Depositional environments of the Meso- to Neoproterozoic Ghanzi-Chobe belt, northwest Botswana

Abstract

The Ghanzi-Chobe belt comprises a volcano-sedimentary basin sequence located in northwest Botswana. This sequence started to accumulate at about 1106 Ma ago and was deformed during the Pan-African event between approximately 750 and 500 Ma. The stratigraphy consists of an older Kgwebe Formation and a younger Ghanzi Group. The Kgwebe Formation represents the first phase of basin evolution that involved extensional tectonics and intracratonic rifting with subsequent bimodal volcanism and the development of lacustrine to fluvial systems. The Ghanzi Group represents the second phase of basin evolution marked by an extensive rift enlargement episode, resulting in a shallow marine basin with the deposition of siliciclastic sedimentary rocks and carbonate beds. The marine basin consisted of a shallow shelf environment dominated by storm and fairweather conditions. Stratabound copper sulphide mineralization was deposited at a redox interface between an alluvial facies and a marine transgressive sequence. The final development of the sedimentary environment involved a progradational shoreline with the deposition of a red arenite facies. Intermediate sub-environments consisted of mixed clastic-carbonate lagoons and possible progradational deltas. Rifting in the Ghanzi-Chobe belt was aborted before the development of an ocean resulting in a failed intracontinental rift basin.