Controls on carbonate and terrigenous deposition in the incipient Benguela upwelling system during the middle to the late Miocene (ODP Sites 1085 and 1087)

Abstract

This study deals with the variability of biogenic carbonate and terrigenous depositional patterns in the Cape Basin area of the South Atlantic during the middle to the late Miocene focusing on ODP Sites 1085 and 1087 sediments at the Benguela Upwelling area, Southwest Africa. The investigations are based on grain-size analysis and clay mineralogy. The sedimentary records at both sites provide information about climate and environmental changes. The direct input of terrigenous material from southwestern Africa is driven by a complex interaction of river and wind transport, and ocean currents. The considerable amount of dust input derived from the Namib Desert started to become important after 11.2 Ma, pointing to an increased supply of cool intermediate waters to mid-latitude surface waters in the upwelling regions, which coincided with the establishment of the wind-driven Benguela upwelling system. A major drop in CaCO 3 concentration between 10.4 and 10.1 Ma is caused mainly by changes in calcareous nannoplankton production, while another drop between 9.6 and 9 Ma is triggered by a combination of production changes of calcareous nannoplankton and dilution, in response to high shelf supply during global lowering of the sea level.