Soil Polygenesis as a Function of Quai”eiinary Climate Change, Northern Great Basin, Usa

The Quaternary environmental history of the northern Great Basin is characterized by a combination of lower temperature and higher moisture than present. Using water-balance analysis of soils sampled along a climatic gradient, we demonstrate that long-term average effective moisture was about 2-4 cm yr-1 greater than present. Although this long-term average represents most of Quarternary time, there are important short-term excursions from these values during full glacial and interglacial times. Full glacial conditions are characterized by effective moisture about 7-9 cm yrl greater than present; interglacial times, similar tc] present conditions, are characterized by dry lake basins that provide major increases in eolian activity. These climatic extremes drive pedogenic processes that leave polygenetic imprints on Pleistocene age soils. Soils that are now dominated by opaline silica, carbonate, and smectite contain evidence of earlier, more acidic, chemical environments conducive to dissolution of primary carbonate and formation of kaolinite. During interglacial time, more eolian activity and less effective moisture combine to c~ecrease the depth of leaching, increase base cations, and modify the soil chemical environment in relict paleosols. In a Bull Lake age soil (=150 ky bp), desert Ioess accumulation created a 25% increase in water holding capacity and decreased the depth of water penetration by 65 cm; climatic drying at the end of the Pleistocene decreased leaching depth by about 150 cm. 1