FROM CONTINENTAL TO OPEN MARINE SETTINGS: ALBIAN TO MAASTRICHTIAN PALAEOENVIRONMENTAL EVOLUTION OF THE ABIDJAN MARGIN (COTE D IVOIRE)

The Ivorian sedimentary basin, which developed along the northern transform margin of the Gulf of Guinea, records the Cretaceous transition from a continental to an open marine domain. This study reconstructs the palaeo environmental evolution of the Abidjan margin through a combined sedimentological and palynological analysis of cuttings from well AB-9X, between 4740 ft (≈ 1445 m) and 11750 ft (≈ 3581 m). Six lithological units were first defined independently of any age assignment, then placed within a palynostratigraphic framework based on the last appearance datums (LADs) of miospores and dinoflagellate cysts, ranging from the middle Albian to the Maastrichtian. The Albian was deposited in a low-energy continental to paralic setting under a hot, rather arid climate, and ends with the progradation of a fluvio-deltaic system. Marine influence was established in the earliest Cenomanian, where the first occurrence of dinoflagellate cysts coincides with a change in lithofacies. The Cenomanian and Turonian correspond to a proximal marine, aggradational setting, and the lower Senonian to a proximal marine setting with reduced terrigenous input. A transgressive surface associated with a hiatus at the Santonian–Campanian transition marks the drowning of the clastic system, probably related to the thermal subsidence of the passive margin.