Electrical Conductivity Depth Functions for Delineating Paleosols

摘要

Soil weathering and leaching lead to increased salt concentrations at the wetting front in soils of semiarid and Mediterranean climates. Burial of silty alluvial fan deposits may preserve these salt signatures in paleosols, with the base of each solumbeing delineated by high electrical conductivity. The buried layer must be thick enough to prevent destruction of the initial signature via leaching. The identification of alluvial strata as paleosol horizons helps to confirm age estimates derived fromstandard soil descriptions. Several examples illustrate the use of conductivity in delineating late Quaternary soils and paleosols. A soil profile along the Hayward fault had a soil underlain by three paleosols instead of the four paleosols as was firstassumed by visual examination. Estimates of soil and paleosol ages were sufficient to assure that no surface fault rupture had occurred during the last 24,000 years. Background conductivity was about 200 uS/cm, while maxima for the soil and three paleosols were 560, 580, 630, and 590 uS/cm, respectively. It was concluded that field electrical conductivity measurements can be used to delineate paleosols.