H.C. CAWTHRA, R. UKEN AND M.N. OVECHKINA 291 NEW INSIGHTS INTO THE GEOLOGICAL EVOLUTION OE THE DURBAN BLUEE AND ADJACENT BLOOD REEE, SOUTH AERICA H.C. CAWTHRA Marine Geoscience Unit, Council for Geoscience, P. O. Box 572, Bellville, Cape Town, 7535, RSA e-mail: hcawthra@geoscience.org.za R. UKEN Discipline of Geology, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, P. Bag X54001, Durban, 4000, RSA e-mail: uken@ukzn.ac.za M.N. OVECHKINA Discipline of Geology, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, R Bag X54001, Durban, 4000, RSA A.A. Borissiak Paleontological Institute, Russian Academy of Sciences, 123 Profsoyuznaya Str., Moscow, 117997, Russia e-mail: saccammina@gmail.com © 2012 September Geological Society of South Africa ABSTRACT The narrow, oceanic current-swept shelf of the Durban Bluff is characterised by Pleistocene aeolianites deposited unconformahly 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. Introduction In the light of Quaternary sea level fluctuations, merged onshore-offshore datasets in the coastal zone are keys in gaining a holistic view of shoreline migration, deposition and erosion processes. In this paper a merged geological map of the Durban Bluff and adjacent continental shelf is presented. Offshore interpretations are derived from bathytnetric, side scan sonar and scuba diving investigations combined with a high-resolution boomer sub-bottom profiling. Sequence stratigraphie interpretations are based on the principles and standardised terminology of Catuneanu et al. (2009). This paper recognises four systems tracts in each complete sequence (as per Coe and Church, 2003 and Catuneanu et al., 2009): the falling stage systems tract (FSST), the lowstand systems tract (LST), the transgressive systems tract (TST) and the highstand systems tract (HST). A systems tract refers to the subdivisions of sequences that consist of discrete depositional units that differ in geometry from other systems tracts and have distinct boundaries (Coe and Church, 2003). The Bluff Ridge forms a prominent linear coastal headland rising 110 m above Mean Sea Level (MSL) and extending uninterrupted for l6 km from the mouth of the Durban Harbour in the northeast, to Lsipingo in the southwest (Figure 1). Blood Reef, a shallow reef complex extending seaward from the Bluff Ridge, derives its unusual name from a plume of whale blood that often blanketed the area between 1908 and 1972 when the now derelict Bluff whaling station was still active (Pearson, 1995). Previous studies Despite several studies of the inner continental shelf fringing the central KwaZulu-Natal coastline (Belderson, 1961; Blomqvist, 2004; Richardson, 2005; Green and Garlick, 2011), the extent and geology of the Blood Reef had never been mapped. Although the Bluff Ridge had received more attention, with an exploratory borehole SOUTH AFRICAN JOURNAL OF GEOLOGY, 2012, VOLUME 115.3 PAGE 291-308 doi:10.2113/gssajg.ll5.3.291