USING RARE EARTH ELEMENTS TO DETERMINE THE POSSIBILITY OF AN AEOLIAN CONTRIBUTIONS IN SEMI-ARID SOILS

The distribution of the rare earth elements (REE) have been used recently to assess the purity of parent materials and to indicate if aeolian contributions have occurred. We selected lone mountain in the Big Bend Region of Texas because the site trachydacite bedrock and the soil series (Lajitas - lithic Torric Orthent) are reasonably uniform and the climate is semi-arid. Three soil samples were taken on each directional aspect (N, S, E, W) on a uniform slope position (10% slope at the toeslope). Routine chemical characterization of the soil included instrumental neutron activation analysis for total elemental analysis, including the rare earth elements. The REE signatures of the bedrock on all four directional aspects were nearly identical, as were other elemental concentrations. Optical examination also revealed a relatively uniform rock assemblage. The REE signatures of the soils were similar to those of the underlying rock in the LREE and HREE distribution, suggesting that these soils evolved by in place weathering. However, the REE signatures of the soils indicate an over all LREE depletion, especially in northern and eastern aspects. The northern and eastern aspects also demonstrate considerable pedogenic carbonates attributable to aeolian deposition. We conclude that careful site selection may allow the use of REE signatures to infer the extent of aeolian contributions.