Comparative soil development of Quaternary paleosols of the central United States

Buried soils in the central United States aid in deciphering stratigraphy and chronology by being stratigraphic markers. Such soils may provide a record of many Quaternary events, particularly that of climatic change. Interglacial soils like the Sangamon Soil may have formed for over 100 000 years, during which the climate shifted from cold to warm to cold again. Interstadial soils formed under cooler conditions and for less time. In this paper, we review our knowledge of Quaternary paleosols in the central United States with emphasis on Indiana and through comparison with the type localities. In Indiana, the Sangamon Soil is the most widespread buried soil of interglacial rank. Exposures of the Sangamon Soil reveal a range of characteristics that are related to soil-forming factors (Jenny, H., 1941. Factors of Soil Formation. McGraw-Hill, New York, 281 pp; Jenny, H., 1980. The Soil Resource: Origin and Behavior: Ecological Studies 37. Springer, New York); the most important of these factors include parent materials, soil drainage, and the duration of soil development. How long a buried soil formed may be determined by whether it is an interglacial or an interstadial soil. Thus, the Sangamon Soil can serve as a standard to which other soils, both interglacial and interstadial, can be compared. The most widespread interstadial soil in the central United States is the Middle Wisconsinan Farmdale/Sidney Soil. Exposures of this soil are less common than for the interglacial Sangamon Soil, although enough data are available to provide an additional basis for evaluation of other soils. Based upon a semi-quantitative ranking of soil-development by an assemblage of characteristics, we have numerically defined soil development for well-developed, moderately developed, and weakly developed categories. The most strongly developed buried soils in the central United States are the early Pleistocene soils and the Yarmouth Soil. Both the Yarmouth Soil and the Sangamon Soil may be more strongly developed in Indiana than in their respective type areas in Iowa and Illinois. Both the Yarmouth Soil and the Sangamon Soil are more strongly developed than the surface soil. The primary reason seems to be the greater time intervals over which the Yarmouth and Sangamon soils developed. As expected, interstadial soils are much more weakly developed than interglacial soils. Soil development is also a function of soil drainage. In general, better-drained profiles of the Sangamon Soil are the best-developed soils.