TY - JOUR
T1 - Geological and soil maps of the Palaeo-Agulhas Plain for the Last Glacial Maximum
AU - Cawthra, Hayley C.
AU - Cowling, Richard M.
AU - Andò, Sergio
AU - Marean, Curtis W.
N1 - Funding Information:
Marine geophysical surveys were funded by the National Geographic Society Expeditions Council ( EC482-10 ) and the South African Council for Geoscience ( ST-2011-1139 ). Michael MacHutchon, Wilhelm van Zyl and Willem Kupido from the Council for Geoscience are thanked for assistance with marine geophysical data collection. Sediment coring and Parasound data collection were financially supported by the Bundesministerium für Bildung und Forschung (BMBF, Bonn, Germany) within the projects “Regional Archives for Integrated Investigation (RAiN)” and PI Dr Matthias Zabel (University of Bremen) is gratefully acknowledged in this regard. This paper was first drafted whilst HC was a visiting junior fellow of the Hanse-Wissenschaft Kolleg in Delmenhorst from November 2017–January 2018. Two anonymous reviews are gratefully acknowledged for their comments and suggestions that improved the quality of this manuscript.
Funding Information:
Marine geophysical surveys were funded by the National Geographic Society Expeditions Council (EC482-10) and the South African Council for Geoscience (ST-2011-1139). Michael MacHutchon, Wilhelm van Zyl and Willem Kupido from the Council for Geoscience are thanked for assistance with marine geophysical data collection. Sediment coring and Parasound data collection were financially supported by the Bundesministerium f?r Bildung und Forschung (BMBF, Bonn, Germany) within the projects ?Regional Archives for Integrated Investigation (RAiN)? and PI Dr Matthias Zabel (University of Bremen) is gratefully acknowledged in this regard. This paper was first drafted whilst HC was a visiting junior fellow of the Hanse-Wissenschaft Kolleg in Delmenhorst from November 2017?January 2018. Two anonymous reviews are gratefully acknowledged for their comments and suggestions that improved the quality of this manuscript.
Publisher Copyright:
© 2019 Elsevier Ltd
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/5/1
Y1 - 2020/5/1
N2 - The South African Cape South Coast is bordered by one of the broadest continental shelves in Africa. The Agulhas Bank, inshore shelf and presently exposed coastal plain make up the Palaeo-Agulhas Plain (PAP), though our area of study extends beyond this limit and as far inland as the first mountain belt. Quaternary sea levels have been significantly lower than at present for ∼90% of the Pleistocene, exposing a terrestrial ecosystem on what is now the submerged shelf. The presently drowned component makes up 94% of the total area of the PAP. Past work has hypothesised a contrast in character of this submerged landscape when compared to the subaerial environment. Here, we assimilate newly-acquired geophysical and geological datasets to produce geological- and soil maps from the Last Glacial Maximum on a scale of 1:750,000, covering an area of ∼55,000 km. Three broad geomorphic zones are defined, including the Western section from Cape Agulhas to Cape Infanta, the Central section from Cape Infanta to Knysna and the Eastern section extending eastward of Knysna. We demonstrate that Mesozoic sedimentary deposits crop out near the surface on this current-swept shelf and soils derived from siltstone and shale bedrock are prominent when the coast is up to 64 km distant from the modern shoreline at its maximum point. Beyond this, weathered limestone dominates the substrate sequences on the Agulhas Bank. We show that the submerged landscape was a unique terrestrial environment and that there is no exact modern-day analogue in the region other than a small (∼70 km2) area located at the edge of the Agulhas Plain near Cape Agulhas, and map major contrasts in the geological, topographic and edaphic nature of the landscape from the onshore to the offshore. The expansion of this plain is coupled with exaggerated floodplains, meandering shallowly incised rivers and wetlands. The submerged shelf is dominated by fertile soils compared to the dissected onshore belt, and extensive calcareous dunefields extending up to 10 km inland from their associated palaeoshorelines covered much of the emergent shelf. Sedimentary bedforms may have obstructed or slowed drainage as suggested by leached palaeosols and carbonate mixing observed in petrographic thin sections and grain mounts. The data show a low-relief “plains” landscape, which contrasts strongly to the topographically complex contemporary coastal foreland.
AB - The South African Cape South Coast is bordered by one of the broadest continental shelves in Africa. The Agulhas Bank, inshore shelf and presently exposed coastal plain make up the Palaeo-Agulhas Plain (PAP), though our area of study extends beyond this limit and as far inland as the first mountain belt. Quaternary sea levels have been significantly lower than at present for ∼90% of the Pleistocene, exposing a terrestrial ecosystem on what is now the submerged shelf. The presently drowned component makes up 94% of the total area of the PAP. Past work has hypothesised a contrast in character of this submerged landscape when compared to the subaerial environment. Here, we assimilate newly-acquired geophysical and geological datasets to produce geological- and soil maps from the Last Glacial Maximum on a scale of 1:750,000, covering an area of ∼55,000 km. Three broad geomorphic zones are defined, including the Western section from Cape Agulhas to Cape Infanta, the Central section from Cape Infanta to Knysna and the Eastern section extending eastward of Knysna. We demonstrate that Mesozoic sedimentary deposits crop out near the surface on this current-swept shelf and soils derived from siltstone and shale bedrock are prominent when the coast is up to 64 km distant from the modern shoreline at its maximum point. Beyond this, weathered limestone dominates the substrate sequences on the Agulhas Bank. We show that the submerged landscape was a unique terrestrial environment and that there is no exact modern-day analogue in the region other than a small (∼70 km2) area located at the edge of the Agulhas Plain near Cape Agulhas, and map major contrasts in the geological, topographic and edaphic nature of the landscape from the onshore to the offshore. The expansion of this plain is coupled with exaggerated floodplains, meandering shallowly incised rivers and wetlands. The submerged shelf is dominated by fertile soils compared to the dissected onshore belt, and extensive calcareous dunefields extending up to 10 km inland from their associated palaeoshorelines covered much of the emergent shelf. Sedimentary bedforms may have obstructed or slowed drainage as suggested by leached palaeosols and carbonate mixing observed in petrographic thin sections and grain mounts. The data show a low-relief “plains” landscape, which contrasts strongly to the topographically complex contemporary coastal foreland.
KW - Cape south coast
KW - Marine geology
KW - Palaeolandscape
KW - Pleistocene geological map
KW - Pleistocene soil map
KW - South Africa
KW - Submerged landscape
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U2 - 10.1016/j.quascirev.2019.07.040
DO - 10.1016/j.quascirev.2019.07.040
M3 - Article
AN - SCOPUS:85070761235
VL - 235
JO - Quaternary Science Reviews
JF - Quaternary Science Reviews
SN - 0277-3791
M1 - 105858
ER -