DETAILED FACIES ANALYSES OF THE DIPHAWANA PALEOPROTEROZOIC SUCCESSION (KANYE, BOTSWANA): IMPLICATIONS FOR THE PALEO ENVIRONMENTAL RECONSTRUCTION OF THE LOWER TRANSVAAL SUPERGROUP

The Kanye area is located on the Kaapvaal Craton in the southern district of Botswana and exposes a mixed volcanic sedimentary succession spanning from the Meso/Neoarchean to the Paleoproterozoic. This includes the complete... [ view full abstract ]

The Kanye area is located on the Kaapvaal Craton in the southern district of Botswana and exposes a mixed volcanic sedimentary succession spanning from the Meso/Neoarchean to the Paleoproterozoic. This includes the complete sequence of the Lower Transvaal Supergroup (LTS). In the Diphawana area, 10 km south from Kanye village, the LTS sedimentary succession unconformably overlies the rhyolites and the siliciclastic sediments of the Lobatse Volcanic Group (LVP). This study aims to shed light on the LTS succession providing for the first time a detailed sedimentological model for the sediments exposed near Kanye village along the Diphawana hills.
The oldest unit exposed in the Diphawana hills is made up of porphyritic rhyolites of the LVP. These are unconformably overlaid by a succession of siliciclastic sediments (ca. 500 m thick). The contact is unevenly exposed in the study area. The bulk of the LVP siliciclastic sediments consist of inter-bedded mudstone and siltstone with massive conglomerate and sandstones. Ripple marks are common within the siltstones. This fine-grained dominate unit is unconformably overlaid by the basal conglomerate of the Black Reef Quartzite marking the base of LTS. The conglomerate grades into a coarse-grained mature crossed bedded sandstones unit, passing up to a fine-grained crossed laminated quartz arenite. On top of this fining upward sequence the cross bedded sandstones (locally arkoses) are interbedded with dark dolomite and mudstone with evidence of desiccation cracks. Toward the top the LTS succession becomes dominantly dolomitic, locally showing relict silicified stromatolites, with a capping unit of cherty dolomite (ribbon dolomite). The contact between the dolomite unit and the above chert is not exposed. The top of the sequence at Diphawana is characterized by jaspilitic chert breccia.

The LTS sequence in the Diphawana area reflects the deposition of high energy deposits on top of the fine grained sediments of the LVG. The Diphawana hills exposes what has been interpreted as Paleoproterozoic deepening upward sequence with continental siliciclastic deposits conformably overlaid by shallow marine fine grained siliciclastic and carbonatic materials. These have been probably deposed within a large tidal flat as suggested by the presence of desiccation cracks and stromatolites. These littoral sediments are followed by shallow marine carbonates and open marine sediments.