Laterite and Ferricrete

Widdowson, Mike (2007). Laterite and Ferricrete. In: Nash, David J. and McLaren, Sue J. eds. Geochemical Sediments and Landscapes. Oxford, UK: Wiley-Blackwell, pp. 46–94.



Chapter 3

Laterite and Ferricrete

The term laterite, in its general sense, is given to a range of iron-rich, sub-aerial weathering products that develop as a result of intense, substrate alteration under tropical or sub-tropical climates. Physically, many laterites are rock-like, yet they cannot be easily placed into any of the major petrological groupings. Neither do they lend themselves readily to description as 'soils', other from the fact that they are the products of processes operating at the atmosphere-substrate interface. They are perhaps best considered to be metasomatic rock materials; i.e. rocks whose chemical, mineralogical and physical characteristics have been substantially changed by low temperature and pressure alteration processes such as those operating under subaerial conditions. The conditions under which lateritic profiles form are primarily:
– a favourable climate, typified by seasonal, high annual rainfall (e.g. a monsoon-like climate). High humidity and high mean annual temperatures further promote chemical weathering and mineral alteration;
– a favourable geomorphological environment, characterised by limited runoff and lack of aggressive erosion. The ingress of rainfall and/or the establishment of a water table may promote element enrichment and depletion processes;
– relative tectonic stability, characterised by minimal uplift and crustal deformation.

The manner in which ferricrete alteration profiles evolve differs from laterite weathering profiles in a number of ways: a genetic distinction between laterite and ferricrete is adopted here.

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