Molecular geochemical evaluation of Late Cretaceous sediments from Chad (Bornu) Basin, NE Nigeria: implications for pale
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ORIGINAL PAPER
Molecular geochemical evaluation of Late Cretaceous sediments from Chad (Bornu) Basin, NE Nigeria: implications for paleodepositional conditions, source input and thermal maturation Adebanji Kayode Adegoke & Babangida M. Sarki Yandoka & Wan Hasiah Abdullah & Izuchukwu Mike Akaegbobi
Received: 20 November 2013 / Accepted: 18 February 2014 # Saudi Society for Geosciences 2014
Abstract 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 nalkanes, 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) A. K. Adegoke : B. M. Sarki Yandoka : W. H. Abdullah Department of Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia A. K. Adegoke (*) Department of Geology, Faculty of Science, Ekiti State University, P.M.B. 5363, Ado Ekiti, Nigeria e-mail: [email protected] B. M. Sarki Yandoka National Centre for Petroleum Research and Development, A.T.B.U., Bauchi, Nigeria I. M. Akaegbobi Department of Geology, Faculty of Science, University of Ibadan, Ibadan, Nigeria
C29 sterane ratios also suggest that the sediments have reached the early to peak stages of hydrocarbon generation. Keywords Fika formation . Late Cretaceous . Biomarkers . Organic matter . Paleodepositional conditions
Introduction Hydrocarbon exploration started in the Chad (Bornu) Basin (Fig. 1), the Nigerian part of the much larger Chad Basin, in the 1980s (Obaje et al. 2004). During this campaign, 23 exploratory wells were drilled, but minor gas shows were encountered in only two of the wells, unlike in the other parts of the basin in Niger (Termit–Agadem Basin) and Chad (Doba, Doseo and Bongor fields), where commercial hydrocarbon deposits have been discovered (Obaje et al. 2004; Mohammed et al. 1999). Although this exploration campaign was suspended for some time, it has since begun again with the commencement of 3D seismic data acquisition. The poor knowledge of the evolution of the subsurface rocks in this part of the basin may ha
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