Abstract:
KARST FEATURES IN QUARTZITE OF SOUTH AFRICA - The author describes karst features developed in quartzite and also, but to a lesser extent, in weathered diabase and in wad. In quartzite, the karst is due to weathering along joints and bedding planes, producing softer areanaceous boundaries. Later, vadose caves form by piping in the weathered material, starting at a spring and progressing upstream. The karst features include dolines, swallow-holes, and caves, grouped in very localised systems. Over most of the quartzite plateaus, however, real karst features are absent and the drainage remains superficial. The only ubiquitous features, reminiscent of lapies, consist of pinnacles left after erosion of sand. As most of the time they are not associated to deep karst systems, the author proposes that they should not be considered as karst features. Other caves are developed in weathered diabase and dolomite (wad), sandwiched between resistant quartzite layers. They result from the erosion of these soft layers. The author is of the opinion that the term karst rather than pseudokarst should be used to describe this morphology developed in silica and silicate rocks. The reason is that not only the features produced compare well with the ones observed in " soluble rocks " (limestone, gypsum, etc.), but that the genetical process is very similar. It is suggested that the term pseudokarst should be used only in cases were the genesis is different.