lable at ScienceDirect

Marine and Petroleum Geology 61 (2015) 82e94

Contents lists avai

Marine and Petroleum Geology

journal homepage: www.elsevier .com/locate/marpetgeo

Research paper

Geochemical characterisation of Early Cretaceous lacustrine sedimentsof Bima Formation, Yola Sub-basin, Northern Benue Trough, NENigeria: Organic matter input, preservation, paleoenvironment andpalaeoclimatic conditions

Babangida M. Sarki Yandoka a, b, *, Wan Hasiah Abdullah a, M.B. Abubakar b,Mohammed Hail Hakimi c, Adebanji Kayode Adegoke a, d

a Department of Geology, University of Malaya, 50603 Kuala Lumpur, Malaysiab National Centre for Petroleum Research and Development, A.T.B.U, PMB 0248, Bauchi, Nigeriac Geology Department, Faculty of Applied Science, Taiz University, 6803 Taiz, Yemend Department of Geology, Ekiti State University, P.M.B. 5363, Ado-Ekiti, Nigeria

a r t i c l e i n f o

Article history:Received 8 July 2014Received in revised form10 December 2014Accepted 18 December 2014Available online 27 December 2014

Keywords:Geochemical characteristicsLacustrine environmentBima FormationNorthern Benue Trough

* Corresponding author. Department of Geology,Kuala Lumpur, Malaysia. Tel.: þ60 166737410.

E-mail addresses: bmsydgombe@yahoo.com(B.M. Sarki Yandoka).

http://dx.doi.org/10.1016/j.marpetgeo.2014.12.0100264-8172/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

The Bima Formation is the oldest lithogenetic unit occupying the base of the Cretaceous successions inthe Yola Sub-basin of the Northern Benue Trough. It is differentiated into Lower (B1), Middle (B2) andUpper (B3) Bima Members. Integrated organic and inorganic geochemical studies were applied on thelacustrine sediments of the Bima Formation with the aim of reconstructing the palaeodepositionalenvironment and organic matter input in response to climate and tectonism. The analysed sedimentswere deposited in a freshwater lacustrine environment with a low-salinity stratified water column andsuboxic to relatively anoxic conditions, as indicated by the bulk geochemical parameters. The biomarkersprovide evidence for a contribution of aquatic algae and microorganisms, with a significant amount ofterrigenous organic matter input. The preservation of the organic matter is possibly attributed to thestratified water column with low salinity and suboxic to relatively anoxic conditions. Based on thegeochemistry of major and trace elements, the sediments were deposited during semi-arid climaticconditions within passive continental margin setting. This agrees with the tectonic events in the Westand Central African Rift System (WCARS) during the Early Cretaceous period.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The Bima Formation is the lateral equivalent of the EarlyCretaceous formations within the West and Central African RiftSystem (WCARS) (Fig.1), which host good petroleum systems in theMuglad Basin of Sudan and in the Termit Basin of Niger and ChadRepublics (Mohammed et al., 1999; Obaje et al., 2004; Abubakaret al., 2008). The Bima Formation was deposited in continentalenvironments under widely varying conditions: alluvial, braidedriver and lacustrine (Carter et al., 1963; Guiraud, 1990; SarkiYandoka et al., 2014). The Lower Bima Member has the same

University of Malaya, 50603

, bmsydgombe@gmail.com

depositional facies, depositional environments (alluvial fan e

braided rivere lacustrine), time equivalence (Early Cretaceous) andorigin with Sharaf and Abu Gabra Formations in the Muglad Basinof Sudan and Tefidet Formation in the Termit Basin of Niger,deposited within same mega-structure (WCARS) (e.g. Schull, 1988;Genik, 1993; Mohammed et al., 1999; Sarki Yandoka et al., 2014).

Barremian to Aptian lacustrine shales are proven source rocksfor the Early Cretaceous petroleum systems in the Termit andMuglad Basins (Mohammed et al., 1999; Obaje et al., 2004;Abubakar, 2014). In the Gongola Sub-basin (Fig. 1), three explor-atory wells were drilled and an estimated reserve of 33 billion cubicfeet of gas was found from Kolmani River e 1 well, confirming thepresence of a petroleum system in the basin (Abubakar et al., 2008;Abubakar, 2014; Sarki Yandoka et al., 2015). There is no reporteddrilled well or core in the Yola Sub-basin and thus, there is no sub-surface data from the Bima Formation in the study area (Fig. 2).

Figure 1. Regional tectonic map of western and central African rifted basins showing the Nigerian Benue Trough and study area (Adapted from United Reef Limited Report, 2004and Abubakar, 2006).

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e94 83

The objective of this study is to integrate organic and inorganicgeochemistry to determine the organic matter source input of theEarly Cretaceous lacustrine sediments of the Bima Formation in theYola Sub-basin of the Northern Benue Trough in relation to paleo-environment of deposition, palaeoclimatic conditions and tectonicsetting during sedimentation. This is as a follow up to SarkiYandoka et al. (2014) sedimentological study, which indicated thepresence of the Early Cretaceous lacustrine sediments in the area,so as to compensate for missing information and significantlyimprove the paleoenvironmental assessment. The general aimhowever, is to suggest presence of potential Lower Cretaceouslacustrine source rocks in the Yola Sub-basin; an impetus that isexpected to provide further insight into the geology of the basin forfuture hydrocarbon exploration campaigns.

2. Geology and stratigraphy

The Benue Trough is one of themajor rift basins formed from thetension generated by the separation of the African and SouthAmerican plates. It is a NEeSW trending, intra-continental, Creta-ceous sedimentary basin in Nigeria that is about 1000 km long and50 km wide (Fig. 1). It extends from the Niger Delta in the south-west to the Chad (Bornu) Basin in the northeast (Guiraud andMaurin, 1992). Several authors have presented tectonic modelsfor the genesis of the Benue Trough (Abubakar, 2014). King (1950)proposed tensional movements resulting in a rift while Stoneley(1966) proposed a graben-like structure. The Rift Rift Fault (RRF)triple junction model, leading to plate dilation and opening of theGulf of Guinea, was proposed by Grant (1971). Olade (1975)considered the Benue Trough as the third failed arm or aulacogenof a three armed rift system related to the development of hotspots.Benkhelil (1982, 1989) and Guiraud and Maurin (1992) considered

wrench faulting as the dominant tectonic process during the BenueTrough evolution and defined it as a set of juxtaposed pull-apartbasins generated along the pre-existing N60�E strike-slip faults.

The Benue Trough is sub-divided geographically into Southern,Central and Northern portions (Nwajide, 2013). The NorthernBenue Trough is made up of two major sub-basins: the NeStrending Gongola Sub-basin and the EeW trending Yola Sub-basin(Fig. 1). Carter et al. (1963), Offodile (1976), Benkhelil (1989),Zarboski et al. (1997), Obaje et al. (2000) and Abubakar (2006)have described the geology and stratigraphy of the NorthernBenue Trough in detail. The stratigraphic succession in the YolaSub-basin of the Northern Benue Trough (Fig. 3) comprises thecontinental Lower Cretaceous Bima Formation, the Cenomaniantransitional marine Yolde Formation and the marine late Cen-omanianeSantonian Dukul, Jessu, Sekuliye Formations, NumanhaShales and Lamja Sandstones (Carter et al., 1963; Abubakar, 2006).

The Bima Formation is the oldest lithologic unit occupying thebase of the Cretaceous successions (Fig. 3). Carter et al. (1963) andGuiraud (1990) differentiated the Bima Formation into threemembers; the Lower Bima (B1), theMiddle Bima (B2) and the UpperBima (B3). These three lithologic units were also identified in theseismic section of the Nigerian sector of the Chad Basin (Avbovboet al., 1986). The Lower Bima (B1) is the oldest member (?LateJurassic e Berremian e Aptian) and has been described as con-sisting of fault controlled conglomerates, sands and gravels withpoorly defined internal structures, and characterized by well-defined fining-upward successions (Guiraud, 1990). Trough crossbeds are common in associationwith minor tabular units. Red, greyand dark clay/shales with fine to medium grained sandstones werereported as lacustrine deposits (Kogbe, 1976; Allix et al., 1981;Guiraud, 1990; Sarki Yandoka et al., 2014). The correlative equiva-lents of the lacustrine sediments are within the oil window in the

Figure 2. Geological map of the study area showing the exposed outcrops of Bima Formation at the core of Lamurde Anticline and the location of measured sedimentary logs(from Sarki Yandoka et al., 2014).

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e9484

Muglad Basin (e.g. Mohammed et al., 1999) and the Termit Basin ofChad (e.g. Genik, 1993) and may have generated hydrocarbons inthe adjacent Gongola Sub-basin (Abubakar et al., 2008; Abubakar,2014).

Paleoenvironmental reconstruction and stratigraphic develop-ment of the Lower Bima Member in the Yola Sub-basin, based onfacies analysis, was provided by Sarki Yandoka et al. (2014) and issummarized in Figure 4 to show the spatial and temporal disposi-tion of the sampled sediments for the present study.

The Late Aptian e Albian Middle Bima (B2) unconformablyoverlies the Lower BimaMember. It is composed of medium to verycoarse grained feldspathic sandstones with trough and tabularcross bedding interbedded with clays (Offodile, 1976; Zarboskiet al., 1997). It is considered to have been deposited in a deeplyentrenched, braided river system (Carter et al., 1963; Abubakar,2006). The Upper Bima (B3) conformably overlies the MiddleBima (B2). It has a relatively homogeneous appearance consisting ofplanar cross bedded, medium to coarse grained sandstone thatshows soft sediment deformation structures (Samaila et al., 2006).

3. Sampling and methods

Fieldwork was carried out on the exposed outcrops of the LowerBima Member at the core of the NEeSW trending Lamurde Anti-cline (Fig. 2). For this study, three sedimentary sections were loggedin detail and fourteen shale samples were collected at differentstratigraphic intervals (Fig. 4). To minimize the effects of surfaceweathering, surface materials were removed before sampling atapproximately 0.5 m.

Organic and inorganic geochemical analyses were performed onthe fourteen shale samples (Fig. 4). The samples were crushed toless than 200 mesh. About 30 g of each sample was subjected tobitumen extraction, using a Soxhlet apparatus for 72 h and using anazeotropic mixture of dichloromethane (DCM) and methanol(CH3OH) (93:7). The extracts were separated into saturated hy-drocarbons, aromatic hydrocarbons and NSO (nitrogen, sulphurand oxygen) compounds by liquid column chromatography. Thesaturated hydrocarbon fractions were dissolved in hexane andanalysed by gas chromatography-mass spectrometry (GCeMS)

Figure 3. Stratigraphy of Yola Sub-basin successions (modified after Abubakar, 2006).

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e94 85

using an HP 5975B MSD mass spectrometer with a gas chromato-graph attached to the ion source (70 eV ionization voltage, 100milliamps filament emission current, 230 �C interface tempera-ture). However, six (6) saturated hydrocarbon fractions wereselected and analysed by gas chromatography-doublet mass spec-trometry (GCeMS/MS). GC/MS/MS was performed on an Agilent7000B Triple quad, fitted with a fused silica capillary column(60 m � 0.25 mm I.D., 0.25 pm film thickness). Helium was thecarrier gas at 30 psi constant pressure and the column was heatedfrom 150 to 300 �C at 2 �C/min, with a final hold at 300 �C for30 min. The GCeMS and GCeMS/MS analyses were carried outrespectively at the departments of Geology and Biology, Universityof Malaya.

About 0.50 g of each sample was prepared for non-destructive wavelength dispersive X-ray fluorescence spec-trometer (PANalyticalAxiosmAX 4 KW sequential XRF spec-trometer). The pellets were prepared with 0.15 g of cellulosepowder in the Department of Geology, University of Malaya. Theconcentration of oxides of major elements was determined by

XRF analysis. About 0.50 g of each sample was prepared forinductively coupled plasma-mass spectrometry (ICP-MS). Thesamples were weighed in teflon beakers and dried at 105 �Covernight. The samples were moistened with a few ml ofdeionized water. 5 ml of Nitric acid (HNO3) was slowly addedand placed on a hotplate at 150 �C until it reached near drynessand was then allowed to cool. 10 ml of hydrofluoric acid (HF) wasslowly added followed by 4 ml of perchloric acid (HClO4). Thesamples were decomposed on a hotplate at approximately200 �C until they reached near dryness. After cooling, the sam-ples were digested with 10 ml of 5 M HNO3 in a fume hood. Thesolutions were diluted with deionized water to 50 ml in avolumetric flask. All digested samples were diluted up to 100times with ultimate pure water (UPW). Standard solutions of theelements with an analyte concentration of 10 ppm were used forcalibration, with a minimum detection limit of less than 1 ppb.The trace and rare earth elements were determined using anICP-MS Agilent Technologies 7500 Series at the Department ofBiology, University of Malaya.

Figure 4. (a) Composite litholog of Lower Bima Member and sedimentary logs of lacustrine sediments showing the sample points and, (b) depositional model of Lower BimaMember (from Sarki Yandoka et al., 2014).

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e9486

4. Results

4.1. Organic geochemical characteristics

Biomarker concentration ratios can be used to describe organicmatter type, source input and paleoenvironmental conditions ofsedimentary rocks (Sun et al., 2014; Farhaduzzaman et al., 2012;Hakimi et al., 2011; Abubakar et al., 2008; Korkmaz and KaraGülbay, 2007; Peters et al., 2005; Holba et al., 2003; Abdullah,1999). The distributions of nealkanes, acyclic isoprenoids, tricy-clic terpanes, hopanes and steranes were performed onm/z 85, m/z191, and m/z 217, respectively from GCeMS fragmentation anddetermined based on the retention time and comparison withpublished work (e.g. Amijaya et al., 2006; Korkmaz and KaraGülbay, 2007; Hakimi et al., 2011; Hakimi and Abdullah, 2013).

4.1.1. Normal alkanes and acyclic isoprenoidsThe chromatograms of normal alkanes and acyclic isoprenoids

display a full range of saturated hydrocarbons between C12eC33 n-

alkanes and acyclic isoprenoids hydrocarbons (Fig. 5). The analysedshale samples display mainly a bimodal n-alkane distribution withdominance of long-chain n-alkanes (n-C22en-C28) molecularweight compounds (Fig. 5).

Acyclic isoprenoids occur in significant amounts (Fig. 5). Pris-tane generally occurs in high relative concentrations, with pristane/phytane (Pr/Ph) ratios in the range of 1.04e1.90 (Table 1).Furthermore, lower amounts of acyclic isoprenoids compared to n-alkanes (Fig. 5), gave distinctively low pristane/n-C17 and phytane/n-C18 ratios in the range of 0.47e0.90 and 0.33e0.91, respectively(Table 1). The degree of waxiness and CPI in this study werecalculated and tabulated in Table 1. Waxiness index and CPI valuesrange from 0.89 to 2.84, and from 0.60 to 1.17, respectively (Table 1).

4.1.2. Terpanes and steranesFigure 6 shows fragmentograms of hopane and sterane distri-

butions of some analysed samples for this study. The identifiedpeaks are listed in Appendix A and the calculated ratios are shownin Tables 1 and 2.

Figure 5. Mass fragmentograms m/z 85 of saturated hydrocarbons of some studied Bima shale samples.

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e94 87

The m/z 191 mass fragmentograms of the saturated hydrocar-bon fractions of all the analysed shale samples show that the ter-panes are dominated by the presence of C30-hopane, C29-norhopane, 17a (H)-trisnorhopane (Tm), and a considerable quan-tity of homohopanes (C31eC33), with moderate amounts of tricyclicand tetracyclic terpanes (Fig. 6a). However, the abundance of C29norhopane is relatively less than that of C30 hopane, with C29/C3017a(H) hopane ratios ranging from 0.78 to 1.27 (Table 1). Tmconcentration is higher than Ts in the investigated samples (Fig. 6a)with Tm/Ts ratios in the range of 1.3e1.8 (Table 1). The homo-hopane distributions are dominated by C31 homohopane anddecrease with increasing carbon number (e.g. Ourisson et al., 1979and Fig. 6a). The concentration of tricyclic terpanes in the analysedBima shale samples is moderate compared to that of tetracyclics(represented by C24 tetracyclic/C26 tricyclic; Table 1). The sampleshave relatively high C24te/C26, low to moderate C24/C23 and C22/C21,and high C26/C25 tricyclic terpane ratios (Table 1). Gammacerane ispresent in almost all the analysed samples in very low

concentration (Fig. 6a). The gammacerane index ranges between0.08 and 0.21 (Table 1).

The steranes are biomarkers derived from sterols found inhigher plants and algae but rare or absent in prokaryotic organisms(Volkman, 1986). In the studied samples, steranes and diasteranesare present in high quantities in saturated hydrocarbon fractions(Fig. 6b). The relative proportions of each of the regular steranes(C27, C28 and C29) can vary greatly from sample to sample,depending upon the type of organic matter input to the sediment.Relative abundances of C27, C28 and C29 regular steranes, and theratios of C27/C29 regular sterane, C27 þ C28/C29 sterane, diasterane/sterane and hopane/sterane ratios, were calculated (Table 2). Theanalysed samples show a high proportion of C27 (26.1e64.1%) andC29 (25.2e55.9%) compared to C28 (8.7e25.2%).

4.1.3. C30Tetracyclic polyprenoidsThe C30 tetracyclic polyprenoids 21R (Ta) and 21S (Tb) isomers

were determined on m/z 414 e 259 and 27-norcholestanes on m/z

Table 1Normal alkanes, isoprenoids, triterpanes and terpanes ratios of Bima shale samples calculated on m/z 85 and m/z 191 from GCeMS.

SampleID

n e alkanes and isoprenoids Triterpanes and terpanes (m/z 191)

Pr/Ph Pr/n-C17 Pr/n-C18 CPI WI C29/C30

G/C30

C31R/C30

C21T/C23T

C22T/C21T

C24T/C23T

C26T/C25T

C24Te/C26T

C23T/C24T

C23/C24Te

Tm/Ts C30M/C30H

22S/22Sþ22R

BM3A 1.16 0.89 0.73 1.09 1.26 1.26 0.13 0.20 1.89 0.40 0.41 1.81 4.32 2.14 0.74 1.40 0.14 0.58BM3B 1.15 0.79 0.68 1.11 1.23 1.27 0.14 0.19 1.26 0.37 0.33 1.09 5.43 3.05 1.03 1.52 0.15 0.62BM4 1.90 0.90 0.48 1.13 1.26 1.08 0.12 0.22 1.55 0.20 0.43 0.92 3.01 2.41 1.44 1.80 0.13 0.63BM5 1.17 0.70 0.65 1.14 2.67 0.91 0.14 0.13 1.39 0.56 0.42 2.66 3.12 2.35 0.66 1.38 0.10 0.63BM7 1.26 0.47 0.33 0.60 0.89 1.13 0.11 0.16 1.40 0.42 0.40 2.28 2.75 2.24 2.44 1.70 0.16 0.58BM9A 1.04 0.74 0.77 1.12 2.81 0.78 0.12 0.17 1.35 0.52 0.58 2.33 2.28 1.72 0.76 1.52 0.13 0.61BM9B 1.22 0.78 0.63 1.15 2.53 0.84 0.11 0.15 1.31 0.44 0.47 2.34 3.28 2.11 0.83 1.50 0.14 0.60BM10 1.32 0.60 0.50 0.92 1.25 0.89 0.16 0.16 1.20 0.48 0.52 2.18 3.25 2.13 0.87 1.45 0.12 0.59BM11 1.25 0.56 0.40 1.17 1.65 0.94 0.21 0.21 1.12 0.29 0.37 1.66 3.60 2.60 1.77 1.60 0.13 0.65BM33 1.30 0.84 0.91 1.13 1.37 0.86 0.13 0.17 1.71 0.41 0.43 1.75 4.57 2.30 0.94 1.69 0.13 0.65BM12,1 1.17 0.78 0.57 1.17 1.11 1.06 0.08 0.14 1.64 0.41 0.42 2.40 3.03 2.44 1.22 1.19 0.12 0.67BM12,2 1.35 0.59 0.41 1.17 2.84 1.23 0.15 0.24 1.38 0.37 0.68 2.04 2.36 2.24 1.42 1.52 0.15 0.58BM12,3 1.24 0.65 0.53 1.13 1.65 0.95 0.18 0.18 1.02 0.23 0.38 0.55 3.50 2.33 2.33 1.24 0.12 0.69BM12,4 1.18 0.88 0.71 1.12 1.40 1.26 0.15 0.17 1.28 0.39 0.33 1.03 5.20 3.01 1.22 1.75 0.16 0.88

Pr e Pristane Ph e Phytane CPI e Carbon preference index (1): {2(C23 þ C25 þ C27 þ C29)/(C22 þ 2[C24 þ C26 þ C28]þ C30)}Waxiness index eP

(n-C21-n-C31)/P

(n-C15-n-C20)C29/C30e C29 norhopane/C30 hopaneG/C30 e Gammacerane/C30 hopane Ts: (C27 18a(H)-22,29,30-trisnorneohopane)Tm: (C27 17a(H)-22,29,30-trisnorhopane)MC30/HC30: C30moretane/C30 hopane.

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e9488

358 e 217 from GCeMS/MS transitions. The C30 tetracyclic poly-prenoids (TPP) compounds were calculated using: [TPPRatio¼ (2 � peak Ta)/(2 � peak Ta) þP

20R steranes]. TPP ratios ofthe analysed shale samples are in the range 0.41e0.48 (Table 2).

4.2. Geochemistry of major and trace elements

Geochemical signatures of sedimentary rocks are the product ofnumerous factors such as mineral composition, climate and

Figure 6. The m/z 191 mass fragmentograms (left) and m/z 217 mass fragmentog

tectonism (Johnsson, 1993), and are used here to give insight to theorigin, type and preservation of organic matter in relation topaleoenvironmental conditions. Major and selected trace elementconcentrations of the shale samples and several widely usedgeochemical ratios are listed in Table 3. The major oxides-SiO2,Al2O3 and Fe2O3 are the dominant constituents with an averageconcentration of 56.66 wt.%, 24.05 wt.%, and 5.23 wt.%, respectively(Table 3). Other major oxides such as CaO, K2O, TiO2, MgO, Na2O,and P2O5 are also present in low concentrations (Table 3). The

rams (right) of saturated hydrocarbon fractions of some studied Bima shales.

Table 2Steranes, diasteranes and TPP ratios calculated on m/z 217, m/z 414 to 259 and m/z 358 to 217 on GCeMS and GCeMS/MS.

Sample ID Steranes and diasteranes (m/z 217) Hopanes/(Hopanes þ P

20R steranes)TPPratios

Regular steranes (%) C29/C27

steraneC27/(C27 þ C29) Diast/Ster. Hop./Ster. 20S/20Sþ20R bb/bbþaa

C27 C28 C29

BM3A 34.1 15.9 50.0 1.46 0.42 1.51 8.36 0.41 0.62 e e

BM3B 37.9 22.7 39.4 1.04 0.49 1.09 8.78 0.44 0.58 0.74 0.46BM4 51.6 12.3 36.1 0.69 0.59 1.31 8.77 0.40 0.53 e e

BM5 45.1 11.2 43.7 0.96 0.57 1.16 11.21 0.54 0.62 0.72 0.43BM7 34.0 18.0 48.0 0.72 0.56 1.19 11.39 0.46 0.61 e e

BM9A 33.0 19.0 48.0 0.73 0.57 1.04 7.42 0.50 0.58 0.70 0.42BM9B 49.3 11.5 39.3 0.79 0.55 0.96 7.86 0.47 0.58 e e

BM10 40.2 13.6 46.2 0.90 0.48 1.02 12.8 0.48 0.57 0.73 0.46BM11 37.9 19.3 42.9 1.13 0.47 1.04 16.02 0.55 0.61 e e

BM33 50.7 14.1 35.2 0.69 0.59 1.11 7.06 0.51 0.52 0.76 0.41BM12,1 64.1 10.7 25.2 0.39 0.72 1.77 8.54 0.60 0.61 e e

BM12,2 47.1 8.7 44.2 0.93 0.52 1.18 7.48 0.44 0.66 0.71 0.48BM12,3 33.3 25.2 41.4 1.24 0.44 1.41 5.41 0.47 0.55 e e

BM12,4 26.1 18.0 55.9 2.14 0.32 1.72 10.3 0.44 0.55 e e

TPP ratio e {(2 � peak Ta/(2 � peak Ta) þ (P

27 norcholestanes)}.

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e94 89

Al2O3, Fe2O3, MgO, CaO, Na2O and K2O generally decrease withincreasing SiO2 content among the studied samples. There istherefore, a negative correlation between them (Adegoke et al.,2014). The Al/Si ratios are low (0.34e0.48) and the TiO2 contentsare relatively high (1.08e1.57 wt%; Table 3).

Most trace elements are concentrated in mudstone than in finegrained sandstone except Sr, Zr, and Hf. The trace element con-centrations of the shale samples of the Bima show Ba, V, Ni, Rb, andSr as the predominant with average values of 196, 144.9, 65.91,53.74 and 45.97 ppm, respectively, whilst Th, Cr, Ga, and Cu haveaverage values of 31.55, 20.27, 17.35 and 8.02 ppm, respectively(Table 3).

5. Discussions

5.1. Organic matter input

The origin of the organic matter was examined based on normalalkanes, hopanoids, steroids and related compounds (Figs. 5 and 6).The n-alkanes distribution patterns of saturated hydrocarbons canbe used to define organic matter input from different producers(Brassell et al., 1978). The long chain n-alkanes (>n-C25) are char-acteristic biomarkers for higher terrestrial plants (Eglinton andHamilton, 1967), whereas the short-chain n-alkanes (<n-C20) arepredominantly found in algae and microorganisms (Peters et al.,2005). The n-alkane patterns of the analysed shale samples showa bimodal distribution with a predominance of long-chain n-al-kanes molecular weight compounds (n-C22en-C28), indicatingmixed organic matter with a significant contribution of terrestrialorganic matter (Ebukanson and Kinghorn, 1986; Murray andBoreham, 1992). These interpretations are supported by moderateCPI ratios (>1.10) and a moderate to high waxiness index(0.89e2.84) (Table 1). Waxiness index is used to determine theamount of land-derived organic matter in sediments, based on theassumption that terrigenous material contributes high molecularweight normal alkane components (Peters et al., 2005). Tm (C2717a(H)-22,29,30-trisnorhopane) and Ts (C27 18a(H)-22,29,30-trisnorneohopane) are well known to be influenced by matura-tion, type of organic matter and lithology (e.g. Seifert andMoldowan, 1978; Peters and Moldowan, 1993). The Tm/Ts ratiosof 1.3e1.8 in the samples (Table 1) further indicate that the samplescontain a mixture of aquatic organic matter and land plants. Thepresence of C29 norhopane in some samples (Fig. 6) may also beassociated with land plant input (Rinna et al., 1996).

The dominance of C27 sterols (steranes) indicates a preponder-ance of mainly planktonic/algal organic matter, while the C29 ste-rols are more typically associated with land plants (Volkman,1986).In most of the analysed samples, the C27 and C29 steranes pre-dominate over the C28 steranes (Table 2; Fig. 6b), reflecting a mixedcontribution of aquatic algae andmicroorganismswith a significantamount of land plant as indicated by the regular sterane ratioternary diagram (Fig. 7; see Huang and Meinschein, 1979). This iscorroborated by low to moderate C29/C27 sterane ratios (Table 2;and Fig. 8). The moderate concentrations of tricyclic terpanescompared to those of tetracyclics terpanes (represented by C24tetracyclic/C26 tricyclic; Table 1) of the analysed samples is alsoattributed to a high contribution of terrigenous organic matterrelative to aquatic organic matter (Qiuhua et al., 2011). This issupported by relatively high C24te/C26, low - moderate C24/C23 andC22/C21, and high C26/C25 tricyclic terpane ratios (Table 2).

5.2. Redox conditions

The pristane/phytane (Pr/Ph) ratio is widely used to indicateredox conditions during sedimentation and diagenesis (Didyk et al.,1978; Chandra et al., 1994; Escobar et al., 2011). Organic matteroriginating predominantly from terrestrial plants deposited underoxidizing conditions is expected to contain high Pr/Ph ratio of >3,while low values of (Pr/Ph) ratio (<1) indicate anoxic conditions,and values between 1 and 3 suggest intermediate conditions(suboxic conditions) (Peters and Moldowan, 1993). In this respect,the Pr/Ph ratios (1.04e1.90, Table 1) of the organic matter in theBima shale sediments suggest deposition under sub-oxic to rela-tively anoxic conditions. The Pr/n-C17 and Ph/n-C18 ratios furtherindicate a suboxic to relatively anoxic environment during depo-sition of the sediments (Fig. 9). This redox condition is consistentwith sedimentological characteristics of the shale/mudstone facies(F11, see Sarki Yandoka et al., 2014). The palaeo-redox conditionscan also be evaluated from trace element data (Table 3). The ratiosof trace elements such as Ba, V, Ni, Rb, Sr and Cr revealed palaeo-redox conditions during sedimentation of siliciclastic rocks(Reimann and de Caritat, 1998; Fu et al., 2011; MacDonald et al.,2010; Harris, 2000; Harris et al., 2004; Sageman and Lyons, 2003;Lerman, 1989; Wang et al., 1997; Roy and Roser, 2013). Particu-larly, Vanadium (V) and Nickel (Ni) are good indicators of redoxconditions during deposition (Galarraga et al., 2008; Bechtel et al.,2001; Barwise, 1990). The relative proportions of V and Ni arecontrolled by depositional environment (Lewan, 1984). A ratio of V/

Nigr

while

tions

high

ewith

were

5.3.E

C3

dep

osgen

erthan

hop

ansu

ggeenvirobserved

insam

ples

derived

fromlow

-salinity

(i.e.fresh

tobrackish

)lacu

strineen

vironmen

tsan

dare

presen

tin

relativelylow

levelsin

samples

derived

fromsalin

e(m

arine

and

lacustrin

e)

Table 3Major (wt.%) and trace (ppm) elements composition of Bima shale samples.

Sample ID Major elements (wt. %) Trace elements (ppm)

SiO2 Al2O3 TiO2 Fe2O3 MnO CaO MgO Na2O K2O P2O5 Ti/Al Log K/N V Ni Cu Cr Sr Ba Rb Ga Th V/Ni Sr/Ba Ga/Rb Sr/Cu

BM3A 52.59 24.25 1.565 3.324 0.003 1.09 1.41 0.27 7.13 0.18 0.06 1.41 160.1 84.3 6.21 17.47 38.68 146.8 39.72 13.63 33.6 1.90 0.26 0.34 6.23BM3B 52.68 24.34 1.495 3.315 0.003 1.09 1.42 0.28 7.13 0.18 0.06 1.40 137.6 54.2 6.17 14.80 44.12 174.0 30.72 17.17 30.4 2.54 0.25 0.56 7.15BM4 56.74 26.67 1.333 3.933 0.020 1.49 1.53 0.31 7.26 0.21 0.05 1.37 158.1 68.1 6.78 17.40 37.60 174.8 45.48 20.3 35.4 2.32 0.22 0.45 5.55BM5 50.94 24.50 1.464 4.061 0.003 1.32 1.49 0.197 7.58 0.39 0.06 1.61 161.1 81.2 6.91 19.65 59.04 149.9 57.16 16.45 29.0 1.98 0.39 0.29 8.54BM7 58.86 24.84 1.298 4.356 0.019 0.94 1.58 0.45 6.96 0.14 0.05 1.19 148.3 61.3 7.60 19.63 74.68 169.4 67.62 14.96 28.2 2.42 0.44 0.22 9.83BM9A 58.51 24.28 1.203 4.656 0.025 1.19 1.69 0.46 6.86 0.27 0.05 1.17 144.1 59.6 8.23 19.00 31.04 141.4 56.56 16.38 33.4 2.42 0.22 0.29 3.77BM9B 58.77 24.17 1.164 5.571 0.026 1.25 1.50 0.57 6.28 0.26 0.05 1.40 143.6 62.1 11.12 19.99 31.82 199.3 59.00 11.06 38.4 2.31 0.16 0.19 2.86BM10 57.96 24.16 1.223 5.665 0.035 1.50 1.67 0.39 6.58 0.35 0.05 1.23 105.5 46.8 6.03 14.08 28.98 141.9 77.86 12.46 21.6 2.25 0.20 0.16 4.81BM11 58.16 24.29 1.249 5.780 0.048 1.37 1.59 0.50 6.33 0.25 0.05 1.20 144.2 63.1 9.30 19.96 37.68 186.8 59.24 34.54 38.2 2.29 0.20 0.58 4.05BM33 57.52 26.18 1.462 3.849 0.015 1.23 1.54 0.32 7.08 0.16 0.06 1.34 139.2 58.9 8.22 20.54 44.18 195.3 68.90 10.88 39.6 2.36 0.23 0.16 5.37BM12,1 57.36 23.31 1.397 7.516 0.063 1.10 2.21 0.47 5.82 0.26 0.06 1.19 145.5 67.1 9.98 20.20 26.32 239.0 53.74 18.40 26.12 2.17 0.11 0.34 2.64BM12,2 57.80 23.35 1.326 7.420 0.047 1.07 2.17 0.47 5.70 0.26 0.06 1.19 156.6 75.2 10.59 21.88 31.58 249.2 48.48 23.48 23.4 2.08 0.13 0.48 2.98BM12,3 55.30 21.70 1.193 7.653 0.123 4.23 3.31 0.79 3.85 0.31 0.05 1.09 148.2 71.7 10.95 38.76 86.78 291.9 54.43 22.66 30.0 2.07 0.30 0.42 7.93BM12,4 60.05 20.64 1.075 6.144 0.116 2.78 2.62 0.29 3.48 0.31 0.05 1.07 136.3 69.2 4.23 20.38 71.02 284.5 33.38 10.49 34.4 1.97 0.25 0.31 16.79Average 56.66 24.05 1.32 5.23 0.04 1.55 1.84 0.41 6.29 0.25 0.05 1.28 144.9 65.91 8.02 20.27 45.97 196.0 53.74 17.35 31.55 2.22 0.24 0.34 6.32

Figure

betwee

shalee

Meinsc

Figure

8.Cross-plots

ofpristane/phytane

ratiosversus

C29 /C

27regular

steranesof

thestudied

Bimashale

samples

suggestingaprom

inentsuboxic

conditionof

deposition.

B.M.Sarki

Yandokaet

al./Marine

andPetroleum

Geology

61(2015)

82e94

90

eaterthan

3indicates

dep

ositionin

ared

ucin

genviron

aratio

of1.9

e3indicates

dep

ositionunder

suboxic

(Galarraga

etal.,20

08).Thecon

centration

ofVan

adium

rthan

Nickel

(Ni)in

allthean

alysedsh

alesam

ples

(TaV/N

iratioin

theran

geof1.90

e2.54,in

dicatin

gthat

the

dep

ositedunder

suboxic

condition

s.

nvironment

ofdeposition

andwater

salinity

1 -22R-hop

ane/C

30 -hop

aneratio

canbe

used

toinfer

dif

itional

environ

men

ts(Peters

etal.,

2005).

This

raally

high

erthan

0.25for

marin

een

vironmen

tswhereas

0.25for

lacustrin

esettin

gs(Peters

etal.,

2005).

C3

eratios

oftheBim

asam

ples

arein

theran

geof

0.13stin

gthat

the

Bim

ash

aleswere

dep

ositedin

alacu

onmen

t(Fig.

10).C30

tetracyclicpolyp

renoid

s(TPP

7.Ternary

diagramof

regularsteranes

(C27 e

C29 )

showing

therela

nsterane

compositions

andorganic

matter

inputindicating

theanalys

xtractsare

composed

ofmixed

organicmatter

(modifi

edafter

Hu

hein,1979).

men

t,con

di-

(V)is

ble3)

shales

ferent

tiois

lower

1 R/C

30e0.24,strin

e)

are

tionshiped

Bima

angand

Figure 9. Phytane to n-C18 alkane (Ph/n-C18) versus pristane to n-C17 alkane (Pr/n-C17),showing depositional conditions and type of organic matter of the analysed Bima shalesamples.

Figure 11. Cross plot TPP ratios versus hopane/(hopane þ P20R steranes) indicating

lacustrine depositional environment of Bima shale sediments (modified after Holbaet al., 2003).

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e94 91

environments (Holba et al., 1999, 2000, 2003; Dzou et al., 1999). TheTPP ratios of the shale sediments are relatively high, ranging from0.41 to 0.48 with an average value of 0.44% (Table 2) indicating thatthe samples were deposited in freshwater lacustrine environment.This is supported by high hopane/sterane ratios (Table 2) whichindicate fresh/brackish water conditions (Holba et al., 2003) andthe plot of TPP ratios against Hopanes/HopanesþP

20R steranes(Fig. 11) which indicates a lacustrine depositional environment.This is consistent with the gammacerane index (Table 2) as gam-macerane is a major biomarker in many lacustrine and marinetypes of sediment. Gammacerane is also generally regarded as anindicator of salinity (and density) stratified water column and apossible marker for photic zone anoxia during deposition. It isbelieved to have been derived from tetrahymanol in bacterivorousciliates living at the boundary of a high salinity water layer with anupper layer of less saline water (Sinninghe Damst�e et al., 1995;Grice et al., 1998). High gammacerane index values are oftenassociated with low Pr/Ph ratios in the extracts (Peters et al., 2005).The low gammacerane concentrations, and thus low gammaceraneindex (Avg. 0.14) (Table 1), provide evidence for low salinity strat-ification during deposition of the sediments. Strontium (Sr) andbarium (Ba) are two elements regarded as empirical indicators ofpaleo-salinity (Liu, 1980; Liu et al., 1984; Deng and Qian, 1993;Wang, 1996). A high Sr/Ba ratio reflects high salinity, and a low

Figure 10. Cross plot of C31R/C30 hopane ratios versus pristane/phytane of the ana-lysed Bima shale samples (modified after Peters et al., 2005).

Sr/Ba ratio indicates low salinity (Deng and Qian, 1993). The shalesamples have low Sr/Ba ratio (avg. 0.24), indicating low salinitywater during sedimentation (Table 3). This agrees with the crossplot of Sr/Ba ratio versus gammacerane index (Fig. 12). Thus, theanalysed Bima sediments are thought to have been deposited inrelatively freshwater lacustrine environment.

5.4. Paleoclimate conditions

Climate has extreme effect on mineralogy and geochemistry ofsediments (Rieu et al., 2007; Yan et al., 2010). Weathering is relatedto climate. Intense weathering (especially chemical) is associatedwith warm and humid climate whereas minimal weathering isassociated with cold and arid climate (Nesbitt et al., 1996). In thisstudy, the palaeoclimatic conditions were evaluated based pri-marily on major and trace elements distribution in the shale sam-ples (Table 3). The Strontium (Sr)/Copper (Cu) ratio is an importantelemental indicator for paleoclimate conditions (Lerman, 1989;Wang et al., 1997). Although Sr and Cu concentrations is influ-enced by the scale of a depositional basin andwater depth (Jia et al.,2013), generally high Sr/Cu ratios of >5.0 are suggested to reflect ahot-arid climate, and low Sr/Cu ratios of 1.3e5.0 indicate a warm-humid climate (Lerman, 1989). The Sr/Cu ratios of the studied

Figure 12. The diagram of Sr/Ba ratio versus gammacerane index for the analysedBima shales showing low salinity.

Figure 13. Bivariate SiO2 versus (Al2O3 þ K2O þ Na2O) contents indicating thepalaeoclimate discrimination of the analysed samples (After Suttner and Dutta, 1986).

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e9492

shales (average 6.4, Table 3) indicate a hot-arid climate. This issupported by plots on the binary SiO2 versus (Al2O3 þ K2O þ Na2O)diagram of Suttner and Dutta (1986) which shows that the analysedsediments were deposited during semi-arid climatic conditions(Fig. 13). Arid to semi-arid paleoclimatic condition of deposition forthe Bima Formationwas earlier suggested from palynological studyby Abubakar et al. (2006).

5.5. Tectonic setting

Major elements distribution in sedimentary rocks is signifi-cantly controlled by the tectonic settings of their provenances (e.g.Maynard et al., 1982; Bhatia, 1983; Bhatia and Crook, 1986; Roserand Korsch, 1986). Roser and Korsch (1986) used log (K2O/Na2O)versus SiO2 to determine the tectonic setting of the source ofterrigenous sedimentary rocks. The SiO2 and K2O/Na2O increasefrom volcanic-arc to the active continental margin, to passivemargin settings. The analysed shale samples of the Bima Formationplot in the field of passive continental margin on the log (K2O/Na2O) versus SiO2 diagram (Fig. 14). This tectonic setting inferredfor the provenance of the studied sediments agrees with the tec-tonic events in West and Central Africa during the Cretaceousperiod (Genik, 1993).

Figure 14. Bivariate SiO2 versus K2O/Na2O indicating tectonic setting discriminationdiagram (After Roser and Korsch, 1986).

5.6. Factors influencing organic matter input and preservation

The preservation of organic matter is a complex physical andchemical process and several factors have been proposed as theprimary controls on organic matter burial and preservation insediments (Zonneveld et al., 2010). These factors include sedi-mentary burial rate, clay mineralogy, and water column oxygena-tion levels (Hofmann et al., 2000). Climate too has been suggestedas one of the factors controlling the organic matter input. As sug-gested above, the sediments of the Lower Bima Formation weredeposited during semi-arid climatic conditions. Generally, semi-arid climatic condition is consistent with moderate phyto-plankton growth and relative increase in biological productivitywithin the photic zone of water columns (Talbot, 1988). This issupported by the relatively high contents of phosphorus (P) (avg.0.25, Table 3) (e.g. Shen et al., 2010).

Stratified water column of low salinity and suboxic to relativelyanoxic depositional conditions, earlier interpreted from the Sr/Ba,V/Ni, and Pr/Ph ratios (Tables 1 and 3) and the presence of gam-macerane (Fig. 6a), may be suggested as an important factor for thepreservation of the organic matter during deposition. Also, theclayey lithology of the studied samples perhaps provided physicalprotection against decay for the organic matter (e.g. Ross andBustin, 2009) which favoured its preservation.

6. Conclusion

An integrated organic and inorganic geochemical investigationof Early Cretaceous lacustrine sediments of the Bima Formation inthe Yola Sub-basin of the Northern Benue Troughwas performed todetermine the organic matter source input, paleodepositionalenvironment, redox conditions and their response to climate andtectonism. The results have led to the following conclusions:

(1) Biomarkers from the shales provide evidence for a shallowlacustrine environment that received contributions ofaquatic algae and microorganisms with a significant amountof terrigenous organic matter input, deposited under suboxicto relatively anoxic conditions.

(2) Based on the ratios of trace elements such as Sr, Ba, V and Niin the analysed sediments, a water column with low salinityand suboxic to relatively anoxic conditions is inferred. Thewater column could be stratified during deposition as evi-denced by the presence of gammacerane biomarker. Hence,these bottom water conditions are recognized as one of thecontrolling factors for the organicmatter preservation duringthe sedimentation.

(3) The lacustrine sediments were deposited under semi-aridclimatic conditions within passive continental marginsetting during the Early Cretaceous period as shown byinorganic geochemical characteristics. This semi-arid cli-matic condition is suggested as one of the controlling fac-tors for relative increase in nutrient supply, leading toincrease in bioproductivity within the photic zone of thewater columns, as supported by relatively high phosphoruscontent.

(4) The paleoenvironment of deposition of the Bima Formation(and its stratigraphic location) is within the context of anEarly Cretaceous regionally extensive alluvial fan e braidedriver e lacustrine depositional system of the WCARS. Thisdepositional system is proven as part of a petroleum systemin contiguous rifted basins of theWCARS. The presence of thelacustrine sediments in the Bima Formation may suggestpotential occurrence of Early Cretaceous petroleum sourcerocks in the Yola Sub-basin of the Northern Benue Trough; an

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e94 93

insight which is expected to guide future hydrocarbonexploration campaign in the basin.

Acknowledgement

The authors wish to acknowledge the financial support of theNational Centre for Petroleum Research and Development, EnergyCommission of Nigeria and the University of Malaya, Malaysia (IPPPResearch Grant No: PG140-2012B). The authors are also grateful forthe technical assistance of Mr. Mohamed Zamri Rashid andMrs. SitiJariani of the Department of Geology and Biology in the Universityof Malaya.

Appendix-A. Peak assignments for alkane hydrocarbons inthe gas chromatograms of saturated fractions in the m/z 191(I) and 217 (II) mass fragmentograms.

Compound abbreviation

(I) Peak no.C21 C21 Tricyclic (Cheilanthane) Tri C21

C22 C22 Tricyclic (Cheilanthane) Tri C22

C23 C23 Tricyclic (Cheilanthane) Tri C23

C24 C24 Tricyclic (Cheilanthane) Tri C24

C24 C24 Tetracyclic Tetra C24

C25 C25 Tricyclic (Cheilanthane) Tri C25

C26 C26 Tricyclic (Cheilanthane) Tri C26

Ts 18a(H),22,29,30-trisnorneohopane TsTm 17a(H),22,29,30-trisnorhopane Tm29 17a,21b(H)-nor-hopane C29 hop30 17a,21b(H)-hopane Hopane30M 17 b,21a (H)-Moretane C30Mor31S 17a,21b(H)-homohopane (22S) C31(22S)31R 17a,21b(H)-homohopane (22R) C31(22R)32S 17a,21b(H)-homohopane (22S) C32(22S)32R 17a,21b(H)-homohopane (22R) C32(22R)33S 17a,21b(H)-homohopane (22S) C33(22S)33R 17a,21b(H)-homohopane (22R) C33(22R)(II) Peak no.a 13b,17a(H)-diasteranes 20S Diasteranesb 13b,17a(H)-diasteranes 20R Diasteranesc 13a,17b(H)-diasteranes 20S Diasteranesd 13a,17b(H)-diasteranes 20R Diasteranese 5a,14a(H), 17a(H)-steranes 20S aaa20Sf 5a,14b(H), 17b(H)-steranes 20R abb20Rg 5a,14b(H), 17b(H)-steranes 20S abb20Sh 5a,14a(H), 17a(H)-steranes 20R aaa20R

References

Abdullah, W.H., 1999. Organic facies variations in the Triassic shallow marine anddeep marine shales of central Spitsbergen, Svalbard. Mar. Pet. Geol. 16,467e481.

Abubakar, M.B., 2006. Biostratigraphy, Palaeoenvironments and OrganicGeochemistry of the Cretaceous Sequences of the Gongola Basin, Upper BenueTrough (PhD unpublished thesis). Abubakar Tafawa Balewa University Bauchi,Nigeria, p. 315.

Abubakar, M.B., 2014. Petroleum potentials of the Nigerian Benue Trough andAnambra Basin: a regional Synthesis. Nat. Resour. 5 (1), 25e58.

Abubakar, M.B., Obaje, N.G., Luterbacher, H.P., Dike, E.F.C., Ashraf, A.R., 2006.A report on the occurrence of Albian e Cenomanian elater-bearing pollen inNasara-1 well, Upper Benue Trough, Nigeria: biostratigraphic and paleo-climatological implications. J. Afr. Earth Sci. 45, 347e354.

Abubakar, M.B., Dike, E.F.C., Obaje, N.G., Wehner, H., Jauro, A., 2008. Petroleumprospectivity of Cretaceous formations of Gongola Basin, Upper Benue Trough,Nigeria; an organic geochemical perspective on a migrated oil controversy.J. Pet. Geol. 31 (4), 387e408.

Adegoke, A.K., Abdullahi, W.H., Hakimi, M.H., Sarki Yandoka, B.M., 2014.Geochemical characterisation of Fika Formation in the Chad (Bornu) Basin,northeastern Nigeria: implications for depositional environment and tectonicsetting. Appl. Geochem. 43, 1e12.

Allix, P.E., Grosdidier, E., Jardine, S., Legeox, O., Popoff, M., 1981. Decouverte d Aptiensuperieur a Albien inferieur date par microfossiles dans la serie detritique(Nigeria). C. R. Acad. Sci. 292, 1291e1294.

Amijaya, H., Schwarzbauer, J., Littke, R., 2006. Organic geochemistry of the LowerSuban coal seam, South Sumatra Basin, Indonesia: palaeoecological and thermalmetamorphism implications. Org. Geochem. 37, 261e279.

Avbovbo, A.A., Ayoola, E.O., Osahon, G.A., 1986. Depositional and structural styles inChad Basin of Northeastern Nigeria. Am. Assoc. Pet. Geol. Bull. 70, 1787e1798.

Barwise, A.J.G., 1990. Role of nickel and vanadium in petroleum classification. En-ergy Fuels 4, 647e652.

Bechtel, A., Gratzer, R., Sachsenhofer, R.F., 2001. Chemical characteristics of UpperCretaceous (Turonian) jet of the Gosau Group of Gams/Hieflau (Styria, Austria).Int. J. Coal Geol. 46, 27e49.

Benkhelil, J., 1982. Benue Trough and Benue Chain. Geol. Mag. 119 (2), 158e168.Benkhelil, J., 1989. The origin and evolution of the Cretaceous Benue Trough

(Nigeria). J. Afr. Earth Sci. 8, 251e282.Bhatia, M.R., 1983. Plate tectonics and geochemical composition of sandstones.

J. Geol. 91, 611e627.Bhatia, M.R., Crook, K.A.W., 1986. Trace element characteristics of graywackes and

tectonic setting discrimination of sedimentary basins. Contrib. Mineral. Petrol.92, 181e193.

Brassell, S.C., Eglinton, G., Maxwell, J.R., Philp, R.P., 1978. Natural background ofalkanes in the aquatic environment. In: Hutzinger, L.H., van Lelyveld, O.,Zoeteman, B.C.J. (Eds.). Pergamon, Oxford, pp. 69e86.

Carter, J.D., Barber, W., Tait, E.A., Jones, G.P., 1963. The geology of parts of theAdamawa, Bauchi and Bornu Provinces in Northeastern Nigeria. Geol. Surv.Niger. Bull. 30, 53e61.

Chandra, K., Mishra, C.S., Samanta, U., Gupta, A., Mehrotra, K.L., 1994. Correlation ofdifferent maturity parameters in the AhmedabadeMehsana block of the Cam-bay basin. Org. Geochem. 21, 313e321.

Deng, H.W., Qian, K., 1993. Analysis on Sedimentary Geochemistry and Environ-ment. Science Technology Press, Gansu, pp. 15e85 (in Chinese).

Didyk, B.M., Simoneit, B.R.T., Brassell, S.C., Eglinton, G., 1978. Organic geochemicalindicators of palaeoenvironmental conditions of sedimentation. Nature 272,216e222.

Dzou, L.I., Holba, A.G., Ramon, J.C., Moldowan, J.M., Zinniker, D., 1999. Application ofnew diterpane biomarkers to source, biodegradation and mixing effects onCentral Llanos Basin oils, Colombia. Org. Geochem. 30, 515e534.

Ebukanson, E.J., Kinghorn, R.R.F., 1986. Maturity of organic matter in the Jurassic ofsouthern England and its relation to the burial history of the sediments. J. Pet.Geol. 93, 259e280.

Eglinton, G., Hamilton, R.G., 1967. Leaf epicuticular waxes. Science 156, 1322e1344.Escobar, M., M�arquez, G., Inciarte, S., Rojas, J., Esteves, I., Malandrino, G., 2011. The

organic geochemistry of oil seeps from the Sierra de Perij�a eastern foothills,Lake Maracaibo Basin, Venezuela. Org. Geochem. 42, 727e738.

Farhaduzzaman, M., Wan, H.A., Islam, M.A., Pearson, M.J., 2012. Source rock po-tential of organic-rich shales in the Tertiary Bhuban and BokaBil Formations,Bengal Basin, Bangladesh. J. Pet. Geol. 35, 357e376.

Fu, X., Wang, J., Zeng, Y., Cheng, J., Tano, F., 2011. Origin and mode of occurrence oftrace elements in marine oil shale from the Shengli River Area, Northern Tibet,China. Oil Shale 28, 487e506.

Galarraga, F., Reategui, K., Martïnez, A., Martínez, M., Llamas, J.F., M�arquez, G., 2008.V/Ni ratio as a parameter in palaeoenvironmental characterisation of non-mature medium-crude oils from several Latin American basins. J. Pet. Sci.Eng. 61, 9e14.

Genik, G.J., 1993. Petroleum geology of Cretaceous-Tertiary rift basins in Niger,Chad, and Central African Republic. Am. Assoc. Pet. Geol. Bull. 77, 1405e1434.

Grant, N.K., 1971. South Atlantic, Benue Trough and Gulf of Guinea Cretaceous triplejunction. Bull. Geol. Soc. Am. 82, 2295e2298.

Grice, K., Schouten, S., Peters, K.E., Sinninghe Damste, J.S., 1998. Molecular isotopiccharacterisation of hydrocarbon biomarkers in Palaeocene-Eocene evaporitic,lacustrine source rocks from the Jianghan Basin, China. Org. Geochem. 29,1745e1764.

Guiraud, M., 1990. Tectono-sedimentary frameworks of the Early Cretaceous con-tinental Bima Formation (Upper Benue Trough, NE Nigeria). J. Afr. Earth Sci. 10,341e353.

Guiraud, R., Maurin, J.E., 1992. Early Cretaceous rifts of Western and Central Africa:an overview. In: Ziegler, P.A. (Ed.), Geodynamics of Rifting, Volume II. CaseHistory Studies on Rifts: North and South America and Africa, Tectonophysics,vol. 213, pp. 153e168.

Hakimi, M.H., Abdullah, W.H., 2013. Organic geochemical characteristics and oilgenerating potential of the Upper Jurassic Safer shale sediments in the Marib-Shabowah Basin, western Yemen. Org. Geochem. 54, 115e124.

Hakimi, M.H., Abdullah, W.H., Shalaby, M.R., 2011. Organic geochemical character-istics and depositional environments of the Jurassic shales in the Masila Basinof Eastern Yemen. GeoArabia 16, 47e64.

Harris, N.B., 2000. The Toca carbonate, Congo Basin: response to an evolving riftlake. In: Mello, M.R., Katz, B.J. (Eds.), Petroleum Systems of South AtlanticMargins, AAPG Memoir, vol. 73, pp. 341e360.

Harris, N.B., Freeman, K.H., Pancost, R.D., White, T.S., Mitchell, G.D., 2004. Thecharacter and origin of lacustrine source rocks in the Lower Cretaceous synriftsection, Congo Basin, west Africa. AAPG Bull. 88, 1163e1184.

Hofmann, P., Ricken, W., Schwark, L., Leythaeuser, D., 2000. Carbon-sulfur-iron re-lationships and 13C of organic matter for late Albian sedimentary rocks from

B.M. Sarki Yandoka et al. / Marine and Petroleum Geology 61 (2015) 82e9494

North Atlantic Ocean: paleoceanographic implications. Palaeogeogr. Palae-oclimatol. Palaeoecol. 163, 97e113.

Holba, A.G., Ellis, L., Fincannon, A.L., 1999. Discrimination of non-marine and marinedepositional environments: testing new and old geochemical parameters. In:Poster Session, 19th International Meeting on Organic Geochemistry, 6e10September, 1999, Istanbul Turkey.

Holba, A.G., Ellis, L., Tegelaar, E., Singletary, M.S., Albrecht, P., 2000. Tetracyclicpolyprenoids: indicators of fresh water (lacustrine) algal input. Geology 28 (3),251e254.

Holba, A.G., Dzoub, L.I., Wood, G.D., Ellisd, L., Adame, P., Schaeffere, P., Albrechte, P.,Greenef, T., Hughes, W.B., 2003. Application of tetracyclic polyprenoids as in-dicators of input from fresh-brackish water environments. Org. Geochem. 34,441e469.

Huang, W.Y., Meinschein, W.G., 1979. Sterols as ecological indicators. Geochim.Cosmochim. Acta 43, 739e745.

Jia, J., Liu, Z., Strobl, S.A.I., Bechtel, A., Sun, P., 2013. Tectonic and climate control ofoil shale deposition in the Upper Cretaceous Qingshankou Formation (SongliaoBasin, NE China). Int. J. Earth Sci. 102, 1717e1734.

Johnsson, M.J., 1993. The system controlling the composition of clastic sediments.In: Johnsson, M.J., Basu, A. (Eds.), Processes Controlling the Composition ofClastic Sediments, Geological Society of America Special Paper, vol. 284,pp. 1e19.

King, L.C., 1950. Outline and distribution of Gondwanaland. Geol. Mag. 87, 353e359.Kogbe, C.A., 1976. Paleogeographic history of Nigeria from Albian times. In:

Kogbe, C.A. (Ed.), Geology of Nigeria. Elizabethan Publishers, Lagos, Nigeria,pp. 237e252.

Korkmaz, S., Kara Gülbay, R., 2007. Organic geochemical characteristics and depo-sitional environments of the Jurassic coals in the eastern Taurus of SouthernTurkey. Int. J. Coal Geol. 70, 292e304.

Lerman, A., 1989. Lakes: Chemistry, Geology, Physics. Geological Press, Beijing,pp. 10e100 (in Chinese).

Lewan, M.D., 1984. Factors controlling the proportionality of vanadium to nickel incrude oils. Geochim. Cosmochim. Acta 48, 2231e2238.

Liu, B.J., 1980. Sedimentary Petrology. Geological Press, Beijing, pp. 13e89 (inChinese).

Liu, Y.J., Cao, L.M., Li, Z.L., Wang, H.N., Chu, T.Q., Zhang, J.R., 1984. ElementGeochemistry. Science Press, Beijing, pp. 283e372 (in Chinese).

MacDonald, R., Hardman, D., Sprague, R., Meridji, Y., Mudjiono, W., Galford, J.,Rourke, M., Dix, M., Kelto, M., 2010. Using elemental geochemistry to improvesandstone reservoir characterization: a case study from the Unayzah A intervalof Saudi Arabia. In: SPWLA 51st Annual Logging Symposium, June 19e23,pp. 1e16.

Maynard, J.B., Valloni, R., Yu, H.S., 1982. Composition of modern deep-sea sandsfrom arc-related basins. In: Leggett, J.K. (Ed.), Trench and Fore-arc Sedimenta-tion, The Geological Society of London, (Special Publications 10), pp. 551e561.

Mohammed, A.Y., Pearson, M.J., Ashcroft, W.A., Illiffe, J.E., Whiteman, A.J., 1999.Modeling petroleum generation in the Southern Muglad rift basin, Sudan. Am.Assoc. Pet. Geol. Bull. 83, 1943e1964.

Murray, A.P., Boreham, C.J., 1992. Organic Geochemistry in Petroleum Exploration.Australian Geological Survey Organization, Canberra, p. 230.

Nesbitt, H.W., Young, G.M., McLennan, S.M., Keays, R.R., 1996. Effects of chemicalweathering and sorting on the petrogenesis of siliciclastic sediments, withimplications for provenance studies. J. Geol. 104, 525e542.

Nwajide, C.S., 2013. Geology of Nigeria's Sedimentary Basins. CSS Bookshops Ltd,Lagos, Nigeria, p. 565.

Obaje, N.G., Ulu, O.K., Maigari, A.S., Abubakar, M.B., 2000. Sequence stratigraphicand palaeoenvironmental interpretation of the heterohelicids for the PindigaFormation, Northeastern Benue Trough, Nigeria. J. Min. Geol. 36 (2), 191e198.

Obaje, N.G., Wehner, H., Abubakar, M.B., Isah, M.T., 2004. Nasara 1 well GongolaBasin (Upper Benue Trough, Nigeria): source rock evaluation. J. Pet. Geol. 27 (2),191e206.

Offodile, M.E., 1976. The Geology of the Middle Benue, Nigeria. PalaeontologicalInstitution of the University of Uppsala, Sweden, pp. 1e116. Special volume 4.

Olade, M.A., 1975. Evolution of Nigeria's Benue trough: a tectonic model. Geol. Mag.112, 575e583.

Ourisson, G., Albrecht, P., Rohmer, M., 1979. Hopanoids: palaeochemistry andbiochemistry of a group of natural products. Pure Appl. Geochem. 51, 709e729.

Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting MolecularFossils in Petroleum and Ancient Sediments. Prentice-Hall, Inc, EnglewoodCliffs, New Jersey.

Peters, K.E., Walters, C.C., Moldowan, J.M., 2005 The Biomarker Guide: Biomarkersand Isotopes in Petroleum Exploration and Earth History, second ed., vol. 2.Cambridge University Press, Cambridge.

Qiuhua, Y., Zhigang, W., Youjun, T., 2011. Geochemical characteristics of Ordoviciancrude oils in the northwest of the Tahe oil field, Tarim Basin. Chin. J. Geochem.30, 93e98.

Reimann, C., de Caritat, P., 1998. Chemical Elements in the Environment. Springer-Verlag, New York, Inc., New York, p. 397.

Rieu, R., Allen, P.A., Pl€otze, M., Pettke, T., 2007. Climatic cycles during a Neo-proterozoic“snowball” glacial epoch. Geology 35, 299e302.

Rinna, J., Rullk€otter, J., Stein, R., 1996. Hydrocarbons as indicators for provenanceand thermal history of organic matter in late Cenozoic sediments from Hole909C, Fram Strait. Proc. Ocean Drill. Progr. Sci. Results 151, 407e414.

Roser, B.P., Korsch, R.J., 1986. Determination of tectonic setting of sandstone-mudstone suites using SiO2 content and K2O/Na2O ratio. J. Geol. 94,635e650.

Ross, D.J.K., Bustin, R.M., 2009. Investigating the use of sedimentary geochemicalproxies for palaeoenvironment interpretation of thermally mature organic-richstrata: examples from the DevonianeMississippian shales, Western CanadianSedimentary Basin. Chem. Geol. 260, 1e19.

Roy, D.K., Roser, B.P., 2013. Climatic control on the composition of Carboniferous-Permian Gondwana sediments, Khalaspir basin, Bangladesh. Gondwana Res.23, 1163e1171.

Sageman, B.B., Lyons, T.W., 2003. Geochemistry of fine-grained sediments andsedimentary rocks. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise onGeochemistry. Elsevier, Amsterdam. Chapter 7.06.

Samaila, N.K., Abubakar, M.B., Dike, E.F.C., Obaje, N.G., 2006. Description of soft-sediment deformation structures in the Cretaceous Bima Sandstone from theYola Arm, Upper Benue Trough, Northeastern Nigeria. J. Afr. Earth Sci. 44,66e74.

Sarki Yandoka, B.M., Abubakar, M.B., Abdullah, W.H., Amir Hassan, M.H.,Adamu, B.U., Jitong, J.S., Aliyu, A.H., Adegoke, K.A., 2014. Facies analysis,palaeoenvironmental reconstruction and stratigraphic development of theEarly Cretaceous sediments (Lower Bima Member) in the Yola Sub-basin,Northern Benue Trough, NE Nigeria. J. Afr. Earth Sci. 96, 168e179.

Sarki Yandoka, B.M., Abdullah, W.H., Abubakar, M.B., Hakimi, M.H., Mustapha, K.A.,Adegoke, K.A., 2015. Organic geochemical characteristics of Cretaceous LamjaFormation from Yola Sub-basin, Northern Benue Trough, NE Nigeria: implica-tion for hydrocarbon-generating potential and paleodepositional setting. Arab.J. Geosci. http://dx.doi.org/10.1007/s12517-014-1713-3.

Schull, T.J., 1988. Rift basins of interior Sudan: petroleum exploration and discovery.AAPG Bull. 72, 1128e1142.

Seifert, W.K., Moldowan, J.M., 1978. Applications of steranes, terpanes and mono-aromatics to the maturation, migration and source of crude oils. Geochim.Cosmochim. Acta 42, 77e95.

Shen, J., Xue, B., Wu, J.L., Wu, Y.H., Liu, X.Q., Yang, X.D., Liu, J., Wang, S.M., 2010. Lakesediments and Environmental Evolution. Science Press, Beijing, pp. 191e227 (inChinese).

Sinninghe Damst�e, J.S., Kenig, F., Koopmans, M.P., Koster, J., Schouten, S., Hayes, J.M.,de Leeuw, J.W., 1995. Evidence for gammacerane as an indicator of water col-umn stratification. Geochim. Cosmochim. Acta 59, 1895e1900.

Stoneley, R., 1966. The Niger Delta region in the light of the theory of continentaldrift. Geol. Mag. 103, 385e397.

Sun, Tao, Wang, Chengshan, Duan, Yi, Li, Yalin, Hu, Bin, 2014. The organicgeochemistry of the EoceneeOligocene black shales from the Lunpola Basi-central Tibet. J. Asian Earth Sci. 79, 468e476.

Suttner, L.J., Dutta, P.K., 1986. Alluvial sandstone composition and palaeoclimate. 1.Framework mineralogy. J. Sediment. Pet. 56 (3), 329e345.

Talbot, M.R., 1988. The Origins of Lacustrine Oil Source Rocks: Evidence from theLakes of Tropical Africa. In: Geological Society, London, Special Publications, vol.40, pp. 29e43.

Volkman, J.K., 1986. A review of sterol biomarkers for marine and terrigenousorganic matter. Org. Geochem. 9, 83e89.

Wang, A.H., 1996. Discriminant effect of sedimentary environment by the Sr/Baratio of different existing forms. Acta Sedimentol. Sin. 14, 168e173.

Wang, J.S., Huang, X.Z., Sui, J.C., Shao, H.S., Yan, C.F., Wang, S.Q., He, Z.R., 1997.Evolutional characteristics and their paleoclimate significance of trace elementsin the Hetaoyuan Formation, Biyang depression. Acta Sedimentol. Sin. 15,65e70 (in Chinese with English abstract).

Yan, D., Chen, D., Wang, Q., Wang, J., 2010. Large-scale climatic fluctuations in thelatest Ordovician on the Yangtze block, South China. Geology 38, 599e602.

Zarboski, P.F., Ugodulunwa, A., Idornigie, P., Nnabo, K., Ibe, 1997. Stratigraphy andstructure of the Cretaceous Gongola Basin, Northeast Nigeria. Bull. Cent. Res.Explor. Prod. Elf Aquat. 21 (1), 154e185.

Zonneveld, K.A.F., Versteegh, G.J.M., Kasten, S., Eglinton, T.I., Emeis, K.-C., Huguet, C.,Koch, B.P., de Lange, G.J., de Leeuw, J.W., Middelburg, J.J., Mollenhauer, G.,Prahl, F.G., Rethemeyer, J., Wakeham, S.G., 2010. Selective preservation oforganic matter in marine environments; processes and impact on the sedi-mentary record. Biogeosciences 7, 483e511.