A Buried Sangamon Soil in Southeastern Wisconsin

Geoscience Wisconsin Volume 7 July 1983 A BURIED SANGAMON SOIL IN SOUTHEASTERN WISCONSIN Allan F. Schneider University of Wisconsin--Parkside Kenosha, Wisconsin 53141 and Leon R. Follmer Illinois State Geological Survey Champaign, Illinois 61820 ABSTRACT "Jhen the site was first examined a decade ago, the upper part of the pale- A truncated paleosol believed to 0801 appeared to be developed in two have formed during the Sangamonian Age parent materials, the outwash and an is well exposed in the highwall of a overlying thin finer grained deposit gravel pit near East Troy in northeast interpreted as (Illinoian) till. A ern WahTOrth County, Wisconsin. If our thin bed of light yellowish-brown silt, interpretation is correct, this paper possibly loess of Altonian age, was ob reports the first positive identifica served between this older till and the tion of a buried Sangamon Soil in the Tiskilwa till above. The upper few area of late Wisconsinan glaciation in centimeters of the silt were darker in the State of Wisconsin. color and suggestive of an incipient paleosol (Farmdale?). Enlargement of The soil- is formed in the upper the pit during the past few years has part of a thick sand and gravel outwash resulted in removal of the apparently unit and is overlain by calcareous pink wedge-shaped intermediate units, so loam till that is considered to be the that today Tiskilwa till is seen rest Tiskilwa till of northeast Illinois and ing directly on the paleosol developed southeast Wisconsin. The main horizon in the outwash" of the paleosol is interpreted as the Bt horizon of a well-drained Alfisol Near the center of the pit wall the (Gray-Brown Podzolic) belonging to the Sangamon Soil reaches the modern sur suborder of Udalfs. It is a dark face, and both the soil and overlying reddish-brown, highly argillic, severe Tiskilwa till are absent in the south ly weathered zone in which many of the part of the pit. Here the outwash is clasts are in an advanced state of de overlain by younger sandy-loan till be compositions In several places the longing to the New Berlin Formation soil has large vertical pendants that (equivalent to the Haeger Till Member hang below the usual base of the soil of Illinois terminology). The contact by as much as a meter. A detailed soil zone involving the three units is un profile jescription, which includes usual and creates a local stratigraphic laboratory data on grain-size distribu problem because the till units abut tion and clay-mineral composition, against each other and New Berlin till through one such pendant i8 presented actually underlies the Sangamon Soil to substantiate our interpretation of for a short distance. The relationship the weathered zone as the Sangamon is interpreted to be the result of de Site. formation that occurred during deposi tion of the New Berlin till. 86 INTRODUCTION his classes between 1975 and 1980. Schneider, Follmer, and Ardith Hansel In Walworth County, about 1.5 krn of the Illinois State Geological Survey southwest of East Troy, the remains of studied the site in 1982. a buried soil are exposed under till in the west-facing high wall of a gravel STRATIGRAPHY pit under a continuous deposit of till. The soil is overlain by 1 to 6 m The pit is located in the NW corner of Sec. 31, T. 4 N., R. 18 E., just north of pink calcareous loam till that is east of the overpass on Wisconsin High believed to belong to the Tiskilwa Mem way 15 over Townline Road in the tow n ber (Early Woodfordian). The Tiskilwa of Spring Prairie. The pit is operated Nember is the upper part of the Zenda Formation in the new Pleistocene litho i.ntermittently by B .. R .. Amon and Sons of Bowers. stratigraphic classification in Hiscon sin (Nickelson and others, 1983) and The prominent feature of the paleo correlates with the Tiskilwa Till Nem osol is a weathered and oxidized, clay ber of the Wedron Formation in Illinois enriched (argillic Bt) horizon devel (Hillman and Frye, 1970). The pinkish oped in an outwash of cobbly sand and gray to brown color of the till, the gravel. The soil was truncated and grain-size distribution of the matrix disturbed by overriding glaciers that (45 percent sand, 34 percent silt, 21 * deposited at least two younger tills. percent clay), and the clay-mineral Based on soil characteristics and composition (24 percent expandable stratigraphic position, we conclude clay, 64 percent illite, 12 percent ka that this paleosol is the Sangamon olini te plus chlorite) are typical of Soil. Tiskilwa till in southeastern Wiscon sin. The till is now known to occur at Buried or relict soil profiles of or near the surface throughout much of possible Sangamonian age have been re central and eastern Walworth County, ported from several locall ties in Wis especially in a belt 11 to 18 krn wide consin beyond the late Wisconsinan gla from the Illinois state line northward cial boundary, mostly in the Driftless to the Kettle Interlobate Moraine Area; the interpretations of most of (Schneider, 1983). It has been ob these sites have been challenged. To served at many sites near the East Troy our knowledge, the Sangamon Soil has pit and was well exposed southwest of not previously been identified from any the pit a few years ago during con site behind the Late Wisconsinan (Wood struction of new Wisconsin Highway 15. fordian) boundary. Therefore, if our interpretation of the East Troy site is The soil is formed in the upper correct, this paper reports the first part of a thick unit of well-stratified identification of the Sangamon Soil in outwash sand and gravel with many cob the area of Late Wisconsinan glaciation bles in the upper part. The thickness in tbe State of Wisconsin. of the outwash exposed in the pit face is estimated to be about 15 m. The site was first visited by * Schneider in 1972� It was independent Grain-size boundaries used in this ly discovered, probably in 1973, by paper are 2 mm, 0.0625 mm, 0.004 mm David W. Hadley, formerly with the Wis and percentages are based on the consin Geological and Natural History less-than-2 mm fraction. Clay miner Survey. Similar interpretations of the al identifications were made by H. D. geology were made by Schneider and P�d Glass from X-ray diffraction data ley, who subsequently examined the site using oriented aggregate techniques together in 1975. Periodic visits to on the less-than-0.002 mm material. the site were made by Schneider with 87 A power-auger hole (Wisconsin Geologi horizontal layer about 1 m thick. The cal and Natural History Survey Boring main body of the soil is a weathered, ET-2) was drilled below the floor of clayey Bt horizon developed in cobbly the pit to a depth of more than 22 m sandy gravel. The Bt is dark reddish without encountering bedrock; the depo brown and strongly contrasts with the sits consisted mostly of well-sorted yellowish-brown gravel below and the sand with some interbedded gravel pinkish-brown till above. In places layers. Some workers have suggested the soil has large vertical pendants, that the outwash here was deposited whose tapered ends extend below the near the axis of the preglacial Troy usual base of the soil by as much as a Valley, but from a recent bedrock to meter (fig. 1). The top of the soil is pography map prepared by Green (1968, truncated at all places observed in fig. 2), it appears that the site more 1982, which suggests either proglacial likely is near the break in slope be fluvial scour or the direct effects of tween the upland surface and the valley the overriding glacier. Small-scale wall of a tributary to the main Troy shear is evident in places where paleo Valley. solic material (Bt) has been sheared or injected into the overlying calcareous Little information is available to till. The displaced material commonly judge the age of the outwash. Beyond pinches out along a thrust plane and the outer margin of the overlying till, appears now as a low-angle joint. In the surficial deposits are mapped as other places the paleosolic material Early Wisconsinan (Frye, Willman, and appears interstrati fied with the till Black, 1965) or Illinoian (Alden, in a contact zone up to 1 m thick. 1918). Outwash deposits older than Wisconsinan were recognized by Borman A soil profile with the largest (1977) in Walworth County, but he did pendant exposed in 1982 in the northern not identify any stratigraphic units. part of the pit was selected for study. South of Walworth County in Boone Coun The major features are sketched on fig ty, Illinois, Berg, Kempton, and Stecyk ure 1. An attempt to discriminate ped (1981) described an Illinoian outwash ologic boundaries from geologic bound that could be related to this site, but aries was made because they are common the correlations at this time are cir ly confused. Commonly a stratigraphic cumstantial. The highest level terrace boundary predetermines the position of mapped by Anderson (1967) along the a pedologic boundary, but in other Rock River near Rockford is likely re cases the boundaries are independent of lated to this site. This terrace is each other. The main pedologic bounda covered by Wisconsinan loess and con ry in the soil here is the base of the tains about one meter of highly Bt horizon, shown as a heavy line on weathered, reddish brown gravel over figure 1.

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