Molecular Organic Geochemistry of Mudstones from Koum Basin, Cameroon: Paleo-environmental, Age, Maturity and Genetic Implication

Nowel Yinkfu Njamnsi^{1, 2,} , Njoh Oliver Anoh¹, George Ngiamte Lemewihbwen¹, Cheo Emmanuel Suh^{1, 3} and Simon Fai Tamfu⁴

¹Department of Geology, Mining, and Environmental Science, University of Bamenda, P.O. Box 39, Bamenda, Northwest Region, Cameroon

²Engineering and Mobilization of Local Resources Section, Pipeline Steering and Monitoring Committee, National Hydrocarbons Corporation (SNH), P.O. Box 955, Yaoundé, Centre Region, Cameroon

³Economic Geology Unit, Department of Geology, University of Buea, P.O. Box 63 Buea, Southwest Region, Cameroon

⁴S T Exploration and Production Consulting Services, P.O. Box 5174 Nlongkak – Yaoundé

Cite this paper:
Nowel Yinkfu Njamnsi, Njoh Oliver Anoh, George Ngiamte Lemewihbwen, Cheo Emmanuel Suh and Simon Fai Tamfu. Molecular Organic Geochemistry of Mudstones from Koum Basin, Cameroon: Paleo-environmental, Age, Maturity and Genetic Implication. Journal of Geosciences and Geomatics. 2022; 10(1):45-64. doi: 10.12691/jgg-10-1-4

Abstract

Hydrocarbon resources are still invaluable to the economic growth and social development of most producing countries. Keeping in pace with studies of global source rock development for resourcing future generations, exposed organic-rich, dark-grey mudstones were collected from the Koum Basin and on the basis of their total organic carbon (TOC) content, noted to range between 5.48-6.91 wt.%, organic matter (OM) was extracted and characterized in order to determine the OM source input, paleo-depositional conditions, thermal maturity, age, by which the hydrocarbon potential was deduced using gas chromatography (GC), medium pressure liquid chromatography (MPLC) and gas chromatography-mass spectrometry (GC-MS) techniques. The extract yield and bitumen composition range between 4291–5116 ppm which depicts a fair to very good source rock generative potential, dominated by saturates (41.86-45.96%), aromatics (9.36-26.36%), and resin/asphaltene (31.78-44.68%) pointing to normal paraffinic generated hydrocarbons. Source-related molecular markers indicate a mixed aquatic algae and clastic-rich terrigenous OM input, preserved under sub-oxic to oxic conditions, typical of fluvial-deltaic lacustrine systems. Gammacerane/Hopane ratios (0.26-0.27), support the fact that the lacustrine source rocks were likely developed under somewhat restricted circulation and moderate/low salinity. From maturity ratios of Ts/(Ts + Tm), C₃₂ 22S/(22S + 22R) homohopane, the 20S/(20S + 20R) and ββ/(ββ + αα) C₂₉ and Methyl Phenanthrene Index with vitrinite reflectance value equivalent of 0.46-0.60%, it can give a conclusion that the analyzed extracts are from early thermal cracking of OM at the incipient oil window. Based on age-specific biomarkers, the extracts were probably derived from the Early Cretaceous. Accordingly, findings are comparable with some active Cretaceous lacustrine source rocks in some basins within the West Central African Rift system (WCARS) and therefore provide a better understanding of source rock development during the Cretaceous in a regional context. Nevertheless, the deeper unexposed organic-rich units of the Koum Basin may have a pod of active source rock.

Keywords:
Source rocks Biomarkers Organic matter Thermal maturity Paleo-redox conditions Cretaceous Koum Basin

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