Depositional History anD paleogeograpHy of tHe Jurassic

Depositional History anD paleogeograpHy of tHe Jurassic plover formation in calliance anD Brecknock fielDs, Browse Basin, nortH

west sHelf, australia

Federico Tovaglieri

This thesis is presentedfor the degree of

Doctor of Philosophy

to The University of Western AustraliaSchool of Earth and Environment

Submitted January 2013

Supervisors:

Prof. Annette GeorgeW/Prof. Mike Dentith

Dr Jennifer Wadsworth

i

Statement of candidate contribution

This thesis is my own original composition except where referenced. It contains no mate-

rial which was been accepted for the award of any degree or diploma in any university

and it is based on openfile data only. Part of Chapters 2, 4, 5 and 6 (with minor modifica-

tions to their present form) were included in the following paper submitted to Sedimentol-

ogy in May 2012 (currently under revision):

Tovaglieri F. and George A.D. (submitted) Stratigraphic architecture of an Early–Middle

Jurassic tidally influenced deltaic system: Browse Basin, Australian North West Shelf.

(I collected and analysed all the data and undertook the bulk of the interpretation, synthe-

sis and manuscript preparation (85%))

Part of Chapter 6, 7 and 8 (with minor modifications to their present form) will be in-

cluded in the following paper:

Tovaglieri F., Jones T., George A.D., Zwingmann H. (in preparation) Depositional His-

tory of the Early to Middle Jurassic deltaic reservoirs in Calliance and Brecknock fields

(Plover Formation), Browse Basin, North West Shelf, Australia.

(Data collection, analysis, interpretation and synthesis and manuscript preparation by me

(70%), Toby Jones (15), Annette D. George (10%) and Horst Zwingmann (5%))

Material presented in Appendix 4 represents an extract from the Honour Thesis of Mr.

Toby Jones (Jones, 2012) and it has been reproduced with the permission of the author.

Federico Tovaglieri

Candidate

Professor Annette D. George

Supervisor

University of Western Australia

January 2013

ii

iii

abStract

The Early to Middle Jurassic Plover Formation in the Browse Basin (Australian North

West Shelf) hosts reservoirs currently targeted for gas exploration and development. The

depositional history and paleogeographic evolution of the Plover Formation in the Cal-

liance and Brecknock fields has been established within a sequence-stratigraphic frame-

work through integrated sedimentological analysis of core and borehole image and wire-

line log analysis incorporating biostratigraphic and seismic data.

Seven siliciclastic and one volcano-sedimentary facies associations have been identified

through facies analysis of core and interpreted as fluvial channel-fill (FA0), tidally in-

fluenced channel- and tidal channel-fill complex (FA1-FA2), crevasse-splay and inter-

channel marsh (FA3), heterolithic mouthbar (FA4), sandy mouthbar (FA5) and offshore-

transition to offshore (FA6) depositional settings. These are associated with igneous and

volcaniclastic rocks (FA7) that are distributed at different stratigraphic levels. Evaluation

of borehole image fabric and interpretation of lithology from wireline log responses have

been used to distinguish fourteen image facies grouped into six image facies associations

(IFA0-IFA5). Paleocurrents obtained through image log interpretation show complex

distribution of unimodal, bimodal (and bipolar) and polymodal patterns. Core-based and

image log analysis have been used to interpret the depositional setting of the Plover For-

mation in the Calliance and Brecknock areas as a tidally influenced delta plain to delta

front. Sandstone composition indicates that sediments were derived from a mixed prov-

enance of recycled sedimentary and plutonic-metamorphic (cratonic) parent rocks. Igne-

ous units are concentrated in the lower part of the formation and have been interpreted

as extrusive flows, thus providing evidence for active volcanism during deposition. One

shallow subvolcanic intrusion has been interpreted in Calliance-3.

Facies association stacking patterns and integration with biostratigraphic data has been

used to identify key stratal surfaces and correlate stratal packages across the study area.

The surfaces bound five third-order sequences (S1 to S5). The three lower sequences S1,

iv

S2 and S3, are separated by a major unconformity (SB4) from overlying S4 and S5, cor-

responding to lower and upper Plover Formation respectively.

Analysis of seismic reflection data highlights the Triassic paleotopography and fault-con-

trolled depocentres. A large structural high in the central and northern parts of the study

area separated the Calliance and Brecknock deltaic settings during S1, S2 and S3. Major

transgressive phases during S2 and S3 were followed by progradational phases towards

the south and southwest in Calliance field and towards east and southeast in Brecknock

field. Volcanic vents active during this period have been interpreted to be located south-

west of Calliance-3 and northeast of Brecknock-4.

A major uplift event, interpreted at the base of S4, is associated with significant time gap

and flooding of the Brecknock structural high. Progradation of delta lobes during S4 and

S5 was dominantly south- and west-directed and occurred during a period of higher sub-

sidence rates that resulted in the accumulation of anomalously thick sandstone packages

that constitute the main gas reservoirs in the area. Retrogradational stacking of facies dur-

ing S5 records a phase of delta lobe abandonment over the entire study area.

v

vi

vii

Contents

statement of candidate contribution i

abstract iii

acknowledgments xvii

chapter 1 - introduction 1

1.1 Introduction .......................................................................................................... 1

1.2 Location of study area .......................................................................................... 2

1.3 Objective and aims ............................................................................................... 5

1.4 Materials and Methods ......................................................................................... 7

1.4.1 Core description and facies analysis .......................................................... 7

1.4.2 Image log analysis ...................................................................................... 8

1.4.3 Petrographic analysis ............................................................................... 10

1.4.4 Seismic analysis ....................................................................................... 10

1.4.5 Biostratigraphy ......................................................................................... 10

1.5 Thesis organization ............................................................................................. 11

chapter 2 - regional setting 13

2.1 Introduction ........................................................................................................ 13

2.2 Paleozoic extension ............................................................................................ 15

2.3 Triassic inversion ................................................................................................ 15

2.4 Jurassic extension ............................................................................................... 17

2.5 Cretaceous to Cenozoic thermal subsidence and inversion ................................ 19

2.6 Jurassic paleoclimate of the Browse Basin ........................................................ 20

2.7 Jurassic stratigraphy and paleogeography ......................................................... 21

chapter 3 - sedimentology 29

3.1 Introduction ........................................................................................................ 29

3.2 Core overview ..................................................................................................... 29

3.3 Ichnology ............................................................................................................ 33

viii

3.4 Sandstone composition ....................................................................................... 33

3.4.1 Detrital composition ................................................................................. 33

3.4.2 Diagenesis ................................................................................................ 39

3.4.3 Provenance ............................................................................................... 40

chapter 4 - facies analysis 43

4.1 Introduction ........................................................................................................ 43

4.2 Facies associations .............................................................................................. 43

4.2.1 FA0 ........................................................................................................... 43

4.2.2 FA1 ........................................................................................................... 44

4.2.3 FA2 ........................................................................................................... 50

4.2.4 FA3 ........................................................................................................... 50

4.2.5 FA4 ........................................................................................................... 54

4.2.6 FA5 ........................................................................................................... 55

4.2.7 FA6 ........................................................................................................... 57

4.2.8 FA7 ........................................................................................................... 58

4.3 Summary of siliciclastic facies associations ....................................................... 61

chapter 5 - image log analysis 65

5.1 Introduction ........................................................................................................ 65

5.2 Image facies and Image facies associations ....................................................... 65

5.2.1 IFA0 ......................................................................................................... 66

5.2.2 IFA1 ......................................................................................................... 66

5.2.3 IFA2 ......................................................................................................... 72

5.2.4 IFA3 ......................................................................................................... 78

5.2.5 IFA4 ......................................................................................................... 80

5.2.6 IFA5 ......................................................................................................... 83

5.5 Analysis and interpretation of Brecknock-1 ....................................................... 84

5.6 Structural dip correction and paleocurrent analysis ........................................... 86

5.7 Effectiveness of image logs for identifying facies and fabric variations ............ 87

ix

chapter 6 - stratal architecture 93

6.1 Introduction ........................................................................................................ 93

6.2 Depositional system ............................................................................................ 93

6.3 Surfaces and well correlation ............................................................................. 97

6.4 Sequence interpretation ...................................................................................... 98

6.4.1 Sequence 1 (S1) ....................................................................................... 98

6.4.2 Sequence 2 (S2) ..................................................................................... 102

6.4.3 Sequence 3 (S3) ..................................................................................... 105

6.4.4 Sequence 4 (S4) ..................................................................................... 107

6.4.5 Sequence 5 (S5) ..................................................................................... 108

6.5 Discussion ......................................................................................................... 109

6.5.1 Progradational and retrogradational trends ............................................ 109

6.5.2 Lowstand deltaic system of Sequence 3 ................................................ 109

6.5.3 Thickness of Sequence 4 ........................................................................ 112

6.5.4 Analogs .................................................................................................. 113

6.5.3 Igneous activity ...................................................................................... 115

chapter 7 - seismic analysis 117

7.1 Introduction ...................................................................................................... 117

7.2 Tectonic structures ............................................................................................ 117

7.3 Significant surfaces ........................................................................................... 118

7.3.1 Surface 1 ................................................................................................ 119

7.3.2 Surfaces 2 to 4 ........................................................................................ 120

7.4 Seismic Units .................................................................................................... 120

7.4.1 Seismic Unit A ....................................................................................... 121

7.4.2 Seismic Unit B ....................................................................................... 122

7.4.3 Seismic Unit C ....................................................................................... 124

7.5 Synthesis and conclusion .................................................................................. 125

x

chapter 8 - Depositional history and paleogeography 137

8.1 Introduction ...................................................................................................... 137

8.2 Depositional history and paleogeographic maps .............................................. 137

8.2.1 Sequence 1 ............................................................................................. 141

8.2.2 Sequence 2 ............................................................................................. 141

8.2.3 Sequence 3 ............................................................................................. 142

8.2.4 Sequence 4 ............................................................................................. 143

8.2.5 Sequence 5 ............................................................................................. 144

8.3 Discussion ......................................................................................................... 144

8.3.1 Paleogeography of the Brecknock-Scott Reef Trend ............................. 144

8.3.2 Early to Middle Jurassic rifting in the Browse Basin ............................ 145

chapter 9 - summary and conclusion 149

9.1 Introduction ...................................................................................................... 149

9.2 Depositional setting .......................................................................................... 149

9.3 Delta evolution and paleogeography ................................................................ 151

9.4 Recommendation for future work ..................................................................... 152

references 155

appendix 1 - well data 175

appendix 2 - petrographic descriptions 177

Brecknock-1 ............................................................................................................ 180

Brecknock-2 ............................................................................................................ 195

Brecknock-3 and Brecknock-4 ............................................................................... 221

Calliance-1 .............................................................................................................. 239

Calliance-2 .............................................................................................................. 259

Calliance-3 .............................................................................................................. 285

Brecknock South ..................................................................................................... 317

xi

Summary tables ...................................................................................................... 337

Appendix 3 - Enlarged summary figures 345

appendix 4 - composition of igneous units 359

enclosure 1 - core description and interpretation

enclosure 2 - image log interpretation

xii

xiii

List of Figures

1.1 The North West Shelf of Australia ............................................................................. 3

1.2 Simplified map of the Browse Basin ......................................................................... 4

1.3 Map of the study area ................................................................................................. 6

2.1 Simplified structural map of the Browse Basin ....................................................... 13

2.2 Schematic cross-sections ......................................................................................... 14

2.3 Late Triassic to Middle Jurassic geodynamic evolution .......................................... 16

2.4 Jurassic lithostratigraphic framework of the Browse Basin .................................... 20

2.5 Simplified regional geological cross-section of the Browse Basin .......................... 22

2.6 Lithostratigraphic correlation chart for Jurassic Formations ................................... 23

2.7 Paleogeographic maps of the Caswell Sub-basin .................................................... 25

3.1 Core photographs of rock types from cored intervals .............................................. 30

3.2 Core photographs of rock types from cored intervals .............................................. 31

3.3 Examples of trace fossil taxa in core ....................................................................... 34

3.4 Composition of examined sandstones ...................................................................... 37

3.5 Photomicrographs of sandstones .............................................................................. 38

3.6 Examples of diagenetic features in the sandstones .................................................. 39

3.7 Gamma-ray logs of Calliance and Brecknock well ................................................. 41

3.8 The QtFL and QmFLt plots to discriminate the tectonic setting ............................. 42

4.1 Core photographs of facies associations identified .................................................. 51

4.2 Core photographs of facies associations identified .................................................. 53

4.3 Heterolithic and sandy mouthbars ........................................................................... 56

4.4 Core photographs of FA7 ......................................................................................... 60

4.5 Gamma-ray logs, graphic core logs, facies, facies associations .............................. 62

4.6 Gamma-ray logs, graphic core logs, facies, facies associations .............................. 63

5.1 Image facies (IF) and image facies associations (IFA) ............................................ 69

5.2 Image facies (IF) and image facies associations (IFA) ............................................ 70

5.3 Example of IFA0 ...................................................................................................... 71

5.4 Example of IFA1 ...................................................................................................... 73

xiv

5.5 IFA1 in static and dynamic BHI data and core photos ............................................ 74

5.6 Example of IFA2 ...................................................................................................... 75

5.7 Example of IFA2 ...................................................................................................... 76

5.8 Example of IFA3 ...................................................................................................... 77

5.9 Example of IFA3. ..................................................................................................... 78

5.10 Examples of IFA4 .................................................................................................. 79

5.11 Examples of IFA5 .................................................................................................. 80

5.12 Examples of IFA5 .................................................................................................. 81

5.13 Examples of volcanic rock fabrics of IFA5 ........................................................... 82

5.14 Synthesis for Brecknock-1 of lithological data ..................................................... 85

5.15 Stereographic chart of dips from mudstone beds for Calliance-3 .......................... 88

5.16 Cumulative dip-azimuth vector plots. .................................................................... 89

6.1 Summary of facies associations and image facies associations ............................... 94

6.2 Summary of facies associations and image facies associations ............................... 95

6.3 Depositional model for the Plover delta in the study area ....................................... 96

6.4 Correlation panel .................................................................................................... 101

6.5 Correlation panel. ................................................................................................... 102

6.6 Cumulative dip-azimuth vector plots ..................................................................... 103

6.7 Cumulative dip-azimuth vector plots ..................................................................... 104

6.8 Chronostratigraphic chart of the Plover Formation ............................................... 110

6.9 Simplified subsidence curves for Calliance and Brecknock wells. ........................ 114

7.1 Area of coverage of the Brecknock 3D MSS (1997) ............................................. 118

7.2 Set of 2D seismic lines used in the present study .................................................. 119

7.3 Strike-oriented composite seismic line CL1 .......................................................... 127

7.4 Dip-oriented composite seismic line CL2. ............................................................. 129

7.5 Dip-oriented composite seismic line CL3. ............................................................. 131

7.6 Structural time maps .............................................................................................. 133

7.7 Isochore maps ........................................................................................................ 135

8.1 Chronostratigraphic chart of the Plover Formation ............................................... 138

8.2 Maps showing the interpreted paleogeographic evolution .................................... 139

xv

List of Tables

1.1 Overview of wells and data available ........................................................................ 9

2.1 Tectonic event history and associated tectonic regime ........................................... 18

3.1 Bioturbation Index (BI) .......................................................................................... 32

3.2 Types of trace fossils identified during core description. ......................................... 35

4.1 Facies identified during core analysis ...................................................................... 45

4.2 Distribution of Facies Associations . ....................................................................... 49

5.1 Image facies scheme ................................................................................................ 67

5.2 Image facies associations identified in the present study. ........................................ 68

5.3 Summary table comparing facies associations ........................................................ 84

5.4 Integration of BHI-derived paleocurrent trends ....................................................... 90

6.1 Classification of bounding surfaces adopted in this study ....................................... 98

6.2 Key stratal surfaces identified. ................................................................................. 99

xvi

xvii

acknowledgmentS

I would like to gratefully thank my main supervisor, Prof. Annette George, for having

given me the opportunity to come to UWA and do a PhD under her supervision. I also

thank her for the trust and support she had been giving me throughout all the phases of

my project. Without her constructive criticism and her professional editorial advice, this

thesis could have never been as it is now.

Thank you to Dr Jennifer Wadsworth, my external superivisor, for introducing me

to the fascinating world of the image log analysis and for advice on thesis chapters. Thanks

also to W/Prof. Mike Dentith, my co-supervisor, for advice on seismic interpretation

in Chapter 7. A special thanks to Woodside Energy Limited for sponsoring this project

and supplying the seismic and borehole image datas. Among Woodside people, special

thanks to Dr Keith Adamson, Dr Simon Lang, Mr Ben Peterson and Dr Neil Marshall for

vaulable discussions.

I am grateful for additional discussions on topics related to my PhD with

Muhammad Mudasar Saqab, Dr Julien Bourget, Dr Nick Timms, Prof. Bruce Ainsworth,

Prof. Joseph Lambiase and Dr John Backhouse. Thank you also to the technical staff

of the School of Earth and Environment, particularly to Lorraine Wilson and Christine

Riordan. A special thank you to Michael Djohan, for IT support.

Many thanks to my parents, Giannina and Gianfranco, and to my siblings, Tiziano

and Iris, who have been always supportive and emotionally close, in spite of the huge

physical distance which separates us. I would also like to thank Zhenlin Zhang, Shahar

Lazar, Zahra Seyedmehdi, Kirsten Dahl, Yinghui (Cathy) Cao, Carol Butland and Lucy

Layland for the friendship and scientific discussions during my PhD.

Finally, this work was supported by Advanced Logic Technology through provision

of the software WellCAD® which was a valuable tool during many phases of this project.

I also acknowledge the financial support of a UWA Scholarship for International Research

Fees (SIRF) and a University International Stipend (UIS) from the School of Earth and

Environment. Thanks also to Geoconferences and UWA Graduate Research School for

travel awards which allowed me to attend the 2012 AAPG ICE at Long Beach (CA).

xviii

1

Chapter 1 - IntroduCtIon

1.1 Introduction

The North West Shelf (NWS), located along the northwestern coast of

Western Australia, is one of the few regions in the world where significant new petroleum

discoveries continue to be made (Geological Survey of Western Australia, 2011).

Petroleum discoveries in the 1980s and ongoing exploration resulted in oil and gas sales

of $18.8 billion in 2009 with the NWS firmly established as Australia’s premier oil and

gas province. (Geological Survey of Western Australia, 2011). The NW-trending NWS

province is composed of the Northern Carnarvon, Offshore Canning (Roebuck), Browse

and Bonaparte basins, and the Timor-Banda Orogen (Longley et al., 2002; Fig. 1.1).

The Browse Basin has been the site of petroleum exploration since 1963 and was

the last basin on the NWS to be explored. Successful gas discoveries in fields such as

North Scott Reef and Brecknock provided impetus for better geological understanding

of the basin and subsequent work on its structural setting, stratigraphy and petroleum

potential based on seismic and drilling data (e.g. Allen et al., 1978; Bradshaw et al.,

1988; Willis, 1988; Stephenson & Cadman, 1994; Symonds et al., 1994; Maung et al.,

1994; Blevin et al., 1998; Struckmeyer et al., 1998; Symonds et al., 1998; Longley et al.,

2002; Brincat et al., 2004; Kennard et al., 2004). Although these studies have provided

considerable information regarding overall basin history, the Browse Basin remains at

the frontier of petroleum exploration (e.g. Longley et al., 2002; Keall & Smith, 2004;

Geological Survey of Western Australia, 2011; Lisssn & He, 2012).

The Jurassic sandstone-dominated Plover Formation hosts the reservoirs currently

targeted in the Browse and Bonaparte Basins (Blevin et al., 1998; Longley et al., 2002;

Ambrose, 2004; Lisssn & He, 2012). It is interpreted as a series of deltaic systems

developed along the northern margin of the Gondwanan Supercontinent at the time of

breakup (Longley et al., 2002; Jablonski & Saitta, 2004; Ainsworth et al., 2008).

Sand-dominated, syn-rift deltas are widely recognized as complex systems in

which deposition is controlled by interplay of sediment supply, wave, tide and fluvial

Introduction - Chapter 12

processes and active tectonics (e.g. Ravnås & Steel, 1998; Bhattacharya, 2006; Gani &

Bhattacharya, 2007; Dalrymple & Choi, 2007; Ainsworth et al., 2011). Understanding

the internal stratigraphic architecture of these systems is critical to a proper assessment

of reservoir architecture and potential development of reservoir models. In the case of

the Plover Formation in the Browse Basin, relatively little has been published on its

stratigraphic architecture and evolution (e.g. Stephenson & Cadman, 1994; Blevin et

al.,1998; Keall & Smith, 2004; Ainsworth et al., 2008). Moreover, the relative scarcity

and uneven distribution of wells in the Browse Basin, with respect to its large size, means

that confident spatial correlation of the various sand bodies (i.e. potential reservoirs) has

been limited to date. A much better understanding of paleogeographic evolution during

deposition of the Plover Formation is, therefore, needed (Blevin et al., 1998; Longley et

al., 2002 ).

Finally, many studies highlighted similarities in the stratigraphic evolution of

large deltaic systems developed during rifting (e.g. Ravnås & Steel, 1998; Lambiase &

Morley, 1999; Young et al., 2002). This means that the knowledge gained from a thorough

study of a large system like that of the Plover Formation has the potential to be useful to

better understand the evolution of other synrift deltaic systems of interest in petroleum

exploration.

1.2 Location of study area

The Browse Basin lies entirely offshore in the southern Timor Sea region, over an

area of approximately 140,000 km2 (Hocking et al., 1994; Baillie et al., 1994 Struckmeyer

et al., 1998; Fig. 1.1). Major regions surrounding the Browse Basin are the Kimberley

Craton to the east and the Argo Abyssal Plain to the west (Fig. 1.2). The basin is contiguous

with the Rowley Sub-basin to the southwest (Fig. 1.1) and with the Ashmore Platform,

Vulcan Sub-basin and Londonderry High of the Bonaparte Basin to the northeast (Fig.

1.2).

Internal subdivision of the Browse Basin (Fig. 1.2) is based on the terminology

introduced by Willis (1988), Elliot (1990), O’Brien et al. (1993), Hocking et al. (1994),

Symonds et al. (1994) and Struckmeyer et al. (1998). The southeastern boundary of the

basin is defined by a series of shallow basement elements, namely the Prudhoe Terrace,

Chapter 1 - Introduction 3

Figure 1.1 The North West Shelf of Australia illustrating the location and extent of the Northern Carnarvon, Roebuck, Offshore Canning, Browse and Bonaparte Basins (from Mantle & Riding, 2012). Rw: location of Rowley Sub-basin.

and Yampi and Leveque Shelves. The central Browse Basin has two major depocentres,

the Caswell and Barcoo sub-basins (Fig. 1.2). The outboard, deep water part of the basin

is the Scott Plateau, underlain by the Scott and Seringapatam Sub-basins, the boundaries

of which are poorly understood but probably extend to the Timor Trough (Struckmeyer

et al., 1998).

The Caswell Sub-basin is the major depocentre of the Browse Basin and is

separated to the south from the Barcoo Sub-basin by a major NNE-trending structural

zone, the Buffon-Brecknock-Scott Reef anticlinal trend (Struckmeyer et al., 1998; Fig.

1.2). The Carboniferous to Holocene stratigraphic succession in the Caswell Sub-basin

is ~15 km thick with up to 1.5 km of Early to Middle Jurassic strata (Struckmeyer et al.,

1998).

The study focuses on the Plover Formation of the Calliance and Brecknock fields

located in the Caswell Sub-basin on the Brecknock-Scott Reef Trend (Fig. 1.2). The study

area is approximately 400 km northwest of Broome and 40 km south-southwest of Scott

Rw


Figure 1.2 Simplified map of the Browse Basin showing major sub-basins (from Geoscience Australia, 2011; after Struckmeyer et al., 1998). Basin is bounded by Kimberley Craton, by structural elements of the Bonaparte Basin to the north and by Rowley and Oobagooma Sub-basins of the Roebuck and Offshore Canning Basins respectively to the south.


Reef, on the edge of the Australian continental shelf (Fig. 1.2).

Brecknock and Calliance fields consist of four wells each and are operated by

Woodside Energy Limited and their joint venture partners (Fig. 1.3). Brecknock field was

discovered in 1979, with the well Brecknock-1, whereas Calliance field was discovered

in 2000 after drilling of Brecknock South-1. The Plover Formation was the main target

and was intersected in both fields at a depth varying from 3830 to 3900 m below Rotary

Table (mRT) (Tab1e 1.1).

Seismic data show that the target structures for both fields are faulted anticlines.

The Plover Formation in Calliance field is approximately 200-450 m thick, whereas in

Brecknock field it is approximately 50-130 m thick. In Calliance field, Calliance-1 is the

only well that intersects the entire thickness of the Plover Formation. The other wells

(Calliance-2, Calliance-3 and Brecknock South) reach different depths within the lower

part of the formation. In contrast, in Brecknock field all the wells reach and penetrate

the Triassic strata (>20 m). No core was taken in Brecknock-1 and Brecknock South,

whereas in Brecknock-2 and -3 core stops before reaching the top of the Formation. Core

from Brecknock -4 encompasses the whole Formation thickness, although in this well

the uppermost part of the Formation is truncated by a fault. Cores from Calliance wells

encompass only the upper 167-226 m of the Formation, leaving the lower part uncored.

1.3 Objective and aims

A detailed study of the stratigraphy and sedimentology of the Plover Formation

in two Browse Basin fields is the focus of this thesis. The objective is to establish the

depositional history and paleogeographic evolution of the Jurassic deltaic system on the

Brecknock-Scott Reef Trend, on the western margin of the Caswell Sub-basin. Integration

of datasets such as core, image and wireline log data and seismic data represents a

key factor in this project. To fulfil the project objective, the following aims have been

identified.

1. Detailed logging of drill cores to identify stacking patterns and key stratal

surfaces, and to characterize the igneous and volcaniclastic intervals.


WA-275-P

WA-28-R

WA-275-P WA-28-R

WA-397-PWA-31-R

WA-396-P

WA-29-R

WA-32-R

TR/5

Calliance-3Calliance-1

Calliance-2Brecknock S.

Brecknock-2

Brecknock-1

Brecknock-3

Brecknock-4

Snarf-1

0 10 20 km121°30'0˝E 122°0'0˝E

121°30'0˝E 122°0'0˝E

14°30'0˝S

14°30'0˝S

N

LegendBlocks

Gas fields

Figure 1.3 Map of the study area showing the location of the wells in the Calliance and Brecknock fields.

2. Facies analysis to establish the lateral extent and vertical evolution of the

siliciclastic facies associations and interpret depositional environments.

3. Detailed image logs analysis and interpretation to determine large scale stacking

patterns, paleocurrent directions as well as correlations and to interpret facies

associations in uncored part of the wells.

4. Petrographic analysis on selected samples in order to determine compositional

variation and to establish likely source terrains.

5. Integration of all sedimentological and image data sets with seismic and

biostratigraphic data available and development of a depositional model and

palaeogeographic maps, highlighting the lateral and vertical distribution of

reservoir sands.


1.4 Materials and Methods

This study integrates sedimentological analysis of drillcore (providing direct

physical information) and interpretation of borehole image log (BHI) which enables

broader interpretation of uncored intervals in wells (e.g. Bourke, 1992; Bal et al., 2002;

Xu et al., 2009; Prosser et al., 1999; Donselaar & Schmidt, 2005). Similar studies that

integrate image logs with other geological and geophysical datasets have been undertaken

and the importance of image logs as a powerful interpretation tool has been highlighted

(e.g. Russel et al., 2002; Khan et al., 2004; Prioul & Jocker, 2009; Lacazette, 2009).

However, the complexity of image signal can easily lead to over- or mis-interpretation

(e.g. Xu, 2007; Slatt & Davis, 2010) and effective interpretation of image facies in

uncored wells remains problematic. Seven wells in the Calliance and Brecknock fields

of the Browse Basin have good quality BHI through a significant thickness of Plover

Formation (Table 1.1). These data provide an excellent opportunity to investigate the

value of image log analysis and its application to uncored intervals through definition of

image facies and image associations directly comparable to those defined from core.

Integration of well data with biostratigraphic and seismic data is also used in

this study to strengthen the interpretation and to extend the correlation between fields.

This approach has been proven valuable in other studies aimed to establish a sequence-

stratigraphic framework as a basis for paleogeographic reconstruction (e.g. Krassay &

Totterdel, 2003; Snedden & Sarg, 2008).

An important aspect considered was the quality of the data available, with

particular reference to image logs and cored intervals. Open file data from Department

of Mines and Petroleum (DMP) were used in this project. These include core photos and

well completions reports.

1.4.1 Core description and facies analysis

Descriptions of cored intervals in Calliance-1, Calliance-2 and Calliance-3 and

Brecknock-2, Brecknock -3 and Brecknock -4 (732 m total length) were undertaken at

Department of Mines and Petroleum Core Library, in Carlisle, Perth, using a logging

scale of 1:50 and WellCAD® software to record observations. Side-wall core were


examined where core was not available (Brecknock-1). Core was logged to document

sedimentological and ichnological features and then, facies analysis and identification

of important stratal surfaces was carried out. Facies analysis has been used to interpret

depositional environments for reconstruction of the deltaic system. Particular attention

has been paid to identification of unconformities and other important stratal surfaces for

intra- and inter-field correlations between wells in a field and between fields.

1.4.2 Image log analysis

Good to excellent quality borehole image (BHI) logs from Calliance and

Brecknock wells, provided by Woodside Energy Limited (WEL), were analysed in order

to extend facies analysis to uncored part of the wells via identification of image facies

and to extract paleocurrent information. Image analysis was performed on Fullbore

Formation MicroImager (FMI) logs from Brecknock-2, -3, -4, Calliance-1, -2, and -3, and

on a Formation MicroScanner (FMS) log from Brecknock South. Following conventional

analytical procedure for image logs (e.g. Bourke, 1992; Rider, 2002; Donselaar & Schmidt,

2005), both statically and dynamically normalized images were analysed and interpreted

using Recall® software at WEL, in conjunction with interpretation of a standard suite of

open-hole wireline logs (e.g. gamma-ray, neutron-porosity, density, photoelectric factor).

Core and wireline log data were used to calibrate the statically normalised image

logs. Identification of image lithology was undertaken on the basis of direct observation

on core and defined by the signatures of a number of wireline logs. Where cored material

was not available, log responses were used to discriminate lithology. Identification of

image fabric, i.e. the spatial arrangement and orientation of the elements or ‘features’

of a borehole image (Bal at al., 2002), may be locally subjective (e.g. Slatt and Davis,

2010) so broad classes of features have been used in this study to minimise potential

over-interpretation. The magnetometer data from the FMI orientation sonde was useful

for identifying magnetic anomalies associated with igneous rock types.

Bedding surfaces, cross-bedding and other planar features visible in borehole

images were manually picked, classified and interpreted using Recall® software. Structural

tilt has been determined by analysing dips from imaged mudstone intervals as the best


Tabl

e 1.

1 O

verv

iew

of C

allia

nce

and

Bre

ckno

ck w

ells

and

dat

a av

aila

ble

for t

he p

rese

nt st

udy.

A m

ore

com

preh

ensi

ve ta

ble

is p

rese

nted

in A

ppen

dix

1. A

bbre

viat

ions

: mRT

, m

eter

s bel

ow ro

tary

tabl

e; F

MI,

Fullb

ore

Mic

roIm

ager

; FM

S, F

orm

atio

n M

icro

Sca

nner

.

Wel

lC

allia

nce

3C

allia

nce

1C

allia

nce

2Br

eckn

ock

Sout

hBr

eckn

ock-

1Br

eckn

ock-

2Br

eckn

ock-

3Br

eckn

ock-

4La

titud

e (d

eg)

-14.

5310

278

-14.

5394

083

-14.

5739

625

-14.

6050

649

-14.

4355

692

-14.

4446

5-1

4.39

4408

3-1

4.36

28Lo

ngitu

de (d

eg)

121.

4981

389

121.

5533

083

121.

5789

275

121.

6403

1612

1.67

3773

112

1.64

2261

112

1.64

3558

312

1.65

94To

tal m

easu

red

dept

h (m

RT)

4262

4178

4188

4008

4300

3872

3948

3971

TD u

nit

Low

er P

love

r Fm

.Tr

iass

icLo

wer

Plo

ver F

m.

Low

er P

love

r Fm

.Tr

iass

icTr

iass

icTr

iass

icTr

iass

icPl

over

Fm

. thi

ckne

ss

(m)

>443

.636

5.5

270.

615

6.3

166

128.

1743

.65

52.5

9

Cor

ed P

love

r Fm

. (t

hick

ness

- m

)22

6.67

193.

3516

7.63

none

none

121.

439

.47

52.5

9

Imag

e lo

g ty

peFM

IFM

IFM

IFM

Sno

neFM

IFM

IFM

IIm

aged

Plo

ver F

m.

(thi

ckne

ss -

m)

443.

636

5.5

270.

615

6.3

166

128.

1743

.65

52.5

9

Wel

l log

sw

irelin

ew

irelin

ew

irelin

ew

irelin

ew

irelin

ew

irelin

ew

irelin

ew

irelin

e


indicators of deposition on an approximately horizontal surface. Abnormally steep dip

values were subtracted where required to correct post-depostional deformation. Structural

tilt correction was needed only for the lower part of Calliance-3, where 2.7° (dip) and

250° (azimuth) were subtracted to the interval from 4036 m to 4259 m. Dips of cross-beds

>5º from imaged sandstone intervals from each well have been used to generate statistical

plots, e.g. rose plots and azimuth vector plots (walkout plots), to determine mean azimuths

and, subsequently, unimodal, bimodal/bipolar or polymodal data distributions.

1.4.3 Petrographic analysis

Petrographic analysis of selected sandstones was undertaken to describe detrital

composition and to determine sediment provenance. Existing sandstone thin sections

from wells (held by WA Department of Mines and Petroleum) were examined using

conventional petrological microscopy (Nikon 50i polarising microscope with Nikon

camera attachment and image capture software).

1.4.4 Seismic analysis

Forty-four 2D seismic reflection lines from Brecknock 3D MSS (1997) and

Brecknock South 3D MSS (1999) surveys, covering an area of 1800 Km2, were collected

from Woodside Energy Limited and analysed using Kingdom Suite®. Seismic interpretation

was used to identify larger scale stratal geometry and highlight the paleotopography at the

time of Plover deposition. Depth structure maps and isochore maps were constructed and

used as a base for the paleogeographic maps.

1.4.5 Biostratigraphy

Biostratigraphic data from the wells is provided in well completion reports on

WAPIMS. Data were incorporated in this study to build correlations based on coeval

ages of strata. The biostratigraphic zonations adopted is based on Helby et al. (2004),

Partridge (2006) and Riding et al. (2010).


1.5 Thesis organization

Following this introductory chapter, Chapter 2 presents a summary of the regional

geological framework. Chapter 3 presents a sedimentological overview of the core material

and petrographic results on selected thin sections. It also represents an introduction to

Chapter 4, which presents the results of the facies analysis of the cored intervals. The

results of image log analysis are presented in Chapter 5. Interpretations derived from

integration of results in previous chapters with biostratigraphic data are used to construct

the sequence-stratigraphic framework for the Plover Formation in the study area. Chapter

7 contains the results of the analysis of seismic data and is followed, in Chapter 8, by the

proposed depositional model and related paleogeographic maps for key time intervals.

Finally, Chapter 9 presents the conclusions of this study and recommendations for future

work.

13

Chapter 2 - regional Setting

2.1 Introduction

The Browse Basin formed as an intracratonic basin during the Late Carboniferous

to Early Permian in response to rifting and formation of the Westralian Superbasin (Yeates

et al., 1987; Longley et al., 2002). It remained a discrete basin until the end of the Early

Cretaceous when its western margin subsided (Willis, 1988; Symonds et al., 1994). The

whole basin was then overlain by widespread deposition of transgressive sediments during

Figure 2.1 Simplified structural map of the Browse Basin showing major sub-basins (Caswell,Barcoo, Scott and Seringapatam) and Paleozoic and Jurassic normal faults (modifiedfrom Kennard et al., 2004). Basin is bounded by Kimberley Craton and by structural elementsoftheBonaparteBasin(grey)tothenorth.BSRT:Brecknock-ScottReefTrend.Rectangles on faults indicate downthrown direction. Study area outlined by yellow box.

Argus-1

Buffon-1

Regional setting - Chapter 214

Figure 2.2 Schematic cross-sections (not to scale) illustratingmajor basin-forming events in theBrowse Basin (from Struckmeyer et al., 1998): A. Upper Carboniferous to Lower Permian extension (Upper Permian basin geometry); B. Upper Permian to Middle Triassic thermal subsidence (Middle Triassic basin geometry); C. Upper Triassic inversion (Hettangian basin geometry); D. Early to Middle Jurassic extension (Callovian basin geometry). BSRT:Brecknock-ScottReetTrend.Faultsshownarerepresentativeofmajornortheast-trending fault systems of the basin.

C

B

A

Plover Fm.

Faults

Basement

Nome Fm.

Triassic strata

Paleozoic strata

DBSRT

Chapter 2 - Regional setting 15

the Cretaceous. Since the Cenozoic carbonate strata have prograded over the entire region

to form the present continental shelf (Willis, 1988).

Thischapterprovidesanoverviewof thetectono-stratigraphicevolutionof the

Browse Basin and the Early to Middle Jurassic paleoclimate. The Jurassic depositional

historyfocusesontheCaswellSub-basinwithemphasisonthePloverFormation.

2.2 Paleozoic extension

The Paleozoic history of the basin is characterized by an overall extensional regime

related to a series of breakups and rifting of various microplates from the Gondwanan

Supercontinent (Li & Powell, 2001; Jablonski & Saitta, 2004; Metcalfe, 2011 and earlier

references therein).Paleozoic extensional events formed anoverall northeast-trending

structuralgraincharacterisedbyeast-andsoutheast-dippingnormalfaultsandledtothe

generationofthemainsub-basins(Struckmeyeret al., 1998; Jablonski & Saitta, 2004;

Figs2.1and2.2).IntheouterScottPlateauthisextensionalregimeresultedinWNW-to

northwest-trendingfaults(Exon&Stagg,1981).

TheCarboniferoustoPermiansedimentaryfillofthebasinhasbeenestimatedto

be at least 8 to 10 km thick (Struckmeyer et al., 1998). However, due to of the paucity of

available data, the Paleozoic stratigraphy remains poorly constrained. Interpretation of

wellandseismicdatasuggeststhatafluvio-deltaictomarinesuccessionwasdepositedin

the central part of the basin during this time interval (Blevin et al., 1998).

2.3 Triassic inversion

The Late Permian to Early Triassic period was characterized by relative tectonic

quiescence and open marine sedimentation in the central part of the basin. Inversion

tookplaceintheearlyNorian,relatedtotheFitzroyMovementandBowenOrogenyand

causedtranspressionalmovementsandreactivationandinversionofpre-existingfaults

(Fig. 2.2). This event generated northeast-trending folds that dominate theMesozoic

structural setting of the basin. Coincident uplift led to the development of a regional

unconformity (Trmid/ TRC1; Struckmeyer et al., 1998; Jablonski & Saitta, 2004; Table

2.1).Northeast-trendingnormalfaultsdevelopedinthecentralBrowseBasinandalong


Australia

SaudiArabia

IndiaAfrica

Antartide

Argo/West Burma

MKSK

PM TWS

BPBR

CR PNGGreater

India

P

NORIAN

SINEMURIAN-CALLOVIAN

S30°

S90°

S60°

S90°

0°

Australia

SaudiArabia

India

Africa

Antartide

Argo/West Burma

MK

SKPMT

WS

BPBRCR PNG

GreaterIndia

P

HETTANGIAN-SINEMURIAN

SH

S30°

S90°

0°

Australia

SaudiArabia

IndiaAfrica

Antartide

Argo/West Burma

AP

SKPMT

WS

BPBRCR

PNG

GreaterIndia

P

SH

ABBREVIATIONS

AP - Ashmore PlatformBP - Bonaparte BasinBR - Browse BasinCR - Carnarvon BasinP - Perth BasinSH - Sahul Platform

MIcroplates:

MK - MangkalihatPM - Paternoster-MeratusPNG - Papua New GuineaSK - Sikuleh (Western Sumatra)T - TimorWS - West Sulawesi

C

B

A

Figure 2.3 Late Triassic to Middle Jurassic geodynamic evolution of Gondwana (from Jablonsky & Saitta, 2004). This time interval is characterised by rifting of microplates from Gondwanan Supercontinent. After rifting in Early Jurassic, Mangkalihat microplate migrates northwards (in map C it is not shown because outside of the map area).


the eastern edge of the Scott Plateau, but movement on the outer Scott Plateau followed

theexistingnorthwest-directedtrends(Exon&Stagg,1981).TheAshmore-Sahulhigh

andthenortheast-trendingstructuralhighoftheBrecknock-ScottReefTrendformedat

this time as a consequence of reactivation of Paleozoic faults (Symonds et al., 1994;

Struckmeyer et al., 1998).

2.4 Jurassic extension

The Late Triassic to Late Jurassic interval was dominated by rifting of microplates

from the Gondwanan Supercontinent (Jablonski & Saitta, 2004; Hoffman and Hill, 2004;

Fig.2.3).Theoverallextensionalregimecausedfragmentationofthebasinintoseveral,

fault-bounded,northeast-trendingtroughsandintenserift-relatedvolcanism(Bradshaw

et al., 1994; Symonds et al., 1998; Keall & Smith, 2004). Jurassic faults are typically

NE-trendingandparallel toextensionalstructuresdevelopedduring the latePaleozoic

and Triassic tectonic phases (Fig. 2.2). Reactivation of major NE-trending Paleozoic

structures also played an important a role during this time interval (Struckmeyer et al.,

1998;Fig.2.1).

LateNorian to Sinemurian rifting of theMangkalihatmicroplate caused post-

inversion subsidence andflooding of the central and outer parts of theBrowseBasin

(Table2.1),andtotheonsetofthedepositionofthePloverFormationintheHettangian

(JH; Blevin et al., 1998; Jablonski & Saitta, 2004; Table 2.1). Extensive faulting created

halfgrabenthatwereprogressivelyfilledbyfluvio-deltaicandshallowmarinestratathat

constitutemostofthePloverFormation.RegionaltransgressiveeventsJP1/JSandJcal/

JC are considered to have been related to the northward movement of the Mangkalihat

microplate during the Sinemurian (JP1/JS) and to the onset of breakup of Argo microplate

during the Callovian (JC; Longley et al., 2002; Jablonski & Saitta, 2004; Table 2.1).

UpliftintheOxfordianmarkedtheendoftheextensionandisrecognisedbya

regionalunconformity(‘MainUnconformity’–JO/MU;Table2.1).Thiseventcorresponds

withtheonsetofseafloorspreadingandgenerationofoceaniccrustoftheArgoAbyssal

Plain (Symonds et al., 1994; Struckmeyer et al.,1998;Heine&Müller,2005).Post-rift

subsidenceandrelativetectonicquiescenceinOxfordiantoTithoniantimesarerecorded


Late Carboniferous to Early Permian

Late Triassic(Early Norian)

Late Permian to early Late Triassic

Late Triassic to Early Jurassic

Middle Jurassic to Oxfordian

Oxfordian to Early Cretaceous

Age of Event Geodynamic Event Browse tectonic regime

Important regional surfaces relevant to this study

Rifting of SE Asia, Sibumasu and Qiangtang micro-plates from Gonwana- Initiation of the Westralian Superbasin.

Fitzroy Movement.

Movement of Sibu-masu and Qiantang microplates.

Riftng of Mangkalihat microplate from Gondwana.

Riftng of Argo micro-plate from Gondwana

Rifting of Greater India from Gond-wana.

NW-SE directed rifting and generation of NE-trending structural grain of the Browse Basin.

N-S transpression; reactivation and inversion of Paleozoic faults. Formation of major anticlinal and synclinal trends.

Relative tectonic quiescence.

Post-inversion subsidence and extensive faulting (NE-trending). Reactivation of older faults.

Faulting (NE-trending). Reactiva-tion of older faults.

Post-rift sag and relative tectonic quiescence.

Middle Miocene to Recent

Collision and subduc-tion of Australian plate under Asian plate in the Banda Arc.

Compression; reactivation and inversion of older faults. Generation of Brecknock and Calliance structures.

Early Cretaceous to Miocene

Rifting of India and Australia from Gondwana.

Thermal subsidence and relative tectonic quiescence.

Trmid/TRC1

JH

JP1/JS

JC

JO/MU

KV

Ktur

TRR

Table 2.1 Tectonic event history and associated tectonic regime for the Browse Basin based on Struckmeyer et al. (1998) and Jablonski & Saitta (2004). Key stratigraphic surfaces with sequencestratigraphicsignificancearealsohighlighted(red:sequenceboundary;green:Transgressive surface of erosion).


byinitialdeepeningfollowedbydepositionofprogradationalfluvio-deltaicsandstones

and mudstones (Blevin et al., 1998).

2.5 Cretaceous to Cenozoic thermal subsidence and inversion

Rifting of Greater India from Gondwana in the Berriasian caused uplift of the

hinterland inboard of the Browse Basin and progradation of deltaic depositional systems

in the Browse area (Longley et al., 2002). Rifting of the Greater India in the Valanginian,

causedpost-riftsagoftheentireBrowseBasinandregionalmarineflooding(KVseismic

event; Blevin et al., 1998, Longley et al., 2002). During this time interval, deposition in

thebasinwasnotsignificantlyaffectedbytectonism(HoffmanandHill,2004).

The Valanginian to Cenomanian succession consists of transgressive marine

claystones and siltstones deposited on an extensive marine shelf (Lavering & Pain,

1991).Thesestratarepresentthefinalphaseofpost-breakupsubsidencethataffectedthe

NWS(Symondet al. 1994). A Turonian unconformity (Ktur; Table 2.1) separates this

successionfromtheoverlyingLateCretaceous-Eocenedominantlycarbonatesuccession

(ASGO,1994;Blevinet al., 1998).

Mid Oligocene uplift and erosion of the eastern part of the basin restricted

carbonate deposition to the outer part of the shelf area (Baillie et al., 1994). However,

accelerated subsidenceduring theLateOligocene renewedbasinwardprogradationof

thick carbonate wedges (Willis, 1988; Hoffman & Hill, 2004). These wedges buried the

underlying sedimentary units and shaped the present day morphology of the continental

shelf and slope.

A compressional episode, related to the collision and subduction of the Australian

Plate under the Banda Arc, has been affecting the Browse Basin since the Late Miocene

and is responsible for minor deformation and overprinting of the whole stratigraphic

succession (Keep et al. 1998; Müller et al., 1998). This tectonic event created the Timor

Trough and, in the Browse Basin, reactivated Paleozoic faults and generated the structural

trapconfigurationoftheBrecknock-Calliancearea(Keep&Moss,2000;Keall&Smith,

2004).


157.3

163.5

166.1

170.3

168.3

174.1

182.7

190.8

199.3201.3

209.5

222.0

Age(Ma)

Periods and stages Spore-PollenZonation

Dynoflagellataecyst biozones

Kimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Aalenian

Toarcian

Pliensbachian

Sinemurian

Hettangian

Rhaetian

Norian

LATE

TRI

AS

EARL

Y JU

RASS

ICM

IDD

LE J

URA

SSIC

LATE

JU

RASS

IC A

B

C

U

L

U

L

U

L

M. florida

C. cooksoniae

D. complex

C. turbatus

C. torosa

A. reducta

M. crenulatus

S. wigginsii

W. listeri

H. balmei

R. rhaetica

D. priscum

No data

Luehndea assemb.

No data

D. caddenseN. deflandreiW. verrucosa

W. indotata

T. balmei

V. tabulataC. ancorum

W. spectabilis

W. clathrata

D. swanense LowerVulcanFm.

MontaraFm.

PLOVERFM.

Nome Fm.

Litho-stratigraphy

TRC1

TRR

JH

JS

JC

JO

JK

Keysurf.

Challis Fm.

Jearly

Climate

warmhumid

not seasonal

warm-hothumid

seasonal

aridseasonal

warm, but cooler

Figure 2.4 Jurassic lithostratigraphic framework of the Browse Basin. Geological Time Scale from Gradstein et al. (2012); Spore-Pollen Zonation SE Standard from Partridge (2006);Dynoflagellataecystbiozones fromRidinget al. (2010). Key surfaces from Jablonski & Saitta (2004) and Struckmeyer et al. (1998): red surfaces are sequence boundaries; and green surfaces are transgressive surfaces of erosion. Climate from van Aarssen et al. (2000). Error on absolute ages ±0.2 to 1.4 Ma. The biostratigraphy of Browse Basin is basedonspore-pollenanddinoflagellataebiozones(e.g.Ridinget al., 2010). Compared to other organisms used in biostratigraphy, the biozonation based on these two taxa proved to be the most reliable, with spore/pollen offering the only continuous fossil record available over the entire region (Apthorpe, 1994).

2.6 Jurassic paleoclimate of the Browse Basin

The paleolatitude of the Browse Basin during the Early to Middle Jurassic was

likelytohavebeenaround35°S(Scoteseet al., 1999; Rees et al., 2000; Metcalfe, 2011).

OnthebasisofdistributionofJurassic fossil leaves, thispaleolatitude in thesouthern

hemisphere is equated with a warm temperate climate (e.g. Rees et al., 2000).

A review of Australian paleoclimatic evidence by Parrish et al. (1996) and

examinationofhigher-plant-derivedbiomarkersfromtheCarnarvonBasin(vanAarssen


et al., 2000) led these authors to propose four climatically distinct periods during the

Jurassic.Theseperiodsrangebetween5 to20myrs induration(Fig.2.4)andshowa

transition from an essentially arid Lower Jurassic to a more humid Middle and Upper

Jurassic.ThesefindingsareinagreementwiththoseofBradshaw&Brakel(1995),who

suggested a Pangaean monsoonal influence and an overall warm and seasonally dry

climate during the Early Jurassic followed by a cooler and/or wetter climate, that was less

monsoonallyinfluenced,duringtheMiddleJurassic.

2.6 Jurassic stratigraphy and paleogeography of the Caswell Sub-basin and Brecknock-Scott Reef Trend

TheCaswellSub-basin is themajordepocentreof theBrowseBasin(Fig.2.5)

and contains a Carboniferous to Holocene stratigraphic succession at least 15 km thick

(Hocking et al., 1994; Baillie et al., 1994 Struckmeyer et al, 1998). Early to Middle

Jurassic strata are up to 1.5 km thick and are represented predominantly by the siliciclastic

PloverFormation(Struckmeyeret al., 1998).

The Plover Formation is equivalent to theNorthRankin,Athol andLegendre

Formations in the Northern Carnarvon Basin and records widespread fluvio-deltaic

depositionalong theNWSafter theNorian inversion (Longleyet al., 2002; Jablonski

& Saitta, 2004; Turner et al., 2009; Fig. 2.6).The formation unconformably overlies

theNomeFormation(JHerosionalsurface)andistruncatedatthetopbyawidespread

unconformity(JO/MU)whichseparatesitfromtheUpperJurassicMontaraandLower

VulcanFormations(Fig.2.4).

ThePloverFormationwasdepositedduringperiodsofactivefaultingduringthe

Jurassicextensionandhasbeen,therefore,interpretedasasyn-riftsuccession(Struckmeyer

et al., 1998; Blevin et al., 1998). It typically infills highly irregular topography that

previous regional studies interpreted as partially inherited fromNorian inversion and

partially created by the ongoing extensional tectonism (Bradshaw et al., 1988; Blevin et

al., 1998; Keall & Smith, 2004). Consequently, thickness and lateral continuity of this

unit are highly variable throughout the Browse Basin (Struckmeyer et al.,1998;Fig.2.5).

The formation thins towards the Scott Reef Trend and the Leveque Shelf and is absent on


Figu

re 2

.5

Simplifiedregionalgeologicalcross-sectionoftheBrowseBasin(fromLongleye

t al.,2002).Synriftstrataarecolouredinpaleblue.TRC1:Norianunconformity;

JP1:Sinem

uriantransgressivesu

rface;JC

:Calloviantransgressivesurface;JO

:OxfordianM

ainUnconformity;K

:Berriasian;K

V:Valanginian;K

A:A

ptian;KC:

Cenom

anian;T:E

arlyPaleogene;TE:M

iddlePaleogene;TO:L

atePaleogene;TM2:EarlyM

iocene;TM1:LateMiocene.W

elllocationsaresh

ownonFig.1.2.

NW

SE


Figure 2.6 Lithostratigraphic correlation chart for Jurassic Formations of theBonaparte, Browseand Carnarvon Basins, matched against the chronostratigraphic scale of Gradstein et al. (2012)andOgget al.(2008).FromTurneret al. (2009).

the Yampi Shelf (Stevenson & Cadman, 1994; Blevin et al., 1998).

Sandstones, mudstones and minor carbonate rocks constitute the main rock types

ofthePloverFormation(Willis,1988;Blevinet al., 1998; Keall & Smith, 2004). The broad

depositional environment proposed is a large, tidally influenced to tidally dominated,

sandy delta fed by rivers draining uplifted areas to the east of the basin (e.g. Precambrian

Kimberley Craton; Longley et al., 2002; Ainsworth et al., 2008). Igneous rocks are

present at several stratigraphic levels within the formation and have been interpreted as

volcanic units and subvolcanic intrusions related to synrift volcanism associated with a

majorvolcanicprovince(Symondset al., 1998; Blevin et al., 1998; Struckmeyer et al.,


1998).

Informal subdivision of the Plover Formation in theBrowseBasin into lower

(?HettangiantoToarcian)andupper(AaleniantoOxfordian)unitscanbeinferredfrom

CadmanandStevenson(1994),althoughtheydidnotdefineitclearly.Struckmeyeret

al. (1998) and Blevin et al. (1998) recognised a Jearlyevent(intra-C. turbatus;Fig.2.4)

on seismic and well data and interpreted it as a sequence boundary marking the onset of

extensionalfaultingintheHeywoodGraben(Fig.1.2)andoveralldeltaicprogradationin

theBarcoo-1area(Fig2.1).Thiseventcouldrepresentaneffectiveboundarybetweena

lower and a upper parts of the formation. In other studies, two important regional seismic

events (JP1/JS and JC) have been recognized in the Jurassic section of theNorthern

Carnarvon Basin and correlatedwith the Browse Basin (Jablonski, 1996; Longley et

al., 2002). These surfaces have been interpreted as regional transgressive surfaces of

Sinemurian (JP1/JS) and Callovian (JC) age because they have been recognized also in

wellsoftheCaswellSub-basin(Blevinet al., 1998; Struckmeyer et al., 1998; Longley et

al., 2002; Jablonski & Saitta, 2004).

BroadpaleogeographicmapsfortheNWShavebeenproposedbyBradshawet al.

(1988 and 1998) and Longley et al. (2002). Early regional paleogeographic reconstructions

of the Browse Basin centred on the Scott Reef Plateau were presented by Exon & Stagg

(1981). Apthorpe 1994 presented a preliminary paleogeographic interpretation of the

Browse area based on the recognition of foraminifera and other marine microfossils as

wellasindicationsofnon-marinedeposition(e.g.woodfragmentsandleaves)fromsix

wellslocatedintheCaswellandBarcooSub-basins.Amorecompletepaleogeographic

analysis,directlybasedondatafromtwenty-threewells,wasalsoproposedbyStevenson

& Cadman (1994).

The Early to Middle Jurassic paleogeography as summarized by Stevenson &

Cadman (1994; Figs 2.7A and 2.7B) is characterized bymajor land areas located to

the east and northeast (Yampi Shelf and Kimberley craton). The possible existence of

Plover sediment source to the west has been also considered likely by some authors (e.g.

Stevenson & Cadman, 1994; Blevin et al., 1998) and implies emergent areas also in the

ScottSub-basintothewest.IntheCaswellSub-basin,partoftheBrecknock-ScottReef


Figure 2.7 PaleogeographicmapsoftheCaswellSub-basinfromStevensonandCadman(1994;mapsAandB)andLongleyet al. (2002; maps C and D). A. Early Jurassic (Hettangian to Toarcian); B.MiddleJurassic(AaleniantoBathonian).NotethepostulatedpeninsulaconnectingLombardina-1(L)tothestudyarea;C. Early to Middle Jurassic (Sinemurian to Callovian) Plover deltaic system according to Longley et al.(2002).Notetheabsenceofemersedlandtothewestinthisinterpretation (compared to A and B). Grey arrow indicates direction of delta progradation; D.UpliftandwidespreaderosionovermostoftheCaswellSub-basinwhichtookplaceintheCallovian.Red-circled‘V’locatespotentialvolcanicvents.Orangeboxindicatesthestudyarea.Reddotsarewells.

V

V

V

V

V

V

V

V

16º

15º

14º

13º

100 km0

Non-deposition

Middle shelf

Fluvio-deltaic

Marginalmarine

Inner shelf

Fluvio-lacustrine

LagoonLagoon

Marginalmarine

Fluvio-lacustrine

Non-deposition

121º 122º 123º 124º

A

V

V

V

V

V

V

V

16º

15º

14º

13º

100 km0

Non-deposition

Middle shelf

Fluvio-deltaic

Marginalmarine

Inner shelf

Shoal

Volcanic/non-dep.

Fluvio-lacustrine

Fluvial

Marginalmarine

121º 122º 123º 124º

B

L

16º

15º

14º

13º

100 km0

121º 122º 123º 124º

Non-deposition

Non-deposition

Shelf - claydominated

Shelf - sanddominated

D16º

15º

14º

13º

100 km0

121º 122º 123º 124º

Upper deltaLower delta

Delta front

Delta slope

Basin

Shelf - sanddominated

Non-deposition

C



Trendandothersmall,northeast-trendinghorstsformedelongatedislandsorpeninsulas,

probably of volcanic origin (Stevenson & Cadman, 1994). Coastal areas were dominated

byfluvio-deltaic to estuarine sedimentation andwere connected to narrow, northeast-

trending shallow marine depositional areas (Stevenson & Cadman, 1994; Bradshaw et al.,

1998). Progradation of an extensive deltaic system which was building westward from

theAustraliancontinentduringtheEarly-MiddleJurassichasbeenproposedbyJablonski

(1997) and Longley et al.(2002;Fig.2.7C).Accordingtotheseauthors,theBSRTarea

wasasand-dominatedshelfsurroundedbywidespreaddeltafrontareas.Distributionof

volcanicvents, althoughstillunknown,waspotentiallyparallel to theoverallNE-SW

structural grain of the basin (Stevenson & Cadman, 1994).

Thepaleogeographicsettingchanged in theCallovian -earlyOxfordian,when

uplift led towidespreaderosionovermostof theCaswellSub-basin,withonlyminor

areas of coastal or shallow marine deposition (Longley et al.,2002;Fig.2.7D).Flooding

intheOxfordianre-establishedmarineconditionsovertheentireregion.

Documents

Depositional History anD paleogeograpHy of tHe Jurassic