A laterite profile near Albertinia, Southern Cape, South Africa: its significance in the evolution of the African Surface.

Abstract

Although the African surface has been reported to be capped by silcrete in the Southern Cape, as opposed to laterite in the eastern coastal hinterland and on the highveld, ferricrete and associated gravels have recently been recorded there. Analysis of an African surface profile from the Albertinia area of the Southern Cape, developed from Bokkeveld shale, shows a typically lateritic leaching progression. Leaching of bases and silica is accompanied by enrichment in iron. The zone of superior weathering is kaolinised here to some 40m depth. The iron enrichment is dominantly of goethite, together with haematite in the nodular surficial horizon. The nodules conserve Bokkeveld shale saprolitic textures. There is no evidence of silcretisation in this profile although silcretes occur elsewhere in the wider vicinity, as do other kaolinised and lateritised profiles similar to the one described. A protracted, lateritic leaching event must be recognised as a major component in the palaeoenvironmental reconstruction of this area, further study of which holds promise of contributing to a better understanding of laterite/silcrete genetic and temporal relationships, a largely unresolved geomorphological problem.