Eolian dust constitutes much of the pedogenic material in late Pleistocene and Holocene soils of many arid regions of the world. Comparison of the compositions and influx rates of modern dust with the eolian component of dated soils at 24 sites in southern Nevada and California yields information on (1) the composition and influx rate of dust in late Pleistocene and Holocene soils, (2) paleoclimate and its effects on the genesis of aridic soils, especially with regard to dustfall events, (3) the timing and relative contribution of dust from playa sources versus alluvial sources, and (4) the effects of accumulation of dust in soil horizons. The <2 mm fractions of A and B horizons of soils formed on gravelly alluvial-fan deposits in the study area are similar to modern dust in grain size, content of CaCO 3 and salt, major oxides, and clay mineralogy; thus, they are interpreted to consist largely of dust. The major-oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust, but the compositions of progressively deeper horizons approach that of the parent material. The clay mineralogy of modern dust at a given site is similar to that of the Av horizons of nearby Holocene soils but is commonly different from the mineralogies of deeper soil horizons and of the Av horizons of nearby Pleistocene soils. These results are interpreted to indicate that dust both accumulates and is transformed in Av horizons with time. Changes in soil-accumulation rates provide insights into the interplay of paleoclimate, dust supply, and soil-forming processes. Modern dust-deposition rates are more than large enough to account for middle and late Holocene soil-accumulation rates at nearly all sites. However, the early Holocene soil-accumulation rates in areas near late Pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust-deflation and-deposition event that caused rapid formation of fine-grained shallow soil horizons on uppermost Pleistocene and lower Holocene deposits. We interpret late Pleistocene soil-accumulation rates to indicate that dust-deposition rates were low during this period but that increased effective moisture during the late Wisconsinan favored translocation of clay and CaCO 3 from near the surface to deeper in the soil profile. Prelate Pleistocene rates are very low in most areas, mainly due to a pedogenic threshold that was crossed when accumulations of silt, clay, and CaCO 3 began to inhibit the downward transport of eolian material, but in part due to erosion.

The C and O isotopic composition and radiometric ages of laminar pedogenic CaCO3 coatings were examined in limestone‐derived alluvium along an elevational and climatic transect of the Mojave Desert of Nevada. The δ13C of the soil CO2 decreased with increasing elevation and was related to plant density and available soil moisture. Laminar pedogenic carbonate coats which formed on the bottoms of clasts were separated into inner and outer laminae. The δ13C of carbonates in the outer laminae decreased with increasing elevation as a result of a decrease in the percentage of detrital carbonate in the sample and a decrease in the δ13C of the soil CO2. The δ18O of the outer laminae also decreased with elevation and, after correcting for contamination by detrital carbonate, appeared to correspond to changes in the isotopic composition of the precipitation. The δ13C of the carbonate in the inner laminae also decreased with increasing elevation; however, carbonate in the inner laminae was much purer than the outer laminae and appeared to be predominantly pedogenic in origin. The δ13C of these layers reflects the δ13C of soil CO2 and, for most samples, corresponded to expected values for modern carbonate. Based on uncertainties in dating techniques and the estimated range in isotopic composition of pedogenic carbonate, however, it was not possible to determine if some of the inner laminae formed in the latest pluvial period and reflect past pedogenic conditions.

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Soil temperature, moisture, and CO were monitored at four sites along an elevation transect in the eastern Mojave Desert from January to October, 1987. Climate appeared to be the major factor controlling CO partial pressures, primarily through its influence of rates of biological reactions, vegetation densities, and organic matter production. With increasing elevation, and increasing actual evapotranspiration, the organic C, plant density, and the CO content of the soils increased. Between January and May, soil CO concentrations at a given site were closely related to variations in soil temperature. In July and October, temperatures had little effect on CO, presumably due to low soil moisture levels. Up to 75% of litter placed in the field in March was lost by October whereas, for the 3 lower elevations, less than 10% of the litter placed in the field in April was lost through decomposition processes.

Four soil chronosequences in the southern Great Basin were examined in order to study and quantify soil development during the Quaternary. Soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation. Lithologies of alluvium are granite-gneiss at Silver Lake, granite and basalt at Cima Volcanic Field, limestone at Kyle Canyon, and siliceous volcanic rocks at Fortymile Wash. Ages of the soils are approximated from several radiometric and experimental techniques, and rates are assessed using a conservative mathematical approach. Average rates for Holocene soils at Silver Lake are about 10 times higher than for Pleistocene soils at Kyle Canyon and Fortymile Wash, based on limited age control. Holocene soils in all four areas appear to develop at similar rates, and Pleistocene soils at Kyle Canyon and Fortymile Wash may differ by only a factor of 2 to 4. Over time spans of several millennia, a preferred model for the age curves is not linear but may be exponential or parabolic, in which rates decrease with increasing age. These preliminary results imply that the geographical variation in rates within the southern Great Basin-Mojave region may be much less significant than temporal variation in rates of soil development. The reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust, erosional history, and internally driven chemical and physical processes.