Abstract

A field investigation resulted in a detailed stratigraphic profile of the full sequence of the Permo-Carboniferous, glaciomarine Dwyka Group in the Elandsvlei-Elandsdrif area. Six cycles of a basal tillite unit capped by a terminal zone of stratified sediments, are documented. Of note is the recurrence in the tillite units of the association diamictite-boulder beds-eskers. This facies association is interpreted as a subglacial deformation tillite, with the boulder beds as products of the deforming-bed process. The sediments of the terminal zones indicate a sub-ice shelf environment. Nine advance/retreat fluctuations are interpreted from the facies associations. The immature eskers and lack of sorted sediments point to a low level of melt water supply, pointing to a polar ice sheet. Westward ice-flow is supported by macrofabric data, basal and boulder pavements. An analysis of the boulder lithologies shows that the source area stayed the same throughout the glacial period. It is proposed that part of the onset area due east is an extrusive-intrusive complex with a chert-carbonate-banded iron formation component. This investigation supports a series of glacial advance/retreat cycles rather than the previous model of deglaciation.

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