Diagenesis, paleoenvironments, and petroleum geology of sediments lining the West and Central African Rift System, Koum Basin, North Cameroon

The West and Central African Rift System (WCARS) hosts all the sedimentary basins of West and Central Africa, and constitutes a priority target for sedimentological studies in the area. Numerous basins in this area, notably the Koum Basin, remain poorly known greenfields, owing to a dearth of studies associated with poor accessibility, security limitations, and accrued exploration focus on hydrocarbon-producing oceanic basins in the area. The present study seeks to reduce the knowledge gap by providing new data on the diagenesis, petroleum system, and paleoenvironments of the Koum Basin. NNW–SSE traverse mapping across the basin aided in the identification of conglomerates, sandstones, and shales/mudstones, hosting dinosaur tracks, plant matter and are intercalated by siltstones and bivalve-rich carbonates. Lithofacies analyses, petrography, scanning electron microscopy, and X-ray diffractometry were applied. The studied facies form three facies associations reflecting fluvio-lacustrine paleoenvironments. Petrography exposed concavo-convex to sutured mineral margins, presenting silicate overgrowths plus calcite, silica, hematite, and clay cements. Albite, quartz, calcite, and microcline dominate bulk mineralogy, with analcime, goethite, and hematite as minors, while chlorite-smectite, illite, and smectite dominate clay mineralogy, all pointing to the pre-eminence of mesodiagenesis within the Koum Basin. Studied shales and siltstones present traces of oil/oil migration paths in organic pores, whereas sandstones and carbonates are devoid of mature organic matter and interconnected porosity. Consequently, a source-rock petroleum system with shales and siltstones playing the dual roles of hydrocarbon source and reservoir is inferred for this basin that can be considered a potential unconventional hydrocarbon reserve.