THE SEDIMENTOLOGY OF THE WATERBERG GROUP IN THE TRANSVAAL, SOUTH-AFRICA - AN OVERVIEW

The Palaeoproterozoic Waterberg Group consists chiefly of a succession of coarse siliciclastic rocks which shows two upward-fining sequences. The main depository evolved as a continental, fault-bounded basin in the northern part of the Kaapvaal craton. The Main basin is bounded in the south by the Thabazimbi-Murchison fault zone and in the north by the southern part of the Melinda fault zone. The Swaershoek and lower Sterk River Formations at the base of the sequence are interpreted to have been deposited as fan deltas and were possibly reworked in a littoral palaeo-environment. The Alma and upper Sterk River Formations are interpreted as a series of alluvial fans forming a bajada along the scarp caused by the uplifted block on the southern side of the Murchison fault zone. The Skilpadkop and Setlaole Formations are considered to have been deposited on narrow braidplains. The Makgabeng Formation was deposited during the more stable period that followed and it is considered to represent a large dune field, which may have been coastal in nature towards the south. The upward-coarsening Aasvoelkop Formation was deposited in a shallow through-flow lake, although fluvial deposition was more important towards the top of the formation. The Mogalakwena and Sandriviersberg Formations are interpreted as having been deposited by large braided rivers, forming an extensive braidplain which probably continued to the southwest, through Bostwana into the northern Cape Province, where it may be represented by the Fuller Member of the Volop Group. As sediment input from the north decreased, the sea transgressed over the braidplain and deposited the Cleremont Formation, which is interpreted as a littoral deposit or a tidally influenced shelf deposit. The Vaalwater Formation, which ended the Waterberg episode, formed within a littoral or a shallow siliciclastic sea palaeo-environment.