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Kaolinisation and the formation of silicified wood on late Jurassic Gondwana surfaces

1983; Geological Society of London; Volume: 11; Issue: 1 Linguagem: Inglês

10.1144/gsl.sp.1983.011.01.04

2041-4927

H. Wopfner,

Geological formations and processes

Summary In some parts of Australia and Africa intense kaolinisation took place on late Jurassic land surfaces, transforming considerable thicknesses of bedrock into masses of pure kaolin and quartz. Overlying these surfaces occur fluviatile, kaolinitic sandstones of late Jurassic or earliest Cretaceous age. They contain an abundance of silicified wood, including whole trunks of trees. The formation of silicified wood has previously been attributed to hot and arid desert environments, but in the examples described here, silicification proceeded under constantly high groundwater levels, requiring humid and probably warm climatic conditions. Silica was liberated by the kaolinisation of silicate minerals. Humic acids, produced during the initial decay of the fossil timber provided the low pH microenvironment for the fixation of SiO 2 .