The nature and origin of gleyed polygenetic paleosols in the loess covered glacial drift plain of Northern Missouri, USA

At four study sites in northern Missouri the Farmdale and Sangamon paleosols, which are developed in loess, are welded to the underlying Yarmouth paleosol, developed in till. Upon initial examination, however, they appear to be a single, thick, continuous gleyed horizon (Gleysol). Along flat tabular drainage divides this welded solum is gleyed and is identical in all respects with the historical definition of gumbotil. The solum may exceed 4 m in thickness, but has little discernable horizonization. The profiles are nearly homogeneous, containing approximately 50% clay throughout most of the solum, of which 70–80% are expandable clay minerals. Variations in texture, clay mineralogy and weathering indices are typical of a welded solum which forms a complex, polygenetic profile. The base of the solum retains abundant slickensided joints, and upon exposure it rapidly develops shrink-swell features typical of Vertisols. This behavior, coupled with the remarkable homogeneity within the solum, indicates that these soils underwent significant mixing, primarily by pedoturbation, a characteristic of modern Vertisols.