A COMPARISON OF SURFACE SOILS AND BURIED SOILS: FACTORS OF SOIL DEVELOPMENT

Abstract

Soils on the Indiana Wisconsin till plain were formed over a period of about 20,000 years from a variety of parent materials, under a range of natural soil drainage, and for variable periods of time. Parent materials include Wisconsin outwash, till, glaciolacustrine deposits, loess, colluvium, and other sediments. Drainage conditions range from well drained to poorly drained. Soil drainage of surface soils is interpreted from soil color, field moisture conditions, and position on the landscape. Well drained soils are more brightly colored and occur primarily along summits, shoulders, and backslopes; poorly drained soils have drab colors and occur mostly along the footslopes and toeslopes. Most surface soils have formed since the recession of the Wisconsin glacier, a period of about 20,000 years. There are also other soils, now buried, throughout much of this terrain. The most ubiquitous and nearest the surface is the Sangamon Soil, which may have developed from late Illinoian glacial through the Sangamonian interglacial and possibly well into the Wisconsin glacial stage at some sites; this is an interval that could be from 90,000 to 120,000 years. There are at least as many soils (really types of soil) in the Sangamon Soil (used here in a stratigraphic sense) as there are in the complex of surface soils on today's landscape. The Sangamon Soil soils formed in parent material similar to the parent material of the surface soils, and the variation in soil drainage was probably similar too. In buried soils, soil drainage is inferred from color and from interpretations of the positions of the buried soils on the paleolandscape. The sedimentological properties of the parent materials aid greatly in the interpretation of paleolandscapes. By placing all soils in four drainage classes and comparing soil characteristics within and between classes, and by paying attention to parent material variations and the possibly different times of development of soils, differences in soil drainage and parent material seem to be more important in explaining differences in soil characteristics within the buried soils than within the surface soils. The buried soils have characteristics that indicate more extensive pedogenesis than the surface soils. This difference is believed to be a reflection of the duration of pedogenesis, with the buried soils having a longer formation period by a factor of about 4.5.