INFLUENCES OF QUATERNARY CLIMATIC CHANGES ON PROCESSES OF SOIL DEVELOPMENT ON DESERT LOESS DEPOSITS

Soils formed in loess are evidence of both relict and buried landscapes developed on Pliocene-to-latest Pleistocene basalt flows of the Cima volcanic field in the eastern Mojave Desert, California. The characteristics of these soils change systematically and as functions of the age and surface morphology ofthe lava flow. Four distinct phases of soil development are recognized: phase 1- weakly developed soils on flows less than 0.18 M.y. old; phase 2-strongly developed soils with thick argillic horizons on 0.18- 0.7 M.y. old flows; phase 3 strongly developed soils with truncated argillic horizons massively impregnated by car-bonate on 0.7 to 1.1 M.y. old flows; and phase 4- degraded soils with petrocalcic rubble on Pliocene flows. A critical aspect of the development of stage 1 soils is the evolution of a vesi-cular A horizon which profoundly affects the infiltration characteristics of the loess parent materials. Laboratory studies how that secondary gypsum and possibly other salt accumu-lation probably occurred uring the period of phase 1 soil development. Slight reddening of the interiors of peds from vesicular-A horizons of phase 1 soils and presence of weakly developed B horizons indicates a slight degree of in situ chemical alteration. However, clay and Fe oxide contents of these soils show that these constituents, aswell as carbonates an