Anastomosing river deposits: palaeoenvironmental control on coal quality and distribution, northern Karoo basin.

Borehole data from an area close to the N margin of the Karoo Basin reveal a 110m thick coalbearing succession of the Vryheid Formation. The lowermost sediments reflect processes of deglaciation with a complex array of glaciolacustrine, glaciofluvial and alluvial- outwash fan deposits. Above this tundra-type peat bogs developed in inactive areas and account for the two basal coal seams. During accumulation of peat which was later to form the extensive No. 2 coal seam, active clastic sedimentation was confirned to laterally restricted river channels. Lateral migration was inhibited by vegetation stabilized river banks. Channel fill consists of coarse-grained bedload sediment deposited in anastomosing streams. Flood episodes are marked by widespread, but thin shale zones that intercalate with the channel sandstones. Both sandstone and shale units are completely enveloped by No. 2 coal seam.-from Author