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Geology of KwaZulu-Natal |
| Dwyka Group - ice sheets cover Gondwana | |||
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The rocks overlying the Natal Group is a thick unit of tillite that was deposited in a glacial environment by retreating ice sheets about 300 million years ago.
Ice cap covering Gondwana 300 million years ago
At this time South Africa was part of the supercontinent Gondwana, which was situated near the south pole and covered with ice. Rocks imbedded in the slowly moving ice sheets scoured and polished the underlying older rocks giving rise to glacial pavements. Striation directions indicate that ice flow was from north to south - valuable information when it comes to reconstructing Gondwana. |
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| The Dwyka Group forms the lowermost and oldest deposit in the Karoo Supergroup basin. This basin extended across much of southern Gondwana and records 120 million years of geological history. | |||
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| Adapted from: The story of Earth & Life (T. McCarthy & B. Rubidge) | |||
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The picture shows a striation on the rock surface caused by the movement of ice and boulders about 300 million years ago. Locality:University of KwaZulu-Natal, Durban-Westville. Move your mouse onto the picture to see the movement direction. |
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Tillite is mostly a very fine-grained, blue-grey rock comprised of clay matrix with inclusions (or clasts) of many other fragments picked up by glaciers during their travels.
A typical example of Dwyka tillite
The tillite in KZN often weathers to a characteristic yellowish colour. In the Durban area, cliffs near the mouth of the Umgeni River, and quarries in the Westville area offer the best exposures of tillite. |
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last updated:
16 Apr 2007
© School of Geological Sciences, University of KwaZulu-Natal
The website was designed and compiled by Dr. G. Whitmore, Ms D. Meth and Dr. R. Uken (modified by T. Reinhardt.)