Winds of change: Climate variability in a mild glacial on the east coast of South Africa, inferred from submerged aeolianites and the archaeological record of Sibudu

摘要

Here we present an optically stimulated luminescence (OSL) age estimate of 64 +/- 5 ka for an offshore aeolianite and draw regional correlations (within 45 km) between the Pleistocene geological sequence offshore of the Durban Bluff, and contemporary palaeoenvironmental records from Sibudu on the South African sub-tropical east coast. Considering this age estimate within the context of high-resolution hydroacoustic data and, in particular, sub-bottom profiles, we tentatively suggest phases of dune building during marine isotope stage (MIS) 4 along the east coast of South Africa. The age and depositional characteristics of the composite Bluff-Blood Reef aeolianites suggest that dune-building events were linked to sea-level stillstands during both highstands (with deposits now preserved above water from MIS 7 and 5e) and lowstands (preserved below water, specifically, MIS 4). Aeolianite remnants of late MIS 4 age show that the wind regime during this mild glacial was dominated by winds typical of modern-day temperate latitudes; prevailing directions preserved in foresets pointing towards northerlies and southeasterlies. This is in contrast to the present-day prevailing northeasterlies and southwesterlies in the study area. We investigate the role of a narrow shelf in the characteristics of the sedimentary depositional system of the Durban Bluff and the role of southeasterlies during MIS 4 in delivering sediment to the contemporary coast. We demonstrate the value in correlating offshore and onshore Quaternary sequences, and the role that submerged deposits can play in unravelling nuances of glacial conditions on ice-free continental shelves. Broadly, the correlations that we draw between the shelf aeolianites and the archaeological record of Sibudu, supports evidence of climatic and environmental variability during MIS 4 in this area.