Physicochemical and Environmental Factors in Clay Dune Genesis

Abstract

ABSTRACT The genesis and environmental relations of dunes of sandy saline clay are reappraised in the light of a literature survey and data which shows that after source clays are salted, they have high hygroscopicity (gain and loss of atmospheric moisture) but undergo no appreciable diagenesis. Besides wind action, factors critical in clay dune genesis are: changes in cohesiveness and volume with gain and loss of moisture. Drying crusts of saline flats of dry climates break down under deflation into sand-sized pellets by (a) disruption by efflorescent evaporite crystals, (b) collapse of crust blisters and (c) rolling of curling sun-crack polygons. One fourth of the deflation products forms lee dunes and three fourths passes off as dust, salting the soil to windward. Dunes form on the margins and the less frequently flooded areas of intermittent lake basins and lagoonal flats having seasonal and wind tides. Stabilized foredunes (lunettes), shrub-coppice mounds, wavy transverse desert ripples, and problematical longitudinal dunes (Volga delta) result. Form, height and abundance vary with the degree of aridity and flooding regime of flats. Stabilization is by atmospheric moisture, rain, flooding, and vegetation. Active dunes are loose, saline, and ashy with poorly zoned soils. Inactive dunes develop zonal soils when denied saline additions for some centuries. Older lacustrine dunes date from a previous wind system, older coastal dunes from an early post-Flandrian time of transgression.