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Toposequences of Loess-derived Soils in Southwestern Indiana¹

ABSTRACT

Soil properties are related to stratigraphy of parent materials and to hillslope position in southwestern Indiana where the landscape consists of gently rolling hillslopes and nearly level plains. Loess was uniform thickness downslope. Two distinct units were recognized. The upper (Peoria) loess contained about 15% less sand and had greater calcium carbonate equivalent, greater field water content, and lesser bulk density than the lower (sandy) loess. The Sangamon paleosol below the loess consisted of an upper slightly developed horizon and lower well developed horizons. The percentages of some heavy minerals were similar in the two loess units and similar in the two paleosol units, but differed between the loess and the paleosols. The lower loess showed slight soil formation. A fragipan was present only on summit and shoulder positions where the paleosol formed in weathered sandstone and shale, but not where it formed in outwash. Apparently there was slight soil formation in the lower loess before its surface was covered by the upper loess. Our data support the hypothesis that fragipans form in loess underlain by less permeable materials at certain depths and that silica (or silicate) acts as a bonding agent in fragipans. We believe that the fragipan forms by processes associated with the modern landscape, but its formation is influenced by pre-Peoria soils or weathering zones.

¹ Contribution from the Agronomy Department, Purdue Univ. Agric. Exp. Stn., West Lafayette, IN 47907. Journal paper no. 6891.

² Former Graduate Assistant, currently Research Associate, Ohio State Univ., Columbus, Ohio; and Professor, respectively.

Received for publication November 14, 1977. Accepted for publication March 3, 1978.