Dwyka Group

The Dwyka Group includes the sedimentary geological formations found in Karoo Basin region of Southern Africa.

In the Eastern Cape Province the Karoo Basin fill commenced with the deposition of the Dwyka Group, followed by the Ecca Group, the Beaufort Group, the Molteno, Elliot, and Clarens Formations and the igneous Drakensberg Group. The basin followed the typical evolution of foreland basins, with the Ecca Group representing the ‘flysch’ component and the Beaufort Group, the overlying Molteno and Elliot Formations representing the ‘molasse’-fluvial type sediments.^[1][2]

During the Late Carboniferous the lithosphere underlying the present day Karoo Supergroup migrated over the South Polar Region. This resulted in southern Gondwana being covered by a major ice sheet. Glacial deposits resulted in the Dwyka Group which includes diamictite, varved shale and mudstone with dropstones, fluvioglacial gravel and conglomerate. The formation ranges in thickness from 600 m to 750 m.^[3]

The Dwyka Formation is considered to be Permo-Carboniferous in age, but due to ambiguities in the fossil record, a more precise dating is not available. Maximum age inferred from fossils found in underlying strata is Late Devonian or Early Carboniferous, and minimum age inferred from fossils in the upper glacial deposits is Early Permian.^[4]

See also

• Karoo Supergroup

References

1. ^ Johnson, M. R. (1991) Sandstone petrography, provenance and plate tectonic setting in Gondwana context of the south-eastern Cape Karoo basin, South African Journal of Geology, 94, 137-154.
2. ^ Catuneanu, O. (2004) Retroarc foreland systems – evolution through time, Journal of African Earth Sciences, 38, 225-242.
3. ^ SACS (South African Committee for Stratigraphy) (1980) Stratigraphy of South Africa. Part 1 (Comp. L.E. Kent). Lithostratigraphy of the Republic of South Africa, South West Africa/Namibia, and the Republics of Bophuthatswana, Transkei and Venda: Handbook Geological Survey of South Africa, 8, 690p.
4. ^ M. J. Hambrey, W. B. Harland, Earth's pre-Pleistocene glacial record, International Geological Correlation Programme. Project 38: Pre-Pleistocene Tillites, p76