A REVIEW OF THE SEDIMENTOLOGY OF THE EARLY-PROTEROZOIC-PRETORIA-GROUP, TRANSVAAL SEQUENCE, SOUTH-AFRICA - IMPLICATIONS FOR TECTONIC SETTING

The sedimentary rocks of the Early Proterozoic Pretoria Group form the floor rocks to the 2050 M.a. Bushveld Complex. An overall alluvial fan-fan-delta - lacustrine palaeoenvironmental model is postulated for the Pretoria Group. This model is compatible with a continental half-graben tectonic setting, with steep footwall scarps on the southern margin and a lower gradient hangingwall developed to the north. The latter provided much of the basin-fill detritus. It is evisaged that the southern boundary faults system migrated southwards by footwall collapse as sedimentation continued. Synsedimentary mechanical rifting, associated with alluvial and deltaic sedimentation (Rooihoogte-Strubenkop Formations) was followed by thermal subsidence, with concomitant transgressive lacustrine deposition (Daspoort-Magaliesberg Formations). The proposed half-graben basin was probably related to the long-lived Thabazimbi-Murchison and Sugarbush-Barberton lineaments, which bound the preserved outcrops of the Pretoria Group.