Bokkeveld Group

Bokkeveld Group
Stratigraphic range: Early-Middle Devonian ~450–400 Ma
Type Geologic group
Sub-units Gydo Formation, Gamka Formation, Voorstehoek Formation, Hex River Formation, Tra-Tra Formation, Boplaas Formation, Waboomberg Formation, Wuppertal Formation, Klipbokkop Formation, Osberg Formation and Karoopoort Formation
Underlies Witteberg Group
Overlies Table Mountain Group
Lithology
Primary sandstone, mudstone, siltstone, shale, and conglomerates
Other calcite
Location
Region Western and Eastern Cape Provinces
Country  South Africa

The Bokkeveld Group is a geological group in South Africa, consisting predominantly of mudstones. After the rocks of the Cape Supergroup had been folded into the Cape Fold Mountains, these soft mudstones readily washed away from the mountain tops, and only remain in the valleys. Here they form the fertile soils on which the vineyards and fruit orchards of the Western Cape flourish with the help of irrigation from the rivers that have their sources in the surrounding mountains.

Geographic extent

The Bokkeveld Group does not extend on to the Cape Peninsula or its isthmus (the Cape Flats). Here the Stellenbosch, Franschhoek, Paarl, Durbanville, Tulbagh and Constantia vineyards have been planted on the weathered Cape Granite and Malmesbury shale soils, which form the basement rocks on which the Cape Supergroup rocks in this region rest.

The Bokkeveld Group extends eastwards to Port Alfred (near Grahamstown), approximately 120 km beyond the eastern extent of the Cape Fold Belt.[1]

Stratigraphic units (oldest to youngest)

Ceres Subgroup:

  • Gydo Formation
  • Gamka Formation
  • Voorstehoek Formation
  • Hex River Formation
  • Tra-Tra Formation
  • Boplaas Formation

Bidouw / Traka Subgroup:

  • Waboomberg Formation
  • Wuppertal Formation
  • Klipbokkop Formation
  • Osberg Formation
  • Karoopoort Formation

Paleontology

The bulk of the fossils found in the Cape Supergroup occur in the Bokkeveld mudstones. They include a variety of brachiopods, as well as trilobites, molluscs, echinoderms (including starfish, crinoids, and the extinct blastoids and cystoids), foraminifera and fish with jaws (placoderms).[2] [3]


References

  1. ↑ Geological Map of South Africa, Lesotho and Swaziland. (1970). Council for Geoscience, Geological Survey of South Africa.
  2. ↑ Truswell, J.F. (1977). The Geological Evolution of South Africa. pp. 93-96, 114-159. Purnell, Cape Town.
  3. ↑ Tankard, A.J., Jackson, M.P.A., Erikson, K.A., Hobday, D.K., Hunter, D.R., Minter, W.E.L. (1982) Crustal Evolution of Southern Africa: 3.8 Billion Years of Earth History. pp. 333-363. Springer-Verlag. New York.
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