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Clay Accumulation in Some Hapludalfs as Related to Calcareous Till and Incorporated Loess on Drumlins in Wisconsin¹

ABSTRACT

A distinct boundary () between the dark-colored, acid solum and the paler calcareous dolomitic sandy loam till in 24 representative Hapludalf profiles on drumlins in southeastern Wisconsin is related to carbonate content of the till (b' = 0.61 and r = 0.75) and depth of a silty covering (b' = 0.68), (R² = 67). In the absence of a silty covering, clay accumulation above the was apparently not influenced by the carbonate content of the till (r = 0.16 and R² = 3) because the solum deepened by leaching of the till at the same rate as clay accumulated.

Clay accumulation is also attributed in part to the admixture into till of loess different from that of the discrete silty coverings and attributable, on the basis of mineralogical studies of five profiles, to a distant source. Coarse silt of the silty coverings is mineralogically similar to the coarse silt of the till beneath the sola, except for that indicated by a higher content of Zr in the coverings.

Eluviation of clay of the loess has been important in the genesis of the argillic horizon in these soils.

Leaching of the till usually has resulted in the concentration of coarser and less weatherable fractions in the lower B horizon adjacent to the boundary. In most profiles clay did not accumulate notably immediately above the coarser of the sandy loam calcareous tills. Dolomite content of the Carbonate fraction of the till 5 cm below the boundary of six profiles averaged 95.6% compared with 97.0% at 55 cm still lower, indicating that the dissolved carbonate from the solum did not form a distinct Cca horizon.

¹ Contribution from the University Extension, Geological & Natural History Survey, and the Department of Soil & Water Science, University of Wisconsin, Madison. This work was supported by the Geological & Natural History Survey of Wisconsin. Published with the permission of the Director of the Wisconsin Geological & Natural History Survey and the Director of the Wisconsin Agr. Exp. Sta.

² Graduate Research Assistant and Professor of Soil Science, in charge, Soil Survey Division, Wisconsin Geological & Natural History Survey, University Extension, University of Wisconsin, Madison.

Received for publication September 1, 1967. Accepted for publication February 20, 1968.