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Adegoke A.K.,University of Malaya | Adegoke A.K.,Ekiti State University, Ado Ekiti | Sarki Yandoka B.M.,University of Malaya | Sarki Yandoka B.M.,National Center for Petroleum Research and Development | And 2 more authors.
Arabian Journal of Geosciences | Year: 2014

The Late Cretaceous Gongila and Fika formation sediments in the Chad (Bornu) Basin, northeastern Nigeria, were analysed to evaluate their paleodepositional conditions and source input as well as to determine their thermal maturity. These were interpreted based on their molecular composition. The composition and distribution of n-alkanes, isoprenoids, and biomarkers indicate a mixture of marine algal/bacterial and land-derived organic matter source input for the Gongila and Fika formation sediments deposited in marine environment. This is indicated by the abundance of short-chain n-alkanes, low CPI and high concentration of tricyclic terpanes, low C24 tetracyclic/C26 tricyclic, low to moderate hopane/sterane ratios and the relationship between regular sterane compositions. These were probably deposited in environmental conditions which are mainly dysoxic. From the waxiness index and terrigenous/aquatic ratio (TAR), it can be deduced that more terrigenous organic materials were deposited towards the northeastern part of the basin, probably because of their proximity to the Lake Chad. Biomarker maturity parameters such as Ts/(Ts + Tm), C32 22S/(22S + 22R) homohopane, moretane/hopane and 20S/(20S + 20R) and ββ/(ββ + αα) C29 sterane ratios also suggest that the sediments have reached the early to peak stages of hydrocarbon generation. © 2014 Saudi Society for Geosciences.

Adegoke A.K.,University of Malaya | Adegoke A.K.,Ekiti State University, Ado Ekiti | Abdullah W.H.,University of Malaya | Hakimi M.H.,Taiz University | And 5 more authors.
Journal of African Earth Sciences | Year: 2014

Trace element contents in isolated kerogen from Upper Cretaceous sediments within Gongila and Fika formations in the Chad (Bornu) Basin, northeastern Nigeria were determined using Inductively-coupled plasma mass spectrometer (ICP-MS), in order to infer the origin of the organic matter and the paleo-redox conditions during their sedimentation. The concentrations of the elements in the kerogen samples varied from 1.01 to 24,740. ppm. The distribution of elements shows that Fe is the most abundant element in Chad (Bornu) Basin kerogen, followed by Ce. Among the biophile elements, V is the most abundant, followed by Ni and Co in that order. Statistical evaluation of the elemental composition data shows that As, Ce, Pb, V, Cr, Fe, Co, Ni and U exhibit good positive correlations with each other. Molybdenum, on the other hand displays no obvious correlation with most of the trace elements determined including TOC, but has good positive correlation with TS and negative correlation with Tmax, Ce and Th, which suggests that the concentration of Mo decreases with increasing maturity and vice versa. Some trace element concentrations and their ratios suggest mixed marine and terrigenous source input for the organic matter (kerogen) in Chad (Bornu) Basin. More so, the concentrations of redox-sensitive elements, such as V, Ni, Cu, Cr Mo and Mn, in the kerogen samples suggest dysoxic bottom water conditions within the Gongila and Fika sediments. Cross-plots of V and Ni and V/(V + Ni) ratio also indicate that the organic matter of these samples was deposited in slightly reducing environments. © 2014 Elsevier Ltd.

Bata T.,University of Aberdeen | Bata T.,Abubakar Tafawa Balewa University | Parnell J.,University of Aberdeen | Samaila N.K.,Abubakar Tafawa Balewa University | And 3 more authors.
Journal of African Earth Sciences | Year: 2015

Paleogeographic studies have shown that Earth was covered with more water during the Cretaceous than it is today, as the global sea level was significantly higher. The Cretaceous witnessed one of the greatest marine transgressions in Earth's history, represented by widespread deposition of sands directly on underlying basement. These sand bodies hold much of the world's heavy oil. Here, we present for the first time, geochemical evidence of a Cretaceous oil sand (Bima oil sand) in the Chad Basin, Nigeria. Bima oil sand is similar to other Cretaceous oil sands, predominantly occurring at shallow depths on basin flanks and generally lacking a seal cover, making the oil susceptible to biodegradation. The bulk properties and distribution of molecular features in oils from the Bima oil sand suggest that they are biodegraded. Sterane maturity parameters and the trisnorhopane thermal indicator for the oils suggest thermal maturities consistent with oils generated as conventional light oils, which later degraded into heavy oils. These oils also show no evidence of 25-norhopane, strongly suggesting that biodegradation occurred at shallow depths, consistent with the shallow depth of occurrence of the Bima Formation at the study locality. Low diasterane/sterane ratios and C29H/C30H ratios greater than 1 suggest a carbonate source rock for the studied oil. The Sterane distribution further suggests that the oils were sourced from marine carbonate rocks. The C32 homohopane isomerization ratios for the Bima oil sand are 0.59-0.60, implying that the source rock has surpassed the main oil generation phase, consistent with burial depths of the Fika and Gongila Formations, which are both possible petroleum source rocks in the basin. © 2015 Elsevier Ltd.

Adegoke A.K.,University of Malaya | Adegoke A.K.,Ekiti State University, Ado Ekiti | Abdullah W.H.,University of Malaya | Hakimi M.H.,Taiz University | And 2 more authors.
Journal of Petroleum Science and Engineering | Year: 2015

The Upper Cretaceous Gongila Formation in the Chad (Bornu) Basin, northeastern Nigeria has always been considered as a transitional sequence between the underlying continental Bima Formation and the overlying marine Fika Formation. So far, little information has been available on this formation, which is regarded as one of the prospective source rocks in this Basin. Elemental and organic geochemical analyses were performed on the shales recovered from this formation in order to define the origin and type of organic matter within the sediments and also to examine the processes controlling organic matter enrichment. Based on their bulk geochemical characteristics and biomarker compositions, the selected Gongila shales were interpreted to be deposited in marine environment. Their biomarkers and chemical compositions also indicate enhanced bioproductivity within the photic zone of the water columns and a contribution by mixed aquatic algae/microorganisms and terrigenous organic matter input. The increased bioproductivity in the selected Gongila shales may be related to enhanced semi-arid/humid to humid-warm climate conditions. Low salinity stratification and suboxic to relatively anoxic bottom water conditions are also supported by Sr/Br, V/Ni, and Pr/Ph ratios. Therefore, a stratified water column with low salinity and suboxic to relatively anoxic bottom water conditions may have contributed to the preservation of organic matter in the sediments. © 2015 Elsevier B.V.

Adegoke A.K.,University of Malaya | Adegoke A.K.,Ekiti State University, Ado Ekiti | Abdullah W.H.,University of Malaya | Hakimi M.H.,Taiz University | And 2 more authors.
Applied Geochemistry | Year: 2014

Late Cretaceous shales of the Fika Formation in the Chad (Bornu) Basin, northeastern Nigeria, were analysed to define paleoenvironment and source of the organic matter, and their relation to tectonic setting. The organic carbon and sulphur contents of Fika shale samples are in the range of 0.51-2.13 and 0.31-1.65wt.%, respectively, pointing that these shales were deposited in suboxic-anoxic marine conditions. The biomarker and chemical compositions provide evidence for a major contribution of aquatic algae and microorganisms with minor terrigenous organic matter input. Moderate salinity stratification and relatively anoxic-suboxic bottom water conditions are also likely in the Fika shales. Therefore, stratified water column with moderate salinity and relatively anoxic-suboxic bottom water conditions have contributed to organic matter (OM) preservation in the Fika shale layer. Fika shale samples are rich in SiO2 (54.80wt.%), followed by Al2O3 (23.75wt.%) and Fe2O3 (10.19wt.%). Compared with average shale, the analysed shale samples are obviously enriched in Al2O3 (23.75wt.%), TiO2 (1.34wt.%), and P2O5 (0.30wt.%), indicating that these sediments are rich in clay minerals and represent a good possibility for enhanced organic matter production and enrichment.Plots of Fika shale on bivariate discriminant function diagram suggest an active continental margin setting for the provenance. The inferred tectonic setting for the late Cretaceous shales of the Fika Formation of the Chad (Bornu) Basin is in agreement with the tectonic evolutionary history of the west and central Africa during the Cretaceous period. © 2014 Elsevier Ltd.

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