1887

oa South African Journal of Geology - Evidence for fluvial sediment transport of Kalahari sands in central Botswana

Volume 101 Number 2
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590

 

Abstract

A textural and mineralogical study has been made of Kalahari cover sand, collected on a regular (approximately 13 km x 13 km) grid, over an area of approximately 78 500 km2, covering much of the central Kalahari region of Botswana. Sand textural characteristics vary systematically over the area sampled, but are not readily explained in terms of the wind patterns which have prevailed from at least the Quaternary to the present day. Rather, they indicate that deposition was dominated by fluvial processes. Zones of coarse sand associated with relatively high concentrations of heavy minerals are interpreted as lags associated with the basin margins. Ephemeral streams and sheetwash transported finer material into the distal portions of the basin, which is characterized by relatively low numbers of heavy minerals. The variation in sand texture and the distribution of heavy minerals indicate that the ground sampled covers the major portion of a subsidiary central Kalahari Basin. This is bounded by the Bakalahari Schwelle in the south, and the Ghanzi ridge in the northwest. The divide between the Limpopo and endoreic fossil drainage lines, which formerly emptied into the Makgadigadi, is inferred to form the eastern margin of this central Kalahari Basin. The mineralogical and textural data presented here have important implications for kimberlite prospecting in the sand veld of the western two thirds of Botswana.


'n Tekstuur- en mineraalstudie van Kalaharideksand is uitgevoer. Laasgenoemde is versamel m.b.v. 'n reelmatige ruitnet (ongeveer 13 km x 13 km) oor 'n gebied van ongeveer 78 500 km2 wat 'n groot deel van die sentrale Kalahari in Botswana dek. Die tekstuureienskappe van die sand varieer sistematies oor die bemonsterde gebied, maar is nie maklik in terme van die windpatrone wat sedert ten minste die Kwarter tot die hede geheers het verklaarbaar nie. Hulle dui eerder aan dat afsetting deur fluviale prosesses oorheers is. Sones van growwe sand wat met betreklike hoe konsentrasies swaarminerale geassosieer is word as draalafsettings wat met die komrande geassosieer is vertolk. Efemere strome en plaatspoeling het fyner materiaal na die distale gedeeltes van die kom, wat gekenmerk word deur betreklik lae hoeveelhede swaarminerale, vervoer. Die variasie van die sandtekstuur en die verspreiding van swaarminerale dui aan dat die bemonsterde grond die grootste gedeelte van 'n ondergeskikte sentrale Kalaharikom dek. Dit word deur die Bakalahari Schwelle in die suide, en die Ghanzi Rif in die noordweste begrens. Die skeiding tussen die Limpopo en die endoriese fossieldreineringslyne wat vroeer tot in die Makgadigadi geloop het, word as die oostelike grens van hierdie sentrale Kalaharikom geponeer. Die mineralogie en tekstuurdata wat hier aangebied is het belangrike implikasies vir kimberlietprospektering in die sandveld van die westelike tweederdes van Botswana.

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/content/journal/10520/EJC-1ac2e39770
1998-06-01
2020-09-25

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