Ecca Group

The Ecca Group is the name given to the sedimentary geological formations found in Karoo Basin region of Southern Africa. It consists mainly of shales and sandstones, laid down in the sandy shorelines of swamplands, during the Permian Period.

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]

It is a carbon-rich sedimentary deposit, owing to the high vegetation content of the original sediment. Coal is mined in the Vryheid area.

Deposits in this group include (in order of deposition):^[3]

• Prince Albert Formation marine mudstones.
• Whitehill Formation marine mudstones.
• Collingham Formation persistent grey shales, alternating with yellow claystones which derive from volcanic ash.
• Ripon Formation
• Fort Brown Formation
• Waterford Formation sandstones and shales .

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

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. ^ Johnson, M.R. (1976). Stratigraphy and sedimentology of the Cape and Karoo Sequences in the Eastern Cape Province. Ph.D. thesis (unpubl.), Rhodes Univ., Grahamstown, 336pp.