NEW INSIGHTS INTO THE GEOLOGICAL EVOLUTION OF THE DURBAN BLUFF AND ADJACENT BLOOD REEF, SOUTH AFRICA

The narrow, oceanic current-swept shelf of the Durban Bluff is characterised by Pleistocene aeolianites deposited unconformably onto a Cretaceous sequence. Subsequent beachrocks were deposited on and erosional features cut into the aeolianites, tracking a series of palaeocoastlines that extend from the supratidal zone to the outer continental shelf and record sea level fluctuations from the Last Interglacial to the present. High-resolution boomer seismics reveal a detailed sequence stratigraphy for the late Cretaceous drift sequence (Early Santonian to Late Maastrichtian) followed by a likely Miocene/Pliocene sequence preserved on the shelf edge, the first record of these deposits from the Durban continental shelf. Seven seismic units are recognised (Units A to G), bounded by regional sequence boundaries, maximum flooding surfaces and wave ravinement surfaces. Mapping of the Bluff Ridge and adjoining Blood Reef by geophysical surveys and scuba diving enabled subdivision of the Quaternary deposits into three aeolianite units and 13 beachrock units. Calcareous nannoplankton preserved in the aeolianite units indicate a late Pleistocene to Holocene age (Zone NN21, maximally 290 ka) for the deposits and the presence of reworked Miocene forms provides further support for the existence of Neogene on the shelf edge. A new Infared Stimulated Luminescence age of 60 ka obtained from offshore aeolianite indicates dune-building during the Marine Isotope Stage 4 glacial period.