Transvaal Basin
Encyclopedia
The Transvaal Basin is one of three basins of the Transvaal Supergroup 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
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-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
and Sishen
at the western Kaapvaal craton rim, extending into
southern Botswana
beneath Kalahari Sands as the Kanye Basin. The two basins are
separated by the broad Vryburg Arch.
Between approximately 2.640 Ga 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 deposited on peritidal flats in the southwest, which were inundated during a transgression 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. Shales 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 (BIF) being laid down over the entire basin.
Kaapvaal craton
The Kaapvaal craton , along with the Pilbara craton of Western Australia, are the only remaining areas of pristine 3.6-2.5 Ga crust on Earth...
. The evolution of this 2.65–2.05 Ga Neoarchaean–Palaeoproterozoic basin is thought to have been derived largely from magmatism
Magmatism
The formation of igneous rocks from magma is known as Magmatism.Magmatism is a process responsible for mountain formation. The process of magmatism produces an additional mass and volume to the Earth’s surface. For example the formation of volcanoes or island arcs at convergent plate boundaries...
, palaeoclimate and eustasy, while plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
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-bounded sequences that surface in two
geographically distinct areas – the Transvaal Basin, which circumscribes the Bushveld Igneous Complex
Bushveld igneous complex
The Bushveld Igneous Complex is a large layered igneous intrusion within the Earth's crust which has been tilted and eroded and now outcrops around what appears to be the edge of a great geological basin, the Transvaal Basin. Located in South Africa, the BIC contains some of the richest ore...
, and the Griqualand West basin, lying between Kimberley
Kimberley, Northern Cape
Kimberley is a city in South Africa, and the capital of the Northern Cape. It is located near the confluence of the Vaal and Orange Rivers. The town has considerable historical significance due its diamond mining past and siege during the Second Boer War...
and Sishen
Sishen
Sishen is a town in Northern Cape, South Africa. It is the location of a large iron ore mine.- Transport :The mine is connected to the port of Saldanha Bay by the Sishen-Saldanha Railway Line. The line is electrified at 50 kV AC and the trains using this line are amongst the heaviest trains in the...
at the western Kaapvaal craton rim, extending into
southern Botswana
Botswana
Botswana, officially the Republic of Botswana , is a landlocked country located in Southern Africa. The citizens are referred to as "Batswana" . Formerly the British protectorate of Bechuanaland, Botswana adopted its new name after becoming independent within the Commonwealth on 30 September 1966...
beneath Kalahari Sands as the Kanye Basin. The two basins are
separated by the broad Vryburg Arch.
Between approximately 2.640 Ga and 2.516 Ga, two successive stromatolitic
Stromatolite
Stromatolites or stromatoliths are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....
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
Siliciclastic
Siliciclastic rocks are clastic noncarbonate sedimentary rocks that are almost exclusively silica-bearing, either as forms of quartz or other silicate minerals. All siliciclastic rocks are formed by inorganic processes, or deposited through some mechanical process, such as stream deposits that are...
sediments and small lava flows. This was followed by the Nauga formation carbonates deposited on peritidal flats in the southwest, which were inundated during a transgression 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. Shales 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 (BIF) being laid down over the entire basin.