Sedimentology, T-R sequence stratigraphy and geochemical characterization of sedimentary successions of the West and Central African Rift System, Koum Basin

Abstract

The Koum Basin (KB) is among the numerous relatively unexplored sedimentary basins lining theWCARS(West and Central African Rift System), hence limiting the understanding of how sedimentation evolved along the full extent of the WCARS. The intensification of petroleum exploration within WCARS has further emphasized the need to study these greenfields. This study contributes in solving the above issue by establishing a sequence stratigraphic framework and expanding the sedimentological databank of the KB. Systematic fieldmapping and lithofacies analyses of theKB along three NNW-SSE traverse lines cross-cutting the basin exposed alternations of conglomerates, sandstones and shales, intercalated by siltstones and carbonate mudstones. Dinosaur, bivalve and plant fossils are common. X-Ray Fluorescence data of studied samples plot as non-marine, immature, low to moderately weathered shales and greywackes of intermediate to felsic igneous and quartzose sedimentary sources. Sedimentation occurred under oxic, through anoxic to dysoxic depositional conditions, in a semi-arid active continental margin. These deposits inferred to be fluvio-lacustrine, have been subjected to outcrop-based sequence stratigraphic analyses through section matching and correlation of its material-based sequence stratigraphic surfaces, following the Transgressive-Regressive sequence stratigraphic model. The deposits have been subdivided into five repetitive T-R sequence stratigraphic units, bounded by four first order unconformities (SB-1, SB-4, SB-5 and SB-6) and two correlative conformities (SB-2 and SB-3), representing deposition under repetitive base level rise and fall regimes. These results demonstrate that any potentialmarine incursion in the WCARS probably did not reach the Koum Basin.