The Gemsbok Sub-basin is situated in the south-western corner of the Kalahari Karoo
Basin and extends south from the Kgalagadi District of Botswana into the Northern Cape
(South Africa); and west into the Aranos Basin (southeast Namibia). The Sub-basin
preserves a heterogeneous succession of Upper Palaeozoic to Lower Mesozoic
sedimentary and volcanic rocks of the Karoo Supergroup. Because the succession is
largely covered by the Cenozoic Kalahari Group, the stratigraphy of the succession is not
as well understood as the Main Karoo Basin in South Africa. Most research in the
Gemsbok Sub-basin is based on borehole data. This study focuses on the intrabasinal
correlation, depositional environments and provenance of the Karoo Supergroup in the
Gemsbok Sub-basin in Botswana and Namibia.
Based on detailed sedimentological analyses of 11 borehole cores of the Karoo
Supergroup in the Gemsbok Sub-basin of Botswana and Namibia, 8 facies associations
(FAs) comprising 14 lithofacies and 2 trace fossil assemblages (Cruziana and Skolithos
ichnofacies) were identified. The facies associations (FA1 to FA8) correspond to the
lithostratigraphic subdivisions (the Dwyka Group, Ecca Group, Beaufort equivalent
Group, Lebung Group [Mosolotsane and Ntane formations] and Neu Loore Formation) of
the Karoo Supergroup. Sedimentological characteristics of the identified facies
associations indicate the following depositional environments: glaciomarine or
glaciolacustrine (FA1, Dwyka Group), deep-water (lake or sea) (FA2, Ecca Group),
prodelta (FA3, Ecca Group), delta front (FA4, Ecca Group), delta plain (FA5, Ecca
Group), floodplain (probably shallow lakes) (FA6, Beaufort Group equivalent), fluvial
(FA7, Mosolotsane and Neu Loore formations) and aeolian (FA8, Ntane Sandstone
Formation).
The Dwyka Group (FA1) forms the base of the Karoo Supergroup in the Gemsbok Subbasin
and overlain by the Ecca Group deposits. Three types of deltas exist within the
Ecca Group: fluvial-dominated; fluvial-wave interaction and wave-dominated deltas. The
Gemsbok Sub-basin was characterised by rapid uplift and subsidence and high sediment influx during the deposition of the Ecca Group. Petrographic and geochemical analyses of
the Ecca Group sandstones revealed immature arkose and subarkose type sandstones
dominated by angular to subangular detrital grains, sourced from transitional continental
and basement uplifted source areas. The sandstones of Ntane Sandstone Formation are
classified as subarkoses and sourced from the craton interior provenances.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/10167 |
| Date | 22 June 2011 |
| Creators | Nxumalo, Valerie |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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