Progress In Understanding Weathering and Soil-Forming Processes In Arid and Semiarid Landscapes.

The prevailing view of dryland weathering and pedogenesis ca. 1960 essentially reflected the prevailing A-B-C profile paradigm, which provided the context for the interpretation that key profile properties were produced mainly by limited leaching and biotic influences, a lower magnitude of chemical weathering that in many circumstances favored pedogenic carbonate and soluble salt accumulation.  Since then, studies of soils of diverse landforms (e.g., spatially extensive alluvial fans, basin floors, sand mantles and dunes, colluvial aprons and associated steep hillslopes, lava flow surfaces) in drylands demonstrate the problematic nature of this paradigm. These studies show that the deposition, incorporation and pedogenic modification of dust -- often below an evolving “desert pavement” (if coarse fragments are available) -- are crucial pedogenic processes that may favor accretionary profile development via soil “inflation”.  This kind of profile development contrasts in important ways with the canonical A-B-C profile model.  Also, a key weathering process that strongly influences pedogenic processes in many drylands is actually insolation, and not mainly salt weathering as had been long assumed. This fundamentally different model for weathering and soil formation has provided important insights into hillslope soil and plant community evolution, and provides the basis for assessing soils and slope development that also contrasts in significant ways with a recently proposed new model for “soil production” on vegetated, soil mantled hillslopes.