Characterization and Stratigraphy of Soil Parent Materials of West‐central Minnesota

Abstract

AbstractWithin the Alexandria Moraine Complex in west‐central Minnesota there are “islands” of fine textured soils and parent materials embedded within a matrix of coarser textured soils. To study the soils and the stratigraphic relationships of the parent materials, deep borings were made along two transects perpendicular to the Alexandria Moraine. A total of 27 sites were investigated. Particlesize distribution, CaCO3 equivalent, clay‐sized carbonate, and the dominant mineralogy of the >2 mm, 1 to 2 mm very coarse sand (vcos), and <2‐µm fractions were determined. Four glacial materials were identified in this study: New Ulm till, Kandiyohi till, Granite Falls till, and a “mixed” drift of mainly New Ulm and Granite Falls materials. The average clay content of the glacial materials ranges from about 370 g kg−1 in the Kandiyohi to about 130 g kg−1 in the Granite Falls and mixed drifts. The average shale content in the vcos fraction ranges from about 620 g kg−1 in the Kandiyohi till to about 60 g kg−1 in the Granite Falls till. The average CaCO3 equivalent ranges from about 220 g kg−1 in Granite Falls till to about 170 g kg−1 in the mixed drift. Statistically significant differences occur among the glacial materials in the concentration of sand, silt, clay, concentration of shale, carbonate, and crystalline pebbles in the vcos fraction, and the concentration of coarse fragments. A stepwise discriminant analysis was made and the four glacial materials were numerically defined by the first two canonical variables. The stratigraphic relationships of the two areas of Kandiyohi till outcrop studied seem to be quite different. The data from the western part of the county indicate much mixing of New Ulm and Granite Falls tills. Data from the eastern transect indicate the Kandiyohi till is an older till that has been thrust to the surface. It is suggested that the Kandiyohi till is a distinctly different glacial till in that: (i) the soils developed on this till are taxonomically distinct from soils on adjacent tills; (ii) the shale concentrations within the four defined glacial materials in the study region are statistically different; (iii) no other areas of this glacial till have been observed except in the Alexandria Moraine; and (iv) the glacial till outcrops are characteristically narrow linear features.