Evolution of an Archaean intracratonic basin: A review of the Transvaal Supergroup lithostratigraphy in Botswana

Abstract Several lithostratigraphic and radiometric-dating studies over the last half century have generated a robust stratigraphic data set about the Transvaal Supergroup sedimentary deposits throughout southern Africa. The Transvaal Supergroup in southern Africa represents one of the best examples of a Precambrian intracratonic sequence, including one of the best preserved and extensive Archaean/Palaeoproterozoic carbonate platforms. Sediments of the Transvaal Supergroup are hosted on the Kaapvaal Craton in three areas of South Africa and Botswana. Critically, the smallest of the three Transvaal depocentres, the Kanye Basin (including the Molepolole-Mochudi sub-basin), is the least known, and the stratigraphic model is still incomplete. The Kanye Basin in southern Botswana exposes a mixed volcanic-sedimentary succession spanning from the Meso-Neoarchaean to the Palaeoproterozoic, including the complete sequence of the Lower Transvaal Supergroup (LTS) and the lower part of the Upper Transvaal Supergroup (UTS). Although no consensus has been reached so far, the deposition of the Transvaal-age sediments in Botswana likely followed the same thermal and tectonic processes recorded in South Africa, albeit diachronously. The initial stage of rifting was followed by sediments that formed in an epicontinental sea setting that recorded the deepening of the basin. The younger sequence records the reactivation of the extensional tectonics alternating with post-rift thermal subsidence. The nomenclature of the lithostratigraphic units in Botswana is often inconsistent, and the correlations with the main Transvaal basins in South Africa are imprecise. Because of the importance of the Transvaal Supergroup for economic (e.g., skarn deposits and placers) and hydrologic (e.g., the Ramotswa trans-boundary aquifer) reasons, the lack of a consistent nomenclature can introduce ambiguity in the scientific literature and lead to misinterpretations. A thorough lithostratigraphic revision of the Transvaal Supergroup in Botswana will also solve the puzzle of the Transvaal-age deposits in southern Africa, allowing reliable interpretations across the three basins. Here, a comprehensive lithostratigraphic and chronostratigraphic description of the Transvaal Supergroup is provided based on literature data and new observations. New lithostratigraphic charts are produced for the Kanye Basin, revealing the stratigraphic relationships within the different Transvaal basins and the effect of cyclicity in the evolution of this Precambrian basin.