Robberg paper_as submitted revision.pdf (2.17 MB)
First evidence for onshore Marine Isotope Stage 3 aeolianite formation on the southern Cape coastline of South Africa
journal contributionposted on 2019-05-16, 09:31 authored by Andrew S. Carr, Mark D. Bateman, Hayley C. Cawthra, Judith Sealy
The southern Cape coast of South Africa boasts an impressive suite of Plio-Pleistocene aeolian dune deposits (aeolianite). Previous research has shown that in this region onshore dune accumulation was generally focused around interglacial sea level highstands, with the locus of coastal dune accumulation shifting onto the adjacent continental shelf during glacial sea level lowstands. Here, using new luminescence dating results, we present the first evidence for preserved onshore glacial age dunes. Specifically, on the Robberg Peninsula, a rocky headland 28 km east of Knysna, two phases of aeolianite formation are identified, corresponding to early (45–60 ka) and late (35–30 ka) marine isotope stage (MIS) 3. Subsequently, during the Holocene, all substantive dune accumulation occurred between 10.2 and 7.0 ka, forming cliff-fronting dunes and filling the limited accommodation space on the headland, including an archaeological rock-shelter. Combining these ages with bathymetric data, we infer that this distinct onshore glacial age aeolianite record reflects: 1) restricted accommodation space during sea level highstands; 2) a regional narrowing of the continental shelf, and 3) liberation of sediments lying on a prominent −45 to −60 m offshore terrace, which would have been exposed during MIS 3. This demonstrates that despite broad regional-scale trends in the timing of coastal aeolian activity - driven by commonalities in relative sea level trends and climate - distinct local variations in late Quaternary coastal evolution can be identified. This is ascribed to local controls on preservation (accommodation space) and sediment supply (shoreline position and antecedent offshore sediment supplies). Such findings may have wider implications for interpretations of site context/resource availability at several notable coastal archaeological sites, and more broadly suggest that local offshore or onshore geologic contexts can at times assume greater influence on a preserved coastal aeolianite record than the regional-scale trends in sea level and climate.
The University of Leicester funded ASC's field and laboratory work. Rob Ashurst assisted with the preparation of the OSL samples in Sheffield. Professor Andy Saunders is thanked for assistance with the ICP-MS measurements. Further support for fieldwork and radiocarbon dating came from the South African Research Chairs initiative of the National Research Foundation and the Department of Science and Technology, Republic of South Africa (grant no 84407) to JS. Sediment samples were collected in accordance with permit number 0052-AAA008-00011, issued by the Western Cape Nature Conservation Board.
CitationMarine Geology, 2018
Author affiliation/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/School of Geography, Geology and the Environment/Physical Geography
- AM (Accepted Manuscript)