The role of playas in pedogenic gypsum crust formation in the Central Namib Desert: A theoretical model

The formation of Namibia's extensive pedogenic gypsum crusts (CaSO4. 2H(2)O ) is interpreted in a new light. It is suggested that gypsum primarily prec ipitates at isolated points of evaporitic concentration, such as inland pla yas, and that deflation of evaporitic-rich gypsum dust from these playas co ntributes to the formation of pedogenic gypsum duricrusts on the coastal gr avel plains of the Namib Desert surrounding these playas. This study establ ishes the nature, extent and distribution of playas in the Central Namib De sert and provides evidence for playa gypsum deflation and gravel plain depo sition. Remote sensing shows the distribution of playas, captures ongoing d eflation and provides evidence of gypsum deflation. It is proposed that, fo llowing primary marine aerosol deposition, both inland playas and coastal s abkhas generate gypsum which through the process of playa deflation and gra vel plain redeposition contributes to the extensive pedogenic crusts found in the Namib Desert region. Copyright (C) 2001 John Wiley & Sons, Ltd.