Interhorizon Transport of Elements in Ultisols Developed in a Loess Mantle Mixed With Rhyolite Residuum in the St. Francois Mountains of Missouri

Abstract

Four soils of the Ultisol order in the St. Francois Mountains of Missouri, which were developed in loess and rhyolite residuum, were characterized to: (i) describe the dominant soil series and landscape characteristics having mass-wasting features, (ii) identify the types of parent materials, and (iii) evaluate the soil profile descriptions and associated geochemical data to estimate the influence of eluviation-illuviation processes on soil profile expression. In particular, we wished to document the interhorizon transport of an array of elements associated with eluviation-illuviation processes and its importance to understanding soil genesis. The presence of argillic horizons and nutrient accumulations in the near-surface horizons infers stable landscapes. Aqua regia digestion Fe concentrations of the four pooled pedons show a positive and linear relationship with clay content, suggesting that the parent materials and their weathering histories are similar across the sampled pedons. Iron, Al, Cu, Zn, K, Ni, Cr, Ga, Sr, Sc, As, Li, Rb, V, P, S, Sn, Cs, Th, and U are preferentially partitioned in the clay fraction. For the pooled pedons, elemental ratios of V, Sc, Ni, As, Cr, Cu, Cs, Li, Rb, Th and U with respect to Fe are presented as evidence that the parent materials are similar and that loess weathering greatly contributes to the fine earth fraction.