Geological and geochemical analyses of Cretaceous oil Shales from the Babouri-Figuil Basin (Northern Cameroon): Implication for Provenance, Paleo-Weathering Conditions and tectonic environment

A detailed study of the Babouri-Figuil Basin oil shale in northern Cameroon was carried out, incorporating lithological, mineralogical, petrographical and geochemical analyses. Oil shales from Mayo-Figuil and Mayo-Tafal series were studied to determine their type and composition, to reconstruct the palaeoenvironment and the tectonic of the basin. The results obtained are as follows: lithologically, both series contain conglomerates, sandstones, limestones, clays, schistose marls and oil shales. Four oil shale types were observed named: black oil shale in thin sheets; black oil shale in slabs; dark- grey oil shale cut into blocks and black oil shale cut into blocks. Oil shale samples include both organic and inorganic matter. Mineral phases consist mainly of quartz, feldspars, cooperite, analcime, kaolinite, smectite and illite. The major elements are dominated by SiO₂, Al₂O₃, Fe₂O₃, and CaO. Trace elements are dominated by Fe, Ca, Ti and In. The oil shales are immature (ICV: 1.36–9.54) and classified as Fe-shale, litharenite, wake and sublitharenite. The Al₂O₃/TiO₂ and Zr vs. TiO₂ diagrams indicate that, the inorganic matrix is derived from intermediate and mafic igneous rocks and quartzose sediments of a felsic origin. The composition of source rock is similar to granite, granodiorite with some volcanic material and have undergone weak, intermediate and intensive chemical weathering, as well as intensive erosion, under dry and humid tropical climate. Sedimentation in the basin is the result of oxic and anoxic conditions. Concerning tectonic, sediments from Babouri-Figuil Basin were mainly deposited in passive and active continental-margin settings, in fluvial and lacustrine environments.