Saturday, 15 July 2006

An Aeolian Explanation for the Asymmetrical Distribution of Deep Sandy Soils on Ridges.

Richard J. Harper, Cooperative Research Centre for Greenhouse Accounting, PO Box 475, Canberra, Australia and Robert Gilkes, Univ of Western Australia, Nedlands, Australia.

Patterns of soil distribution and surface mineralization are often explained by conceptual soil landscape models based on water borne transport of soil parent materials. In some previously arid environments parent materials have been distributed by aeolian processes, such as in south-western Australia. Here many of the soils have distinct texture contrast profiles, surface sand horizons are often deeper, and more extensive, on slopes with south–eastern and eastern aspects, compared to those with north-western aspects. The deep sandy soils occur in terrain of quite different provenance (Quaternary clayey sediments, deeply weathered granites), and on landscape features ranging from 3 to 40 m in elevation. This patterning is considered due to the interference of topography on wind flow and thus transport of the soil parent materials. There is unequivocal of prior aeolian activity in this landscape, in the form of sand dunes, clayey lunettes, and elliptically-shaped playas, formed by predominantly north-westerly winds. Microclimatic and vegetation influences on soil development on slopes of different aspects are discounted as the deep sands do not occur on all ridges, similarly differential erosion of the windward slopes and crests is discounted as there is no evidence of extensive downwind deposits. Understanding how wind, topography and sand transport interact may provide a framework and the development of models for predicting soil properties and underlying mineralization in similar semi-arid environments. Similarly, the deposits may provide a marker indicating the aeolian transport across the landscape under previous periods of climate change.

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