FACIES, DEPOSITIONAL ENVIRONMENT,GEODYNAMIC SETTING, AND CLIMATIC IMPLICATIONS OF THE COMO FORMATION (LOWER APTIAN) FROM THE GABONESE INTERIOR BASIN

This work presents a sedimentological and palaeo environmental study of the Como Formation (early Aptian) in the Gabonese interior basin, based on five outcrop sections and two boreholes (NKG1, WE1). Fourteen elementary lithofacies were identified and grouped into seven Facies Associations (FA1-FA7), encompassing alluvial fans, braided and meandering fluvial systems, vegetated floodplains, deep anoxic lacustrine deposits with bituminous mudstones, cyclic anoxic/mesoxic alternations, deltaic progradation, and terminal evaporitic confinement. Rock-Eval data (TOC 0.45-25.5 wt.%; HI 270-764 mg HC/g TOC; Tmax 427-448 C) confirm the source-rock potential of the anoxic lacustrine facies within a complete lacustrine petroleum system. Sequence stratigraphic analysis reveals two complete third-order cycles. The first comprises a degradational phase (alluvial fans, braided rivers),a transitional tract(isolate channels, fining upward conglomerates), and an aggradational anoxic lacustrine phase (black shales, varved dolomitic argillites). The second culminates in a lacustrine maximum flooding surface represented by anoxic bituminous varved argillites at the Cocobeach Landing Stage, and terminates with forced regressive deposits (composite sequence L8). Major erosional surfaces act as sequence boundaries recording pronounced falls in the accommodation-to-supply ratio.