Saturday, 15 July 2006

Geochemistry and Morphology of Soils in the Southern Basin and Range Province, Trans-Pecos, Texas.

Susan Casby-Horton, USDA-NRCS, PO Box 163, Cross Plains, TX 76443, Melanie A. Barnes, Geosciences Dept., Texas Tech Univ, 2815 23rd St, Lubbock, TX 79410, and B.L. Allen, Texas Tech Univ, PO Box 42122, Lubbock, TX 79409.

The geochemistry of soils within a study area in Hudspeth County is primarily related to the spatial distribution of igneous and sedimentary bedrock and derived sediments. Soluble, NH4OAc-extractable, and total elemental compositions were determined on eight soil pedons representing a variety of soil parent materials, including limestone bedrock and fan alluvium derived from limestone bedrock, igneous bedrock, and mixed sources. Soils that formed in igneous fan alluvium typically have argillic and calcic horizons with buried soils and lithologic discontinuities. In contrast, soils that formed in limestone bedrock or limestone fan alluvium have calcic or petrocalcic horizons and may have buried soils. Windblown dust particles can introduce elements (and minerals) not present in initial parent materials. In this area, soil geochemistry is also related to pedogenesis and soil morphology, particularly as they relate to lithologic discontinuities and calcic or petrocalcic horizons. Levels of trace elements are relatively higher in fan alluvium from igneous or mixed sources. Elevated levels of Sr and Ba generally occur in horizons of significant CaCO3 accumulation. Spatial and vertical distributions of major and trace elements in this area demonstrate the need for site-specific geology and soil geochemistry baseline data in order to be valid for risk assessment and environmental regulatory applications.

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