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Reconsidering the glaciogenic origin of Gondwana diamictites, Dwyka Group, South Africa
  • Mats O. Molén,
  • J. Johan Smit
Mats O. Molén
Umeå FoU AB, Umeå FoU AB

Corresponding Author:[email protected]

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J. Johan Smit
Tsunami Resources, Tsunami Resources
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Abstract

The Gondwana Late Paleozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to be subglacially formed, as are diamictites which have been interpreted as in situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well studied areas, throughout South Africa. Detailed analyses focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreted to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4271 quartz sand grains were subsampled from outcrops that are mainly considered to be tillites formed by continental glaciation. These grains, analyzed by SEM, do not demonstrate the characteristic surface microtextures combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.
01 Aug 2022Published in Geologos volume 28 issue 2 on pages 83-113. 10.2478/logos-2022-0008