The Transvaal Basin is one of three basins of the
Transvaal Supergroup
The Transvaal Supergroup is a stratigraphic unit in northern South Africa and southern Botswana, situated on the Kaapvaal Craton, roughly between 23 and 29 degrees southern latitude and 22 to 30 degrees eastern longitude. It is dated to the boun ...
on the
Kaapvaal craton. The evolution of this 2.65–2.05
Ga Neoarchaean–
Palaeoproterozoic basin is thought to have been derived largely from
magmatism,
palaeoclimate and
eustasy, while
plate tectonics
Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large t ...
played an intermittent role. The supergroup is made up of basal ‘
protobasinal’ rocks, upon which followed the
Black Reef Formation,
Chuniespoort Group and the uppermost
Pretoria Group.
The Transvaal Supergroup displays three
unconformity
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...
-bounded sequences that surface in two
geographically distinct areas – the Transvaal Basin, which circumscribes the
Bushveld Igneous Complex, and the
Griqualand West basin, lying between
Kimberley
Kimberly or Kimberley may refer to:
Places and historical events
Australia
* Kimberley (Western Australia)
** Roman Catholic Diocese of Kimberley
* Kimberley Warm Springs, Tasmania
* Kimberley, Tasmania a small town
* County of Kimberley, a ...
and
Sishen at the western Kaapvaal craton rim, extending into southern
Botswana
Botswana (, ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label= Setswana, ), is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory being the Kal ...
beneath the
Kalahari Sands as the Kanye Basin. The two basins are
separated by the broad Vryburg Arch.
Between approximately 2.640 and 2.516 Ga, two successive
stromatolitic carbonate platforms developed in the basin of the Kaapvaal craton. Oldest was the Schmidtsdrif Subgroup, deposited in the southwestern part of the basin, showing stromatolitic carbonates,
siliciclastic sediments and small
lava flows. This was followed by the Nauga formation
carbonates
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
deposited on
peritidal flats in the southwest, which were inundated during a
marine transgression
A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...
of the Transvaal Supergroup continental sea, at some 2.550 Ga. This resulted in a carbonate platform in the Transvaal and Griqualand West Basins, lasting
for 30–50 Ma.
Shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...
s were deposited during this period over the Nauga Formation carbonates. Following this a subsidence led to immersion of the stromatolitic platform and to sediments of iron-rich
banded iron formations being laid down over the entire basin.
[P. G. Eriksson, W. Altermann; ''An overview of the geology of the Transvaal Supergroup dolomites (South Africa),'' Environmental Geology November 1998, Volume 36, Issue 1-2, pp 179-18]
abstract
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References
{{reflist
Geology of South Africa
Sedimentary basins of Africa