Anomalously large marine potholes on a submerged relict shore platform: The Eastern Cape shelf of SE Africa

Andrew Green, Warwick Hastie, Andrew Cooper, Dylan Lightfoot

Research output: Contribution to journalArticlepeer-review


Marine potholes are common features along rocky shore platforms from around the world. Their occurrence can be used as a palaeo-sea level indicator, however, little attention has been given to submerged marine potholes found on relict shore platforms below the depth limits of SCUBA (≤50 m). This paper examines (n = 238) anomalously large potholes found on a submerged aeolianite shore platform on the outer shelf of the Eastern Cape, South Africa. Using a combined ultra-high resolution seismic reflection, side scan sonar and multibeam bathymetry approach, together with remote observation vehicle dives, the pothole occurrences are mapped.

Potholes are either individual or occasionally conjoined, form on sediment-free aeolianite platform and cluster mostly between water depths of 85–95 m. Their sizes are an order of magnitude larger than previously documented, and larger than their fluvial equivalents. Pothole strings are common, associated with the high points between NNW-SSE striking bedding planes of the aeolianite that crop out at the seabed. Potholes are often elongated and aligned with these bedding planes, or in a coast parallel fashion, associated with joints and micro-cliffs in the aeolianite.

The potholes possibly formed during several slowstands or stillstands surrounding the Last Glacial Maximum (LGM, 25,000 to 20,000 yr BP) and the Bølling-Allerød interstadial (B-A, 14,500 yr BP). Given their sizes, we ascribe part of their development to chemical weathering of the platform, especially during the periods where sea spray could pond to form dissolution pans in the supratidal part of the aeolianite platform. A wet and warm B-A climate exacerbated chemical weathering, with karst processes initially dominant, followed by mechanical weathering with shoreline migration. Once submerged, only horizontal enlargement ensued. Geological contingencies (joints, bedding planes and platform lowpoints), modified by early weathering-dominant and later wave-dominant processes, were responsible for the evolution of the shore platform morphology.
Original languageEnglish
Article number108673
Pages (from-to)1-14
Number of pages14
Early online date26 Mar 2023
Publication statusPublished (in print/issue) - 1 Jun 2023

Bibliographical note

Funding Information:
We acknowledge Eskom, Dr. Peter Ramsay and the erstwhile Marine GeoSolutions Pty Ltd. for access to the data sets presented here. In this regard, Doug Slogrove is acknowledged for the quality data collection. We further acknowledge funding from the National Research Foundation for ACEP Grant Number 97969 (Imida Project), from which the ROV imagery stemmed. We thank Ryan Palmer in this regard. eThekwini Municipality are thanked for the coastal aeolianite LiDAR data shown in Fig. 11 . This paper benefited from three exceptionally thorough reviews by the editor in chief, Prof. David Kennedy, an anonymous author, and Prof. Shaocheng Ji, to whom we extend our thanks.

Publisher Copyright:
© 2023 Elsevier B.V.


  • Marine potholes
  • Shore platform
  • Last Glacial Maximum
  • submerged shoreline
  • Submerged shoreline


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