TECTONICS, SEDIMENTATION AND SEDIMENT SUPPLY SYSTEMS AT THE SOUTHERN MARGIN OF THE CONGO CRATON: THE KATANGA SUPERGROUP, NEOPROTEROZOIC-LOWER PALAEOZOIC OF CENTRAL AFRICA

The Neoproterozoic-Lower Palaeozoic Katangan sedimentary sequence occurs at the southern margin of the Congo Craton, between the Democratic Republic of Congo and Zambia. It rests unconformably upon granitic and metamorphic basement ranging in age from 2.0 to 0.88 Ga and records a complete Wilson Cycle. The terrigenous detritus was initially derived from the external cratonic source in the north. Subsequent orogenesis between the Zimbabwe Craton to the south and the Congo Craton to the north resulted in northward-oriented thrusting and elevation of nappes with the Katangan sedimentary strata. These acted as internal orogenic sources supplying sediment to the foreland basins in the north of the belt. Three major stages of basin evolution can be identified. Rifting between the Zimbabwe Craton and the Congo Craton, followed by a marine transgression, led to the deposition of the Roan Group continental and shallow marine proximal clastics supplied from the cratonic source in the north and grading to distal carbonate facies in the south. The succeeding Guba Group represents an early foreland setting and records a prominent northward shift of the basin margin and marine transgression onto the Congo Craton. The lateral distribution of facies associations, with mainly fine-grained continental clastics, impure dolomites and black shales, testifies to a two-fold subdivision of the depository. The northern sub-basin was moderately to poorly supplied from the craton, while the southern one was an undersupplied to starved basin filled with black shales. The synorogenic Fungurume Group was deposited ahead of the Katangan nappes at a late stage of foreland evolution and consists of two facies associations: continental red beds and subaquaeous olistostromes. Their composition reflects multiple recycling of detritus derived from the Katangan units involved in the northward-propagating orogenic front. Sediment provenance is among the criteria which recently revealed new genetic aspects of the Katangan succession and are applicable in mineral exploration for Cu-Co orebodies.