Beaufort 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 | |
The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup of geological strata in Southern Africa. It follows conformably after the Ecca Group and consists essentially of sandstones and shales, deposited in the Karoo Basin from the Middle Permian to the early part of the Middle Triassic periods.
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 of the Stormberg Group 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.[3][4]
Deposits in this group include (in order of deposition):
- Lower Adelaide Subgroup comprising:
- Koonap Formation: Transitional brackish lacustrine to fluvial. Greenish-grey sandstones grading upwards into fine-grained siltstones and mudstones.
- Middleton Formation: Semi-arid climate supported a lush flora and fauna that thrived along meander belts and semi-permanent lakes.[5] Cyclic deposits of lenticular sandstone bodies grading into greenish-grey mudstone. The thickest formation in this succession, constituting 37% of the Beaufort Group and 47% of the Adelaide Subgroup.[6] The formation has lenses of red mudstone which are likely to have been deposited in a sub-aerial fluvial environment.
- Balfour Formation: The upper part of the Adelaide Subgroup and part of what was called lower to middle Beaufort.
- Upper Tarkastad Subgroup comprising:
- Katberg Formation: Arenaceous deposits of red and olive-yellow mudstones. Deposited in a braided fluvial system.
- Burgersdorp Formation: Deposited in a low-sinuosity fluvial system.[7]
Paleontology
Fossils of tetrapods, especially therapsids, are common, and the vertebrate biostratigraphy has been mapped out in detail, beginning with the work of Robert Broom at the start of the 20th century and developed and revised a number of times since. Currently eight faunal zones are recognised, tracing the development of terrestrial life through the Permo-Triassic, and named after a characteristic genus that serves as an index fossil.
In order the assemblage zones are:
- Cynognathus Assemblage Zone (Youngest)
- Lystrosaurus Assemblage Zone
- Dicynodon Assemblage Zone
- Cistecephalus Assemblage Zone
- Tropidostoma Assemblage Zone
- Pristerognathus Assemblage Zone
- Tapinocephalus Assemblage Zone
- Eodicynodon Assemblage Zone (Oldest)
The Beaufort Group deposits also yield numerous plant and insect fossils.
See also
References
- ↑ 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.
- ↑ Selden, P.; and Nudds, J. (2011). "Karoo". Evolution of Fossil Ecosystems (2 ed.). Manson Publishing. pp. 104–122. ISBN 9781840761603.
- ↑ 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.
- ↑ Catuneanu, O. (2004). Retroarc foreland systems – evolution through time. Journal of African Earth Sciences, 38, 225-242.
- ↑ Smith, R.M.H., Eriksson P.G. and Botha W.J. (1993) A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa. Journal of African Sciences, 16, 143-169
- ↑ 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.
- ↑ Neveling, J. (2003). Stratigraphy and sedimentological investigation of the contact between the Lystrosaurus and the Cynognathus Assemblage Zones (Beaufort Group: Karoo Supergroup). Council for Geoscience, Bulletin 137, 165pp.
- John Hancox, P. J. and Rubidge, B. S. (1997), The role of fossils in interpreting the development of the Karoo basin, Palaeontologica Africana 33: 41-54.
- Ponomarenko, A. G. and Mostovski, M. B. 2005. New beetles (Insecta: Coleoptera) from the Late Permian of South Africa, African Invertebrates, 46: 253-260.
- Sukatsheva, I. D., Beattie, R. and Mostovski, M. B. 2007. Permomerope natalensis sp. n. from the Lopingian of South Africa, and a redescription of the type species of Permomerope (Insecta: Trichoptera). African Invertebrates 48 (2): 245-251.