PETROGRAPHY AND GEOCHEMISTRY OF SANDSTONES INTERBEDDED WITH THE ROOIBERG FELSITE GROUP (TRANSVAAL SEQUENCE, SOUTH-AFRICA) - IMPLICATIONS FOR PROVENANCE AND TECTONIC SETTING

The 2150 Ma Rooiberg Felsite Group, Transvaal Sequence, contains thin sandstone interbeds within its 3500-5000 m thick volcanic succession. Whereas uppermost feldspathic arenites and wackes are thought to represent reworked felsitic material, quartz arenites and subordinate lithic sandstones, present throughout most of the Rooiberg sequence, comprise mainly reworked sedimentary detritus, probably belonging to the underlying Pretoria Group. Sandy braided-river systems probably transported elastic material into the basin from relatively stable source areas, subject to intense chemical weathering. Geochemistry and sandstone petrography indicate that mixing of Pretoria Group detritus with sediment derived from erosion of felsitic material occurred within the basin during late Rooiberg times. The inferred hiatuses in volcanism represented by the predominant siliceous sedimentary interbeds appear to have been of relatively short duration and occur throughout much of the Rooiberg stratigraphy. Upper arkosic sandstones indicate longer breaks in volcanism as Rooiberg eruptions came to an end. The sandstones provide evidence compatible with an impact origin for the Rooiberg Felsite Group, and for its successor, the Bushveld Complex.