干旱区生态环境知识资源中心

In this paper we present the results of recent field and laboratory studies of the mineralogy and magnetic properties of young and/or weakly developed soils in Montana and California. The Chevallier Ranch UXO site in Montana is characterized by a basaltic plug and radiating feeder dikes, which is found surrounded by shales of the Spokane Formation. The site in California consists of an offset alluvial fan soil chronosequence of Little Rock Creek along the Mojave section of the San Andreas fault. The fan sediments include significant amounts of mafic material. The fan ages range from 16 to 413 thousand years. The results of magnetic susceptibility measurements and laboratory analysis of mineralogy demonstrate that the magnetic susceptibility in these soils is predominantly correlated with parent material and less with age or landscape position. Slow rates of soil forming processes lead to relatively low frequency dependence in magnetic susceptibility as compared to similar-age soils in tropical environments. The magnetic character of the soils can be accurately predicted with a previously developed model.