GEOSTROPHIC SAND RIDGE, DUNE FIELDS AND ASSOCIATED BEDFORMS FROM THE NORTHERN KWAZULU-NATAL SHELF, SOUTH-EAST AFRICA

Subaqueous dunes are formed on the KwaZulu-Natal outer-shelf due to se diment transport by the Agulhas Current (geostrophic current). These d unes occur within two dune fields at depths of -35 to -70 m. The net s ediment transport direction is south, but short-period reversals form northward-migrating bedforms. The dune fields are physically bounded b y late Pleistocene beachrock and aeolianite ledges. A bedform hierarch y has been recognized in the dune fields comprising a system of three generations of climbing bedforms. The outer dunefield has given rise t o a sand ridge (H=12 m; L=4 km; W=1 . 1 km; and an 8 degrees lee slope ) whereas the inner dune fields have achieved large-scale dune status. Bedload parting zones within the dune fields occur where the sediment transport direction switches from north to south due to reversals in the geostrophic flow; these zones occur at depths of -60, -47 and -45 m. An interpretative stratigraphic model is presented on what such geo strophite deposits would look like in the ancient sedimentary record.