Cenozoic bottom current sedimentation in the Cape basin, South Atlantic

SUMMARY The Agulhas Ridge, which rises up to 2.5 km over the ocean floor of the adjacent Cape and Agulhas basins, located along the Falkland‐Agulhas fracture zone, acts as a barrier for northward flowing deep‐water masses, deflecting them along the bathymetric contours of the Agulhas Ridge. Seismic data recorded over the Agulhas Ridge shows that the sediments transported by these deep‐water currents accumulate in contourite drifts. Several hundred metres of sediments have accumulated since the onset of intrusion of Antarctic Bottom Water (AABW) derived water masses into the basins of the South Atlantic. An erosional surface in early Oligocene sediments appears to mark a prominent change in the sedimentation pattern. Up to this event, strong and varying currents formed a rapidly accumulating sheet of sediments subdivided into units with significant seismic impedance contrasts and thus strong reflections in the seismic image of these sediments. After the early Oligocene erosional event, a stable unidirectional bottom current was established, with sedimentation of mainly muddy material, leading to the formation of a more than 200‐km‐long, approximately 30‐km‐wide elongate contourite drift. A period of non‐deposition during the middle Miocene is followed by an increase of well‐defined seismostratigraphic units, most pronounced for sediments of Quaternary age. This suggests that build‐up of the drift structure generally continued, with alternating episodes of erosion and sedimentation in response to glacial cycles.