Quaternary Paleoclimatic Implications of Soil Clay Mineral Distribution in a Sierra Nevada-Great Basin Transect

Abstract

Glacial outwash, pluvial lake deposits, and possible pre-glacial gravel crop out along the Truckee River from the eastern Sierra Nevada to the western Great Basin. Deposits range in age from Tioga to pre-Donner Lake. Soils of varying degree of development have formed on the deposits; most are at the surface, but a few are buried. Halloysite is the dominate soil clay mineral under pine forest in the humid climate west of Verdi, whereas montmorillonite > illite > kaolinite comprise the characteristic assemblage under desert shrub vegetation in the semi-arid climate east of Verdi. Thus, halloysite reflects a high degree of leaching, montmorillonite a much lesser degree of leaching. The uniformity of clay mineral assemblage in all soils formed from Quaternary sediments east of Verdi suggests that climate and vegetation patterns have not changed drastically in the lowlands in middle and late Quaternary time. Montmorillonite may alter to kaolinite in a leaching environment, whereas kaolinite and halloysite probably will not alter readily to montmorillonite if conditions change toward less leaching. As large amounts of halloysite and kaolinite are absent in the soils east of Verdi, leaching conditions much greater than those of the present probably have not existed in the lowlands for long periods of time.