Quaternary foraminifera and mollusc assemblages on the southwestern African shelf

Abstract

The distribution of fossil foraminifera and mollusc assemblages is documented in vibracores recovered from the Namibian and South African shelf to determine changes in depositional environments during the Pleistocene-Holocene. An Uvigerina spp.dominated assemblage appeared in the early Pleistocene during the intensification of cold-water upwelling of the Benguela Upwelling System (BUS). The palaeoenvironment experienced periodic maximal shoaling after the onset of major glacial periods since the mid-Pleistocene transition (ca. 900 ka) as indicated by the appearance of shallow water benthic foraminifera, dominated by Ammonia japonica and Elphidium spp., replacing Uvigerina spp.-dominated assemblage. The mollusc assemblages also change with Carditella spp., Lucinoma capensis, Nassarius vinctus, Dosinia lupinus, and Tellina analogica becoming the dominant species on the shelf. The benthic foraminifera and molluscs indicate greater productivity over the middle and outer shelf as the BUS intensified and high-amplitude sea-level fluctuations reworked and condensed sediment packages on the shelf. The planktic foraminifera show similarities to other upwelling regions globally, with Globigerina bulloides the dominant species. Warm water species such as Globigerinoides ruber, Globorotalia menardii, and Trilobatus sacculifer occur as minor to trace components attributed to the episodic inflow of warm water currents north and south of the region.