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. An excellent example of about 6 m of unweathered gravel. We cross-cutting relationships is illus conclude that the terrace described by trated by the layer of fine gravel. Andersor, is Illinoian and was weathered This layer passes through the pendant. during :he Sangamonian. Therefore, Near the middle of the pendant the lay considering the regional stratigraphic er sags about 5 cm, which is evidence relations, the East Troy outwash is for solution collapse. assigned to the Illinoian Stage. The Bt is a zone of excessive accu DESCRIPTION AND INTERPRETATION mulation of reddish-brown clay with ac OF THE PALEOSOL cessory features such as preponderant diffuse iron stains and discrete man At times during pit operations, the ganese stains. Selected details are soil has been continuously exposed for described in table 1. So much clay has a lateral distance of about 50 m. It accumulated in the Bt that the sand, appears as a leached dark reddish-brown

88 3 pinkish Tiskilwa Till

gray silt

olive till 11

3 c gravelly clay ;: e , ..c ,.-- ..c , ..,.� I 4 .., , � \ ,:"" E C'o "" "y 4 "'" , ::-(°6 \ c cobbly 0", I>/. a5 cobbly \ ;: gravel v06* 0 clay � I>/� ..c �'" fine gravel 5 I , sandy slump. covered 6 / , clay ,.- 5 , ,.- , 7 / \ I cobbly \ gravel I , ,.- 8 ,

8 sample number

geo·boundaries clean, sandy bedded 9 C2 pedo-boundaries sand gravel 6i-______� ______L______�IS�G�S�;�98�.

FIGURE l.--Sketch of part of high wall of pit showing major features of buried soil. gravel, and cobbles are totally enve is clearly related to the Bt develop loped in layers and masses of translo ment because it is adjacent to the Bt cated clay (argillans). During forma horizon and disappears with depth. tion, pedoturbation and desiccation cracking continually opened up avenues At the contact with the clean bed for continued soil-water movement and ded sand, the argillans abruptly stop clay accumulation. and clay-free iron stains continue into the upper few centimeters. Below and Surrounding the pendant is a dif to the left on figure 1 the sand is fuse zone of localized clay enrichment clean and gray (gleyed). Argillans re that dissipates laterally away from the appear in the sandy gravel at the base pendant into the calcareous gravel as though they went around the clean sand. The circumstances suggest that (C2t) • The outer margin of this zone is shown on figure 1 with a short the sand formed a hydraulic discontinu dashed line. This zone appears to be ity and remained wetter than the sur constricted near the base of the pen rounding gravel. The staining and ar dant, but below it appears to fan out. gillan patterns indicate a direction of The outer margin is very difficult to soil-water movement. Funneling may determine because of the discontinuous have occurred in the upper Bt. Leach nature of the clay accumulation, which ing water appears to break broken seems to occur in a random pattern of through the Bt boundary and fanned out enrichment. However, this penomenon below the pendant.

89 Table 1. Sangamon Soil profile description at East Troy Gravel Pit

Geologic Sample Horizon Depth Description Unit no. (em)

Tiskilwa C2 0-290+ 7.5YR 5/4 loam; few stains, jointed; few secondary carbonates; till dolomitic.

silt C1g 290-300 5Y 5/2 silt loam; few iron stains, pinches out to right above Sample 11.

till 11 C1g 300-340 2.SY 5/4 loam with common 5/6 mottles; stratified in places with layers of Bt material; leaL:heu; uasal deformation zone of meltout till(?).

Outwash 1 Btl 300-340 7YR 5/6 gravelly sandy clay loam; common red and dark stains; weakly cemented, traces secondary carbonates along joints; leached; eroded upper surface.

2 Bt2 340-350 7YR 5/8 loamy sand lense; uniform.

3 Bt3 350-410 6YR 4/4 to 5/6 gravelly sandy clay loam; few 2.5YR 3/4 and 211 stains; many argillans; many rotten igneous and sedimentary cobbles; traces of carbonates.

" 4 Bt4 410-450 5YR 3/3 gravelly clay, many thick masses of argillans, some slickensided; some large areas of manganese staining; many rotten rocks 1 to 10 cm in diameter; traces of carbonates.

5 Bt5 450-460 SYR 3/3 gravelly sandy clay lense; coarse fraction better sorted than adjacent horizons; sags about 5 cm in middle of pendant, leached.

6 Bt6 460-490 5YR 3/3 gravelly sandy clay loam; poorly sorted; fewer cobbles. nearly all hard; leached.

7 Bt7 490-510 5YR 3/3 to 4/4 gravelly sandy loam; more color and textural vari ation; friable; a decrease in argillans and stains cause a color boundary at base where uncoated coarse fragments dominate color appearance; base of beta horizon pendant.

8 C2t 510-550 Yellow. gray and brmvn gravelly sandy loam; partly t.,leathered 9 550-580 gravel dominated by carbonates, many soft; weakly cemented; 10 540-580 common 5YR 4/4 argillans around pendant that decrease away to form a discontinuous boundary with clean bedded sand lense; argillans reappear in sandy gravel at base of exposure.

Comments: 1. This profile contains the main part of a truncated Sangamon Soil that has the morphology of a Fox-like soil with an overdeveloped Bt pendant. Classification: best fit is Typic Paleudalf.

2. Bt horizons 3 to 6 in the exposure are very hard and coarsely crazed by desiccation. Natural soil structures are confounded with exposure-induced cracking. Iron staining is essentially continuous, but redder in places, and dominates matiix color. Argillans appear to diffuse away from the pendant.

3. Sampled from the northlolest r..:rall of a gravel pit in the northwest corner ,of Sec. 31, T. 4 N. � R. 18 E., Walworth County.

90 Table 2. Particle size and cl.::;y mineral data of Sangamon Soil profile at East Troy Gravel Pit

Sample Depth SandI Siltl Clayl Exp2 13 K + C4 Number Horizon (em) (%) (%) (%) (%) (%) (%)

11 C2g 300-340 54 28 18 38 45 17

1 Btl 300-340 56 15 29 29 52 19

2 Bt2 340-350 84 2 14

3 Bt3 350-410 64 7 29

4 Bt4 410-450 23 29 48

CO - 5 Bt5 450-460 52 10 38 28 58 14

6 "t6 46[)-490 55 8 37 26 54 20

7 Bt7 490-510 76 3 21

8 C2t 510-550 64 16 20 26 57 17

9 C2t 550-580 70 18 12 32 49 18

10 C2g 540-580 16 66 18

1. Weight percent of less than 2 �m fraction; sand - 2.0 to 0.62 mm. silt - 0.62 to 0.002 mm, clay - less than 0.002 mm.

2. Exp - expandable clay minerals (17A. glycolated).

3. I - illite (mica, IDA).

4. K + C - kaolinite and chlorite (7A). Other geologic boundaries in the CLASSIFICATION OF THE PALEOSOL profile control or at least are coin cident with weathering boundaries. The best modern soil analogs of The material below the Bt horizon is this buried soil are the deep phases of yellowish-brown, calcareous cobbly gra the Fox and Ockley Series, which are vel. Most parts seem to contain about both Alfisols. At present, Fox is de 50 percent limestone and dolomite cob fined as having a solum (A and B) bles. This zone, which shows some al thickness of less than 1 m, and Ockley teration, some argillans, and yet con has a solum thickness up to 1.5 m. To tains primary carbonate minerals is classify a paleosol according to modern designated a C2t horizon. Many cobbles soil taxonomy is dif ficul t because the up to 10 em in diameter are in the C2t actual climatic and chemical parameters and seem to disappear in the pendant. during formation must be estimated. Near the middle of figure I, above the Considering the morphological expres final gravel lens, the amount and orien sion alone, this soil can be considered tation of the cobbles delineate a sub' a Udalf or in older soil classification tIe boundary. More cobbles are present terms, it is similar to a reddish, above the bouridary which represents a clayey Gray-Brown Podzolic of the Mid change in the depositional environment. west or a minimal Red-Yellow Podzolic Weathering and clay accumulation follow of the Tennessee region. this geologic boundary to the left of and above the .small pendant, but depart Particle-size distribution and at the pendant where the Bt boundary clay-mineral data (table 2) were deter cuts up across the "many cobbles" lay mined on samples collected through the er. A more sandy layer occurs stra pendant as shown on figure 1 in order tigraphically above and to the right to aid our attempts to classify the and appears to be detached from the soil. Although the presence or absence "sandy clay" layer in the Bt. This of pendants is secondary in the classi suggests early detachment, perhaps by fication of soils of this type, we slump, during parent-material for think that this large pendant is the mation, followed by the development of most interesting part of the soil the soil. stratigraphic unit exposed in the pit wall. At the sampling location, the soil · is abruptly truncated by a gray silt. The lack of an A horizon presents No interstratification is present but an obstacle, so we at tempted to recon the silt pinches out to the right above struct the nature of the original soil. olive-brown loam till that is inter In doing this, the B horizon provides stratified with Bt material. The till the clues--features that are dependent seems to be related to the overlying on A-B horizon relationships. All of Tiskilwa till, as if it is a basal de the subdivisions of the Bt horizon con formation zone of the Tiskilwa. How tain evidence of illuviation, (thick ever, the silt is not deformed and ap continuous clay skins or argillans). pears to be a fluvial deposit on an The variation in sand, silt and clay erosion £urface. A possibility is that contents reflects the original strati the olive till was deposited by an fication of the outwash. The clay of early advance of the ice, then exposed the upper Bt is similar to the Fox and to glaciofluvial erosion during a minor Ockley series, but the large size of retreat of the glacier. Then, the main the pendant suggests development that body of Tiskilwa till was deposited is greater than what is considered to during a subsequent advance. be normal for these soil series. Many

92 cobbles up to about 10 cm in diameter The method used by the Illinois State in the Bt are in an advanced stage of Geological Survey is one that is rou decomposition and can be cut with a tinely employed for distinguishing knife. Most of the cobbles are igneous stratigraphic boundaries and the corre and sedimentary (silty) types that also lation of material units. In view of might have contributed to the clay con this constraint, the unresolved x-ray tent upon weathering, but the in-situ diffraction peaks indicate a moderate clay could not be identified because of ly to strongly weathered, oxidized ma the large amount of argillans. terial.

The large amount of illuvial clay sug Considering all available informa gests that this soil belongs to the tion, the best fit classification for Alfisol Order, although Mollisol and the profile is a Typic Paleudalf. A Ultisol options are possible. The dark Paleudalf is distinguished from a P.ap color of the argillans suggests that ludalf mainly on the basis of clay dis the original epipedon was rich in hu tribution. A Paleudalf as described by mus, as in a Moll isol, but the color of the Soil Survey Staff (1975) must meet the lower half of the Bt closely match the requirement that the clay content es the type concept of the Ockley Se does not decrease from the maximum by ries, a Typic Hapludalf. A forest or more than 20 percent within a depth of grassland origin is not interpretable 1. 5 m below the soil surface. A Udalf from the morphology, but other parame that decreases in clay content� more ters) not measured in this study, such than that is a Hapludalf. At the other as the composition of the contained locations where the Bt is about a meter humic acids, could theoretically be thick, a Hapludalf classification seems used to differentiate the dominant best in spite of the redness which fa sources of the humic material. vors the Paleudalf interpretation.

The large size of the pendant sug In reconstruction of the probable A gests the more intense or longer weath and E horizons, it would be expected to ering conceptually associated with be sandy because its parent material Ultisols rather than Alfisols. However, was probably outwash. Modern equiva the clay-mineral data indicate that lents of Paleudalfs that have been de substantial amounts of illite are still scribed (Soil Survey Staff, 1975) on present. One of the requirements of an sandy parent material on the coastal Ultisol is that less than 10 percent of plains in Texas have sandy epipedons the weatherable minerals remain in the that are about 1 m thick. Where the 20 to 200 pm fraction of the Bt horizon epipedon is sandy (loamy sand) the pro (Soil Survey Staff, 1975) . Because the file is classified as an Arenic Paleu illite was determined from the less dalf. If our pendant profile here had than-2 p fraction, even less weathering less sand in the epipedon, it would re would be expected in the coarser frac main in the taxon of a Typic Paleudalf. tions. Therefore, the type of weather However, one must rememeber that this ing indic: ted by the clay mineral data is a borrowed classification from a places this soil into the range of system for living soils. The soil fea Alfisols. Samples with no clay mineral tures described here are the remains of results presented in table 2 were ana a fossil soil. lyzed, but clay-mineral species were not resolved by the no-pretreatment LOCAL STRATIGRAPHIC method employed. This appears to be CORRELATION PROBLEMS caused by the abundant iron, which in terferes with the x-ray diffraction The Sangamon Soil rises southward method for measuring clay minerals. from the described profile (fig. 1) and reaches the ground surface near the

93 center of the pit wall (fig. 2). Both relationship of the Tiskilwa till and the soil and the overlying Tiskilwa the New Berlin till is well established till are absent in the southern part of by regional relations and hy many the pit, and they terminate in a way stratigraphic sections that show the that creates a local stratigraphic New Berlin Formation ovelying the Tis problem. Beyond the termination, the kilwa Member of the Zenda Formation. gravel is overlain by calcareous yel Thus, there is no question about the lowish-brown pebbly sandy loam till of relative age of the tills, although the the New Berlin Formation (Mickelson and relationship cannot be demonstrated in others, 1983). The New Berlin till was the East Troy pit. We interpret the deposited by the Delavan Sublobe of the relationship seen here as the result of Lake Michigan Lobe (Alden, 1904, 1918; deformation produced by the bulldozing Schneider, 1982) in Late Woodfordian action of the ice that deposited the time. It is the surface till in the New Berlin till. Although the mechan immediate area of the East Troy pit and ics are not understood, the snout of throughout much of southeast Wisconsin, the advancing ice apparently shoved and mostly in Walworth and Waukesha Coun lifted the inclined part of the Sanga ties. It also covers parts of Kenosha, mon Soil and overlying Tiskilwa till Racine, Milwaukee, Washington, and and injected a mass of basal New Berlin Ozaukee Counties. New Berlin till is till into and below the paleosol (fig. found behind (northeast of) the Darien 2). In that part of the pit south of Moraine and between the Kettle Inter the contact zone, the Sangamon Soil and lobate Moraine on the west and the Val Tiskilwa till were completely eroded paraiso Moraine or its equivalent on before basal New Berlin till was plas the east. The New Berlin till is about tered on top of the outwash sequence. equivalent to the Haeger Till Member of Less than a kilometer to the south, the Hedron Formation in Illinois (Hill however, 5 m (exposed) of Tiskilwa till man and Frye, 1970). is overlain sharply by 3 m of New Ber lin sand and gravel. The New Berlin till is distin guished from the Tiskilwa till by its lVhen this site was examined in 1972 lighter and yellowish-brown color, and 1975, additionsl stratigraphic greater stone content, and coarser ma units were present between the paleosol trix. Results of particle-size analy and the overlying pink till. The lat ses of three samples of New Berlin till ter was observed to overlie a thin bed from the East Troy pit average 62 per of light yellow calcareous silt cent sand, 27 percent silt, and 11 per (loess?), the upper few centimeters of cent clay. Results of clay-mineral which were darker in color and sugges analyses of five samples of New Berlin tive of a faint A1 horizon of an incip till from the East Troy pit average 20 ient paleosol (Farmdale?). Although percent expandable clay minerals, 66 Altonian loess has not been previously percent illite, and 14 percent kaolin identified in southeastern Hisconsin, ite plus 2hlorite. the silt is possibly equivalent to the Roxana Silt of Illinois (Frye and Will Near the center of the pit wall the man, 1960; Willman and Frye, 1970). two tills are in contact with each oth er in an unusual way (fig. 2). The The silt either rested upon a stone stratigraphic relationships between the line (Schneider's interpretation) or tills and between the New Berlin till contained a concentration of cobbles at and the paleosol are unclear. The its base (Hadley's interpretation). In tills abut against each other, and the either case, this stone concentration New Berlin till underlies the paleosol marked the top of the paleosol. The for a distance of about 1 m. The age upper part of the paleosol, although

94 N s () ) � New Berlin till �")

co m 5m � deformed zone . �Sal'lgamon sOil7 pendants un 1 Sangamon Soil stratitied sand and gravel yellowish - brown o 10 m New Berlin till o �==�==:::"_ __-.!floor�f pit ------

FIGURE 2.--N brth-south sketch of part of the East Troy gravel pit as seen in 1982. The Sangamon Soil is continuous across the exposure, as shown. but is partially concealed by slump and slope wash. Modern soil profile ( not shown) is at the sketched surface in some places, but in other places it has been removed or truncated by mining operations. Height of pit wall is about 10 m; approximate length of section is 50 m.

- r- similar in most of its characteristics lVoodfordian features are widespread be to that below, contained fewer stones yond the Hisconsinan border, it follows and had more silt; it resembled a that they should occur under Late lVis strongly developed B horizon developed consinan deposits where spared from from till rather than gravel. Both glacial and other causes of erosion. Schneider and Hadley interpreted this to be a two-material profile, with the The fragmentary information devel upper part of the B horizon having oped from the study of this site leads formed from till and the lower part to the conclusion that the weathered, from gravel. However, the geologic clayey paleosol exposed in the wall of contact between the gravel and the the pit is the Sangamon Soil. The pa till, if present, was masked by pedo leosol is developed in a coarse cobbly genesis; both parent materials were outwash that is judged to be Illinoian weathered by the same soil-forming in age. Morphology and composition of episode. the overlying unweathered till indicate that it can be identified as the Tis Unfortunately, these additional kilwa till, which was deposited by an stratigraphic units have not been vis.i early glacial advance of lVoodfordian ble in recent years. Pit enlargement Age. The confidence of this iden during the past 5 or 6 years has re tification and the assumption that the sulted in the removal of the weathered paleosol represents the last intergla till, the stone line, and the overlying cial age or the last time during which silt with its possible incipient soil; a warm-climate soil could have formed thus, the pink Tiskilwa till is now in this area form the main arguments seen in direct contact with the paleo for this interpretation. The relation sol. Apparently the sand and gravel of the Sangamon Soil and Tiskilwa till unit was overlapped from the west by a to the younger New Berlin till at this wedge of till and a thin layer of silt, exposure creates some confusion but can both of which have been removed as min be explained as a local anomaly caused ing operations have moved the pit face by glacial deformation. It appears eastward. that New Berlin till was down thrusted through Tiskilwa till into the Sangamon Neither the Illinoian till (weath Soil at the only place where the two ered or unweathered) nor the younger tills are in contact at this site. silt are now exposed elsewhere in the pit, and neither the till, the paleo ACKNOlVLEDGEMENTS sol, nor the silt have been identified at any other site in southeast lViscon ,Ie wish to express our thanks to sin.. Fortunately, however, samples of Richard Amon of B. R. Amon and Sons, both the till and the silt were col operator of the pit, for permission to lected from the East Troy site in 1977. study the site. Schneider's joint vis Analyses of these samples seem to con its to the Amon pit and other exposures firm the field interpretations. in lValworth County with David Hadley contributed much to our understanding CONCLUSIONS of the site. Analytical data present ed in this paper was provided by the The exposure at the East Troy pit III inois State Geological Survey; the reveals stratigraphic relationships clay-mineral identifications were made that have been suspected to exist for by H. D. Glass, and the particle-size some time, probably since Alden's re analyses were run by R. Bianchini. The port in 1918 or longer, but they have manuscript was reviewed by Lee Clayton, not been confirmed until now.. Because David Mickelson, and Dan Muhs. the Sangamon Soil and other pre-

96 REFERENCES

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