Seismic stratigraphy of the broad, low-gradient continental shelf of the Palaeo-Agulhas Plain, South Africa
- Published
- Accepted
- Subject Areas
- Natural Resource Management, Spatial and Geographic Information Science
- Keywords
- South Africa, Pleistocene, Palaeo-Agulhas Plain, continental shelf, seismic stratigraphy, Post-glacial Marine Transgression
- Copyright
- © 2019 Cawthra et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2019. Seismic stratigraphy of the broad, low-gradient continental shelf of the Palaeo-Agulhas Plain, South Africa. PeerJ Preprints 7:e27757v1 https://doi.org/10.7287/peerj.preprints.27757v1
Abstract
The continental shelf of the Palaeo-Agulhas Plain (PAP) is scattered with Pleistocene deposits with subdued topography. Their exaggerated lateral extension is the expression of a flat underlying substrate and availability of accommodation space, depositional processes and response to glacio-eustatic sea-level change have influenced deposition and distribution of these units. We present new results for the upper ~30 m (up to ~200 ka) of the stratigraphic record in this area and show that this shelf offers the opportunity to examine the response of a stable tectonic setting to the effects of sea-level change. This paper presents the results of extensive sub-bottom profiling surveys and chronostratigraphic investigations from marine sediment vibracores. Radiocarbon and Optically stimulated Luminescence dates are integrated into a seismic stratigraphic model composed of twenty Quaternary units, where two depositional sequences are bounded by shelf-wide unconformities. The upper sequence was cored where Pleistocene deposits were observed to be close to the seafloor and are draped in a thin veneer of marine shelf sediment and allow us to describe the environments of deposition of the PAP. The most pervasive stratigraphic pattern in these shelf deposits is made up of the depositional sequence remnant of the Falling Stage Systems Tract (FSST) forced regression from Marine Isotope Stage 5e–2. The other dominant stratigraphic group is the Transgressive Systems Tract (TST) associated with the Postglacial Marine Transgression. Surprisingly, the TST makes up an almost equal proportion of deposits in both sequences in the sedimentological record as the FSST, despite the shorter temporal span of the TST. The sub-bottom profiles were acquired on regional surveys extending from the Breede River in the west to Plettenberg Bay in the east, and to a maximum depth of 110 m below Mean Sea Level, with the exception of one ~200 m deep shelf-edge profile.
Author Comment
This manuscript will form part of a Special Issue of Quaternary Science Reviews that focuses on an extinct ecosystem, the Palaeo-Agulhas Plain. It is based on the structural elements of the southern South African continental shelf.