Optical and geochemical assessment of petroleum source rock potential and palaeodepositional environments of Cretaceous mudstones, Koum Basin, North Cameroon

• Published in: Journal of African earth sciences (1994) 2022-12, Vol.196, p.104674, Article 104674
• Main Authors: Njamnsi, Nowel Yinkfu, Njoh, Oliver Anoh, Ngiamte, George Lemewihbwen, Ndengwe, Alexander Tangwa, Suh, Cheo Emmanuel, Tamfu, Simon Fai
• Format: Article
• Language: English
• Subjects: Kerogen; Koum basin; Organic geochemistry; Paleodepositional environment; Source rock; Thermal maturity
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2022.104674

Limited organic matter (OM) characterisation studies on Cretaceous mudstone successions in the Koum Basin have resulted in a significant knowledge gap in the source rock potential; a petroleum system prerequisite. Field mapping and lithofacies analysis of outcrop sections point to fluvial channel and marginal to profundal lake deposits. Representative mudstone samples were evaluated using multiproxy organo-petrographic and bulk geochemical analyses to assess the kerogen type, thermal maturity, hydrocarbon generation potential, and deduce the paleodepositional environment. Results reveal that ∼90% of the samples are organic-lean and ∼10% organic-rich with TOC content of 2.81–6.91 wt%. Rock-Eval pyrolysis S2 yields of 14.50–54.18 mg HC/g rock and hydrogen index (HI) 784–846 mgHC/gTOC, suggest excellent potential for oil generation. High S1 values of 1.18–1.45 mg HC/g rock and low production indices (PI) of 0.02–0.03 indicate in situ generated free hydrocarbons. PI and Tmax of 438°C–443 °C, consistent with measured vitrinite reflectance (Ro% = 0.28–0.53%), Spore Colour Index (SCI = yellow to golden brown) and Thermal Alteration Index (TAI = 1.5 to 2.6) on the Chevron scale, portraying an immature to marginally mature OM. Oil-prone kerogen Type I-II dominates and to a lesser extent gas-prone Type III, derived from algal-terrestrial organic facies, typified by the predominance of amorphous OM 51.2%, liptinites 24.6%, vitrinite 16.4% and inertinite 7.8%. Based on lithofacies, and palynological evidence, a fluvio-lacustrine depositional setting with limited marine influence, under fluctuating warm humid to hot semi-arid paleoclimates, is inferred. A comparison with surrounding petroleum-producing basins further enhances the understanding of the Koum Basin's hydrocarbon potential within the West Central African rift system context. •Koum Basin is a rift-related Cretaceous intracontinental basin and with no previous detail organic matter studies.•Source rocks evaluated using multiproxy optical microscopic and bulk geochemical parameters.•Fluvio-lacustrine paleodepositional environment inferred, constrained by humid to arid climatic fluctuation.•Good generative potentials for liquid hydrocarbons but thermally immature. However, deeper unexposed portions of the basin may contain mature organic matter.•The Koum Formation correlates with the Bima Formation in Nigeria, based on sedimentological, palynological and organic geochemical similarities.