Submarine debris flow deposits from the Upper Carboniferous Dwyka Tillite Formation in the Kalahari Basin, South Africa |
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| Authors: | J N J VISSER |
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| Institution: | Department of Geology, University of the Orange Free State, 9301 Bloemfontein, South Africa |
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| Abstract: | ABSTRACT Four types of sediment gravity flow deposits occur interbedded with rhythmite shale, siltsone, mudstone and minor diamictite in a 230-m thick Carboniferous glacial sequence. Shear and plug zones are present in the cohesive debris flow deposits which have a diamictic texture. The high-density turbidity flow deposits which consist of coarse to medium-grained clastics, are characterized by both normal and reverse grading. The medium to fine-grained low-density turbidity flow deposits show normal grading and consist of Bouma units A, B, D and E. Deposition occurred by gravity flow, suspension settling and minor basal melt-out during ice retreat along the southern margin of the Kalahari Basin. Immediately basinwards of the ice grounding line a proximal diamictite facies consisting predominantly of cohesive and high-density turbidity flow deposits, and minor melt-out tills formed. A distal sedimentary facies of graded sandstone and siltstone units deposited by low-density turbidity flows and suspension settling of muds with ice-rafted debris is located basinwards. |
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