Origin of Silcretes of Central Australia

Abstract

I TAKE Prof. Brückner's remarks to mean that he almost exclusively favours the hypothesis of relative accumulation of silica within the profile in which it has been released by weathering. Examples of this are widespread in Australia for both laterite and silcrete, but in the case of the Central Australian silcretes the general and detailed evidence is markedly in favour of absolute accumulation following lateral movement in drainage waters. In addition to the general evidence set out in my letter the following details are significant. (1) Water-worn quartz gravels are frequently found in the matrix of silcrete. (2) Water-worn silcrete from some higher residuals is often included in the silcrete of lower surfaces, thus pointing to a complex erosional and depositional history rather than simple widespread planation. (3) Some of the silcrete overlies gypseous, calcareous and alunitic lacustrine deposits from which it is most unlikely to have been derived. (4) The present ephemeral stream pattern and the associated soils and rock exposure taken together with the higher situated water-worn quartz gravels point to topographic inversion of a landscape in which the originally lower silicified surfaces are now preserved as the higher topographic elements.