 1 30 1 1 9 P P 9 21 78 90 3 20 4 21 1 15 1 1 2 15 180 3 45 180

31-3 (4-5) 469.44 1 2 40 P P P 1 1 6 1 P 5 P 4 1 P 1 3 1 1 1 4 P 5 1 1 P 2 3 30 75 6 60 25 150 P 3 P 9 P P 3 30 200 2 7 210

32-1 (132-133) 472.32 1 4 90 P P 1 P 5 1 P 2 1 10 3 21 2 2 1 2 1 P 3 6 15 78 42 5 P 27 6 1 P P 180 1 30 150

32-2 (82-83) 473.19 P 3 1 170 P 5 5 P 2 1 4 1 24 7 3 2 4 2 7 1 1 1 15 3 3 45 5 33 1 15 12 3 2 P 1 200 2 45 90

33-1 (142-143) 477.42 1 2 1 180 1 P 1 5 2 3 5 P 2 2 4 6 P 8 1 P 4 4 1 1 1 1 12 P 5 3 2 22 1 36 30 6 30 13 18 6 2 5 1 270 2 21 210

33-2 (138-139) 478.88 P 1 1 2 6 1 1 P 6 1 1 2 1 270 108 10

33-3 (58-59) 479.58 5 480 1 5 2 16 P 2 2 10 6 P 4 P 2 2 2 ?P 21 2 1 18 1 10 2 2 48 10 3 36 160 P 33 30 42 4 21 P 10 P P 16 8 10 1 42 1 160 1 P 30 120

34-1 (122-123) 481.92 2 1 240 3 3 1 1 3 P 4 14 1 4 1 1 51 52 52 1 24 30 2 96 3 4 2 6 1 30 P 230 P 36 240

34-2 (132-133) 483.52 4 P 112 P 3 12 P 1 1 P 1 4 3 18 P 2 2 5 5 2 1 12 3 11 22 1 P 2 P 170 2 32 130

34-3 (45-46) 484.15 7 1 200 1 21 10 16 15 1 3 3 3 21 1 9 4 3 5 6 2 4 1 39 14 2 7 3 1 12 36 33 45 P 21 36 1 4 8 1 340 14 8 370

34-3 (112-113) 484.82 3 P 160 2 18 3 10 1 48 2 P 1 P 8 P 18 P 18 2 8 12 12 10 15 1 P 3 24 12 P 1 1 2 10 24 39 21 12 39 4 18 P 21 P 30 2 P 4 3 330 3 27 240

UC5

UC1

NC9a

ea

rly

Ce

no

ma

nia

n

late Campanian

late middle Albian -

early late Albian

late

Alb

ian

UC16

mid Turonian

UC3

UC2

NC10a (lower)

late Cenomanian

Ag

e

NF

Zo

ne

CO

RE

SA

MP

LE

De

pth

(m

)

Ax

op

od

orh

ab

du

s d

ietz

ma

nn

ii

Bis

cu

tum

co

ns

tan

s

Bro

ins

on

ia g

all

ois

ii

Bro

ins

on

ia s

ten

os

tau

rio

n

Bu

kry

lith

us

am

big

uu

s

Ch

ias

toz

yg

us

lit

tera

riu

s

Co

roll

ith

ion

sig

nu

m

Cru

cib

isc

utu

m n

eu

qu

en

en

sis

Cru

cic

rib

rum

an

gli

cu

m

Ep

roli

thu

s f

lora

lis

Fa

rha

nia

sp

.

Fla

be

llit

es

ob

lon

gu

s

Ga

rtn

era

go

co

xa

llia

e

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Gra

nta

rha

bd

us

co

ron

ad

ve

nti

s

Ha

ye

sit

es

alb

ien

sis

He

len

ea

ch

ias

tia

He

mip

od

orh

ab

du

s g

ork

ae

He

lic

oli

thu

s c

om

pa

ctu

s

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

mm

ato

ide

a

Pre

dis

co

sp

ha

era

co

lum

na

ta

Pe

rciv

ali

a f

en

es

tra

ta

Re

pa

gu

lum

pa

rvid

en

tatu

m

Re

tec

ap

sa

sp

p.

Re

tec

ap

sa

an

gu

sti

fora

ta

Rh

ag

od

isc

us

an

gu

stu

s

Rh

ag

od

isc

us

as

pe

r

Rh

ag

od

isc

us

ac

hly

os

tau

rio

n

Ro

tela

pil

lus

cre

nu

latu

s

Sto

ve

riu

s a

ch

ylo

su

s

Te

gu

me

ntu

m s

tra

dn

eri

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

ph

ac

elo

su

s

Wa

tzn

au

eri

a b

arn

es

ae

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

hrh

ab

do

tus

ho

we

i

Ze

ug

rha

do

tus

mo

ull

ad

ei

54-3 (70) 491.3 P 2 2 P P 1 2 2 2 1 P 2 1 1 2 11 1 4 2 P 7 2 1 1 18 11 22

54 (CC) 491.32 1 8 1 P 3 1 2 P P 1 1 P 1 P 4 1 2 10 2 2 4 1 1 1 1 1 5 P 8 15

early Middle

AlbianNC8C

Chapter 5

233


Table S 5.2 – Distribution charts of calcareous nannofossils from the seven wells studied.

5.10 REFERENCES

Allen, P.A. and Allen, J.R., 2013. Basin analysis: Principles and application to petroleum play assessment. John Wiley & Sons.

Ando, A., Huber, B.T., MacLeod, K.G. and Watkins, D.K., 2015. Early Cenomanian “hot greenhouse” revealed by oxygen isotope record of exceptionally well‐preserved foraminifera from Tanzania. Paleoceanography, 30(11), pp.1556-1572.

Armstrong, H., Brasier, M., 2013. Microfossils. John Wiley & Sons.

Bally, A.W., 1981. Atlantic-type margins, pp.1-48.


Basile, C., Mascle, J. and Guiraud, R., 2005. Phanerozoic geological evolution of the Equatorial Atlantic domain. Journal of African Earth Sciences, 43(1-3), pp.275-282.

Basile, C., Maillard, A., Patriat, M., Gaullier, V., Loncke, L., Roest, W., De Lepinay, M.M. and Pattier, F., 2013. Structure and evolution of the Demerara Plateau, offshore French Guiana: Rifting, tectonic inversion and post-rift tilting at transform–divergent margins intersection. Tectonophysics, 591, pp.16-29.

Behar, F., Beaumont, V. and Penteado, H.D.B., 2001. Rock-Eval 6 technology: performances and developments. Oil & Gas Science and Technology, 56(2), pp.111-134.

Below, R., 1982: Scolochorate Zysten der Gonyaulacaceae (Dinophyceae) aus der Unterkreide Marokkos. Palaeontographica, Abteilung B, v.182, p.1-51, pl.1-9.

Ben‐Avraham, Z., Schattner, U., Lazar, M., Hall, J.K., Ben‐Gai, Y., Neev, D. and Reshef, M., 2006. Segmentation of the Levant continental margin, eastern Mediterranean. Tectonics, 25(5).

Benkhelil, J., Mascle, J. and Tricart, P., 1995. The Guinea continental margin: an example of a structurally complex transform margin. Tectonophysics, 248(1-2), pp.117-137.

Bland, S., Griffiths, P. and Hodge, D., 2004. Restoring the seismic image with a geological rule base. first break, 22(4).

Bown, P., 1998. Calcareous nannofossil biostratigraphy. Chapman and Hall; Kluwer Academic, pp.1–315.

Bown, P.R, Rutledge, D., Crux, J.A. and Gallagher, L.T., 1998. Lower Cretaceous. In Bown, P. (Ed.), Calcareous Nannofossil Biostratigraphy. (pp. 86-131). Chapman and Hall; Kluwer Academic.

Ag

e

NF

Zo

ne

CO

RE

SA

MP

LE

De

pth

(m

)

Ah

mu

ell

ere

lla

oc

tora

dia

ta

Am

ph

izy

gu

s b

roo

ks

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An

fra

ctu

s s

hil

oh

en

sis

Ark

ha

ng

els

kie

lla

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mb

ifo

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Ax

op

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ab

du

s a

lbia

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s

Ax

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du

s d

ietz

ma

nn

ii

Bis

cu

tum

co

ns

tan

s

Bis

cu

tum

co

ron

um

Bis

cu

tum

ga

ult

en

sis

Bra

aru

do

sp

ha

era

pri

mu

la

Bra

aru

do

sp

ha

era

qu

inq

ue

sti

co

sta

ta

Bra

aru

do

sp

ha

era

ste

no

rhe

tha

Bro

ins

on

ia e

no

rmis

Bro

ins

on

ia p

arc

a c

on

str

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Bro

ins

on

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ign

ata

Bro

ins

on

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all

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ii

Bu

kry

lith

us

am

big

uu

s

Ca

lcic

ali

thin

a a

lta

Ca

lcio

so

len

ia f

os

sil

is

Ca

lcu

lite

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isp

ar

Ch

ias

toz

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lit

tera

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Co

roll

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Cre

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Cre

tarh

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s i

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eq

ua

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Cre

tarh

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Cri

bro

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be

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Cru

cic

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cu

m

Cy

lin

dra

lith

us

sc

ulp

tus

Dis

co

rha

bd

us

ig

no

tus

Eif

fell

ith

us

ex

imiu

s

Eif

feli

thu

s p

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go

gu

s

Eif

fell

ith

us

tu

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Ep

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Fa

rha

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sp

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Fla

be

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s

Ga

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Ga

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m

Ga

rtn

era

go

pra

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bli

qu

um

Gla

uk

oli

thu

s d

iplo

gra

mm

us

Go

rka

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eri

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Gra

nta

rha

bd

us

co

ron

ad

ve

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s

Ha

ye

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alb

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He

len

ea

ch

ias

tia

He

mip

od

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ab

du

s g

ork

ae

He

lic

oli

thu

s a

nc

ep

s

He

lic

oli

thu

s t

rab

ec

ula

tus

Ka

mp

tne

riu

s m

ag

nif

icu

s

La

gu

nc

ula

do

roth

ae

a

Lit

ha

str

inu

s s

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ten

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us

La

gu

nc

ula

do

roth

ea

e

Lo

rdia

xe

no

ta

Ma

niv

ite

lla

pe

cte

n

Ma

niv

ite

lla

pe

mm

ato

ide

a

Mic

rorh

ab

du

lus

de

co

ratu

s

Mic

ula

sta

uro

ph

ora

Na

nn

oc

on

us

sp

p (

top

vie

w)

Na

nn

oc

on

us

qu

ad

ria

ng

ulu

s q

ua

dri

an

gu

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Na

nn

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on

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s a

pe

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Ora

str

um

pe

rsp

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Ow

en

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art

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Pre

dis

co

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co

lum

na

ta

Pre

dis

co

sp

ha

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tac

ea

Pre

dis

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Qu

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tec

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sc

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ob

rac

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ta

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an

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ag

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ag

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ac

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m p

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lla

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Sta

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ns

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Sta

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lith

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Str

ad

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s f

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ve

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s a

ch

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s

Sto

ve

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s p

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sig

nu

m

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ntu

m s

tra

dn

eri

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tra

po

do

rha

bd

us

de

co

rus

Tra

no

lith

us

ga

ba

lus

Tra

no

lith

us

min

imu

s

Tra

no

lith

us

ph

ac

elo

su

s

Un

ipla

na

riu

s g

oth

icu

s

Un

ipla

na

riu

s s

iss

ing

hi

Un

ipla

na

riu

s t

rifi

du

s

Ve

ks

hin

ell

a s

p.

Wa

tzn

au

eri

a b

arn

es

ae

Ze

ug

rha

bd

otu

s b

icre

sc

en

tic

us

Ze

ug

rha

bd

otu

s e

mb

erg

eri

Ze

ug

hrh

ab

do

tus

ho

we

i

Ze

ug

rha

do

tus

mo

ull

ad

ei

Ze

ug

rha

bd

otu

s s

cu

tula

ss

p.

turo

nic

us

Ze

ug

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bd

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igm

oid

es

3-1 (125-126) 163.25 1 8 1 54 6 7 4 1 P 2 3 65 21 2 5 90 P P P P 1 P 126 60 4 2

4-2 (146-148) 173.96 2 2 1 P 18 P 1 2 1 4 15 28 1 18 18 P P 3 1 P P P 170 18 1 1

mid - late Turonian UC9 5-1 (15-106) 181.05 P 3 P 1 2 11 1 7 4 2 1 P 1 5 24 P 2 3 1 P 1 9 30 4 2 P

4-2 (96-98) 215.46 7 15 12 2 4 78 42 4 39 14 P 3 3 24 1 P 54 3 1 5 1 5 1 300 P 270 210 2

4-3 (36-38) 216.36 6 1 3 18 15 5 1 130 30 2 15 33 8 P 1 7 11 130 3 1 1 2 4 1 2 6 210 P 96 470 1

5-1 (14-16) 264.14 P 4 7 3 2 P P 1 1 P 7 1 8 5 P 1 3 16 7 2 12 1 5 3 1 2 5 108 P 16 150

5-1 (125-127) 265.25 1 15 3 5 2 P 1 1 3 P 2 15 1 P 33 1 5 P P 1 4 5 9 4 3 3 P 1 4 2 1 2 30 4 60

6-1 (126-128) 296.26 P P 2 P P P 1 P 1 P 1 P 1 P 1 P P 3 1 P P P P 5 5 1 2

7-1 (73-75) 298.73 4 P 1 P 2 P 2 1 P P P P 6 1 2 1

7-1 (128-130) 299.28 1 P 1 P 3 1 P 3 1 P P P P P P P P P 2 P P P 2 1 1 P 1 1 2 P P 1 2 7 1 2 1

8-3 (103-105) 328.03 2 1 P P P 1 1 P 1 P P P 4 6 4

8-3 (135-137) 328.35 5 1 P 2 P P P 2 P P P P 2 2 1 P P 1 1 1 P 1 P 2 8 1 5

early middle

Albian

late Campanian UC16

late Cenomanian

NC8C

UC5


234

Bown, P.R., 2001. Calcareous nannofossils of the Gault, Upper Greensand and Glauconitic Marl (Middle Albian-Lower Cenomanian) from the BGS Selborne boreholes, Hampshire. Proceedings of the Geologists' Association, 112(3), pp.223-236.

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6 Synthesis

Synthesis

242

6.1 INTRODUCTION

In order to synthesise the results generated, five palaeographic maps are constructed that document the

Cretaceous tectono-stratigraphic evolution of the eastern Central Atlantic, the conjugate northwest African

and South American continental margins. The revised stratigraphic framework underpins the age calibration

for these maps, with dating uncertainty discussed (Fig. 0.1).

Synthesising the new chrono-stratigraphic results from the biostratigraphic analysis (Chapters 2; 3; 5) allows

major stratigraphic events and sequences to be correlated from the Equatorial Atlantic (offshore French

Guiana), across the Demerara Rise, into the Central Atlantic oceanic domain (DSDP sites/Maio, Cape Verde).

The main objective is to investigate the effects of the middle Cretaceous opening of the Equatorial Atlantic

on post-rift sedimentary systems and geomorphology (i.e. palaeogeography) of the adjacent continental

margins. Renewed tectonism interrupted the relatively ‘passive’ post-rift subsidence and sedimentation

established in the Central Atlantic, impacting the source-to-sink system through hinterland uplift (source),

tectonic deformation of the basin (sink), and associated effects on sedimentary systems, routing,

depositional style etc.

Fig. 0.1 (next page) – Chronostratigraphic summary of the key revised DSDP/ODP boreholes, exploration wells and outcrop locality (Maio, Cape Verde) of the Central Atlantic. Total organic carbon (TOC) data produced in this study is averaged over sub-stage intervals. A compilation of tectonic phases and regional events documented during this study, and synthesised from previous work is provided, alongside the relative sea level curve (Haq, 2014). A geological sketch based on regional two-dimensional seismic data profiles from the Central to Equatorial Atlantic, through the Demerara Rise is shown to display the relative positions, depths of penetration for each of the revised wells and stratigraphic architecture. DSDP 368 and Maio are not displayed on the geological section.

Chapter 6

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Synthesis

244

Data produced in this study is integrated with an extensive compilation of data from existing studies. All

published work utilised is documented in Table 0.1. The tectonic framework and reconstructions for the

palaeogeographic maps is supported by the Geognostic Earth Model (GEM, 2020), modified where

appropriate to reflect the new evidence. Additional exploration well data (primarily end-of-well reports and

digital logs) from Senegal were provided by Petrosen, as well as limited information from other published

studies and company presentations. Observations from the available seismic datasets are incorporated.

To link the studied sedimentary response in the ‘sink’ to the geological evolution of the hinterland i.e.

‘source’, additional results from North Africa Research Group exhumation studies (low-temperature

thermochronology – Gouiza et al., 2019), provenance models (Mourlot et al., 2018b) and subsidence analysis

(Latil-Brun & Lucazeau, 1988) are amalgamated. However, it must be acknowledged that the resolution of

the hinterland studies is much broader and of a lower order of temporal resolution than the stratigraphic

framework developed based on the biostratigraphy and well database.

The generated maps record five different depositional environments spanning non-marine to deep marine.

Facies data for the wells that penetrate the mapped succession are drawn as pie charts for each individual

well. Wells that penetrate stratigraphy younger and older than the mapped strata, but do not recover

sediments of the mapped age are also added to indicate a recognised hiatus (for example, if the well reaches

total depth (TD) in Paleozoic sediments and the immediately overlying sequence is Albian in age, a hiatus is

interpreted through the intervening pre-Albian time stages). Significant structural features are also

displayed. The available data is used to predict major sediment input points linked to depocentres on the

shelf and in the basin. For the organic-rich intervals, latest Albian to Cenomanian-Turonian boundary,

average total organic carbon percentage is recorded for each well, with the dominant organic matter type.

Chapter 6

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Table 0.1 – Public data synthesised for the following palaeogeographical reconstructions.

Mid

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Data Source 142 - 135 125 - 113 113 - 102 102 - 94 94 - 78

Reconstructions, structural geology, basement terranes both GEM, 2020 x x x x x

Platform depocentre, Guinea Plateau NWA Serrano-Suarez et al. 2018 x

PGO-6 well data NWA Serrano-Suarez et al. 2018 x

Paleogeographies NWA Mourlot et al. 2018a x x x x

Extent of volcanics, Guinea Plateau NWA Benkhelil et al. 1994; Olyphant et al. 2017 x x

Grabens preserved subsurface, offshore Suriname SA Griffith, 2017 x

Extent of volcanics, Demerara Rise SA Gouyet et al. 1994 x

Deep water channel-lobe system, N. Senegal NWA Kosmos Energy, 2020 x

Guyana Shield exhumation, French Guiana SA Derycke et al. 2018 x

Nd isotope provenance both Mourlot et al. 2018b x x x

Deep water channel-lobe system SA Erlich et al. 2003 x x x

Basin floor fan systems, Guyana SA Mourlot, 2018 x x x

Ab-1, AR-1, CO-1, ESS-2, Ma-1, NCO-1 well data SA Yang & Escalona, 2011; Mourlot, 2018 x x x

WAC exhumation NWA Gouiza et al. 2019 x x

Base-of-slope systems, Senegal NWA African Petroleum, 2013; Clayburn et al, 2017 x x

Paleo-Senegal river deep water channel-lobe system NWA Kosmos Energy, 2016 x x

Salt distribution & style NWA Tari et al. 2003 x

GU-2B-1 & Sabu-1 well data NWA Edge, 2014 x

Sediment input paleo-Geba river system NWA Envoi, 2015; Bourne et al. 2019 x

Sangomar GDE NWA Hathon, 2018 x

JAMM-1XB well result NWA Total press release, 2019 x

Kora-1 well data NWA Envoi, 2015 x

TOC data, Senegal exploration wells NWA Herbin et al. 1986; Nzoussi, 2004 x

TOC data SA Mourlot, 2018 x

Dakar, GDE NWA Nzoussi, 2004 x

Hydrocarbon discoveries SA various press releases x

Dakar, GDE NWA Gladimi, 1977 x

Palaeogeographic Maps (Ma)

No

rthw

est Africa (N

WA

)

/ Sou

th A

merica (SA

)

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6.2 PALAEOGEOGRAPHICAL RECONSTRUCTIONS

6.2.1 Middle Berriasian unconformity (142 Ma) to Upper Valanginian maximum flooding

surface (135 Ma)

Fig. 0.2 – Palaeogeographical reconstruction to the interval, Middle Berriasian unconformity (142 Ma) to Upper Valanginian maximum flooding surface (MFS; 135 Ma). The map shows the depositional systems at maximum transgression. Facies distribution (%) for the interval encountered in each well is shown. A key is provided for reference in the following maps.

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Stratigraphy – The base horizon for this reconstruction is defined as the middle Berriasian unconformity (142

Ma) identified in Core 33 at DSDP Site 367, representing the Jurassic-Cretaceous (J/K) boundary. This

unconformity is not recognised on the Demerara Rise in well A2-1 likely due to large sampling gaps.

Additionally, in the Senegalese exploration wells, the Top Jurassic is used as the base of this reconstruction.

In the future, revised biostratigraphy of these wells may reveal the presence of the middle Berriasian

unconformity. The top of this interval is the super-regional Upper Valanginian maximum flooding surface

(MFS; 135 Ma) identified in well A2-1 and reported across the Central Atlantic (Morocco – pers. obs.) and

into the Gulf of Mexico (Loucks et al., 2017). The MFS is not observed at DSDP 367, likely due to a ca. 50 m

core gap (cores 29 to 30).

Within the oceanic domain of the Central Atlantic (i.e. Maio, DSDP Site 367), this interval is characterised by

white pelagic limestones with chert and interbedded marls. On the island of Maio, the interval is represented

by the outcropping Morro Fm., and throughout Central Atlantic, in the Blake-Bahamas Fm. Platform wells,

offshore Senegal, Guinea Bissau and Suriname, all recovered limestones typical of carbonate platform

sedimentation, occasionally dolomitized with interbedded sequences of marine mudstones. No reef-type

limestones were recovered. The sequence is condensed in the deep basin and expanded across the platform

reaching over 1 km in thickness. Senegalese wells further inboard recovered Lower Cretaceous-aged non-

marine sandstones and mudstones.

Tectonics – Following Early Jurassic opening of the Central Atlantic and the drifting of North America away

from Gondwana (Labails et al., 2010), the surrounding continental margins entered a period of relative

tectonic quiescence. Accommodation was likely generated through thermal sag of the continental margin;

the zone of maximum accommodation, i.e. greatest thickness of Lower Cretaceous sediment, is located

landward of the continent-ocean boundary/escarpment margin (Fig. 0.2).

Palaeogeography – Prior to Equatorial Atlantic rifting, an extensive carbonate platform surrounded the early

Central Atlantic. The present-day eroded carbonate margin marks approximately the location of the slope

to basin-floor transition, although it is noted this may have extended further oceanward, as there has been

considerable erosion post-deposition (Late Cretaceous). The oceanward extent of the carbonate platform

appears to have been controlled by the location of the continental-ocean boundary, as mapped by Labails

et al. (2010). From the seismic data interpretation, the carbonate platform shows mainly aggradational

stacking patterns. North of Dakar, the basement hinge zone (Flicoteaux et al., 1988) which marks greater

subsidence rates oceanward, influenced the location of the transitional facies belt (Fig. 0.2). Whereas south

of Dakar, there appears to be less of a basement control, evidenced by the occurrence of shelfal limestones

further basinward in wells KAF-1 and Bn-1. Proximal non-marine strata were deposited and not preserved

due to reworking associated with low accommodation (landward of basement hinge), as indicated in many

proximal wells. An onlap surface is clearly observed on seismic data from the Demerara Rise (Fig. 0.2), and

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onshore Senegal (Ndiaye, 2012; see their Fig. 2.6) representing the Upper Valanginian MFS. The gradual

landward transgression, shown by the onlap of this stratigraphic interval onto pre-rift sediments and

basement coincides with a first-order relative sea level rise (Fig. 0.1).

6.2.2 Base Aptian unconformity (125 Ma) to base Albian unconformity (113 Ma)

Fig. 0.3 – Palaeogeographical reconstruction to the interval, base Aptian unconformity (125 Ma) to base Albian unconformity (113 Ma), effectively representing the Aptian stage.

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Stratigraphy – The base of this reconstruction is the base Aptian unconformity (125 Ma). This stratigraphic

surface has not been encountered biostratigraphically in any of the revised wells but is identified in the

Senegalese well database (base Aptian/top Neocomian) and in the literature (Sapin et al., 2016; Olyphant et

al., 2017) as representing temporally the onset of rifting in the Equatorial Atlantic.

An unconformity at this level is supported by seismic interpretation from offshore French Guiana, on the

Demerara Rise and Guinea Plateau (Fig. 5.11). The Aptian interval is sand-rich on the Demerara Rise in the

revised wells, A2-1 and FG2-1. New palynology dating undertaken as part of this study was unable to detect

the base Aptian unconformity, due to a combination of poor palynological recovery and low sampling

resolution. The interval extends up to the base Albian unconformity (113 Ma) discussed in more detail in the

following section, and is therefore representative of the entire Aptian stratigraphy in the Central Atlantic.

Throughout the Senegalese wells, the base Albian unconformity is equivalent to the top Aptian pick, which

is typically taken as the top of the carbonate platform. No new biostratigraphical analysis of these wells has

been performed to verify this.

The uppermost Morro Fm. on Maio and the equivalent Blake-Bahama Fm. in DSDP Site 367 is of Late

Barremian age (Fig. 0.1). On Maio, an informal ‘upper transitional unit’ can be recognised towards the top

of the Morro Fm., that containing more marly facies, indicating more terrigenous input into the oceanic

domain. There is a clear distinction between carbonate-siliciclastic dominant facies encountered along the

continental margins (Fig. 0.3). The South American margin is sand-rich; with sands in wells A2-1 and FG2-1

being recorded as fine-grained, poorly sorted, immature litho-quartzose sandstones. South of Dakar, the

shelfal wells record limited siliciclastic input, with mainly platform carbonates, and only occasional

calcareous sandstone interbeds. Well CVM-1 is the exception, being dominated by very fine-grained

calcareous sandstones. Additionally, North of Dakar, well TB-1 is sand-dominated.

Tectonics & volcanism – Rifting of the Equatorial Atlantic initiated in the Early Aptian times. Northeast-

southwest orientated extension reactivated CAMP volcanic lineaments and basement terrain boundaries

(GEM, 2020). These CAMP volcanic intrusions orientated northwest-southeast are located throughout

northeast Brazil (Roraima and Cacipore dykes; Marzoli et al., 1999) and are predicted to extend offshore

based on gravity and magnetics data (GEM, 2020). A rift system progressively migrated through the proto-

Equatorial Atlantic forming a series of en-échelon half grabens, i.e. the Cacipore Graben, offshore Brazil,

separated by dextral transforms now preserved as oceanic fracture zones (Pindell, 1985). Extrusive

volcanism associated with the second-phase of rifting is recorded on both the Demerara Rise (well FG2-1)

and Guinea Plateau (wells GU-2B-1 and Sabu-1; Olyphant et al., 2017). Previous work, dated these flood

basalts as 125 Ma (Gouyet et al., 1994) and 120 ± 6 Ma (ESSO, 1978), indicating extrusion during rifting

times. Re-dating of the volcanics in well FG2-1 was not completed in time for inclusion in this study to test

these ages; (samples have been irradiated for argon-argon dating and await final dating). Exhumation of the

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Guyana Shield in French Guiana is documented by low-temperature thermochronological (LTT) data by

Derycke et al. (2018), postulated to be induced by the renewed tectonism.

Palaeogeography – Progradation of a major fluvio-deltaic system (Stabroek Fm.) across the Demerara Rise

is evidenced by sandstone sequences recorded in wells A2-1, FG2-1 and GLO-1, associated with a thick

depocentre and clinoform geometries observed on seismic (Fig. 5.11B). Post-depositional erosion, due to

emergence and exhumation at the base Albian unconformity, erodes this sand-prone interval on the

Demerara Rise. Whether this system extends onto the conjugate Guinea Plateau is poorly constrained,

however seismic data presented in Edge (2014) shows a much thinner equivalent sequence.

A major axial river system is interpreted to have flowed towards the west (Central Atlantic) through the en-

échelon half grabens, captured drainage systems from both the Leo Man (Africa) and Guyana Shield (South

America). Another fluvio-deltaic system is observed at the palaeo-Essequibo river, evidenced from thick

sands in wells AR-1 (Mourlot, 2018) and ESS-2 (Yang & Escalona, 2011). Offshore Senegal, carbonate

platform sedimentation continued, with occasional incursions of minor siliciclastic systems across a shallow

shelf. Karstification of the most distal Aptian carbonate platform occurred prior to deposition of an Early

Albian shelf edge delta. Karstification may have been sub-aerial or submarine (groundwater percolation). If

sub-aerial karstification, this suggests the distal platform was tilted and emergent in the latest Aptian to

Early Albian, related to regional transpression. Reefal bodies may have developed offshore on rejuvenated

topography (i.e. Wolverine prospect, AGC profond; Garyfalo, 2019). Based on the presence of sands in well

TB-1, sediment input through the palaeo-Senegal river system was established during the Aptian. The

offshore extension of this fluvial system, i.e. slope channel and basin floor fans, was suggested by Kosmos

(2020) following the drilling of well Orca-1.

Organic-enrichment associated with the Early Aptian global oceanic anoxic event (OAE-1A) has not been

encountered in the studied wells, but is hypothesised (Bralower et al., 1993).

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6.2.3 Base Albian unconformity (113 Ma) to intra Late Albian unconformity (102 Ma)

Fig. 0.4 – Palaeogeographical reconstruction to the interval, base Albian unconformity (113 Ma) to intra Late Albian unconformity (102 Ma), effectively representing the Albian stage.

Stratigraphy – The base Albian unconformity (113 Ma) delineates the basal surface of the interval; this major

sequence boundary is interpreted throughout the studied area forming a pronounced angular unconformity

across the Demerara Rise (Fig. 0.1), a disconformity surface within the Central Atlantic oceanic domain (i.e.

at DSDP sites 367 and 534A) and throughout the Equatorial Atlantic domain (de Figueiredo et al., 2007). This

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unconformity is interpreted from seismic data at DSDP Site 367, as core recovery limits the biostratigraphic

interpretation of the base Albian unconformity at this locality (Fig. 3.10). This disconformity in the oceanic

domain is recognised across the Central Atlantic as Reflector (Jansa et al., 1978). Importantly, sediments

recovered above this unconformity are loosely dated on the Demerara Rise i.e. at well A2-1 the Potoco Fm.

carbonates are Early to Middle Albian in age. We choose to report the oldest age, base Albian, for the age

of the unconformity. This is supported by the interpretation of the base Albian unconformity at DSDP Site

534A (US Atlantic margin), with Early Albian sediments above this event. The top of this interval is defined

by the intra Late Albian (pre-NC10A) unconformity (102 Ma), identified during this study at ODP Site 1258C

on the Demerara Rise (Fig. 0.11).

The Albian stratigraphy on the South American margin is carbonate-dominated. Limestones are encountered

at well A2-1 and offshore Guyana representing the Potoco Fm. platform (Fig. 0.4). Outboard of the carbonate

platform, ODP and DSDP sites on the Demerara Rise recovered calcareous clays with organic matter. Similar

carbonate-dominated facies were observed within the Casamance Marine (CM) wells in southern Senegal.

In The Gambia, and just to the north in Senegal, wells (Jammah-1; SNE-1), drilled on the shelf, are sand-

prone forming the hydrocarbon reservoirs in the Sangomar Field (Clayburn, 2017). These sands are very fine-

grained, ripple laminated, amalgamated to thinly-bedded, and are interpreted to be deposited in a pro-delta

apron by turbidity currents, possibly influenced by shelfal contourite currents (Cunningham-Gray et al.,

2018). In Senegal, away from the major siliciclastic sediment axis, wells become more carbonate-rich i.e. Br-

1 and DS-1. Wells drilled on the Cap Vert peninsula, around Dakar, are mudstone-dominated. In the Central

Atlantic oceanic domain, the base Albian unconformity marks the carbonate-siliciclastic transition, with

Albian sediments at DSDP Site 367 being variegated, plant-debris rich, non-calcareous mudstones; similar

facies are observed at outcrop on Maio at Ribiera do Morro.

Tectonics – Major transpression caused by wrenching of the Equatorial Atlantic resulted in compressional

deformation across the conjugated Demerara Rise and Guinea Plateau (Gouyet, 1988). Compressional

features observed on seismic include thrust faults with associated roll-overs, basement pop-up structures,

imbricate thrusts and broad folding (Fig. 3.9; Fig. 5.13). Up to ca. 1 km of exhumation of the distal Demerara

Rise is indicated, subsequently peneplained by the base Albian unconformity. Additionally, major shelf

margin collapse is documented on the Central Atlantic side of both plateaus, redistributing a voluminous

section of the underlying carbonate platforms associated with the renewed tectonism.

Deformation extended into the Central Atlantic oceanic crust, forming an intra-oceanic transpressional fold-

thrust belt along the proto Demerara-Guinea fracture zone (GEM, 2020). The effects of this tectonism are

observed over 1000 km away along the northwest African continental margin. Thrusting is prominent at the

base of the carbonate platform forming a tight base-of-slope anticline offshore The Gambia (Fig. 4.3). The

deformation is postulated to be located here as the tectonism reactivated lineaments along the continent-

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ocean boundary, uplifting the continental basement terrane. Compressional features extend to northern

Senegal and Mauritania, reactivating basement structures associated with the hyper-extended continental

crust (Kosmos Energy, 2017; Whittaker, 2018). Kilometre-scale exhumation of the Mauritanides of the West

African Craton (WAC) has been documented by LTT data with a significant cooling event through 120-100

Ma (Gouiza et al., 2019). Of note, ages generated from this analysis are at a much coarser resolution (tens

of Myr) to the biostratigraphic data presented. It is conceivable that the Equatorial Atlantic rifting also

induced long wavelength hinterland movements in the WAC, causing exhumation that rejuvenated the

siliciclastic sediment budget. Provenance studies using neodymium isotopes (Mourlot et al., 2018b) indicate

that the southern Mauritanides (Hercynian belt) and Bove Basin (Paleozoic sediments) were candidate

source areas.

Palaeogeography – Re-establishment of the basin fringing carbonate platform along the South American

margin extended from Guyana across the Demerara Rise (Potoco Formation), with a sand-prone more

proximal depositional environment located landward towards the South American continent. Deep isolated

oceanic basins i.e. offshore French Guiana, formed in the extensional segments of the opening Equatorial

Atlantic where accommodation was greatest, evidenced in the well GM-ES-3. Deep marine connections in

the proto-Equatorial Atlantic between rift segments were established before finally breaking through the

Demerara-Guinea arch, following the continental breakup at the base Cenomanian unconformity (see

Chapter 5 for discussion). A deep-marine sedimentary system on the western margin of the Demerara Rise

was confined by topography generated by the underlying margin collapse (Fig. 0.4; Fig. 5.12).

The Albian saw the first major period of siliciclastic delivery along the northwest African continental margin.

Shelf-edge deltas (well-constrained by seismic and well data in Chapter 4) prograded completely across the

shelf, sourced from the palaeo-Gambia river (Sangomar delta). Additional areas of major sediment input and

interpreted deltaic systems are interpreted from the palaeo-Geba (Bourne et al., 2019), -Saloum and -

Senegal river systems. A sand-rich pro-delta apron formed at the front of the Sangomar delta (palaeo-

Gambia), with many subaqueous channels meandering to the shelf edge leading to early canyonisation of

the margin and feeding base-of-slope fans with short run-out distances (i.e. FAN discovery). Sediment was

likely ponded in this area by a combination of the structural deformation and reworking by contourite

currents at the base-of-slope (Mourlot et al., 2018a). Off the major sediment axes, the shelf remained

carbonate-dominated i.e. southern Senegal, and elsewhere. Deep marine systems from the palaeo-Geba

river system interacted with active sea-floor topography generated by salt tectonism in the Casamance salt

basin offshore Guinea Bissau (Bourne et al., 2019).

Much larger slope to basin-floor sand-rich systems developed in strike-limited points along the margin, i.e.

near Dakar (palaeo-Saloum river system), proven by the JAMM-1XB exploration well, and from the palaeo-

Senegal river system to form the Upper Albian reservoirs in the Greater Tortue Ahmeyim field development

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and Marsouin discovery (Kosmos Energy, 2017). In comparison to the palaeo-Gambia river system, where

the majority of the sediment was trapped on the shelf, the Greater Tortue Ahmeyim systems were more

efficient at delivering sediment into the deep basin. This may be related to the volume of sediment

transported by these rivers and/or the margin architecture. North of Dakar, the Albian margin had a low

gradient slope typical of continental margins (e.g. modern-day Equatorial Guinea; Jobe et al., 2011) where

the relief of the underlying carbonate platform had been filled/healed. In contrast, the carbonate

escarpment south of Dakar was affected by the compressional deformation creating ca. 1 km of relief and

exaggerating the steep escarpment-type geometry, which impacts delivery of sediment into the deep basin

by trapping sediment on the shelf. The contrast in the margin architecture and hence sediment routing

systems can also be related to the underlying basement terranes, where features such as the Kaolack fault

(Fig. 0.6), a major terrane boundary, separates the Mauritanide (North) from the Guinea Wedge terrane.

Major progradation of the deltaic systems south of the Kaolack fault possibly indicates that the Guinea

Wedge basement terrane was reactivated and uplifted, supported by the absence of Albian sediments in

well DM-1 (Fig. 0.4).

The arrival of the renewed siliciclastic systems is time-transgressive along the margin. Sands in the Sangomar

delta (palaeo-Gambia) are thickest in the Lower Albian, also recorded in the Middle Albian and decrease into

the Upper Albian; whereas in the north, i.e. palaeo-Senegal river system reservoirs, the onset of sandstone

deposition is later, dated as Upper Albian to Lower Cenomanian. This progradational period is temporally

associated with a first-order fall in relative sea-level (Fig. 0.1), implying eustacy amplified the stratigraphic

response.

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6.2.4 Intra Late Albian unconformity (102 Ma) to Cenomanian-Turonian boundary (94 Ma)

Fig. 0.5 – Palaeogeographical reconstruction to the interval, intra Late Albian unconformity (102 Ma) to Cenomanian-Turonian boundary (94 Ma), effectively representing the major organic-rich interval.

Stratigraphy – Along the South American margin, the base of this interval is defined as the intra Late Albian

unconformity as recognised at ODP Site 1258C (Fig. 0.1). However, this event is typically overprinted by

truncation associated with the overlying base Cenomanian unconformity, i.e. in wells A2-1 and FG2-1. Within

the oceanic domain of the Central Atlantic, the intra Late Albian unconformity forms a discontinuity surface

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and major facies change discussed below. The Cenomanian-Turonian boundary, above the OAE-2 level, is

taken as upper bounding surface of this interval. The top Cenomanian is biostratigraphically well-constrained

by nannofossil markers, the last occurrence of A. albianus, G. praeobliquum and H. chiastia.

This interval is characterised by high organic enrichment from the latest Albian through the Cenomanian,

with the majority of wells recording a mudstone-dominated sedimentation. Dark black laminated

carbonaceous shales of the Hatteras Fm. are encountered throughout the studied area, i.e. DSDP Site 367.

Distal wells drilled on the Senegalese shelf are typically limestone-dominated, with some more sand-rich

successions. This organic-rich sequence is named the Canje Fm. along the South American margin.

Tectonics – Following the cessation of minor continental-continental collision, due to rotation between the

Demerara Rise and Guinea Plateau, associated with the base Cenomanian unconformity, sea-floor spreading

and oceanic crust accretion resulted in the drifting and separation of the two continents. Passive margins

established on both continents.

Palaeogeography – From Guyana to Brazil, the continental margin was transgressed, with organic-rich

sedimentation extending across the shelf to slope (Fig. 0.5). However, in the deep water, discrete channel-

lobe systems punctuate this mud-prone interval along the margin. Latest Albian (NC10a nannofossil zone),

and younger turbidite systems were established offshore French Guiana, with a short run-out length due to

the narrow steep margin, likely point sourced related to fault topography inherited from the rifting process.

A carbonate-dominated shelf was re-established across much of the northwest African margin. From seismic

observations offshore The Gambia, this sequence transgresses the shelf, shifting depositional environments

landward; a clear transgressive surface is observed above the Albian delta. Jammah-1 recovered

Cenomanian-aged sands (Clayburn, 2017), suggesting continued input through the palaeo-Gambia river

system, albeit backstepped and positioned further inboard.

The palaeo-Senegal river system continued to act a major sediment input point along the margin, with

significant volumes of Lower Cenomanian sands transported to the deep basin by slope channels and basin

floor fans (Fig. 0.5). These form the high-quality reservoirs in multiple gas fields in Senegal-Mauritania,

reported as comprising of very fine- to fine-grained sub-arkosic sands (Kosmos Energy, 2016). Provenance

studies suggest a major drainage reorganisation at this time, capturing more Precambrian detritus from the

Kédougou-Kéniba inlier further to the east (Mourlot et al., 2018b), with continued exhumation of the

hinterland (Gouiza et al., 2019). Climatic models predict a tropical climatic belt to extend across the source

areas (WAC) of the African margin (Saunders, 2016), suggesting an increase in rainfall and denudation rates,

and thus potentially volume of sediment supply.

Organic-enrichment – Although the detail of geochemical data are discussed in previous chapters, a few key

themes are worth summarising here. Organic-enrichment typically peaks in sediments that correlate to the

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OAE-2, latest Cenomanian, and also occasionally extending into the Early Turonian, related to relative sea-

level rise, and an expanded Hadley Cell during the Cenomanian-Turonian climate optimum (Wagner et al.,

2013). The onset of organic-enrichment is well calibrated to start in the NC10a nannofossil zone in the latest

Albian. It is appears that the organic-enrichment along the northwest African margin terminates around the

Cenomanian-Turonian boundary, whereas it extends into the Coniacian in Guyana (Canje Fm.) and

Venezuela (La Luna Fm.). This may be related to palaeoceanographic changes related to establishment of

bottom-water connection through the opening Equatorial Atlantic seaway (Friedrich and Erbacher, 2006),

creating a more active ocean floor as currents flowed along the African margin (Mourlot et al., 2018a).

Although not investigated in this study, Cretaceous oceanic red beds (CORBs) described by Hu et al., (2012),

that are present through the Central/North Atlantic, indicate organic-enrichment and subsequent oxidation.

Throughout the studied region, strong nutrient upwelling in coastal regions and in the deep basin elevated

organic-richness (Arthur et al., 1987). This coincided with regional flooding of the shelf during the

Cenomanian-Turonian transgression / highstand and warming global sea-surface temperatures (Erlich et al,

2003). Organic-enrichment is encountered across the shelf, generally less rich (1-5% average TOC) than in

the deep basin (14-19% average TOC; Fig. 0.5). Through this thesis, heterogeneities in the organic-rich

sedimentary facies are reported, and the type of organic-matter is shown to vary primarily dependant on

the proximity to terrestrial organic matter input.

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6.2.5 Cenomanian-Turonian boundary (94 Ma) to Middle Campanian unconformity (78 Ma)

Fig. 0.6 – Palaeogeographical reconstruction to the interval, Cenomanian-Turonian boundary (94 Ma) to Middle Campanian unconformity (78 Ma).

Stratigraphy – This interval effectively represents the Late Cretaceous palaeogeography, from the Turonian

to Campanian. On the South American margin, a major Middle Campanian unconformity has been identified

in all studied wells across the Demerara Rise forming the top of this sequence. A time-equivalent sequence

boundary has not been proven in the oceanic domain of the Central Atlantic, likely due to the poor core

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recovery over this interval in the DSDP wells and resolution in the palynology dating as a consequence of the

low number of samples analysed. However, a regional composite unconformity (RCU – Chapter 4) is now

well documented on the shelf edge south of Dakar (Fig. 0.1). This unconformity was previously termed the

Senonian (Coniacian to Maastrichtian) unconformity (Martin et al., 2010) and the pre-Maastrichtian

unconformity (Hathon, 2018). While no new biostratigraphic analysis of the Senegalese exploration wells

was performed, many of the wells have Campanian sediments resting unconformably on Cenomanian and

older deposits, i.e. wells DKM-2, RF-2, Jammah-1, GLW-1 (Fig. 4.2). Hence, it is interpreted in this study that

these unconformities recognised on the distal continental margins are synchronous and of middle

Campanian age.

Siliciclastic-prone sedimentation occurs throughout the wells on the South American margin (Fig. 0.6). This

interval is truncated by the middle Campanian unconformity in the DSDP and ODP wells on the Demerara

Rise. Mixed lithologies are recorded throughout southern Senegal, and moving further north beyond Dakar,

the wells record sand-rich strata. The two DSDP boreholes in the Central Atlantic are characterised by

variegated non-calcareous claystones with occasional sandy turbidites of the Plantagenet Fm. No sediments

of this age are recorded on the island of Maio (subsequently eroded due to exhumation or not deposited

during uplift).

Tectonics – The two continental margins have fully rifted and have begun drifting away from each other,

with oceanic crust accretion continuing within the opening Equatorial Atlantic. Unconformities (RCU and

Middle Campanian unconformity) developed on both distal margins associated with major slope instability.

Several similarly timed geodynamic events are documented within the Central Atlantic, related by authors

to the distal effects of the Santonian-aged early Alpine Orogeny compressional event, a shift in the pole of

rotation of Atlantic spreading due to continental separation between Africa and South America (Guiraud &

Bosworth, 1997; Labails, 2007) and rifting episodes in Central Africa (Guiraud, 1998). Again, it is interesting

to note that the erosion of the distal platform only occurs south of Dakar i.e. south of the Kaolack fault

terrane boundary. This either suggests that the Guinea Wedge experienced uplift related to the

aforementioned far-field effects of these tectonic events, or the margin architecture (escarpment margin)

was prone to collapse. Similarly, the Middle Campanian unconformity is only registered on the northern

distal margin of the Demerara Rise. These unconformities likely extend into the basin as major sequence

boundaries with associated lowstand delivery of sand-rich systems (i.e. Guyana).

Palaeogeography – This period is the first major delivery of siliciclastic sediment along the South American

margin. Deep-water slope-fan systems are extensive offshore Guyana and Suriname, forming the recently

discovered prolific hydrocarbon reservoirs, fed by sediment shed from the Guyana Shield. Shorter fan

systems exist along the French Guiana margin. By contrast, coeval major deep-marine systems are not

developed along the African margin, perhaps indicating sediment is trapped/stored in the onshore basin at

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this time, where a wide low relief basin from the shelf landward was established, forming wide facies belts.

Shoreface progradation is documented in northern Senegal (Ndiaye, 2012). Mixed systems interacted on

the distal shelf. Following establishment of the RCU, margin collapse mechanisms dominated deposition in

the basin, with the shelf margin becoming heavily canyonised. Canyons develop retrogressively eroding over

a kilometre into the underlying stratigraphy. Debris-rich lobes are recorded extensively offshore The Gambia

at the base-of-slope; mass transport complexes (MTCs) are present along the entirety of the margin

indicating massive slope instability (Fig. 4.7; Mourlot et al., 2018a). Climatic belts in the Late Cretaceous

shifted south by comparison to the Cenomanian interval, resulting in arid conditions extending across

Senegal; Sauders (2016) model shows the WAC source areas to be still positioned within the tropical climatic

belt.

6.3 SUMMARY

In summary, five Palaeogeographical maps are constructed for tectono-stratigraphic intervals defined in the

revised stratigraphic framework. These maps document our current understanding of southern Central

Atlantic continental margin evolution across the conjugate margins of northwest Africa and northeast South

America, based on findings from this thesis integrated with reviewed published material. With the

Cretaceous focus, the tectono-stratigraphic response of the opening Equatorial Atlantic, a major plate-scale

event is investigated. Spatio-temporal changes in sedimentary systems, margin architecture, siliciclastic

sediment input points and organic-enrichment are constrained at a regional scale. A source-to-sink style

approach links our findings to results from hinterland studies, to be further investigated by NARG. Additional

follow-on work can use these maps as models to be tested and further refined as data and results are

generated within the NARG Geodatabase.


Dave Cox and Jonathan Redfern are thanked for reviewing the content of this chapter.

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6.5 REFERENCES

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Bourne, M. et al., 2019. New plays in an exploration hotspot: AGC Profond, Senegal and Guinea Bissau. PESGB Africa E&P Conference, London 2019.

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Clayburn, J. 2017. Realising the deepwater hydrocarbon potential of Senegal. AAPG/SEG 2017 International Conference and Exhibition, London, England. Search and Discovery Article 70345.

Cunningham-Gray, A., Nicholson, U., Stow, D.A.V., Arnold, D., Underhill, J.R., Clayburn, J. and Cullen, B. 2018. Internal architecture and external geometry of sediment waves offshore Senegal. British Sedimentological Research Group 57th AGM.

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Envoi, 2015. Offshore Senegal / Guinea-Bissau AGC farm-in on behalf of Oryx Petroleum.

Erlich, R.N., Villamil, T. and Keens-Dumas, J., 2003. Controls on the deposition of Upper Cretaceous organic carbon–rich rocks from Costa Rica to Suriname.

de Figueiredo, JDJP, Zalán, PV and Soares, EF, 2007. Foz do Amazonas Basin. B. Geocience Petrobras , 15 , pp.299-309.


Friedrich, O. and Erbacher, J., 2006. Benthic foraminiferal assemblages from Demerara Rise (ODP Leg 207, western tropical Atlantic): possible evidence for a progressive opening of the Equatorial Atlantic Gateway. Cretaceous Research, 27(3), pp.377-397.

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Gouiza, M., Bertotti, G., Charton, R., Haimoudane, K., Dunkl, I. and Anczkiewicz, A.A., 2019. New Evidence of Anomalous' Vertical Movements along the Hinterland of the Atlantic NW African Margin. Journal of Geophysical Research: Solid Earth.


Gouyet, S., Unternehr, P. and Mascle, A., 1994. The French Guyana margin and the Demerara Plateau: geological history and petroleum plays. In Hydrocarbon and petroleum geology of France (pp. 411-422). Springer, Berlin, Heidelberg.

Guiraud, R., 1998. Mesozoic rifting and basin inversion along the northern African Tethyan margin: an overview. Geological Society, London, Special Publications, 132(1), pp.217-229.

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Hathon, E., 2018. The SNE Discovery Offshore Senegal-Moving a Frontier Basin to Emergent. In 80th EAGE Conference and Exhibition 2018 (Vol. 2018, No. 1, pp. 1-5). European Association of Geoscientists & Engineers.

Hu, X., Scott, R.W., Cai, Y., Wang, C. and Melinte-Dobrinescu, M.C., 2012. Cretaceous oceanic red beds (CORBs): Different time scales and models of origin. Earth-Science Reviews, 115(4), pp.217-248.

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Jobe, Z.R., Lowe, D.R. and Uchytil, S.J., 2011. Two fundamentally different types of submarine canyons along the continental margin of Equatorial Guinea. Marine and Petroleum Geology, 28(3), pp.843-860.

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Kosmos Energy, 2016 The Petroleum System of the Deepwater Mauritania / Senegal & the discovery of the Ahmeyim Field

Kosmos Energy, 2020. Yakaar-2 Appraisal Well Confirms World-scale Gas Resource Offshore Senegal, press release. Available at: [http://investors.kosmosenergy.com/news-releases/news-release-details/yakaar-2-appraisal-well-confirms-world-scale-gas-resource].

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Marzoli, A., Renne, P.R., Piccirillo, E.M., Ernesto, M., Bellieni, G. and De Min, A., 1999. Extensive 200-million-year-old continental flood basalts of the Central Atlantic Magmatic Province. Science, 284(5414), pp.616-618.



Mourlot, Y., Roddaz, M., Dera, G., Calvès, G., Kim, J.H., Chaboureau, A.C., Mounic, S. and Raisson, F., 2018. Geochemical Evidence for Large‐Scale Drainage Reorganization in Northwest Africa during the Cretaceous. Geochemistry, Geophysics, Geosystems, 19(5), pp.1690-1712.

Ndiaye, M., 2012. Etude sismostratigraphique et sédimentologique du Bassin Sénégalo-Mauritanien dans le secteur de Diourbel et Thiès (Doctoral dissertation, University of Geneva).

Nzoussi-Mbassani, P., 2003. Le Cénomano-Turonien de l'Atlantique Nord (bassin du Sénégal): environnement de dépôt et évolution diagénétique (Doctoral dissertation).


Pindell, J.L., 1985. Alleghenian reconstruction and subsequent evolution of the Gulf of Mexico, Bahamas, and proto‐Caribbean. Tectonics, 4(1), pp.1-39.

Sapin, F., Davaux, M., Dall'Asta, M., Lahmi, M., Baudot, G. and Ringenbach, J.C., 2016. Post-rift subsidence of the French Guiana hyper-oblique margin: from rift-inherited subsidence to Amazon deposition effect. Geological Society, London, Special Publications, 431(1), pp.125-144.

Sauders, C. 2016. North-west Africa, Africa’s New Hot Spot? Neftex Exploration Insights.

Sømme, T.O., Helland‐Hansen, W., Martinsen, O.J. and Thurmond, J.B., 2009. Relationships between morphological and sedimentological parameters in source‐to‐sink systems: a basis for predicting semi‐quantitative characteristics in subsurface systems. Basin Research, 21(4), pp.361-387.

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7 Conclusions

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The evolution of the continental margins of northwest Africa and northeast South America surrounding the

southern Central Atlantic have been investigated by integrating a variety of new datasets and multi-

disciplinary techniques.

7.1.1 Central Atlantic Stratigraphic Framework

Previous and ongoing NARG research to develop a Central Atlantic stratigraphic framework has been

extended from key well-calibrated reference outcrop sections in Morocco to the Central Atlantic. The

principle objective driving this research is the poor applicability of Tethyan and Boreal frameworks to the

study area. Three exploration wells, seven scientific boreholes and outcrop localities across the island of

Maio, Cape Verde have been re-sampled and analysed. This is supplemented with re-analysis of previously

published material in order to leverage as much biostratigraphic information out of these data. Calcareous

nannofossil, ammonoid, foraminifera, calpionellid and palynology dating have been fully integrated to

provide a much greater age-resolution than previously published. The application of these techniques was

primarily dependant on the sedimentary facies. Although microfossil biostratigraphy has been relied upon

due to the dominant data type being cuttings and core. Uncertainties still remain primarily due to data

limitations (core gaps/sampling program) and the resolution of key bio-events (i.e. correlation to the

reference sections outside Morocco), these have been quantified where recognised. Through this work, it is

clear that various chronometers experience endemism and therefore local zonations are required. These

have been established for the oceanic domain of the Central Atlantic (Maio and DSDP sites) and northeast

South American continental margin.

Key biostratigraphic findings are summarised below:

- Basal ages of two of the key Central Atlantic sections, Maio and well A2-1 (Demerara Rise) have

been considerably revised from the original Jurassic interpretations, to Lower Valanginian and

Tithonian, respectively. This has important consequences for the potential of a Central Atlantic

Jurassic-aged organic-rich interval, plate models and palaeogeographical reconstructions of the

early Central Atlantic.

- Aptian-aged strata are rarely recovered from studied sections, either due to primary data recovery,

post-depositional erosion associated with the base Albian unconformity and/or a basin-wide hiatus.

- The carbonate-siliciclastic transition within the northwest African oceanic domain occurs at the

Aptian-Albian boundary. This event occurs slightly earlier at the base of the Aptian along the

northeast South American margin (Guyana-Suriname basin). In both cases the demise of the Lower

Cretaceous carbonate platform is associated with the first significant siliciclastic sediment influx and

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establishment of siliciclastic-dominated depositional systems, whether this is a causal relationship

remains to be demonstrated and investigated in detail.

- The onset of marine type organic-enrichment within the studied area of the Central Atlantic occurs

within the Late Albian (nannofossil zone NC10a), this event is well documented in all studied wells,

boreholes and sections. High levels of organic-enrichment (discussed below) persist into the latest

Cenomanian (offshore Senegal, DSDP Site 367), earliest Turonian (offshore Mauritania, DSDP Site

368) and Coniacian to Santonian (Guyana-Suriname basin).

- Major unconformities are identified during the Middle Berriasian (type locality – DSDP Site 367),

base Albian (A2-1), intra Late Albian (ODP Site 1258C), base Cenomanian (ODP Site 1258C/A2-1)

and Middle Campanian (ODP Site 1258C). Additional events may be recognised with access to

additional data in different settings. Despite some of these unconformities only being identified in

one or more studied sections, seismic stratigraphy allows their extent and impact on continental

margin evolution to be realised, and where possible correlated with other published sections to

understand the geographical distribution.

Our comprehensive study of the Mesozoic oceanic domain stratigraphy exposed on Maio provides a modern

and critical revision. Globally, there are very few opportunities to study sediments deposited on the ocean

floor at outcrop after exhumation, especially those of Mesozoic age, only in obduction or oceanic volcanic

island settings. The findings can be used to calibrate the evolution of oceanic volcanic islands formed in intra-

plate settings and create a new age model for the oceanic domain of the. Central Atlantic. Dating of new

material reveals the oldest sedimentary strata on Maio, i.e. basal facies of the Morro Fm. is Lower

Valanginian in age, resting conformably on oceanic crust pillow basalts (Batahla Fm.). The deep-water pelagic

limestones of the Morro Fm. extend through the upper Hauterivian, becoming more marl-rich (upper

transitional unit), reflecting increased terrigenous input into the deep basin until early upper Barremian

times. A major unconformity separates carbonate- and siliciclastic-dominated lithologies, Albian-aged

Carquiejo Fm., containing bleached black shale facies and distal turbidites.

7.1.2 Continental Margin Evolution

Using a combination of the lithological data (facies analysis from well and outcrops), regional 2D and 3D

seismic data (seismic stratigraphy/geomorphology) has helped characterise the Mesozoic depositional

systems within the Central Atlantic, synthesised in five palaeogeographical reconstructions. The location of

3D seismic data offshore The Gambia critically images the shelf to basin floor transition, a key position within

the source-to-sink system and a highly prospective region from a hydrocarbon exploration perspective.

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Regional seismic data reveals seaward dipping reflectors (SDRs) northwest of the Guinea Plateau, reported

here for the first time on the African margin. This further demonstrates significant volcanic addition during

early seafloor spreading within the Central Atlantic and links with the occurrences of SDRs documented

below the Demerara Rise and on the eastern US Atlantic margin in Carolina Trough and Blake Plateau. The

SDRs on the African margin are on-trend with the African Blake Spur magnetic anomaly (ABSMA) perhaps

indicating this feature is related to the location of SDRs.

Post-rift pelagic sediments accumulated in the Central Atlantic oceanic domain outboard of the major

carbonate platform until the arrival of a shelf edge delta system during the Early Albian (offshore The

Gambia). This system fed a sand-rich base-of-slope apron and distal turbidites at the foot of the carbonate

escarpment margin. A clear correlation between the active shelfal depositional systems and response within

the oceanic domain is established using the stratigraphic framework and regional seismic profiles.

Shelf margin collapse is documented on both margins during discrete periods within the Cretaceous, this is

associated with submarine canyonisation (The Gambia) and subsequent creation of seabed topography

capable of controlling overlying deep-water sedimentary systems (Guyana). The major margin collapses off

the Demerara Rise and conjugate Guinea Plateau have a combined spatial extent of over 1000 km2. Early

canyonisation of the carbonate escarpment offshore The Gambia occurred due to downslope flowing

turbidity currents originating from the shelf edge delta, and later amplified by retrogressive failure. Our

findings conclusively support a submarine model for the canyonisation, previously considered to be

subaerial.

Through quantified seismic geomorphology, two submarine lobe types in base-of-slope settings are

differentiated offshore The Gambia related to the abundance of carbonate debris from the eroded

escarpment. These recognition criteria were used to provide an estimate of the amount of intra- versus

extra-basinal sediment input into the basin. Quantitative seismic geomorphology shows that the average

volume of sediment transported through shelf-incised canyons is an order of magnitude higher than the

slope-confined systems. Few studies document the seismic geomorphology of buried escarpment margins

and holistically analyse both the canyon features and deposits at the terminus of canyons to understand

their spatio-temporal evolution. Additionally, techniques from hydrogeology were adapted for use in

geospatially mapping the submarine canyon system drainage. This integrated and quantitative methodology

analysing source-to-sink systems is exportable to other datasets in the study of submarine canyon systems

and their deposits.

Through the palaeogeography maps, major basinal depocentres are identified linked to several palaeo-river

systems suggestive of the antecedent and long-lived nature of these fluvial systems. Margin architecture,

which can be inferred to be related to the underlying basement terranes, is postulated as one of the principal

controls on the geometry and location of siliciclastic depositional systems (i.e. deltas, fans). This work

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contributes to the knowledge of spatial heterogeneities and segmentation of continental margins, linked to

underlying basement and structural inheritance.

7.1.3. Geochemical Analysis

Geochemical and sedimentological analysis of 110 mudstone samples reveals heterogeneities within the

main latest Albian to Cenomanian/Turonian organic-rich interval, one of the key source rock candidates

within the Central Atlantic. Pyrolysis results reveal the varying nature of the organic matter, related to

temporal and spatial variations in terrigenous sediment input, oceanic conditions and palaeogeography

indicating the internal complexity of this sequence. Deeper and older organic-rich intervals form isolated

horizons within the Lower Cretaceous stratigraphy that have terrestrially derived organic matter that thicken

towards the continental margin and have gas-prone source rock potential. Well A2-1 on the Demerara Rise

was used as evidence for a Jurassic source rock within the Central Atlantic, however our new analysis shows

only minor organic-enrichment (<1% TOC). Hence, no Jurassic source rock has been penetrated thus in the

southern Central Atlantic.

7.1.4. Unconformity Development

Several super-regional Cretaceous unconformities have been identified with enhanced dating during this

work from biostratigraphy and seismic interpretation, extending in some cases over 1000 km across the

studied area of the Central Atlantic. Some of these appear to be more local features or restricted to one

domain (i.e. the regional composite unconformity – RCU), whereas most appear to be regional in extent,

with profound but differing character and implications throughout the basin.

Using structural restorations, the base Albian unconformity recognised on the Demerara Rise is linked to a

major transpressional tectonic phase within the opening Equatorial Atlantic system, forming a suite of

compressional features and peneplaning up to 1 km of sediment. Structural and stratigraphic effects

diminish from this epicentre on the Demerara Rise into the Central Atlantic, but still impact the stratigraphic

response in the oceanic domain and are causally linked to exhumation in the hinterland. Deformation and

hiati are not restricted to the continental domains, palaeohighs and intra-oceanic deformation is

documented. In this example, rejuvenated tectonic stresses associated with the opening Equatorial Atlantic

are key drivers in the tectono-stratigraphy. Further work on the conjugate US margin will test how far the

effects of the opening Equatorial Atlantic can be discerned. The RCU that records the submarine collapse of

the distal continental margin of northwest Africa, appears to be driven by far-field tectonic activity and

amplified by erosion during lowstand periods of relative sea-level.

Further insights into the timing and nature of the opening western end of the Equatorial Atlantic can be

discerned from the results of the stratigraphic framework integrated with structural models. Continental

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breakup between the Demerara Rise and Guinea Plateau is associated with the base Cenomanian

unconformity, identified for the first time in this study on the Demerara Rise. Prior to this major plate-scale

‘unlocking’ event, oceanic crust had begun to form within the final Equatorial Atlantic rift segment offshore

French Guiana. Furthermore, a marine connection between the Central and Equatorial Atlantic is

demonstrated by middle Late Albian times, this was established over a relatively shallow Demerara-Guinea

arch.

7.2 FUTURE RESEARCH

A brief overview of areas for future research in the Central Atlantic is provided below.

7.2.1 Sediment provenance of sands in the Senegal basin

Through the numerous sampling campaigns of DSDP core, Senegalese exploration wells (Petrosen) and in

the field (Cap de Naze, Cap Rouge), sand-grade material was sampled. Using this data, the principle aims of

would be to investigate any temporal and spatial shifts in sediment provenance using heavy mineral analysis,

characterise the sedimentology and use this to develop source-to-sink models for the margin. Mudstone

samples taken from the DSDP cores (sites 367 and 368) should be analysed for clay minerology studies to

discern provenance switches in the deep basin and climatic controls. Scaling relationships could also be

applied to calculate drainage size, deep-water depositional system length, river length etc. (i.e. Sømme et

al., 2009). Sands have also been sampled from the South American wells so an extension of this study is

possible to compare the signatures of the WAC and Guyana Shield.

7.2.2 Geophysical studies of the MSGBC basin

With increased access to seismic datasets within the MSGBC basin regional isopachs and seismic mapping

will help to characterise the major depocentres and margin architecture and will be useful in refining the

GDE maps presented in this chapter. Additional areas to investigate are as follow:

- Comparison of shelf margin evolution documented offshore The Gambia (Chapter 4) with the

remainder of the margin.

- Structural-focussed study investigating the distal effects of Equatorial Atlantic tectonism, i.e.

faulting, tilting of the carbonate platform, folding at the base-of-slope, karstification of the platform.

- Basement characterisation and definition of a structural domain framework.

- Investigation into the demise of the Lower Cretaceous carbonate platform; did Albian siliciclastic

influx lead to collapse of carbonate sedimentation?

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- A continued investigation into the results discussed in the synthesis where margin architecture is

recognised to be a major control on the overlying sand-rich depositional systems during the Albian-

Cenomanian. Examining and characterising the sediment input points, i.e. palaeo-Senegal versus

palaeo-Gambia river systems will help to understand the spatial heterogeneities in depositional

systems and associated hydrocarbon reservoirs along the margin.

7.2.3 Regional megasequence characterisation of the US Atlantic margin

During the authors PhD project, sampling of DSDP sediment cores from the US Atlantic margin was

performed (DSDP sites 101A, 105A, 390 and 534A), albeit only partially worked up (Chapter 3). Further work

across the Central Atlantic could be performed, using well and seismic data to characterise the

megasequence and stratigraphic framework and comparing to the two margins studied.

7.2.4 Re-examination of Mesozoic outcrops at Cap de Naze & Cap Rouge

As reported in the introduction of the thesis, the initial field work for this study has been performed and

samples, logs and a photogrammetry dataset collected. Further work, refining the stratigraphic

interpretation of Tessier et al. (1952), Khatib et al. (1990) and Barusseau et al. (2009), and correlating with

the Senegalese exploration wells would improve the characterisation of the Late Cretaceous interval and its

potential as a viable hydrocarbon reservoir.

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Documents

Tectono-stratigraphic evolution of the Mesozoic continental