Palaeoenvironments and palaeobiogeography of the Late Cretaceous Casamance transect (Senegal, NW Africa): distribution patterns of benthic foraminifera, organic carbon and terrigenous flux

Cenomanian to Maastrichtian benthic foraminiferal assemblages, clay minerals, kerogen types and carbonate microfacies are examined in four offshore wells along a transect across the Casamance margin, extending from the inner shelf to the abyss. Material available for this study includes cuttings and cored sections from three csmmercial wells drilled on the inner/middle and outer shelf and cores from DSDP Hole 367 in the Cape Verde Basin. Laminated sediments with smectite-rich clay mineral assemblages, high amounts of marine organic matter and a typical buliminid benthic foraminiferal biofacies characterise sea level highstands at the Cenomanian/Turonian boundary and in the early Campanian. Sea level lowstands in the Coniacian-Santonian and Maastrichtian are characterised by illite-kaolinite-rich clay mineral assemblages, low organic matter content, high terrigenous flux and benthic foraminiferal assemblages dominated by agglutinated forms. The palaeobathymetric distribution patterns of organic rich. partly laminated sediments and benthic foraminiferal assemblages diagnostic of high organic carbon flux rates provide evidence that a productivity-driven oxygen minimum zone was established along the Casamance margin for most of the Late Cretaceous. During sea level highstands at the Cenomanian/Turonian boundary and in the early Campanian the oxygen minimum zone intensified and expanded to reach more proximal environments of the inner shelf.