The geology of the Waterberg group in the southern Portion of the Waterberg basin

Abstract

The Waterberg Group consists chiefly of a succession of coarse elastic sedimentary rocks which shows two upward-fining sequences. The sedimentary rocks belong to the Mokolian erathem and they are 1700-1900 Ma old. The depository evolved as a continental, fault-bounded basin in the northern part of the Kaapvaal craton. The basin is bounded in the south by the Murchison lineament and in the north by the southern part of the Pal al a shear zone. The Murchison lineament is interpreted to be a long-lived, fundamental strike-slip fault system. Deformation lamellae in quartz in the Alma Formation near Thabazimbi, are thought to have resulted from transpressive strain along this fault zone. The Swaershoek and lower Sterkrivier Formations are interpreted to have been deposited as fan deltas and were possibly reworked in a littoral palaeo-environment. The Alma and upper Sterkrivier 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 strike-slip 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 interpreted to be the result of a large dune field, which may have been coastal in nature towards the south. Problematic trace-like structures occur in the southeastern part of the basin in a littoral intercalation in the Makgabeng Formation. The upward-coarsening Aasvo~lkop Formation is thought to have been deposited in a shallow through-flow lake, although fluvial deposition was probably 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 Botswana into the northern Cape Province, where it may be represented by the Fuller Member