Parent Material and Pedogenic Processes in South Africa

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Abstract
The soils over about half of South Africa are developed from sedimentary rocks of the Karoo Supergroup. Some units within the Karoo strata display variations in their mineralogical composition which correlate with fluctuations in the environment of deposition and with palaeotemperature. The former trends are reflected in the ratio of kaolinite to 2:1 layer-silicates, range from kaolinite-dominated to kaolinite-free, and are particularly evident in rocks of the Vryheid Formation. Geothermal history is preserved in various stages of smectite illitization ranging from R = 0 structures with 25% illite to 100% illite. Compositional trends may be significant on a regional, local or topographic scale down to a distance equal to the depth of a soil profile or even an horizon.