Ellisras Basin
| Ellisras Basin Stratigraphic range: Karoo Supergroup |
|
|---|---|
| Type | Structural basin |
| Location | |
| Coordinates | 23°40′S 27°31′E / 23.67°S 27.52°ECoordinates: 23°40′S 27°31′E / 23.67°S 27.52°E |
| Country |
 Botswana South Africa
|
The Ellisras Basin is a geological basin that spans the border between South Africa and Botswana, extending west from the town of Lephalale (formerly Ellisras) in Limpopo province. Basin fill consists of sedimentary rocks of the Karoo Supergroup, with maximum thickness of 1,500 metres (4,900 ft).
The principal economic resources in the basin are the Waterberg Coalfield in South African and the Mmamabula coalfields in Botswana.
The Ellisras Basin is about 320 kilometres (200 mi) north of the main Karoo Basin. It extends east from the Kalahari Basin that underlies much of Botswana. The South African portion of the Ellisras basin is about 90 kilometres (56 mi) from east to west and 35 kilometres (22 mi) from north to south. The portion in Botswana extends much further to the north and south.
The basin formed at the same time as the Karoo Supergroup, and is around 310 to 180 million years old. It has the asymmetrical cross-section typical of a half-graben, bounded on the north side by a fault zone that slopes steeply down to the axis of the basin, while the southern side slopes down more gently. On the north it is bounded by the Melinda Fault Zone (MFZ), a zone of block faulting in the highly deformed and metamorphosed Archean-age rocks of the Limpopo Belt. The Eenzaamheid Fault Zone defines the southern boundary of the basin, where basin sediments abut older coarse-grained sandstones and minor mudstones in the Waterberg Group.
There is an unconformity where the Karoo rocks of the basin overlie much older rocks. The southern flank of the basin is underlain by Waterberg Group rocks, which form between two-thirds and three-fourths of the basin floor. Mafic rocks of the Limpopo Belt underlie the basin floor in the northeast. The Bushveld Complex underlies the basin in the southeast.
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