Sediment deposits in the Cape Basin; indications for shifting ocean currents?

The Benguela Current system, running off Southwest Africa, is one of the world's largest upwelling regions. The current has strongly influenced sedimentary features on the continental margin. To unravel its development, seismic stratigraphy, tied to drilling results from Ocean Drilling Program Leg 175 sites 1085-1087, was established. Four units, Southern Cape Basin (SCB)-1 to SCB-4, were defined for the Cenozoic sediments. The upper unit, SCB-1 (<1.5 Ma), characterized by continuous high-amplitude reflectors, represents global cooling and glacial-interglacial cycles. Unit SCB-2 (<14 Ma), distinguished by low-amplitude reflections, is associated with the onset of the upwelling system and establishment of the modern circulation pattern in the Cape Basin. Slump scarps are concentrated along the middle and upper shelf slope, suggesting they are caused by a combination of mass movements triggered by bottom currents and slope instabilities because of increased deposition associated with the upwelling. A westward extension and/or movement of upwelling filaments is interpreted from the observed seaward shift of scarp locations with time. Erosion associated with stronger currents probably thinned unit SCB-2 in the south. The two lower units, SCB-3 and SCB-4 (<56 Ma), probably represent material eroded from the shelf break and deposited during a major Oligocene-early Miocene regression that is consistent with a significant uplift of Southern Africa. The basal reflector SCB-D of unit SCB-4 is associated with the prominent reflector D or L described in previous publications.