Soil Formation on Loess in Southwestern Indiana: I. Loess Stratigraphy and Soil Morphology

Abstract Thin loess deposits and underlying Sangamon paleosols were studied and related to modern soil development. Ninety‐one sites were sampled along four traverses extending 60–80 km eastward from the lower Wabash River, the main loess source. The ground soils, located mostly on primary divides, have a parent material sequence of silty loess (Peoria), sandy loess, upper part of Sangamon paleosol, and lower part of Sangamon paleosol. The paleosols developed in till or outwash of Illinoian age or in residuum of Pennsylvanian or Mississippian age. Soil development increases with increasing distance from the loess source. Thick loess (> 2m) soils have an A‐B2t‐C horizon sequence, whereas the thinner loess (1–2 m) soils have an A‐B2t‐(A′2)‐Bx horizon sequence. Soils with < 0.75 to 1 m of loess have B2t horizons in both loess and residuum and usually do not have fragipans. Fragipans tend to be associated with sandy loess, but usually do not coincide with it. They may be just above the sandy loess, coincident with it, or in some combination of sandy loess and adjacent parent materials. It is believed that soil moisture relations influenced by the sandy loess, or the underlying paleosols, or both promote fragipan development.