A genetic stratigraphy for the Vryheid Formation in the northern Highveld Coalfield, South Africa.

A genetic stratigraphic subdivision for the Vryheld Formation in the N Highveld Coalfield is described. Six bituminous coal seams are present in a 120m succession of sedimentary lithologies which overlie Dwyka Formation diamictite or pre-Karoo basement. These coal seams are numbered from No 1 seam at the base to No 6 seam at the top. The major coal seams are used to delineate the termination of packages of sediment which constitute genetic sequences. The coarsening-upwards assemblages of the 4, 5, and 6 Seam Genetic Sequences are commonly modified by post-depositional channelling and removal of the underlying strata, followed by deposition of coarser-grained sandstone. Palaeotopographic relief controlled the distribution of the 2 Seam Genetic Sequence by confining conglomeratic sandstone to palaeovalleys which channellized fluvial flow S into the basin. The overlying 4, 5,and 6 Seam Genetic Sequences were less affected by basement topography. Their distribution was primarily controlled by the palaeoenvironments in which sediment deposition took place. Differences in stratigraphy with neighbouring coalfield areas are ascribed to variations in basement relief and different depositional systems.-from Authors