Ecca Group

Stratigraphy of the Karoo Supergroup in the Karoo Basin
Period Group Formation west of 24°E Formation east of 24°E Assemblage Zone
Jurassic Drakensberg Hiatus Drakensberg
Stormberg Clarens
Triassic Elliot
Molteno
Beaufort
Burgersdorp Cynognathus
Katberg Lystrosaurus
Balfour
Permian Dicynodon
Teekloof
Cistecephalus
Middleton
Tropidostoma
Pristerognathus
Abrahams-Kraal Koonap
Tapinocephalus
Eodicynodon
Ecca Waterford Waterford
Tierberg / Fort Brown Fort Brown
Laingsburg / Ripon Ripon
Collingham Collingham
White Hill White Hill
Prince Albert Prince Albert
Carboniferous Dwyka Elandsvlei Elandsvlei
References: Rubidge (2005),[1] Selden and Nudds (2011).[2]

The Ecca Group is a group of sedimentary geological formations found in southern Africa. A component of the Karoo Supergroup, it consists mainly of shales and sandstones, laid down in the sandy shorelines of swamplands during the Permian Period.

Description

The type area for the Ecca Group is in the Karoo Basin of South Africa and Lesotho. In the southwestern Karoo Basin, the Ecca Group has a total thickness of approximately 1300 m.[3] There is no single location where the entire vertical section of the Ecca Group is exposed. At Skoorsteenberg in the southwestern basin there is a 900-m exposure of the unit.[4]

The Ecca Group sandstones and shales originated as clastic sediment deposited in a large and shallow inland sea. Swamps and forest vegetation developed at many places and times during its deposition, resulting in widespread coal deposits. Almost all of South Africa's coal resources and one-third of the coal resources in the Southern Hemisphere are in rocks of the Ecca Group.[5]

Karoo Supergroup stratigraphic sequence

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.[6][7]

Ecca Group stratigraphy in the Eastern Cape Province

The Ecca Group is recognized throughout southern Africa. Stratigraphic units in this group in the Eastern Cape Province include, in order of deposition:[8]

The Pietermaritzburg Formation and the younger Vryheid Formation are also named deposits within the group.

See also

References

  1. Rubidge, B.S. (2005). "Re-uniting lost continents – Fossil reptiles from the ancient Karoo and their wanderlust". South African Journal of Geology 108 (1): 135–172. doi:10.2113/108.1.135.
  2. Selden, P.; and Nudds, J. (2011). "Karoo". Evolution of Fossil Ecosystems (2 ed.). Manson Publishing. pp. 104–122. ISBN 9781840761603.
  3. H. deV. Wickens and A. H. Bouma. 2000. The Tanqua Fan Complex, Karoo Basin, South Africa. In A. H. Bouma and C. G. Stone, eds., Fine-Grained Turbidite System. American Association of Petroleum Geologists Memoir 72/SEPM Special Publication 68. ISBN 9780891813538. pp. 153-164.
  4. Goldhammer, R.K., H. deV. Wickens, A. H. Bouma, and G. Wach. 2000. Sequence Stratigraphic Architecture of the Late Permian Tanqua Submarine Fan Complex, Karoo Basin, South Africa. In A. H. Bouma and C. G. Stone, eds., Fine-Grained Turbidite System. American Association of Petroleum Geologists Memoir 72/SEPM Special Publication 68. ISBN 9780891813538. pp. 165-172.
  5. Schlüter, Thomas (2008). Geological Atlas of Africa: With Notes on Stratigraphy, Tectonics, Economic Geology, Geohazards and Geosites of Each Country. Springer. pp. 233–234. ISBN 9783540763734.
  6. 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.
  7. Catuneanu, O. (2004). Retroarc foreland systems – evolution through time. Journal of African Earth Sciences, 38, 225-242.
  8. Johnson, M.R. (1976). Stratigraphy and sedimentology of the Cape and Karoo Sequences in the Eastern Cape Province. Ph.D. thesis (unpubl.), Rhodes University, Grahamstown, 336pp.
  9. 1 2 H. Martin (2011) [1981]. "The Late Palaeozoic Dwyka Group of the South Kalahari Basin in Namibia and Botswana and the subglacial valleys of the Kaokeveld in Botswana". In M. J. Hambrey, W. B. Harland. Earth's Pre-Pleistocene Glacial Record. Cambridge University Press (Cambridge Earth Science Series). pp. 61–70. ISBN 9780521172301.
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