Transvaal Supergroup
The Transvaal Supergroup in the Earth's history , a lithostratigraphic rock unit in the northern part of South Africa, the geochronological in the late Archean to early Proterozoic is dated.
Geographical location
The Transvaal Supergroup stretches from around 23 ° to 29 ° South and 22 ° to 30 ° East on the northern border of South Africa. The formations were deposited in the following three basins:
- the eastern Transvaal basin ,
- the western Griqualand West Basin ,
- and the small Kanye Basin in southern Botswana .
The Transvaal and Grinqualand West Basins are separated by the Vryburg Ridge, a paleotopographical height.
Definition, depository and dating
The deposits of the Transvaal Supergroup date from the late Archean and early Proterozoic . This area is limited by the Witwatersrand Supergroup at around 2700 Ma at the base and by the Bushveld Intrusion at around 2050 Ma at the top. This period can be divided into five first-order sequences.
- The protobasinal rocks, which only occur in the Transvaal Basin, point to deep marine facies and tectronic structures of pull-apart and rift basins.
- In the young intercratonic “Sag Basin”, the first fluvial deposits in the form of thinly layered sandstones can form.
- In the overlying Chuniespoort Group, a thermal subsidence enables biogenic carbonate growth during a high system train. These carbonates form the basis for ribbon iron ores.
- The fourth and fifth sequences belong to the Pretoria Group. Both sequences show rift tectonics in the low-level system tract with associated subsidence and shallow lake deposits, followed by a transgression system train with deeper deposit conditions due to a forming inland sea. Both sequences therefore show deposits of stratified sandstone as well as arenite and fluvially transported quartzitic sandstone. The fourth sequence is glacial. The Bushfeld intrusion is indicated by a magmatic induced uplift in connection with a falling-stage system tract in the fifth sequence.
The “ Great Oxidation Event ” and the global Huronian Ice Age also fall within the time frame of the Transvaal Supergroup .
structure
The Transvaal Supergroup from bottom to top is divided into the following units:
- Pretoria Group (with Rooihoogte Formation , Timeball Hill Formation , Boshoek Formation , Hekpoort Formation , Dwaalheuwel Formation , Strubenkop Formation , Daspoort Formation , Silverton Formation , Magaliesberg Formation , Vermont Formation , Lakenvlei Formation , Nederhorst Formation , Steenskampsberg Formation and Houtenbek Formation )
- Chuniesport Group (with Oaktree Formation , Monte Cristo Formation , Lyttrlton Formation , Eccles Formation , Frisco Formation , Penge Formation and Duitschland Formation )
- Black Reef Formation
- the so-called protobasinal rocks
literature
- Octavian Catuneanu, Patrick G. Eriksson: The sequence stratigraphic concept and the Precambrian rock record: an example from the 2.7-2.1 Ga Transvaal Supergroup, Kaapvaal craton. Precambrian Research, 97: 215-251, 1999
Individual evidence
- ↑ Eriksson, PG, et al .: Late Neoarchaean-Palaeoproterozoic supracrustal ba-sin-fills of the Kaapvaal craton: Relevance of the supercontinentc cycle, the "Great Oxidation Event" and "Snowball Earth". In: Marine and Petroleum Geology. Vol. 28, 2011, pp. 1385-1401.
- ↑ Eriksson, PG: Palaeoproterozoic epeiric sea palaeoenvironments: The Silverton Formation In: Spec. Publ. Int. Ass. Sediment. Vol. 33, 2012, pp. 351-367.
- ↑ Bumby, AJ et al .: Meso-Archaean and Palaeo-Proterozoic sedimentary sequence stratigraphy of the Kapvaal Craton In: Marine and Petroleum Geology Vol. 33, 2012, pp. 92-116.