Contourite depositional systems within the Orange Basin, South Africa: a Neo-Quaternary account of bottom current movement and sedimentation

A Neo-Quaternary Contourite Depositional System (NQCDS) within the Orange Basin is documented for the first time. The NQCDS is situated in water depths of 185–4840 m and is likely to have been shaped since the Miocene by the Benguela Current (BC), Antarctic Intermediate Water (AAIW), North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). Contouritic depositional elements are described at a regional scale by defining their extent, and then by classifying them into zones represented by plastered, mounded and sheeted drifts. The datasets used for this work comprise two multichannel 2D reflection surveys, together with ODP, DSDP and proprietary well data for age determination. The NQCDS is 450 km long, extending from the shelf to the abyssal plain, up to 400 km wide and covers an area of 201 000 km 2 . Thicknesses are between 25 and 1450 m, with the thickest parts (plastered drifts) on the upper slope gradually thinning seawards. The system changes across different physiographical domains owing to the slope gradient, hydrodynamic conditions, seafloor morphology and sediment influx. The NQCDS comprises sheeted, mounded and plastered drifts, and sediment waves. Erosional elements are present as abraded surfaces, moats and contourite channels, together with concomitant features such as mass transport deposits (MTDs) and pockmarks.