Hydrocarbon Source‐Rock Generation Potentials of Cenozoic Lignite and Mudstone in Bali‐Boh Paludal Depression on the Western Flank of the Bamenda Highlands, NW Cameroon

Abstract

ABSTRACT Studies in the Bamenda Highlands were focused on intrusive felsic and volcanic rocks, and geochemistry of lignite and argillites. No study has been done on organic matter (OM) enrichment and hydrocarbon source‐rock characteristics in the Bamenda Highlands and environs. This study elucidates the processes of OM accumulation, evaluate hydrocarbon source‐rock and generation potentials of lignite and carbonaceous mudstones from Boh Etoma II (Section‐1) and Boh Muyangka and Boh Muyangka‐Banda (Section‐2) in the Bali‐Boh paludal depression, western flank of Bamenda Highlands. The rocks were analysed for δ 13 C org pyrite sulphur (δ 34 S py ), organic bound sulphur (δ 34 S OS ), TOC, SEM, TS, proximate analysis, elemental geochemistry and Rock‐Eval pyrolysis. The paleoclimate of the study area during the Cenozoic period was semi‐humid to warm and the studied rocks were sourced from felsic igneous rocks. The proxies for paleoredox and paleosalinity conditions revealed that sedimentation took place under relatively stable sulfidic anoxic fresh‐ to brackish paludal waters. Variation in salinity led to the stratification of the water column, providing excellent conditions for OM accumulation and preservation. Paleoproductivity proxies like Ba‐bio, δ 34 Sos, δ 34 S py , δ 13 C org , TS, Mo/Al, and Cu/Al exhibit positive relationships with TOC indicating that sulfidic anoxic conditions and sufficient supply of nutrients stimulated high productivity, leading to OM enrichment. The model of OM accumulation demonstrates that δ 13 C org , δ 34 S OS , and δ 34 S py were anaerobically recycled by sulphate reducing bacteria and microbial sulphate reduction (MSR), stimulating the proliferation of photoautotrophs, resulting in abundant OM accumulation and enrichment. The negative carbon and sulphur isotopes excursions were caused by volcanic events and MSR, releasing large amounts of isotopically lighter carbon and sulphur isotopes during bacterial sulphate reduction (BSR), and methane from microbial activity into the paludal waters. The prevalence of type II and III kerogen, thermal maturity levels, and hydrocarbon yield reveals immature to early mature source rocks that are gas‐prone and in the early‐stages of hydrocarbon oil‐generation.