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

Cenomanian to Maastrichtian benthic foraminiferal assemblages, clay mineral s, kerogen types and carbonate microfacies are examined in four offshore we lls 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. Laminate d sediments with smectite-rich clay mineral assemblages, high amounts of ma rine 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 assem blages, low organic matter content, high terrigenous flux and benthic foram iniferal assemblages dominated by agglutinated forms. The palaeobathymetric distribution patterns of organic rich. partly laminated sediments and bent hic foraminiferal assemblages diagnostic of high organic carbon flux rates provide evidence that a productivity-driven oxygen minimum zone was establi shed along the Casamance margin for most of the Late Cretaceous. During sea level highstands at the Cenomanian/Turonian boundary and in the early Camp anian the oxygen minimum zone intensified and expanded to reach more proxim al environments of the inner shelf.