Abstract
Mamu Formation sediments that were encountered at depth range of 1015–1185 m in the Akukwa-II well from the Anambra basin were described and subjected to total organic carbon and gas chromatography-mass spectrometry analyses to determine their organic richness, thermal maturity, the source of organic matter and depositional environment. The sediments are composed of fine grained, dark grey shales and medium grained, dark coloured sandy shales. The TOC results ranged from 1.72 to 2.70 wt%. The biomarker results showed relatively low Pristane/Phytane ratios, strong predominance of medium molecular weight n-alkanes and slight predominance of odd numbered n-alkanes, low ratios of Pr/nC17 and Ph/nC18 and moderate carbon preference index (CPI). The TOC results indicated that the samples have good source rock potential. The n-alkanes isoprenoid, CPI ratios and odd even predominance (OEP) results indicated a marginal to thermally mature organic matter from marine and terrestrial setting. The CPI values of the samples indicate marginal to thermally mature mixed organic matter deposited under relatively anoxic to dysoxic conditions. Pr/nC17 and Ph/nC18 results also suggested mixed organic matter deposited in dysoxic environment. Pr/Ph data suggested that the samples are within the oxidising field in the mature oil zone. Regular steranes data suggested organic matter within early oil generative window while ternary diagram of steranes shows domination of terrestrial organic matter and a lacustrine environment of deposition for the sediments.
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Adeleye, M.A., Okedoyin, O.E. (2022). Molecular Geochemistry of the Mamu Formation Sediments in Anambra Basin, Nigeria. In: Meghraoui, M., et al. Advances in Geophysics, Tectonics and Petroleum Geosciences. CAJG 2019. Advances in Science, Technology & Innovation. Springer, Cham. https://doi.org/10.1007/978-3-030-73026-0_86
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