ILUHOtS GECM-OW** SURVEY UBftARY JOHN A, HARRISON STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION SUBSURFACE STRATIGRAPHY OF THE PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS John P. Kempton ILLINOIS STATE GEOLOGICAL SURVEY John C. Frye, Chief URBANA CIRCULAR 356 1963 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/subsurfacestrati356kemp SUBSURFACE STRATIGRAPHY OF THE PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS John P. Kempton ABSTRACT The subsurface Pleistocene drift sequence in central north- ern Illinois (Boone, DeKalb, and parts of Kane, LaSalle, Lee, McHenry, Ogle, and Winnebago Counties) is separated into sev- eral major units. These units are differentiated on the bases of lithologic character, stratigraphic position, and physical prop- erties, including X-ray and grain- size data. The following are the major units recognized. Unit A is a basal, predominantly quartz sand that is probably pre-Illinoian in age. Unit B, overlying Unit A, contains a brown, montmoril- lonitic, kaolinitic, sand- silt-clay to silty sand till of probable Illinoian age. Unit C (Winnebago drift), the surface drift of the northwestern part of the area, consists of illite-chlorite, silty sand, and sandy silt tills that can be subdivided into three Sub- units C-l, C-2, C-3, which are separated by local peat beds and organic silt. A C 14 date of >38,000 years B.P. (W-1144) was determined from the base of a peat bed above Sub-unit C-2, while the upper till of Sub-unit C-3 may be as young as 31,000 years B.P. All of Unit C is included in the Altonian Substage of the Wisconsinan Stage. The remaining drifts (Units D, E, and F) are illite-chlorite tills predominantly sand- silt-clay and are as- signed to the Woodfordian Substage of the Wisconsinan Stage. INTRODUCTION During Pleistocene glaciation, northern Illinois was covered by ice moving westerly from the Lake Michigan basin and by a subsidary lobe moving southwest- erly from Green Bay. The glacial deposits form the surficial materials in this part of the state and contain important resources of ground water and supplies of sand and gravel. The age and classification of the deposits made by these glaciers has long been a subject for discussion. The deposits have been assigned various ages 1 2 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 from Kansan to Wisconsinan (Chamberlin and Salisbury, 1885; Leverett, 1898, 1899; Alden, 1909, 1918;Bretz, 1923; Leighton, 1923; Ekblaw, 1929; Shaffer, 1954, 1956; Leighton, 1958, 1960; Leighton and Brophy, 1961, 1963; Frye and Willman, 1960; Frye, Glass, and Willman, 1962; Willman, Glass and Frye, 1963). Previous interpretations have been based primarily on topographic and drainage relations, degree of dissection, depth of carbonate leaching and oxida- tion, and the presence of identifiable loess units, utilizing available outcrops and auger borings. Some recent interpretations have been based on lithologic and stratigraphic descriptions of the drifts of the area (Shaffer, 1956; Doyle, 1958) and on radiocarbon dates (Leighton, 1960; Frye and Willman, 1960). Investigations of the subsurface glacial stratigraphy for parts of this area have been reported by Horberg (1953) and Hackett (1960). The present restudy of the area is based on core samples from test borings along the Illinois Northwest Toll Highway and on carefully collected samples obtained from water well contractors. The detailed subsurface methods employed in this report, using specific physical property data, have been summarized by Kempton and Hackett (19 62). Knowledge of the subsurface glacial stratigraphy is needed for accurate delineation of the glacial drift aquifers and evaluation of their water-yielding potential. In addition, such knowledge can lead to a better understanding of the water transmitting properties of the nonaquifer drift units, engineering character- istics of the drift, mineral resources available, and the character and distribution of the parent material of soils. The Illinois State Geological Survey is investigating the subsurface stratigraphy, lighologic character, and physical properties of the glacial deposits as a part of a state-wide evaluation of the ground-water resources of the drift. The area of the present study is in the eastern part of central northern Illinois and includes Boone and DeKalb Counties and portions of Kane, LaSalle, Lee, McHenry, Ogle, and Winnebago Counties (fig. 1). The area contains Troy Valley, one of the larger bedrock valleys of Illinois, and portions of its drainage basin (McGinnis et al., 1963). This report describes the basic glacial stratigraphy. The ground -water geology of the area and additional stratigraphic data will be presented in a subsequent report. Acknowledgments The excellent cooperation of several water well contractors who provided well logs and samples of drill cuttings is gratefully acknowledged. The X-ray analyses were made by H. D. Glass of the Illinois Geological Survey, who made helpful suggestions in interpretation of the clay mineralogy of the drift. I am in- debted also to Professor Paul R. Shaffer, Department of Geology, University of Illinois and John C. Frye, James E. Hackett, H. B. Willman, and George E. Ek- blaw of the Illinois Geological Survey for numerous discussions and critical re- views of the manuscript. This report is adapted from a doctoral dissertation sub- mitted to the University of Illinois, based on research conducted at the Illinois Geological Survey. Professor George W. White, thesis advisor, provided many helpful suggestions and encouragement during the course of the study. All radio- carbon dates used in this report were determined in the Washington Laboratories of the U. S. Geological Survey. PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 3 STRATIGRAPHY The Pleistocene fill of the Troy Valley averages more than 350 feet thick and is locally in excess of 550 feet thick. The deposits are largely Wisconsinan, but Illinoian and older deposits are present within the fill in DeKalb County (fig. 2). The till and outwash that cover much of northern Illinois, which previously were called Illinoian (Horberg, 19 53) and later Farmdale (Shaffer, 19 54, 19 56), have been named Winnebago (fig. 3) and have been assigned to the Altonian Sub- stage of the Wisconsinan Stage (Frye and Willman, 1960). The remaining Wis- consinan drift of the area has been assigned to the Woodfordian Substage. Informal letter designation shave been assigned to rock stratigraphic units that are recognized in the present study. The locations of wells and borings used in this study are shown in figure 4 and table 1. Grain size and mineral analyses of typical samples are given in tables 2 and 3. Descriptions of samples from selected reference wells and borings are given in table 4. Pre-Illinoian (?) Stage Unit A. — Unit A is defined as the lowermost deposit encountered in the Troy Valley and is a basal sand or sand and gravel. A typical development of this unit is recorded from samples taken at 5-foot intervals from 405 to 445 feet in well 63 (fig. 4): Thickness Base (ft) (ft) Pleistocene Series Pre-Illinoian Stage Unit A Sand, clean, medium to coarse, little fine, subrounded to rounded, white, mostly quartz; some dolomite, chert, and few igneous grains 15 420 Gravel, slightly sandy, about 50% chert (some oolitic), 40% quartz, 10% igneous 10 430 Sand, slightly gravelly, chert (20%), mostly quartz, little dolomite, few igneous 15 445 Unit A may attain a maximum thickness of more than 140 feet where present in the deepest parts of the Troy Valley. The maximum thickness reported, in well 62 (fig. 4), is 78 feet, but this well encountered bedrock at least 70 feet higher than the bottom of Troy Valley. Unit A has not been found north of T. 40 N. , in central DeKalb County, and is probably limited in extent to the southern part of the valley (figs. 5, 6, 7). The sand consists principally of quartz grains that are usually subrounded to rounded and occasionally polished. Aside from the quartz, the grains are com- posed of light and dark igneous rocks, dolomite, and chert. A gravel bed within this unit (see above sample study) contains an abundance of oolitic chert. The average grain count of Unit A from wells 61, 62, 63, and 70 is as follows: quartz, some feldspar 74% chert 12% dolomite 10% igneous 4% ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 The sand is generally white or has a pale pink tinge. Locally, the presence of weathered dolomite and chert grains at the base gives a light buff to light yellowish- brown appearance to the sand. Unit A is generally medium grained but ranges from very fine silty sand to coarse gravelly sand. A maximum of about 20 feet of weath- ered-appearing very silty to clayey sand is present at the top in well 62. It is quite possible that some lacustrine sediments also may be included in the upper portion of the unit, giving a weathered appearance. Horberg (1950, p. 51-52) named the basal sand of the bedrock valleys in the Peoria region the Sankoty Sand for its development in the Sankoty "water" field north of Peoria. Horberg (1953) later extended this unit throughout the re- mainder of the area covered by Wisconsinan drift, including the Paw Paw and Rock Valleys. He traced the Sankoty as far north as Mendota in LaSalle County or about three miles east of the southwestern part of this study area (figs. 1, 4). Horberg (19 53, p. 20) states that the basal sand at Mendota is without distinc- tive properties and his correlation is based on elevation and stratigraphic posi- tion. Unit A is similar in general appearance, quartz-grain percentage, position, and elevation to the Sankoty Sand (Horberg, 1953, fig. 3, p. 15). The major difference is the presence of large proportions of chert and dolomite in the sand in Troy Valley. Fig . 1 - Locatic ajor bedrock valleys. PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS Stage(s) hickness (ft) Till, variable texture; outwash; lake deposits Till, sand-silt- clay; outwash Woodfordian Wisconsinan D-3 D-2 D-l Till, sand-silt- clay; outwash; lake and wind deposits Farmdalian Interstadial Silt, organic silt, sand Till, silty sand; outwash; lake, colluvial, and wind deposits Peat, organic silt, silt, clay Till, silty sand; outwash; lake, colluvial, and wind deposits Till, sandy silt, sand-silt-clay; outwash and lake deposits [Weathering, erosion] Till, silty sand; outwash and lake deposits Pre-Illinoian(?) Sand; some gravel; lake deposits Fig. 2 - Classification of glacial deposi 6 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 Fig. 3 - Glacial map of northeastern Illinois (modified from Ekblaw, 19 60). PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 7 Horberg (19 53, p. 14) suggested that the Sankoty Sand is present under Kansan drift and under drift possibly of Nebraskan age in central Illinois. In the Troy Valley, Unit A is directly overlain by deposits of probable Illinoian age. No evidence of leaching of carbonates was found at the top of Unit A in the samples studied. The age of the unit in the Troy Valley and elsewhere is in doubt, and it is assigned to a pre-Illinoian (?) age until more definite relations can be estab- lished. There is no indication of the position of the ice front during deposition of Unit A. Although the sand has not been found in the Troy Valley in Boone County, Hackett (19 60) suggests that the thin basal sand in the Ancient Rock Valley in Winnebago County may be eguivalent in age to the Sankoty. If this interpretation is correct, the glacier probably reached the upper portions of the Troy and Ancient Rock drainage basins, and much of the outwash deposited in the upper portions of these valleys was subsequently eroded. The silty character of the upper part of Unit A may indicate ponding of the Troy Valley during latter stages of outwash deposition. Illinoian (?) Stage Unit B . — Unit B is defined as the sequence of deposits that either overlies Unit A or directly overlies the bedrock in the Troy Valley and adjacent areas (figs. 6, 7). It consists of till, outwash sand and gravel, and lacustrine sediments. A distinctive clay mineral suite and grain- size distribution aid in separating the till from the tills of Unit C. An excellent section was encountered in well 68 at a depth of 155 to 210 feet (table 4, fig. 8). In the lower part of the Troy Valley, Unit B can be identified from T. 38 N. , R. 3 E. to T. 40 N., R. 3 E., DeKalb County, but it appears to be absent on the uplands adjacent to the valley. It is present in a valley tributary to the Troy in T. 41 N., R. 4E., DeKalb County (well 68) . In general, tne till of this unit is sand- silt-clay (fig. 14) although it bor- ders the silty sand range (size ranges used-sand, 2.0 to 0.062 mm; silt, 0.062 to 0.0039 mm; clay <0.0039 mm). The till is variable in color, but most often is dark brown, brown, or grayish brown (10YR 4/3 to 10YR 4/2; all Muncell colors used in this report are taken from wet samples). The upper part of Unit C, as much as 20 feet, is commonly greenish or yellowisn brown (2 . 5YR 4/4-3/2 or 10YR 4/4). The bulk of the outwash included in this unit occurs in the vicinity of the northernmost extent of the till (fig. 6) . Here the upper 20 feet is a typical glacial outwash with about 20 percent of the grains of igneous or metamorphic origin. Be- low 20 feet the outwash becomes more typical of Unit A and may actually belong to that unit. Although there is ordinarily no indication of weathering at the top of the outwash, one driller's log (well 55) reports a green clay at this position. The lacustrine sediments in Unit B, consist of dark brown (10YR 3/2 to 10YR 2/2), faintly laminated, clayey silt with abundant small woody fragments on the bedding planes (well 70, 375-395 feet, table 4). Some appear more like bedded tills and are greenish brown (2.5YR 3/2 to 10YR 4/4) in color (well 68, 175-190 feet, table 4) . The relatively high percentage of montmorillonite and the presence of kaolinite (well 62., 340-360 feet, well 68, 155-210 feet, tables 2, 3, fig. 8), distinguish Unit B from Unit C . The relatively small amount of both calcite ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 Fig. 4 - Index map of wells and c PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 9 and dolomite present and the erratic distribution of these minerals in the fine fractions of the sediments are characteristic of the lower part of the unit (fig. 8) . The assignment of Unit B to the Illinoian Stage is based primarily on stratigraphic position and clay mineralogy. The clay mineralogy is generally the same as the Payson drift, which was deposited by the earliest and most widespread of the Illinoian advances (Willrnan, Glass, and Frye, 1963, p. 17-22 and fig. 7, p. 21). The absence of a leached zone on Unit B leaves the possibility open that Unit B may be part of the Winnebago drift (Unit C) and Altonian in age. However, few well samples are available, and active erosion within the valley area could have removed evidence of leaching. Also, the suggestion of a truncated weathering profile on Unit B in well 68 (table 2, 4, fig. 8), as evidenced by the progressively greater alteration of chlorite upward, supports a pre-Wisconsinan age for Unit B. The dark brown clayey silt at the base (well 70, 375-395 feet, tables 2, 4) may be pro-Illinoian and eguivalent to the Petersburg Silt of western Illinois (Willrnan, Glass, and Frye, 1963, p. 6). Although the predominant direction of movement of the Illinoian glacier in this region was westward from the Michigan Basin, a tongue moved northward into the Troy Valley, spread over onto the immediately adjacent upland at some Fig. 5 - Cross section A-A' (North). 10 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 places, and flowed into the tributary valleys. The presence of kaolinite in the deposits also indicates that the ice moved over the kaolinitic Pennsylvanian rocks to the south before moving into the Troy Valley. When the ice occupied the valley, drainage was ponded in the upper part of the valley forming an extensive lake. During oscillations of the ice front, deposits in the lake were overridden by readvances of the ice. The outwash fan, extending northward in front of the advancing ice, was also partially overridden. With the retreat of Illinoian ice, drainage again returned to a southward direction, and it continued southward during the Sangamonian Stage. Wisconsinan Stage Altonian Substage Unit C (Winnebago drift) .— Unit C is the complex sequence of deposits of the Winnebago drift (Shaffer, 1956; Hackett, I960, Frye and Willman, 1960). It overlies Unit B or the bedrock in the Troy Valley area, and it is exposed at the surface in much of northern Boone and Winnebago Counties. Within this unit at Fig. 6 - Cross section B-B' (Central). PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 11 least three tills can be recognized locally. Along with related outwash and lacus- trine sediments, these tills are designated C-l, C-2, C-3 from the base to the top of the unit (fig. 2) . Samples from test drilling along the Northwest Toll High- way (fig. 4, table 1) have aided materially in defining the sub-units. Their identi- fication from water well samples is more difficult. The character of the sub-units is shown in boring 11 (fig. 10, tables 2, 4). One or more sub-units of Unit C are present throughout nearly all of the Troy Valley area and adjacent uplands. Unit C attains a maximum thickness of about 400 feet in Tps. 44 and 45 N., Rs. 3 and 4 E., Boone County, where it includes most of the drift recognized in the northwestern part of the area (figs. 3, 5). Thus Unit C is the most extensive and often the thickest drift of the study area. Unit C consists of till, outwash sand and gravel, and minor amounts of lacustrine sediments. In general, the tills are silty sand (figs. 14, 15) and are dark brown, dark reddish or violet gray, or dark gray in color. They are also very hard with a consistency or relative density (N value) generally above 100 as indicated by the standard penetration tests conducted during the test boring and sampling along the toll highway. The unaltered till of Unit C contains, on the average, 7 percent montmorrillonite, 68 percent illite, and 25 percent chlorite (table 3). Kaolinite has not been found to be present in the till samples analyzed. Fig. 7 - Cross section C-C (South). 12 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 3 5 £ GRAIN SIZE Q O -z. -I < o t x ^ Q_ ZD < cr X-RAY DATA Sand Silt m □ Percen 25 50 Clay m t 75 CLAY MINERALS Montmo- rillonite Illlte Chlorite S • □ E2 Percent 25 50 75 CARBONATES Calcite Dolomite Counts per Sec. 25 50 75 E , SN Y// \\N J// yy.-y.yyy.-y/\ L-z-zz-z-z- \N V/A \N r>/// yyyyy/ysA |z-z-z-z-z-: ::--.:-Xv:-vj t-z-zz-z- Ci V///y XI f//// ::-:v:v:-v:-x-:::j L-z-z- ^ ^// ::-::-::v:v::v::| p-z-z- ^ kV//, \N r//// q x//// >i 1//// 'P-3T \\\^ r//, ."-■.v.'v'.v.v'.\v.\| |ZZ-Z-ZZ- wn Pv> 1 "-^-^S # ^ 1 F— \\\I v// \\N K///, :•:■.:■[■:■'. :-y.y.-y.y.-y/. : //. : \ |ro \N r//// ^ I///V :-:v:-:v::-::v::::::i |zz-z- zz \\\^ P//, ^\\\\3 VA - \\\\\\\\\N K// \\\\\\\\\n r// :•:•:•:•:•:•:•:•:•:•--•-:, iz-z-z- wwww^ \//. sis WWWWN t/X :-:-:| |::>- ------- \\\\\\^ r/// \\\\\\\\\\1 K/// \\\\\\S K//// :-y,-.y.-yyyy.\ t-z-z-z SS^ Y/. :-:-:-:v:-:-:-:v:'v1 t-z-z-z-: n\n r/j Bedrock (Galena- Platteville Dolomite) ^Kaolinite present ■ Percentage of sand, silt, and clay, and X-ray data for well 68. PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 13 Sub-unit C-l.— The till of Sub-unit C-l is distinguished primarily by sand- silt-clay to sandy silt texture (fig. 15) and gray, dark grayish brown, or dark brown to reddish brown color (10YR 4/1, 10YR 4/2, 10YR 3/3). There is no leach- ing but indication locally of some weathering at the top of the unit, and a thin organic zone rests on C-l at two localities (fig. 5, wells 78, 80). The till of Sub-unit C-l has an average clay mineral composition of 6 percent montmorillonite, 71 percent illite, and 23 percent chlorite. It can be identified with assurance only along and generally north of the toll highway in Winnebago, Boone, and McHenry Counties (figs. 5, 9, 10, 11). Sub-unit C-2.— This sub-unit is composed predominantly of till with some associated outwash. The till is brownish gray to gray (10YR 4/2, 10YR4/1), silty sand (fig. 15), and frequently contains fragments of tough, brownish black shale with tasmanites. The average clay-mineral composition of the till is 7 percent montmorillonite, 67 percent illite, and 26 percent chlorite (table 3). A locally thick sand and gravel, with some interbedded silt and clay, is present at the top of the sub-unit over large areas (fig. 5). A leached organic silt and peat (boring 2, figs. 5, 11, table 4) overlies an oxidized zone at the top of this unit and substantiates the presence of at least two sub-units of Unit C in the area where the Winnebago drift is the surface drift. The organic-rich deposits consist of black, leached, slightly sandy silt with a few pebbles (some dolomite) and abundant fine particles of organic material. The peat sampled in boring 41 is a loose accumulation of woody materials and plant tissue with some twigs, 2 to 3 inches long. Some silt and sand is present in the KEY EZ3 Till Gravel mi3 Sand F--"- 1 ) Silt and clay £H Peat or organic zone SCALE I 2 3 Miles Fig. 9 - Northwest Toll Highway c ; section 1 (West). ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 middle of the peat zone. A radiocarbon data of >38, 000 years B.P. (W-1144) was obtained from the base of the peat in boring 41 (35-36j feet). Below these deposits, the till or sand of C-2 are generally dark yellowish brown (10YR 4/4) to greenish brown (2.5YR 4/4) in color for a few feet. In boring 41 the leached material direc- tly below the peat is probably an accretion-gley. Elsewhere no leaching of C-2 has been found where it is covered by younger deposits. Sub-unit C-3.— The till of Sub-unit C-3 is composed principally of silty sand (fig. 15), often interbedded with lenses of sand and gravel. The till of this unit is generally violet-gray to brown (7.5YR 4/2 or 10YR 4/3) and occasionally grayish brown (10YR 4/2). The clay mineral content of the unaltered till averages 8 percent montmorillonite, 65 percent illite, and 27 percent chlorite. Where Sub-unit C-3 forms the surface drift, the till is deeply oxidized to light yellowish to reddish brown (10YR 5/4 to 7 . 5YR 5/4). Shaffer (19 5 6) describes the upper 7 to 10 feet of the till as being frequently light pink to salmon in color (7.5171 8/4 dry). Where the loess capping is thin (boring 11, tables 2, 4), oxida- tion and alteration of the chlorite in the till may extend as deep as 2 5 to 35 feet. Where the loess is more than 5 feet thick weathering of the till is less than 15 feet (boring 5, tables 2, 4). The till is leached less than 3 feet under thick loess and as much as 6 or 7 feet under thin loess. Shaffer (1956, p. 16) reports that leaching and staining may be as much as lli feet where stratified drift is very sandy. There is also subsurface evidence of leaching or alteration at the top of this unit, with local thin organic silt capping the Sub-unit C-3 and underlying Unit D (boring 40, well 51, figs. 6, 11, 13). The regional extent, age, and correlation of the sub-units of Unit C are not known precisely at present although numerous lines of evidence are now available. In the Rock Valley at Rockford, Hackett (1960, p. 31-33, and fig. 7, W E KEY CZ3 Till IS8SJ Gravel mm Sand E23 Silt and clay feSM Peat or organic zone SCALE Fig. 10 - Northwest Toll Highway c PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 15 p. 30) demonstrated the presence of two tills (then assigned to earlier and later Farmdale advances), which may be correlative to Sub-units C-2 and C-3. Willman, Glass, and Frye (1963, p. 7-8 and fig. 1) indicate that drift deposits at Danville (Ekblaw and Willman, 1957; W-256) and at Bloomington (Ekblaw, 1946; W-186) may be assigned to the Altonian Substage and may be contemporaneous with one or more sub-units of the Winnebago. Black (1958) describes the occurrence of wood dated at 31, 800±1, 200 radiocarbon years (W-638) taken from a pinkish till on the uplands south of Lake Geneva in extreme southern Wisconsin. Along with other dates in this range further north, Black (1959, 1962) has postulated an advance probably equivalent to that which deposited Sub-unit C-3. From the evidence presented, it appears that Sub-unit C-l records the earliest advance of Altonian ice and therefore of the Wisconsinan Stage. Deposits of this sub-unit are generally thin and scattered and often absent or not recogniz- able. There is evidence of a time lapse between the deposition of C-l and C-2, mainly in the form of peat and some channeling. One of the two major glacial advances of the Altonian began prior to 38, 000 radiocarbon years ago and covered the entire area, as indicated by the widespread occurrence of Sub-unit C-2. This ice sheet advanced from the east or northeast from the Lake Michigan basin. As it advanced over the southern part of the Troy KEY EZ3 Till B'rf'Sg.l Gravel ES3 Sand I ZD Silt and clay EH Peat or organic zone SCALE Fig. 11 - Northwest Toll Highway c 16 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 Valley, it produced moderate to large amounts of outwash, which filled channels cut into older deposits. Thick drift was deposited throughout most of the region and made a relatively flat till plain over the uplands, particularly in Boone and McHenry Counties (fig. 5). However, Troy Valley was not completely filled. After the ice retreated, peat bogs, trees, and other vegetation developed over the area, and shallow depressions were filled with organic silts and clays. Soils developed on the higher areas, but the deposits generally were leached only to shallow depths. Drainage was reestablished along the Troy Valley and deep channels were cut into the till. The streams generally regained a southward flow. These developments marked an important interstadial within the Altonian, which began more than 38,000 years B.P. The final Altonian advance came from the northeast, reached Lake Geneva 31, 800±1200 radiocarbon years ago, and eventually covered most if not all of the area of this study. This advance appears to have been relatively short, as the Farmdale silt that overlies this unit is at least 26, 1000±600 years B.P. (W-381) elsewhere in Illinois. The evidence in the Troy Valley area indicates that it did build moraines during retreat. Some were low, as under the ridge just southeast of Belvidere in southeastern Boone County (figs. 3, 10), but others were rather large and extensive, as under Marengo Ridge (figs. 3, 5) and also the till spur at Rockford (Hackett, 19 60, p. 31 and fig. 7, p. 30). The drift surface was much more irregular than the preceding (C-2) outwash and till plain surface. Thus, end moraines and other irregularities of the surface, as expressed by these deposits, locally appear to form an ancestral topography to that visible today, where over- lain by younger drift. Woodfordian Substage Unit D . —Unit D is the oldest of the Woodfordian drifts. It forms much of the surface drift in front of the Bloomington and Marengo end moraines up to and including the White Rock end moraine (figs. 3, 5). In the subsurface south of the front of the Bloomington end moraine, the unit is directly overlain by Unit E (figs. 6, 7) . The tills of Unit D have not been identified over the bedrock uplands east of the Troy Valley in eastern DeKalb County, where only a thin sand occurs between Units C and E (fig. 6). Unit D attains a maximum thickness of about 150 feet over the Troy Valley in central DeKalb County. The tills of this unit are generally pinkish gray, pinkish brown to brown in color (7.5YR 4/2, 7 . 5YR 5/4 to 10YR 4/3). The tills oxidize to dark yellowish brown, yellowish brown to light brown (10YR 4/4, 10YR 5/4 to 10YR 5/8). The tills of Unit D are less compact than the deposits of Unit C and have a N value less than 50 and commonly under 30 (fig. 12). The tills can generally be classified as sand- silt-clay (fig. 17) and usually are distinct from those of Units C and E at a given locality (fig. 14). The grain size of the tills of Unit D is quite comparable to that of the "Shelbyville" to the west (Shaffer, 1956, p. 24 and fig. 3, p. 23). The textural distinction of Unit D from Unit E is somewhat narrow, although Unit E is slightly more silty (fig. 17). Where Unit D is the surface drift, the upper 3 to 5 feet is leached. Unit D is divided into Sub-units D-l, D-2, and D-3. These sub-units are differentiated on minor and somewhat inconsistent textural variations (fig. 16) and are based on samples from borings 23-38 (fig. 4, tables 1, 2) along the Northwest Toll Highway. The sub-units are developed best in boring 29 (table 4). PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 17 GRAIN SIZE o Q O 2 -i :v:v:vl p-z-z-z-: v\N V/ :v:-:v:.:-:v/.v,-J t-z-zz-z- \\l K/, - N D-2/ x • XWWWWWN f/, :•:•:•:•:•:•:•-! Lzz-z-zz- l\\\N V, ".■•.'•:•:•:•'.•'.•'.'.•:•■. -.| |z-z-z-2- \\\\1 1// /D-'l - / \ x. \\\\N Y// ;::::-x:v::| t-z-zz-z-z- v\\1 1///. :;:-::::-:i |r.-i-z-z-z-z-z \1 K/// \ ■ ' . t 'C-3 V ; ^ ■ \ ■ ■ \ ■ ■ X !■.■•.'■.'•■.■:•■.■■.•■.•".•".■'.•■.•:•'.". -J IzztZ- y X/// ;-;-;-;-;•;• ;-:-:-:-:-;-:->;-:>:-;| [>z- a y///) :-:v:v:-:v:-:-xv| |:-r-z-z-z-z- * V//// ::-::-:v:-:v:.:vX.;.:| t _ = _ = . ^ V//// V ^ V . • C-2- :::::::::-Xv| c-z-z-z- \1 v/// \1 X/// Fig. 12 - Percentage of sand, silt, and clay, with X-ray data for boring 29. 18 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 356 The average clay-mineral composition of the tills of Unit D is montmoril- lonite 7 percent, illite 64 percent, and chlorite 29 percent (table 3) and is simi- lar to the tills of Units C and E. The sensitivity of the chlorite to the slightest weathering aids in separating the sub-units of Unit D. Alteration may be seen in the upper 22 feet along the toll highway where sampling is at a foot and a half in- terval, but it is difficult to recognize in samples representing 5 or 10 foot intervals from the water wells. The zone of clay-mineral alteration (e.g. boring 29, 13.5- 15.0 feet, fig. 12, table 2) at the top of Sub-unit D-2, may represent weathering during a minor retreat of the ice. The only occurrence of kaolinite in Unit D is in Sub-unit D-3 in boring 28 (13.5-15.0 feet, table 2), but tills of Unit E in the Marengo end moraine to the east and northeast contain some kaolinite. Several moraines are present behind the Shelbyville and in front of the Bloomington end moraines in central Illinois, and the sub-units in this area may record similar oscillations of the ice. Sub-unit D-3 may represent an advance of a later glacier, possibly an extension of the glacier that deposited Unit E to about the position of the White Rock end moraine. Some indication of this is the till sample in boring 28 (fig. 10, table 2), which overlies an organic-rich, partially leached sand. Leighton (1923) assigned the drift in the outcrop area of Unit D to the Belvidere lobe and to an "Early Wisconsin" Substage. This was based primarily on the relatively shallow depth of leaching of the drift in comparison to that of the drift to the west (Unit C) . Prior to this assignment, the drift generally had been mapped as Iowan (Leverett, 1899, p. 131) and considered intermediate between Illinoian and Wisconsinan. Shaffer (1954, 1956) correlated the drift with the Shelbyville drift of central Illinois. Horberg (1953, pi. 1, A-A', B-B') also iden- tified Shelbyville drift in the subsurface under the Marengo and Bloomington drifts (Unit E) . The deposits of Unit D probably represent the earliest advance of the Woodfordian ice and are probably eguivalent to Shelbyville and related pre- Bloom- ington drifts. However, the relations do not preclude the possibility that the thin patchy till of Sub-unit D-3 along the toll highway represents a somewhat later Woodfordian advance. On the other hand, Sub-unit D-3 could be the earliest Woodfordian deposit, and Sub-unit 1 and Sub-unit 2 could be Altonian in age. Unit E . —This unit is primarily till of Woodfordian age. A greater silt and clay content of the till is diagnostic where it overlies older units. A typical sec- tion of the drift is described from samples taken from well 57 (0-55 feet, tables 2, 4) . This unit is the surface drift of the Bloomington end moraine and is the exposed drift in DeKalb County south to the Cropsey end moraine (fig. 3). It is also the surface drift on Marengo Ridge to the east in Kane and McHenry Counties (fig. 3) . The till is pinkish gray to reddish gray (7.5YR 4/2 to SYR 4/2) in color. Oxidized till of this unit is usually light pinkish brown or reddish brown (7.5YR 5/4 to 5YR 4/3). It is only slightly pebbly and is sand- silt-clay (figs. 14, 17) with an average of 38.2 percent sand, 37.2 percent silt, and 24.6 percent clay for all samples. Variations in grain size are generally minor within a vertical sequence of Unit E (e.g. well 68, fig. 8, table 2). The average percentage of sand, silt, and clay for each vertical sequence of the unit throughout the area remains consistent within narrow limits of the sand-silt-clay designation (figs. 14, 17). The clay-mineral composition of the till of Unit E averages 6 percent montmorillonite, 63 percent illite, and 31 percent chlorite (table 3). The till of PLEISTOCENE DEPOSITS OF CENTRAL NORTHERN ILLINOIS 19 GRAIN SIZE a o 7- -i 38,000 yrs. B.P. (W-1144) (IS 30-31%; 32-34; 35-36%) Sub-v : C-2 Silt and clay (accretion gley) , slightly sandy and pebbly, very dark grayish brown to very dark gray (10YR 3/2-4/1) , slightly calcareous at base (IS 36.5- 37.3; 37.3-38.1) ] Sand, light yellowish brown to light olive brown (2.5YR 6/2-5/2), very ilty; alcj :ill (IS 38.1-39.5) : WELL 51 2istocene Series Visconsinan Stage Woodfordian Substage Richland Loess gray (10YR 4/1-4/2), leached; :tle brownish yellow (10YR 5/2) f Unit E , dark brown to brown (5YR 4/2- /2) ; contains calcite and dolo- 1C kish brown (5YR 4/2) ; contains and dolomite 3i t D y silty, very fine to fine, medium to coarse, grayish brown 5/2-5/4); contains calcite, dolomite, and a trace of shell frag- ments at top 1C Farmdalian Substage Sand, extremely silty, slightly clayey, dark grayish brown (2.5YR 4/2); contains calcite and dolomite; some greenish brown (10YR 3/3) f Altonian Substage Unit C (Winnebago drift) Sand (till?), extremely silty, very fine to medium, little coarse to very coarse, dark grayish brown (10YR 4/3); contains calcite and dolomite f Till, sandy, silty, dark grayish brown (7.5YR 4/4 to 10YR 5/3); contains cal- cite and dolomite y Ordovician System - Maquoketa Group WELL 57 Wisconsinan Stage Woodfordian Substage Unit E Till, gravelly to sandy, sligh yellowish brown (7.5YR 4/4), iy ilty Gravel , very sandy, slightly s lty Till, gravelly, silty to sandy (7.5YR 4/4), No sample Till, compact, silty to clayey, slight- ly sandy, slightly gravelly, grayish brown (7.5YR 4/2), calcareous Unit D Till, silty to clayey, slightly sandy, slightly gravelly, gravelly to sandy at base, grayish brown to brown (7.5YR 4/2-5/4), calcareous Sand (till?), slightly gravelly, slightly silty, multicolored, fine to Silt, clayey, brown (7.5YR 4/2), cal- bedded till, very silty to sandy, very gravelly, brown to yellowish brown (10YR 5/3-4/3-4/4), calcareous; also contains interbedded gravel, silty, multicolored, medium to coarse Depth of base (ft)) Sub-t. : C-2 Till, very sandy to silty, little gravel, yellowish brown (10YR 6/4- 5/3), calcareous Sand and gravel, multicolored, fine to Sub-unit C-l (?) Till, very gravelly, sandy to silty, brown to dark brown (10YR 5/4-7. 5YR 5/4 to 10YR 3/3), calcareous Illinoian (?) Stage Unit B(?) Sand, slightly gravelly, slightly silt) l System-Gal< a-Platt« ille Woodfordia Unit E >stage Soil, black to brown (10YR 2/l) , leached 5 Till, sandy to gravelly, slightly clayey, pinkish brown (7.5YR 4/2), calcareous; silty to very silty at top (no samples 20-25, 40-45, 80-85) 80 Unit D Till, silty to clayey, slightly gra- velly to sandy, pinkish brown (7.5YR 4/2), calcareous 50 Altonian Substage Unit C Sub-t : C-3 Till, very sandy to silty, dark browi (10YR4/3), calcareous; grayish brown (10YR 5/2) at base Silt (till?), clayey, grayish brown (10YR 5/2) , calcareous Sub-unit C-2 Till, very sandy to silty, greenish brown to yellowish brown (10YR 4/4-5/3), calcareous Till, compact, silty to clayey, sligl ly sandy, dark brown (10YR 4/3) , calcareous; grayish brown (10YR 4/2) , at top Till, very sandy to very gravelly, si at top, greenish brown to brown (10YR 5/3-4/4), calcareous Silt (till?), compact, very clayey, slightly sandy, greenish brown (10YR 5/3), calcareous Sand, silty, slightly gravelly, multi- lty Sub-u • (?) Till, very silty to s: Llty, slightly clayey, greenish br< jwn to brown (10YR 4/3-4/4-5/4), calca: Pre-Illinoian Stage Unit A Sand, slightly silty 1 :o silty, slightly gravelly, yellowish buff to yellowish Ordovician System-Glenwood-St . Peter Sandstone Wisconsinan Stage Woodfordian Substage Unit E No sample Till, gravelly, silty, pinkish brov 5/6); contains calcite, dolomite, spores Till, silty, slightly sandy, pinkis brown (5YR 4/3-4/4) ; contains cal cite, dolomite, and spores Till, silty, slightly sandy, browni gray (5YR 4/2-4/3) ; contains cal- cite and dolomite Unit D Till, sandy, slightly gravelly, ;ilty t .ayey, 4/2-4/3); c dolomite Till, very sandy to gravel'. brown (10YR 4/3), calcar< Till?, very sandy to very ; silty, brown (10YR 5/3); calcite and dolomite Sub-u : C-3 Till, sandy to silty, green (10YR 6/4) ; contains calcite and dolomite Till, silty, slightly sandy to slightly gravelly, brown (7.5YR 5/4); contains calcite and dolomite Till, gravelly to sandy, silty, reddish brown (5YR 4/2) ; contains calcite and dolor T ill, extremely sandy t :o grave] .ly, silt grayish brown (10YR 1 ,/3) ; cor itains calcite and dolomite Sub-unit C-2 T ill, very sandy to grs cvelly, 1 irown (10YR 4/4) ; contains calcite and dole Illinoian Stage Unit B T ill, sandy, slightly g ish brown (10YR 4/4) ; and dolomite ;ravelly : is^alcit T ill, dark grayish bro^ m (10YR 4/2), sandy, slightly grave aiy; coi itains C£ cite and dolomite S ilt, clayey, slightly gravelly i and sandy, dark grayish brown to brown (10YR 3/4-4/4) , faintl; i lami- nated, dolomitic T ill, dark grayish brown (10YR 4/4), dc omitic, very gravell} S slight :ly sand} Ity, (ft) Thick- Depth Till, gr< lyish brown (2.5YR 5/4); con- et) (ft) dolomii Ordovici; in System-Galena-Plattev ille 15 210 Unit F Till, sandy to silty, slightly gravelly reddish brown (5YR 4/3) , calcareous Till, silty to clayey, compact at base, slightly sandy to slightly gravelly, l (10YR 4/2-4/3) , < Gravel , :olored; :ill, i (10YR 3/4), ilty Till, silty to sandy, brown (10YR 4/3), 15 calcareous; slightly gravelly to verj gravelly at base Till, silty, slightly clayey, slightly 20 sandy, reddish brown (7.5YR 4/2), calcareous; slightly gravelly to gravelly at base 50 No sample Unit D Till, silty to clayey, slightly gravelly, slightly sandy, greenish brown (10YR 4/4), calcareous 80 No sample Till, silty to clayey, grayish bro* 90 (10YR 4/2), calcareous; sandy to gravelly at base Till, extremely sandy, slightly gra 100 ly, yellowish brown (10YR 5/3), c Altonian Substage Unit C (Winnebago drift) Sub-unit C-3 105 Till, extremely sandy, slightly gre ' , yellowish brown (2.5YR 5/4) No £ mple 120 Till, yellowish brown to brown (10YT 4/4-5/4), calcareous; very sandy t slightly sandy at base, gravelly s 130 top, silty to clayey at base Sand, slightly gravelly, multicolore (pinkish hue) , fine to coarse 145 Silt, clayey, slightly sandy, dark i (10YR 3/3), Sub-L : C-3 Till, silty t :o sandy, slightl; / clayey, dark brown to grayish brown (10YR 3/3- 4/2), calc; Illinoian £ Stage Unit B Sand, multicc )lored, medium to coarse grained, sc >me fine; lower 20 feet slightly gi ravelly Silt, clayey, , slightly sandy, light brown and dark brown (10YR : 2/1-3/2), calcareous, , laminated; cont; lins wood fragments Pre-Illino: .an Stage Unit A Sand, multicc )lored (pinkish t: i-nge) , Unit C (Winnebago , sandy, brownish gray (10YR i le clay, gray (10YR 5/1), cal. , slightly gravelly, slightly Unit E, D? t gravelly, sandy, j 1 System-Galena-Plal Ity, y (10YR Till, slightly gravelly, reddish brov (5YR 4/2), calcareous Unit C (Winnebago drift) Silt, organic, slightly sandy, black (10YR2/1), noncalcareous Sand, clayey, fine to coarse, organic " \ greenish brown (10YR 4/2) , ale; , da yellowish brov , slightly grave] lty, gravelly, bi System-dolomite , fin< REFERENCES Depth of bast (ft) Alden, W. C, 1918, The Quaternary geology of southeasl U. S. Geol. Survey Prof. Paper l (abs.): Geol. Soc Black, R. F., 1959, Friends of the Black, R. F., 1962, Pleistocene chronology of Wise >nce, v. 130, no. 3368, p. 172-173. nsin (abs.): Geol. Soc. America Spec. Paper 68, p. 13 s of the Kings Quadrangle: Illinois Geol. Survey Bull. a of the Upper Mis iek, Boone County: Illinois Acad. Sci. Trans., v. Geol. Soc. America Bull., v. 57, Ekblaw, George E., I960, Glacial map of northeastern Illinois: Illinois Geol. Survey. 1957, Farmdale drift near Danville, Illinois: Illinois Acad. Sci. -i of the Wisconsinan Stage in the Lake Michigan 16 p. Frye, J. C Glass, H. D., and Willman, H. B., 1962, Stratigraphy and mineralogy of the Wisconsinan loesses of Illinois: Illinois Geol. Survey Circ. 334, 55 p. Illinois Geol. Survey Horberg, Leland, 1950, Bedrock topography of Illinois: Illinois Geol. Survey Bull. 73, 111 p. lan drift in northeastern Illinois: Illinois ties in subsurface studies of glacial 210. i of the drift sheets of northwestern Illinois: Jour. Geology, v. 31, nents in the classification of the Wisconsin glacial stage: Jour. ;Cial stage of North-Central United States: Leighton, M. M.,and Brophy, J. A., 1961, Illinoian glaciation in Illinois: Jour Geology, v. 69, no. 1, p. 1- 19 63, Illinoian and Wisconsinan (Farmdale) drifts recently exposed at v. 139, no. 3551, p. 218-221. i zone (Sangamon) between the Iowan loess and Illinoian till sheets: 181. , Frank, 1899, The Illinois glacial lobe: U. S. Geol. Survey Mon. 38, p. 1-817. 1959, Geology of the Buda Quadrangle, Illinois: Illinois Geol. Shaffer, P. R., 1954, Farmdale drift: Science, v. 119, no. 3098, p. 693-694. Shaffer, P. R., 1956, Farmdale drift in northwestern Illinois: Illinois Geol. Survey Rept. Inv. 198, 25 p. Shepard, F. P., 1954, Nomenclature based on sand- silt-clay ratios: Jour. Sed. Petrology, v. 24, p. 151-158. Suter, Max, Bergstrom, R. E., Smith, H. F., Emrich, G. H., Walton, W. C, and Larson, T. E., 1959, Pre- liminary report on ground -water resources of the Chicago region, Illinois: Illinois Water Survey and Illinois Geol. Survey Coop. Ground -water Rept. 1, 89 p. Willman, H. B., Glass, H. D., ar CIRCULAR 356 ILLINOIS STATE GEOLOGICAL SURVEY URBANA