Micromorphological Evidence of Polygenesis of Three Aridisols, Western Mojave Desert, California

Abstract

Abstract Soils in arid regions are often polygenetically related to climatic variation. On a dissected alluvial fan in the western Mojave Desert, a Typic Durorthid (loamy, mixed, thermic, shallow; Alko series) and two Typic Haplargids (fine‐loamy, mixed, thermic; Neuralia and Garlock series) were selected for micromorphological investigation to determine the sequence of pedogenic events. The micromorphology of pedogenic silica, carbonate, and clay is described for duripans, duric horizons (Btqk), and underlying buried Bt horizons in these soils. In the Alko and Neuralia soils, rodent bioturbation has transported subsurface calcareous fragments, thereby enriching the soil surface with silica and CaCO 3 . These fragments are not completely removed from the surface by leaching under the present‐day climate. Clay illuviation and silicification occurred simultaneously in the lower duripan (40–150 cm) of the Alko, with subsequent accumulation of CaCO 3 in seams and root channels. Silicification of the Btqk and buried Bt horizons in the Neuralia and Garlock soils occurred after clay illuviation. The complete cementation of the lower duripan in the Alko soil has apparently isolated the buried Bt, but the buried Bt, horizons in the Neuralia and Garlock soils have undergone further calcification and silicification. We speculate that the polygenesis of soils in the study area is related to climatic fluctuations since the mid‐Pleistocene and to bioturbation of surface horizons. Development of carbonate‐free argillic horizons probably occurred during pluvial periods, whereas calcification occurred during drier periods. Silicification appears to have been contemporaneous with both clay illuviation and calcification and, thus, may be related to pedochemical conditions rather than to climate.