Clay Movement and Carbonate Accumulation in Ustolls of Central Kansas, U.S.A

Abstract

The micromorphology of three polygenetic soils along a toposequence in the Central Loess Plains of Kansas was examined in order to study the processes of clay movement and carbonate accumulation. Soils within this region have an ustic moisture regime and a mesic temperature regime. The three pedons of study developed in loess overlying a paleosol at depths ranging from 87 to 185 cm. The solum of the modern soil was merged with that of the paleosol for two of the pedons. All three pedons exhibited sufficient clay increase from the A to B horizons to meet the classification criterion for an argillic horizon. Although occasional, illuvial argillans were evident in thin section in the Bt horizons of the modern soils, most of the oriented clay consisted of stress argillans around skeleton grains. The skelmasepic and lattisepic plasmic fabrics observed in the Bt horizons of the modern soils are indicative of stress orientation of plasma caused by shrink-swell activity. Similar stress features were also observed in the paleosols. However, illuvial void argillans with continuous orientation were significantly more abundant in the paleosols than in the overlying modern soils. The paleosols were also enriched with pedogenic carbonates that were translocated during the weathering of the overlying loess. Forms of pedogenic carbonate included micritic calcans, neocalcans, and nodules. Void argillans were coated with calcans in the paleosols, which indicates that clay illuviation occurred prior to secondary carbonate enrichment.