Cretaceous separation of Africa and South America: the view from the West African margin (ODP leg 159)

The opening of the Equatorial Atlantic Gateway (EAG) during the Cretaceous was accompanied by the disruption of the sedimentary basins that had develo ped on the conjugate margins of Africa and South America, Drilling along th e Cote d'Ivoire-Ghana Transform Margin (ODP Leg 159) provided a transect ac ross the northern rim of this gateway. The interplay of tectonic and oceani c processes along the gateway created a complex continental margin that evo lved in three stages interrupted by dramatic changes in sedimentary facies, waterdepths, and subsidence rates. The earliest stage records the formatio n of small basins with restricted connection to the world ocean and rapid i nfill with siliciclastic deposits in an Early Cretaceous intracratonic rift or wrench tectonic setting. This stage ended with an uplift event and the formation of a regional unconformity. During the late Albian to middle Coni acian, the oceanward side of the margin subsided below the calcite compensa tion depth (CCD) and a deepwater connection between Central and South Atlan tic became established. Deepening of the basement ridge and its landward sl ope, in contrast, were delayed and detrital limestones intercalated with ca rbonaceous shales accumulated at shelf to slope depths. During the ensuing, latest Cretaceous to present stage, passive margin subsidence led to conti nuous deepening of the basement ridge and on its landward slope. Condensati on and gradually decreasing organic contents: point to an intensified expos ure to deepwater circulation. The replacement of the zonal circulation syst em through the Mesozoic Tethys and Central Atlantic with a modern, oxidizin g meridional circulation system through the EAG appears to be intimately re lated to the changing depositional conditions over large parts of the Creta ceous Atlantic. (C) 2001 Elsevier Science Ltd. All rights reserved.