Pedogenesis of Vesicular Horizons, Cima Volcanic Field, Mojave Desert, California

Abstract

An existing model of desert pavement formation suggests desert pavement clasts rise vertically on an accreting eolian mantle and the underlying vesicular horizon coevolves with pavement formation. Results presented here support this model and provide a mechanism whereby eolian material is transported from the ground surface to ped interiors, thereby increasing the thickness of the vesicular horizon underlying desert pavements. Basaltic desert pavements in the Cima Volcanic Field are underlain by a vesicular horizon with strong coarse columnar and strong medium platy soil structure. Peds collected from three sites along a topographic gradient were subsampled into seven ped domains to quantify physical, chemical, and micromorphological properties within peds and along the topographic transect. Ped interiors have up to 40% clay and 12% CaCO3 whereas sediments adhering to ped sides have <7% clay and 2% CaCO3 Argillans and siltans lining platy surfaces in ped centers and bottoms indicate desert dust is translocated vertically along the macropores between peds and horizontally along platy boundaries to ped interiors. Once soils develop a strong columnar and platy structure, translocation to ped interiors is enhanced. Calibrated radiocarbon ages between 5440 and 5045 BP for Av ped centers suggest enhanced dust flux and pedogenesis occurred during the drier middle Holocene, an inference supported by luminescence dating and correlations with regional eolian chronologies.