Facies Evolution, Carbonate Dissolution Cycles in Sediments from the Eastern South Atlantic (DSDP Leg 40) Since the Early Cretaceous

Abstract

Facies evolution in continental margin sediments recovered on Leg 40 from the eastern South Atlantic reflects a progressive disappearance of stagnant conditions and a decrease of the terrigenous influx at the end of the Cretaceous. The Maestrichtian-Paleocene is characterized by the definitive installation of well-oxygenated oceanic conditions. The first up-welling phenomena off Southwest Africa occurred during the Eocene. Carbonate dissolution cycles have recurred several times since the Early Cretaceous. A tentative mean CCD curve for the South Atlantic since the Late Cretaceous is presented. Carbonate dissolution is considerably enhanced in upwelling areas, such as the easternmost Walvis Ridge and the Angola Margin, and is not comparable with that observed in adjacent oceanic basins, such as the Cape Basin. The carbonate dissolution cycles are reflected in the carbonate content of the sediments, in the degree of fragmentation of planktonic foraminifers, and in the relative abundance of benthic foraminifers and fish debris. This evidence is in general agreement with that deduced from the degree of dissolution of calcareous nannofossils (Noel and Melguen, this volume).