Contourite Depositional Systems within the Orange Basin, South Africa: A Neo-Quaternary account of Bottom current movement and sedimentation

We document for the first time a Neo-Quaternary Contourite Depositional System (NQCDS) within the Orange Basin. The NQCDS is situated in water depths of 185m to 4840m and has likely 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 450km long extending from the shelf to the abyssal plain, up to 400km wide and covers an area of 201000km2. Thicknesses are between 25m to 1450m with the thickest parts (plastered drifts) on the upper slope gradually thinning seaward. The system changes across different physiographic 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 like mass transport deposits (MTDs) and pockmarks.