! I‘ ‘- ' “‘ 611- vna .. _ M-L¢41.J_~f“\ a". . ~ ~ -— . .. . ‘ lllllllllllllllllllllllllllllllllllllllllllllll 1*? f .. 3 1293 10411 This is to certify that the thesis entitled DIFFERENTIATION AND CORRELATION OF TILL SHEETS USING 7A/1OA X-RAY DIFFRACTION PEAK HEIGHT RATIOS, ALLEGAN COUNTY, MICHIGAN presented by Gregory David Gephart has been accepted towards fulfillment of the requirements for W5 degree in % Mfl [/ J'orroesspf DaW 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU LIBRARIES m v RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is - returned after the date stamped below. Fiji—3m DIFFEREgTIA ION AND CORRELATION OF TILL SHEETS USING 7 /10 X-RAY DIFFRACTION PEAK HEIGHT RATIOS, ALLEGAN COUNTY, MICHIGAN BY Gregory David Gephart A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geology 1982 -\ I“. w l g, ("i l 1 Q" ABSTRACT DIFFE NT ATION AND CORRELATION OF TILL SHEETS USING 7 /10 X-RAY DIFFRACTION PEAK HEIGHT RATIOS, ALLEGAN COUNTY, MICHIGAN BY Gregory David Gephart The objective of this research was to determine whether semi-quantitative clay mineral analyses can be used to dif- ferentiate multiple till sheets exposed in stratigraphic section, and to correlate these till sheets to moraines that occur further inland. Till samples were collected from each of three till units exposed stratigraphically in the Glenn Shores section, located along the Lake Michigan shoreline in southern Allegan County, Michigan. Tills that comprise each of four moraines that occur inland in the county were also sampled. The clay- size fraction of each sample was analyzed using x-ray dif- fraction, and the 72/10: peak height ratios were calculated. The results of these analyses show that the three tills exposed in the Glenn Shores section have significantly dif- ferent clay mineral compositions, and tills that comprise each of the moraines in the county each have similar clay mineral compositions to that of the uppermost till unit at Glenn Shores. dedicated to my parents ii Acknowledgement I would like to express my sincere appreciation and gratitude to my thesis advisor, Dr. Grahame Larson, for the advice, encouragement, and friendship he has given throughout the completion of this project. I would also like to thank my committee members, Dr. William Cambray and Dr. John Wilband for their help and advice. Special thanks also go to Bill Monaghan, for the countless dis- cussions (and arguments?) we have had that aided in solving many of the problems encountered in the project, and es- pecially to my wife Carol, for her moral support and en— couragement throughout my graduate career. iii TABLE OF CONTENTS LIST OF FIGURES O O O O O O O O O O O O O O O O 0 LIST OF TABLES O O O O O O O O O O O O O O O O O 0 INTRODUCTION 0 O O O O I C C O O O O O O O O C C 0 PART 1: SURFICIAL GEOLOGY AND PLEISTOCENE HISTORY OF ALLEGAN COUNTY, MICHIGAN . . . . . . . Pleistocene Geology . . . . . . . . . . . . . Post- Glacial Geology . . . . . . . . . . . . Pleistocene History . . . . . . . . . . . . . Post- Pleistocene History . . . . . . . . . . PART II' DIFFERENTIATION AND CORRELATION OF TILLS USING 73/108 DIFFRACTION RATIOS OF THE CLAY-SIZE FRACTION OF TILL . O O O O O O O O O O O O O C . 0 Sampling Procedure . . . . . . . . . . . . . Sample Preparation and x-Ray Procedure . . . Results 0 O O O O O I O O I O O O O O O O O O DiSCUSSion O O O O O O O O O O O O O O O O 0 SUMMARY AND CONCLUS IONS O I O O O O O O O O O O 0 REFERENCES 0 O O O O O O O O O O O O O O O O O O 0 iv Vi 18 20 39 42 44 46 49 60 65 68 Table Table Table Table Table Table Table 2: LIST OF TABLES o o 7A/10A x-ray diffraction ratios for clay- size fraction of till samples collected from lower (Glenn Shores) till . . . . . o o 7A/10A x-ray diffraction ratios for clay- size fraction of till samples collected from middle (Ganges) till . . . . . . . . o o 7A/lOA x-ray diffraction ratios for clay- size fraction of till samples collected from upper (Saugatuck) till . . . . . . . o o 7A/10A x-ray diffraction ratios for clay- size fraction of till samples collected from Lake Border: Morainic System . . . . o o 7A/10A x-ray diffraction ratios for clay- size fraction of till samples collected from Inner Valparaiso Moraine . . . . . . o o 7A/10A x-ray diffraction ratios for clay- size fraction of till samples collected from Outer Valparaiso Moraine . . . . . . o o 7A/10A x-ray diffraction ratios for clay- size fraction of till samples collected from shoreline exposure of Lake Border: Moraine . . . . . . . . . . . . . . . . . 52 52 54 54 55 56 56 Figure Figure Figure Figure Figure Figure Figure Figure Figure l: 2: 3: LIST OF FIGURES Location of Allegan County, Michigan . Bedrock lithology of Allegan County . Statigraphic section at Glenn Shores, Allegan County, Michigan . . . . . . . Surficial geologic map of Allegan County, Michigan . . . . . . . . . . . Shoreline sampling locations . . . . . Moraine sampling locations . . . . . . o 0 Calculation of 7A and 10A peak heights 0 0 Histogram showing 7A/lOA ratio values for till collected from shoreline exposures in Allegan County . . . . . o 0 Histogram showing 7A/10A ratio values for till collected from moraines in Allegan County . . . . . . . . . . . . vi . . 6 . . 7 . . 21 inside back cover . . 45 . . 47 . . 50 . 57 . . 58 INTRODUCTION Since the 1940's, numerous researchers in the Great Lakes region have shown that till sheets can sometimes be traced over extensive distances using one or more lithologic criteria (Dean, 1969; Dreimanis and Morgan, 1975; Gwyn and Dreimanis, 1979; Killey, 1980; Shilts, 1973a; 1973b; 1978; Lineback, et al., 1979). Some of the most successful strat- igraphic correlations within drift deposits of a single ice lobe have involved the use of semi-quantitative clay mineral analyses. For example, Killey (1980) has used semi-quant- itative clay mineral data to differentiate between two till units of the Yorkville Till Member in a morphologically com- plex area of northeastern Illinois, and was able to relate each till unit to individual moraines occurring in the area. In addition, Lineback, et a1. (1979) has used semi-quantit- ative clay mineral analyses to differentiate and correlate Late Wisconsinan till units and post-glacial lake sediments in lakes Superior and Michigan. Several researchers are also employing the use of semi-quantitative clay mineral analyses in an attempt to solve the "Valders" problem in Wisconsin and northern Michigan (Glass, 1981; Taylor, 1981). As yet, however, no attempts have been made to differentiate and correlate till units associated with drift of the Lake 1 Michigan Ice Lobe in southwestern Michigan. It is the ob- ject of this research to test whether semi-quantitative clay mineral analyses can be used to differentiate multiple till units exposed in stratigraphic section along the Lake Mich— igan shoreline in Allegan County, Michigan, and then to cor- relate these till units to moraines that occur further inland in the county. In order to attempt correlations between till sheets and moraines, however, a thorough understanding of the sur- ficial geology and glacial history of the study area is es- sential. For example, before an attempt can be made to cor- relate the till sheets exposed along the Lake Michigan shore- line with moraines that occur inland, the moraines must first be identified. Recent research involving geochemical prospecting in glaciated areas underscores the need for a prior knowledge of the glacial history of the area under study. Levinson (1974, p.451-452), in discussing mineral exploration in glaciated regions of Canada, states that "numerous studies in recent years have shown that geochemical methods can be used successfully in many glaciated areas of Canada provided that there is a careful selection and ad- aptation of the well-established sampling and analytical procedures; above all, an understanding of the glacial hist- ory of the area is essential". For this reason, a detailed surficial geologic map, based on field observations of drift materials exposed in road cuts, gravel pits, and eroded stream banks, was produced for Allegan County (Figure 4). Both 7% and 15 minute tOpographic maps were used as base maps, and the con-‘ tacts were drawn on the basis of lithology and topography. Descriptions of the map units and a discussion of the Pleist- ocene history of Allegan County are included in part I of the thesis. The differentiation and correlation of the till units exposed along the Lake Michigan shoreline by using semi-quantitative clay mineral analyses are then discussed in part II. PART I: SURFICIAL GEOLOGY AND PLEISTOCENE HISTORY OF ALLEGAN COUNTY, MICHIGAN Allegan County is located in southwestern Michigan between latitude 42025' and 42°46' north and longitude 850 40' and 86011.3' west. It extends 35 miles (56.4 kilometers) east from the shore of Lake Michigan, and 24 miles (38.6 kilometers) north to south (Figure l). surficial deposits in Allegan County are comprised mostly of drift associated with the Late Wisconsinan retreat of the Lake Michigan Ice Lobe - a retreat that began 18,000 to 21,500 years BP (before present) from the Late Wisconsinan maximum, with the entire state becoming ice—free about 10,000 years BP (Dreimanis, 1977; Farrand and Eschman, 1974). Allegan County was de- glaciated during the approximate time period 14,800 to 13,800 years BP (Farrand and Eschman, 1974). Two morainic systems, the Lake Border and Valparaiso, extend through the county, trending in a southwest-northeast direction. Separating these moraines are till plains, out- wash deposits, and glacio-lacustrine deposits. Post-glacial deposits include dunes, floodplains, and marsh areas. The county is underlain by rocks that are Mississippian in age (Figure 2). The Coldwater Shale underlies most of the county, and the Napoleon Sandstone underlies the north- eastern portion. The Michigan Formation, which is comprised of dark shale, limestone, beds of gypsum and anhydrite, breccias, and red sandstone and shale, underlies a small 5 MICHIGAN LAKE -—-—-—-fi - - INDIANA omo Figure 1: Location of Allegan County, Michigan. Figure 2: Bedrock lithology of Allegan County. area in the east-central portion of the county (Martin, 1936). The thickness of the drift overlying the bedrock in the county varies greatly but is generally between 150 and 300 feet (46 and 91 meters) thick. PLEISTOCENE GEOLOGY Valparaiso Morainic System - The Valparaiso Morainic System was first studied by Chamberlin (1883) who described it as an "immense U, embracing the great lake (Lake Michigan) in its arms", referring to its parallelism with the shore of Lake Michigan, and was named by L.C. Wooster (Leverett, 1897, from manuscript by L.C. Wooster) for the city of Valparaiso, Indiana, which is situated on a prominant ridge of the system hlnorthwestern Indiana. Leverett (Leverett and Taylor, 1915) identified it as a system because the Valparaiso System in- cludes two or more separate ridges that tend to merge at short intervals throughout the course of the system, and did not deem it necessary to name the individual ridges. Because it is important to distinguish between the constituant ridges on a detailed surficial geologic map such as this study of Allegan County, the two ridges of Leverett's Valparaiso Mor- ainic System in Allegan County have been given informal names - the eastern-most ridge will be referred to as the "Outer Valparaiso Moraine", and the western-most ridge will be referred to as the "Inner Valparaiso Moraine". Outer Valparaiso Moraine - The Outer Valparaiso Moraine occurs as a prominant southwest-northeast trending ridge in the eastern part of the county. It extends from the southern border of the county just west of the city of Otsego, to just west of Green Lake in the northeastern corner of the county. The elevation of the moraine ranges from approxim- ately 710 feet (216 meters) to over 970 feet (295 meters) above sea level, and stands 50 to 200 feet (15 to 61 meters) higher than the till plain to the west. The moraine consists primarily of massive, unsorted heterogenous till that ranges from clay-rich to sandy. In the area south of, and extending approximately one mile (1.6 kilometers) northeast of the Kalamazoo River, the Outer Valparaiso Moraine attains its greatest elevations, and tends to be more "kamic" in character. The surficial deposits in this area are coarse-textured, ranging from fine sand to boulders. Between the northern edge of this kamic area and a position approximately two miles (3.2 kilometers) east of the city of Moline in northern Allegan County, surficial de- posits of the Outer Valparaiso Moraine are comprised mostly of a dense, massive, clayey till overlying sand and gravel. At the locations where this stratigraphy was observed, the overlying till was 5 to 10 feet (1.5 to 3 meters) thick. Between the northern border of the county and a position ap- proximately two miles (3.2 kilometers) south of the border, the moraine is again quite kamic in character. The surficial deposits of this portion of the moraine are comprised prim- arily of sand, pebbles, and cobbles. Where exposure was 10 good (ie. SW% SE% SWk sec.9 T4N R11W), these deposits were observed to be well stratified. Also, several sand and gravel excavations in the Outer Valparaiso Moraine immed- iately north of the county line show exposures of stratified sand, pebbles, cobbles, and boulders. Inner Valparaiso Moraine - The Inner Valparaiso Mor- aine forms a series of prominant ridges and knolls that ex- tend from the southern border of the county near the town of Cheshire, to the northern border of the county northeast of the town of Dorr. The moraine ranges in elevation from approximately 700 feet (213 meters) to over 980 feet (297 meters) above sea level. The lowest elevations occur on the proximal side of the moraine where glacio-lacustrine sediments lap up onto the moraine, and the highest elevations occur in the vicinity of the town of Monterey. The sur- ficial materials comprising the moraine consist of a till that ranges from clay-rich to sandy. Boulders and cobbles commonly occur at the surface. Between the city of Allegan and the southern border of the county, the Inner Valparaiso Moraine consists of two ridges that are comprised of a clay-rich till and are sep- arated by a highly collapsed deposit of fine to medium— grained sand. Between the Kalamazoo River and the town of Dorr, the Inner Valpariaso Moraine forms a belt that is generally 3 to 5 miles (5 to 8 kilometers) wide. This part of the moraine is comprised of till that is highly variable in texture, and the moraine is characterized by extensive 11 collapsed areas and numerous kamic deposits. The northern portion of the moraine is breached by the Dorr Channel. The portion of the moraine that occurs east and north of the Dorr Channel attains elevations greater that 830 feet (252 meters), and is comprised of clay-rich till. Lake Border Morainic System - The Lake Border Morainic System consists of a series of till ridges that lie between the Inner Valparaiso Moraine and the Lake Michigan shoreline. Leverett (1899) was the first to study the Lake Border Mor- ainic System in Allegan County, and described the constituent till ridges of the system. The ridge that extends from the southern border of the county, along the Lake Michigan shore- line to the Kalamazoo River, and then northeastward from the town of East Saugatuck to the town of North Dorr he termed "Covert Ridge", named for the town in van Buren County that is situated on its crest. "Zeeland Ridge", named for the town of Zeeland in Ottawa County, extends from the Kalamazoo River northward along the Lake Michigan shoreline to the Ottawa County border. The portion of Covert Ridge that occurs south of the Kalamazoo River is generally 1.5 to 2 miles (2.4 to 3.2 kilometers) wide, thinning to about .25 mile (.4 kilometer) near the Kalamazoo River. The elevation of the crest of this ridge is generally slightly greater than 700 feet (213 meters), but reaches elevations greater than 720 feet (219 meters), standing 50 to 70 feet (15 to 21 meters) higher than the lake plain to the east, and 30 to 50 feet (9 to 15 12 meters) higher than the till plain to the west. North of the Kalamazoo River, Covert Ridge is generalqu to 2 miles (1.6 to 3.2 kilometers) wide, and in places is as much as four miles (6.4 kilometers) wide. Elevations greater than 770 feet (234 meters) are attained, but the crest is gener- ally 730 to 740 feet (222 to 225 meters) in elevation, stand- ing 70 to 110 feet (21 to 33 meters) higher than the lake plain to the southeast and 30 to 70 feet (9 to 21 meters) higher than the till plain to the northwest. Zeeland Ridge is generally 0.5 to 1 mile (0.8 to 1.6 kilometers) wide and stands 720 to 730 feet (219 to 222‘ meters)in elevation, loc- ally reaching elevations greater than 770 feet (234 meters). It stands 100 to 120 feet (30 to 37 meters) higher than the lake plain to the west, and 30 to 50 feet (9 to 15 meters) higher than the till plain to the east. Covert Ridge, both north and south of the Kalamazoo River, is comprised mostly of massive, clay-rich till that contains pebbles and cobbles. Fine to medium-grained sand overlies the till locally, eSpecially between the town of Ganges and the Kalamazoo River. Zeeland Ridge is also com- prised of a massive, clay-rich till that contains pebbles and cobbles. The portion of the moraine that lies south of the town of Graafschap is overlain in several areas by fine to medium-grained eolian sand deposits. Shelbyville - Martin Outwash Plain Deposits — The Shelbyville-Martin outwash deposits form a plain, the surface of which slopes gently east-southeastward from the Outer 13 Valparaiso Moraine. Materials comprising the outwash plain include fine to coarse sand, pebbles, and cobbles. Boulders commonly occur at the surface. The plain is pitted and con- tains numerous kettle lakes and marshy areas. Extensive muck fields occur within the northern portion of the outwash plain. Gun Plain Outwash Deposits - The Gun Plain Outwash Dep- osits form a valley train system, the surface of which slopes gently from northeast to southwest at an approximate grad- ient of 2.5 feet per mile (.5 meters per kilometer). The valley train system is comprised of fine to coarse sand, with gravel occurring in some areas. Muck fields are also common throughout. South Monterey Outwash Deposits - The South Monterey Outwash Deposits form an apron that slopes east-southeast- ward from the Inner Valparaiso Moraine, and are comprised of fine to coarse sand, and pebbles. Kamic deposits, muck fields, and small areas of till occur at the surface in sev- eral areas throughout the outwash apron. Dorr Channel Outwash Deposits - Leverett (Leverett and Taylor, 1915) described a meltwater drainage channel that he termed the "Ross Channel". It is graded to an outwash apron south of the city of Grand Rapids, and extends south- ward from the apron past a point approximately one mile (1.6 kilometers) east of the town of Byron Center, to the Rabbit River near the town of Dorr. The Dorr Channel, an apparent continuation of the Ross Channel, extends l4 southward from the town of Dorr along the eastern margin of the Inner Valparaiso Moraine, past the town of Hopkins, and enters the Kalamazoo Valley approximately four miles (6.4 kilometers) northwest of the city of Otsego. The channel continues westward through the present Kalamazoo'Valley, breaches the Inner Valparaiso Moraine where the city of Allegan is located, and terminates at the western margin of the Inner Valparaiso Moraine where it entered a proglacial lake. The materials forming the floor of the Dorr Channel vary in texture, but all are glaciofluvial or glaciolac- ustrine in origin and are comprised chiefly of fine sand and silt. Large areas of muck and clay deposits occur throughout the channel, and medium to coarse-grained sand and gravel deposits occur locally. New Salem - Burnips Outwash Deposits - The New Salem - Burnips Outwash Deposits form small aprons that slope south- southeastward from the east ridge (Covert Ridge) of the Lake Border Morainic System north of the Kalamzoo River, term- inating in a lake plain that lies to the southeast. These outwash aprons are comprised of fine to coarse sand, and pebbles. Some boulders occur at the surface, and muck fields, kamic deposits, and small areas of till are common. Fennville Outwash Plain Deposits - The Fennville Outwash Deposits from a pitted plain near the town of Fennville, the surface of which slopes southeastward from the Lake Border Moraine at an approximate gradient of 25 to 50 feet per mile (4;7 to 9.4 meters per kilcmeter). These deposits are 15 comprised mostly of fine to coarse sand and pebbles, and include a few cobbles and boulders. Muck fields and small areas of till are common throughout the Fennville Outwash Plain. Till Plains - Till plains comprised of lodgement till occur in various locations throughout Allegan County. An extensive till plain occurs between the Inner and Outer Valparaiso moraines, and extends from the southern border of the county to the northern border. The till is dense, massive, clay-rich, and contains pebbles and cobbles. South of the Kalamzoo River, numerous kettle lakes and swampy areas occur within the plain. North of the river, stratified fine sand and silt deposits commonly overly the till. The till plain exhibits flat to gently rolling topography, the flat- test areas being those that are overlain by the sand and silt deposits. Another extensive till plain occurs within the Lake Border Morainic System north of the Kalamzoo River, between Zeeland Ridge and Covert Ridge. It is characterized by a gently rolling topography, and is comprised of a clay-rich till that contains pebbles and cobbles. Much of the till plain is overlain by deposits of fine to medium sand, some of which is eolian and forms dunes. A small till plain occurs immediately west of the Inner Valparaiso Moraine near the southern border of Allegan County. It exhibits a gently rolling topography, and is comprised of a sandy-clay till, with boulders commonly 16 occurring at the surface. Deposits of fine to medium sand often overlie the till. Several northwest-southeast trend- ing sand and gravel-cored drumlins occur within the till plain near the town of Chicora. Another small, gently rolling till plain occurs immed- iately west of Covert Ridge, and extends from the Kalamazoo River southward to the town of Glenn. It is bordered by glaciolacustrine sand deposits on the west, and grades east- ward to Covert Ridge. It is comprised of a dense, massive, clay-rich till, and is commonly overlain by fine to medium- grained eolian sand deposits. Undifferentiated Sand And Gravel Deposits - Several individual kames occur within the lake plain north of the Kalamazoo River between the Lake Border Morainic System and the Inner Valparaiso Moraine. Exposures within these kames ShOW’ stratified and cross-bedded sand, pebbles, cobbles, and boulders, which indicate a glaciofluvial origin. Also, deformation structures (i.e. folding and faulting) suggest deposition into large ice holes in a disintegrating ice front. Kame fields also occur adjacent to the Inner Valparaiso Moraine, on both the proximal and distal sides of the mor- aine in the following areas: southwest of the town of Dorr; near and within the South Monterey Outwash Plain; and with- in the till plain southwest of the town of Chicora near the southern border of the county. Exposures within these kames show stratified glaciofluvial sediments comprised of sand, l7 pebbles, cobbles, and boulders. A highly collapsed out- wash deposit comprised of fine to medium—grained sand and pebbles also occurs between two ridges of the Inner Valpar- aiso Moraine south of the Kalamzoo River. Extensive kamic deposits occur in both the northeastern and southeastern corners of Allegan County, and form the kame and kettle topography that is characteristic of both areas. These deposits are comprised of a variety of stratified sed- iments ranging from sand to boulders. Glacial Lake Deposits - Glaciolacustrine sediments occur extensively in the western two-thirds of Allegan County, and form a plain that covers most of the area between the Lake Border Morainic System and the Inner Valparaiso Moraine. These deposits are comprised mostly of fine to coarse sand, and contain small pebbles. Small isolated areas of silt and clay occur throughout the lake plain; muck fields occur in the areas of lowest elevation, mostly in the western part of the lake plain south of Hutchins Lake. These glacial lake deposits occur at elevations up to approximately 700 feet (213 meters) along the Inner Valparaiso Moraine, and up to approximately 650 to 660 feet (198 to 201 meters) along the northeast portion of Covert Ridge in the Vicinity of the town of Burnips. Kettle lakes and swampy areas, indicating ice collapse, are common in the southeast part of the lake plain, east of a line that runs from the town of Pearl southward to the southern border of Allegan County. Sand dunes are common 18 throughout the area south of the Kalamazoo River. Glaciolacustrine deposits also occur between the Lake Michigan shoreline and the Lake Border Morainic System at elevations up to 650 to 660 feet (198 to 201 meters). These deposits are also comprised of fine to coarse sand, and pebbles. POST -GLAC IAL GEOLOGY Eolian Sand Deposits - Eolian sand deposits, generally 3 to 9 feet (1 to 3 meters) thick, cover two extensive areas along the western margin of the Inner Valparaiso Moraine. One of these deposits, approximately 1 to 2 miles (1.6 to 3.2 kilometers) wide, occurs immediately south of the Kalamazoo River and extends for approximately five miles (8 kilometers) along the margin of the moraine. The other deposit occurs about three miles (4.8 kilometers) north of the river and extends northward approximately six more miles (9.7 kilo- meters) along the moraine. These deposits are comprised of wind-blown sand and small pebbles derived from glaciolac- ustrine deposits that occur in the lake plain to the west. Numerous dunes and deflation basins occur throughout these eolian sand deposits. Dune Deposits - Dunes are abundant throughout the west- ern portion of Allegan County. Numerous barchan dunes occur on the glacial lake plain between the Inner Valparaiso Mor- aine and the Lake Border Morainic System, especially south 19 of the Kalamazoo River. Barchan dunes also occur on the Lake Border Morainic System, and on the till plains that sep- arate, and are adjacent to, the constituent ridges of the Lake Border System. In addition, numerous barchan dunes occur on the glacial lake deposits that occur immediately west of Zeeland Ridge. Extensive shoreline dunes extend along the Lake Michigan shoreline southward from the northern border of the county to the town of Douglas, and spread inland as much as 1.5 miles (2.4 kilometers). Many of these dunes reach heights that are more than 250 feet (76 meters) greater than the elevation of the present beach (approximately 580 feet - 176 meters), and most possess a well-developed forest cover. Both the barchan and shoreline dunes are comprised of wind-deposited sand and granules, generally derived from glaciolacustrine and modern beach sand deposits. Marsh And Swamp Deposits — Marsh and swamp deposits occur in several kettle holes, and in river and stream val- leys throughout the county. These deposits are comprised mostly of decaying freshwater plants, mixed with sand and silt. Several of these deposits contain standing water. Recent Floodplain Deposits - Modern floodplain deposits occur along several streams throughout Allegan County, with the most extensive deposits occurring along the Kalamazoo and Rabbit rivers. These deposits are comprised mostly of bedded sand and silt. PLEI STOCENE HI STORY The surficial drift of Allegan County was deposited during the Late Wisconsinin retreat of the Lake Michigan Ice Lobe. Older drift deposits occur in the county, but are not exposed at the surface. For example, till and lacustrine sediments associated with pre-Late Wisconsinin glaciation can be observed along the Lake Michigan shoreline about one mile (1.6 kilometers) southwest of the village of Glenn in southern Allegan County (SW% SW% section 31 T2N R16W). These sediments are exposed in a 66 to 82 feet (20 to 25 meter) high section, and record several fluctuations of the Lake Michigan Lobe (Figure 3). The sequence begins at present lake level (580 feet - 177 meters) with the uppermost meter of a dense silty-clay till of unknown thickness. The till is overlain by a thin (2 to 4 inches - 5 to 10 centimeters) discontinuous beach gravel and 6.6 feet (2 meters) of lac- ustrine silt and sand containing large pieces of abraided wood, reworked organic mat, and peat balls. Samples of the wood have been dated at 37,150 I 540 (BETA 3311), 38,130 t 740 (BETA 3310), >'37,000 (GX-8193), and > 48,000 (ISGS-948) radio-carbon years BP, and a sample of organic mat has been dated at :>43,000 years BP (SI 5183). Above the silt and sand is another till 16.4 to 19.7 feet (5 to 6 meters) thick. 20 21 ELEVATION LITHOLOCY 2225 meters 200 " 650 - 'LMW$$? LACUSTRINE SAND 630 TILL 190 620 LACUSTRINE SAND 610 185 600 TILL 180 SAND AND GRAVEL (WOOD) 59o SILT WITH ORGANICS ___._.——GRAVEL (WOOD) 580 177 -.1-..1 TILL - PRESENT BEACH Figure 3: Stratigraphic section at Glenn Shores, Allegan County, Michigan. 22 The upper part of this till is water-laid in places, and is overlain by a 16.4 to 19.7 feet (5 to 6 meters) thick lac- 1ustrine sand. This second lacustrine unit is overlain by a; third till that is 8 feet (2.5 meters) thick. The section is capped by 6.6 to 9.9 feet (2 to 3 meters) of Lake Chicago (Glenwood Stage) sediments and a series of dunes that in places overlie wood dated at 5,780: 90 (BETA-2048) radio- carbon years BP (Gephart, et al., 1982). The lower part of the section (lowest till unit and overlying lacustrine sediments with incorporated organic debris) records a major retreat of ice out of the Lake Michigan basin and subsequent low lake level probably during the Middle Wisconsinan (Port Talbot), followed by a readvance that blocked drainage north and eastward and raised the lake to a higher-than—present level. The middle till unit rep- resents a later advance of the Lake Michigan Lobe, and is probably Late Wisconsinin (Woodfordian) in age. The thick deposit of lacustrine sand that overlies the middle till unit indicates that another retreat of the ice margin occurred after deposition of the middle till unit. The uppermost till unit, which can be traced southward to Covert Ridge, resulted from a Late Woodfordian readvance of the Lake Michigan Lobe to the Lake Border Morainic position. The Lake Chicago (Glenwood Level) sediments that overlie the upper till unit were deposited during the final retreat of the Lake Michigan Lobe from southwestern Michigan (Gephart, et al., 1982). The maximum extent of the Late Wisconsinan ice advance 23 occurred approximately 18,000 to 21,500 radio-carbon years BP. This is based on radio-carbon dates of spruce and other organic debris incorporated in tills near the terminal pos- ition of Late Wisconsinan ice that, in the Great Lakes region, extended nearly to the Ohio River in western Ohio and eastern Indiana, and a little south of the middle parts of western Indiana and eastern Illinois (Dreimanis, 1977; Farrand and Eschman, 1974). The glacial margin was characterized by minor oscillations attflmaterminal zone until about 17,500 years BP when a significant retreat, followed by a readvance, occurred (Dreimanis, 1977). Following this event, all three ice lobes in Michigan (the Huron-Erie, Saginaw, and Lake Michigan lobes) began a general retreat about 16,000 years BP that culminated in the total deglaciation of the state by about 10,000 years BP (Farrand and Eschman, 1974). This general retreat, however, was interupted by several signif- icant readvances of the ice margin, with each readvance generally falling short of the previous advance (B1ack,l978; 1980; Evenson, 1973a; 1973b; Evenson, et al., 1976a; Farrand and Eschman, 1974). The first part of Michigan to become ice-free was the middle portion of the state just north of the Indiana state line, and by approximately 15,000 (Farrand and Eschman, 1974) to 15,600 (Mérner and Dreimanis, 1973) years BP, the ice margin stood at the position of the Kalamazoo Moraine of the Lake Michigan and Saginaw lobes, and the Mississinnewa Moraine of the Huron-Erie Lobe. Meltwater drainage at that time was 24 to the southwest, through the Kankakee Torrent (Farrand and Eschman, 1974). The Erie Interstade, a major retreat of the ice that began approximately 15,600 tears BP and culminated about 14,800 years BP, is documented for the Huron—Erie Lobe by Marner and Dreimanis (1973). This retreat, however, has not yet been recognized in the Lake Michigan Lobe (Farrand and Eschman, 1974). The deglaciation of Allegan County began sometime after 14,800 years BP with the retreat of the Lake Michigan Lobe from the Kalamazoo Moraine. As the ice retreated, kamic and highly collapsed sand and gravel was deposited along the proximal (western) margin of the moraine. These deposits form a belt that is approximately 2 to 5 miles (3 to 8 kilo— meters) wide in southwestern Barry County, northeastern Kalamazoo County, and southeastern Allegan County, and ex- tends southwestward into Van Buren County and northeastward to the interlobate area of the Kalamazoo moraines of the Lake Michigan and Saginaw ice lobes. In Allegan County, these deposits occur in the extreme eastern part of Gun Plain Township. The coarse texture and kamic, highly collapsed nature of these deposits suggest that they were the result of a stagnating, disintegrating ice margin. Kamic sand and gravel deposits also occur in the north- easternrcorner of Allegan County, east of the Outer Valparaiso Moraine. These deposits may represent a continuation of the kamic deposits that occur in the southeast part of the county, or may be interlobate deposits as is suggested by 25 Leverett (Leverett and Taylor, 1915) amd Martin (1955). Only detailed surficial geologic mapping of Barry and Kent counties can provide an answer to this problem. Following the retreat from the Kalamazoo Moraine, the margin of the Lake Michigan Lobe occuppied the position of the Outer Valparaiso Moraine. This moraine represents either a readvance, or a temporary pause in the retreat of the ice front. No conclusive evidence has yet been found that would confirm either possibility. The evidence that does exist, however, tends to support the formation of the moraine as a readvance of the ice. For example, the moraine is composed primarily of a massive, dense till that overlies sand and gravel - a situation that would more likely occur as a result of a readvance of the ice, overriding older outwash deposits and depositing lodgement till on top, than from a receding ice front that would more likely produce a head of outwash with flow till and ablation till common near the crest of the moraine. The occurrence of till overlying sand and gravel deposits was observed at the following locations: NE% NE% NW% sec.13 TlN R12W; NE& SE% SWk sec.9 T3N R11W; SW% SW% SW% sec.22 T4N RllW; NW% NW% NE% sec.17 T4N RllW. The Outer Valparaiso Moraine is characterized by the occurrence of several gaps in the morainic ridge, the most obvious and extensive being the gap that occurs north of the town of Watson where approximately 3.3 miles (5.3 kilometers) of the moraine is absent. The surficial deposits within this area are comprised mainly of sand, pebbles, and cobbles, and 26 extend up to five miles (8 kilometers) west of the moraine. These deposits are highly collapsed, and contain numerous kettle lakes and swampy areas. This extensive collapsed outwash deposit probably formed as a large crevasse-fil- ling near the margin of the ice when it occuppied the pos- ition of the Outer Valparaiso Moraine. The other gaps in the moraine were most likely formed as a result of the melting of buried masses of ice follow- ing the retreat of the ice margin from the Outer Valparaiso Moraine. These occur at the following locations: west of the city of Otsego, where the Kalamazoo River breaches the moraine; immediately east of the city'ci'Wayland and about 1.5 miles (2.4 kilometers) south of the northern border of the county. The surficial materials in these areas are com- prised primarily of fine to medium-grained sand. Glacial meltwater, as well as post-glacial drainage, has most likely altered these collapsed areas. The Shelbyville-Martin Outwash Plain formed when the ice margin stood along the position of the Outer Valparaiso Moraine. The numerous kettle lakes and swampy areas that occur within the outwash plain formed as a result of the melting of ice masses that had broken off the ice margin and were buried in the outwash sediments. The extensive swampy areas and muck deposits that occur in the northern portion of the outwash plain represent large kettle lakes that drained subsequent to the retreat of the ice margin from the Outer Valparaiso Moraine. Meltwater drained southward, 27 probably along the western edge of the kamic deposits that occur along the western side of the Kalamazoo Moraine. The drainage probably followed roughly the same course as the later Gun Plain Valley Train System, which truncates the Shelbyville-Martin Outwash Plain. Following the formation of the Outer Valparaiso Moraine and the Shelbyville-Martin Outwash Plain, the ice margin continued to retreat west-northwestward and exposed the till plain that lies between the Inner and Outer Valparaiso moraines. Deposits of stratified sand and silt overly large areas of the till plain east and northeast of the city of Allegan and near the city of Wayland. These sand and silt deposits resulted from the localized ponding of meltwater as the ice margin receded westward. The sur- face of the till plain that lies south of, and immediately north of the Kalamazoo River is higher in elevation than the portion of the till plain that occurs further to the north, and is generally free of sand and silt deposits at the sur- face. Kettle lakes, produced from the melting of ice masses that became detached from the glacier as it retreated across the till plain, are common in the till plain south of the Kalamazoo River. At approximately the same time, the Gun Plain Valley Train System developed. It recieved meltwater mainly from a northeastern source (Saginaw Ice Lobe), but also from the retreating Lake Michigan Lobe via the channel that cuts through the Outer Valparaiso Moraine east of the city of 28 Wayland. In the southeastern corner of Allegan County near the city of Plainwell, the Gun Plain Valley Train System joined the westward-flowing glacial Kalamazoo River, and continued to flow southwestward between the Outer Valparaiso and Kalamazoo moraines. Following the retreat of the ice margin from the Outer Valparaiso Moraine, the ice readvanced to the position of the Inner Valparaiso Moraine. Evidence for this readvance can be observed two miles (3.2 kilometers) north of the Allegan County border at Dias Hill in Kent County (sections 19 and 30 TSN RllW) where the Inner Valparaiso Moraine ap- pears to override and truncate the Outer Valparaiso Moraine a situation that could only occur with a readvance of the Lake Michigan Lobe.i The elevation of the surface at the point of intersection of the two moraines is dramatically higher than the surrounding region, which would be expected in an overriding situation. When the ice margin stood at this morainic position, sand and gravel was deposited on the distal side of the moraine, forming the South Monterey Outwash Deposits. During the retreat of the ice margin from the Inner Valparaiso Moraine, the small till plain that occurs west of the moraine south of the Kalamazoo River was exposed. The northwest-southeast trending drumlins that occur in the western portion of the till plain near the town of Chicora were also exposed at this time. Also, kames were deposited immediately south of these drumlins, and between the Inner 29 Valparaiso Moraine and the Lake Border Morainic System north of the Kalamazoo River as the ice retreated westward. As the ice margin continued to recede from the Inner Valparaiso Moraine, a channel referred to by Leverett (Leverett and Taylor, 1915) as the "Ross Channel" developed behind the moraine in southern Kent County and drained melt- water southward into Allegan County. Leverett stated that the extension of this channel southward from the town of Dorr is difficult to interpret, and postulates the following two scenarios: 1) If the ice margin had not retreated far enough westward in Allegan County to allow meltwater to flow between the ice margin and the moraine, flow would had to have continued southward through the Dorr Channel east of the Inner Valparaiso Moraine, then eastward up the Kalamazoo Valley to Otsego, where the flow again turned southward; 2) If the ice had retreated far enough westward from the Inner Valparaiso Moraine, drainage may have passed through the Ross Channel, and then southwestward between the ice margin and the moraine in Allegan County. This drainage did occur eventually, if not from the beginning (Leverett and Taylor, 1915). The history of the Dorr Channel cannot be interpreted with any certainty with the present available data. For example, Leverett (Leverett and Taylor, 1915) traced the Ross Channel northward from the town of Dorr to an apron of outwash near Grand Rapids that is at an elevation of approx- imately 700 feet (213 meters). Divides occur, however, 30 within the Dorr Channel about 1.5 miles (2.4 kilometers) south of the town of Dorr at an elevation of 710 feet (216 meters), and about three miles (4.8 kilometers) south of the town of Hopkins at an elevation of 725 feet (220 meters). The variability of the elevation of the channel floor is most likely due to several factors that include crustal rebound, the melting of buried ice blocks, and post-glacial drainage alteration. In addition, there may have been more than one stage in the history of the Dorr Channel. It does appear, however, that the flow of meltwater through the Dorr Channel was westward through the present Kalamazoo Valley - not eastward as Leverett (Leverett and Taylor, 1915) believed. Evidence for a westward flow dir- ection is the presence of two terrace levels in the Kalamazoo Valley between the point of entrance of the Dorr Channel and the western margin of the Inner Valparaiso Moraine. The higher of these terrace levels grades to the floor of the Dorr Channel, and terminates in the lake plain at the west- ern margin of the Inner Valparaiso Moraine. The lower terrace level was produced from the Kalamazoo River, and grades to the mouth of the river at Lake Michigan. The higher terrace also occurs within the gap where the Kalamazoo River breaches the Outer Valparaiso Moraine west of the town of Otsego. This indicates that the glacial Kalamazoo River may have breached the Outer Valpariaso Moraine and joined the westward-flowing Dorr Channel. The Dorr Channel breached the Inner Valparaiso Moraine where the city of Allegan is now located, and resumed a southward flow between the ice 31 margin and the Inner Valparaiso Moraine. The breaching of the moraine was probably aided by the melting of a large mass of buried ice, which created a sag in the moraine at that location. With further retreat of the ice margin, the Dorr Channel was abandoned and meltwater flowed south- ward along the entire eastern margin of the Inner Valparaiso Moraine in Allegan County. While the Dorr Channel was forming, meltwater was ponded between the retreating ice margin and the Inner Valparaiso Moraine in the southern portion of Allegan County. This proglacial lake, referred to by Leverett (Leverett and Taylor, 1915) as "The Lake on the Lower Kalamazoo" and later named Lake Pullman by F.W. Terwilliger (1954), was part of a series of similar lakes that formed a southward—flowing integrated lake system in southwesterm Michigan, culminating in the incipient Lake Chicago at the southern end of the Lake Michigan basin (Leverett and Taylor, 1915). This whole system ultimately drained down the Illionios River to the Mississippi. The landward margin of Lake Chicago generally was the Valparaiso Morainic System that 100ped around the southern end of the Lake Michigan basin. Until late in the formation of the Lake Border Morainic System, incipient Lake Chicago, the level of which was about 640 feet (195 meters), most likely occupied an area entirely outsidesthe present Lake Michigan basin (Leverett and Taylor, 1915; Bretz, 1951). Leverett (Leverett and Taylor, 1915) found that the small lakes comprising this integrated lake system did not 32 form easily recognizable beaches that would permit easy mapping. He did determine, however, that Lake Pullman had a surface elevation of approximately 680 feet (207 meters), based on the following evidence: 1) The lake is limited on the east by the Valparaiso Morainic System at an elevation of approximately 680 feet (207 meters); 2) The lake is bor- dered by a well-defined terrace of the Kalamazoo Valley at 680 feet (207 meters); and 3) An apron of outwash that is graded to the Lake Border Moraine near the town of Fennville occurs at an elevation of about 680 feet (207 meters) (Leverett and Taylor, 1915). Recent mapping by the author, however, has determined that in Allegan County this lake reached levels as high as 700 feet (213 meters) along the western side of the Inner Valparaiso Moraine, probably early in the lake's development. It initially drained southward through a channel that flowed past the towns of Breedsville and Bangor in Van Buren County, through swampy channels near the town of McDonald, coming to the Paw Paw River near Hartford (Leverett and Taylor, 1915). Topographic maps indicate that the elevation of the drainage threshold at a point about two miles (3.2 kilometers) north of Breedsville was nearly 690 feet (210 meters). When the ice margin had retreated to Covert Ridge of the Lake Border Morainic System, a lower outlet was exposed along the east— ern margin of this moraine. The elevation of the drainage threshold for this outlet was about 660 feet (201 meters), near the town of Friendsville in Van Buren County. 33 Glaciolacustrine deposits occur at elevations up to 650 to 660 feet (198 to 201 meters) along the northeastern portion of Covert Ridge near the town of Burnips. Most of the area that lies between the Lake Border Morainic System and the Inner Valparaiso Moraine was occup- pied by this proglacial lake. The kettle lakes and swampy areas that occur in the southern part of the lake plain were produced from the melting of buried ice blocks that became detached from the ice margin as it receded westward across the lake plain. These large masses of ice probably were partially buried in the lake-bottom sediments when the level of the lake was about 700 feet (213 meters) in elevation, and were most likely not totally submerged. As the ice margin continued to recede westward, it exposed the lower outlet along Covert Ridge. The lake level subsequently dropped to about 660 feet (201 meters) — an elevation that is lower than the surface where these collapsed features occur - thus allowing the buried ice blocks to melt without the resulting basins being filled in with lake sediments. Following the retreat from the Inner Valparaiso Moraine, the margin of the Lake Michigan Ice Lobe occuppied the pos- ition of the Lake Border Morainic System, the history of which is very complex in Allegan County. For example, two till ridges (Covert Ridge and Zeeland Ridge) occur north of the Kalamazoo River, whereas only one (Covert Ridge) occurs south of the river. Which of the two ridges that occur north of the river is the continuation of the ridge that 34 occurs south of the river is not known with any certainty - one can only speculate. Leverett (1899) believed that the ice occuppied the position of Covert Ridge first, following the retreat from the Valpariaso Morainic System. The ice margin then retreated further westward to form Zeeland Ridge. The portion of Zeeland Ridge that had extended south of the Kalamazoo River would have since been cut away as a result of erosion along Lake Michigan (Lake Chicago). Alternatively, the portion of Covert Ridge that occurs south of the Kalamazoo River may actually be the continuation of Zeeland Ridge. If this is the case, then this moraine truncates the older, northern portion of Covert Ridge. The crescent-shaped eastward lobation of this moraine into the Kalamazoo Valley may have been due to a pre-existing topo- graphically low area, now occuppied by the Kalamazoo River, and would suggest a readvance of the Lake Michigan Lobe. The small ridge of sandy till that lies just east of Covert Ridge near the town of Liesure may represent a remnant of the southward extension of the northern portion of Covert Ridge. Another possibility is that the southward continuation of the northern portion of Covert Ridge extended southwest- ward into what is now the Lake Michigan basin, and was sub- sequently eroded away by the waters of Lake Chicago after the ice had receded to the west. The ice margin would then have readvanced, forming Zeeland Ridge and the southern por- tion of Covert Ridge. 35 Morphologic evidence tends to support Leverett's (1899) interpretation that the portions of Covert Ridge that occur north and south of the Kalamazoo River represent time-equiv- alent ice-edge positions. For example, wave-cut slopes occur on the till plain at the southwestern end of Covert Ridge just north of the Kalamazoo River, and along the western and northern margin of Covert Ridge immediately south of the river. The elevation of the base of these slopes is about 650 feet (198 meters), which suggests they were formed by the erosive action of the waters of Lake Chicago (Glenwood Stage). Since these slopes appear to have been continuous across the river and occur at equal elevations on both sides, they are probably time—equivalent and were formed after the formation of both the southern and northern portions of Covert Ridge. Zeeland Ridge occurs west of the wave-cut slope and would therefore be younger than both portions of Covert Ridge. The New Salem-Burnips outwash sediments were deposited in the form of small aprons on the distal side of the moraine when the ice margin occuppied the position of the northern portion of Covert Ridge. The apron that occurs northwest of the town of Hamilton terminates in the lake plain southwest of the moraine at an elevation of approximately 660 feet (201 meters). The outwash aprons that occur near the towns of Burnips and New Salem terminate at elevations of about 670 to 680 feet (204 to 207 meters). The lower portions of these outwash aprons, however, could well have been deposited sub- aqueously, therefore making correlations with specific lake 36 levels tenuous at best. Sand and gravel that forms the Fennville Outwash Plain was deposited when the ice margin occuppied the position of the southern portion of Covert Ridge. The numerous depres- sions and kettles that occur within this outwash plain, the most obvious being Hutchins Lake, were produced by the melt- ing of several buried ice blocks that had become detached from the retreating ice margin. If the portions of Covert Ridge north and south of the Kalamazoo River represent time-equiv- alent ice-edge positions, then the Fennville Outwash Plain and the New Salem-Burnips Outwash Deposits are of the same age. If, however, the southern portion of Covert Ridge is time- equivalent to Zeeland Ridge, then the Fennville Outwash Plain is younger than the New Salem-Burnips Outwash. With the retreat of the Lake Michigan Ice Lobe from the Lake Border Morainic System, the Late Wisconsinan deglaciation of Allegan County was complete. At this time, connections between Lake Pullman and Lake Chicago (Glenwood level) were opened all along the Lake Border System. As these connections were opened, the level of Lake Pullman dropped to that of Lake Chicago (640 feet — 195 meters). Evenson (1972; 1973a) has traced the Glenwood Stage shoreline along the Lake Border Morainic System in Allegan County using localized occurrences of beaches, wave-cut lepes, and transitions from flat to rolling t0pography, and determined that the Glenwood shoreline occurs at elevations of 650 to 655 feet (198 to 199 meters) in the southern part of the county, and at elevations of 655 37 to 660 feet (199 to 201 meters) in the northern part. Sev- eral of the shoreline features he defined are included on the geologic map, as wellaussome additional shoreline feat- ures recognized by this author. The occurrence of Glenwood level shoreline features at elevations above 640 feet (195 meters), and the general rise in elevation of these features from 650—655 feet (198-199 meters) to 655-660 feet (199-201 meters) from the southern border of Allegan County to the northern border is due to isostatic rebound following the retreat of the Lake Michigan Ice Lobe (Evenson, 1972; 1973). Mantles of eolian sand that overly portions of the west- ern side of the Inner Valparaiso Moraine, and some of the barchan dunes that occur on the eastern portion of the lake plain west of the moraine probably began to form when the level of Lake Pullman dropped as it merged with Lake Chicago. The drop of the level of Lake Pullman exposed a barren, sandy plain west of the Inner Valparaiso Moraine that provided a source of sand for these eolian deposits. Lake Chicago stood at the Glenwood level beginning with the retreat of the ice margin from the Valparaiso Morainic System,_and remained at that level throughout the formation of the Lake Border Morainic System, and persisted for a period of time after the ice had receded well westward and northward from southwestern Michigan (Bretz, 1959; 1959; 1964; Hough, 1966; Evenson, 1972; 1973; Farrand and Eschman, 1974; Fullerton, 1980). Farrand and Eschman (1974) believe that the Glenwood Stage lasted some 1500 years, and did not drop 38 to the Calumet level (620 feet - 189 meters) until after the ice had retreated from the Port Huron Moraine, which was built approximately 12,600 years BP. Also, they speculate that a low water stage within the Glenwood Stage could have occurred 13,300 years BP, when the ice margin retreated at least as far north as the Indian River lowlands in the north- ern part of Michigan's lower penninsula, allowing drainage to pass through to lakes Huron, Erie, and Ontario, and into the St. Lawrence lowlands further to the east (Farrand and Eschman, 1974; Farrand, et al., 1969). With the drop of Lake Chicago to the 620 foot (189 meter) Calumet Stage, Lake Pullman drained completely. The barchan dunes that occur on the lake plain at elevations below about 650 feet (198 meters) began to form at this time. The source of sand for these eolian sand deposits was the newly exposed barren, sandy lake plain. Following the Calumet Stage, Lake Chicago drOpped to a level of 605 feet (184 meters) (Toleston Stage) due to down- cutting of the Chicago outlet (Leverett and Taylor, 1915; Bretz, 1951b; 1959; 1964; Hough, 1958; 1963; 1966; Kelley and Farrand, 1967; Farrand and Eschman, 1974). While ex- tensive Glenwood Stage deposits cover much of the western portion of Allegan County (up to elevations of 650 to 660 feet (198 to 201 meters), Calumet and Toleston Stage deposits occur only in the extreme northwest corner of the county, covering an area of about .75 square miles (1.2 square kilo-‘ meters) immediately east of the shoreline dune belt and 39 adjacent to the northern border of the county. Surface el- evations below 620 feet (189 meters) also occur locally between Zeeland Ridge and the shoreline dune belt; however any Calumet Stage deposits in these areas have since been masked by post-glacial eolian sand. With the final retreat of the Lake Michigan Ice Lobe out of the southern penninsula of Michigan and the Straits of Mackinac about 11,500 years BP, the 605 foot (184 meter) Early Lake Algonquin in the Huron basin merged with the 605 foot (184 meter) Toleston Stage of Lake Chicago, forming Main Lake Algonquin. As the ice margin retreated further northward, successively lower outlets east of Georgian Bay were uncovered. The lowest of these outlets was the North Bay Outlet,vfidrfl1resulted in a very low water stage in both the Huron basin (Lake Stanley, 50 to 100 feet - 15 to 30 meters) and in the Lake Michigan basin (Lake Chippewa, 230 feet? - 70 meters). With further retreat of the ice margin, the North Bay Outlet rebounded, causing the drainage to shift to the south. This resulted in the Nipissing (595 feet - 181 meters), Algoma (589 to 591 feet - 179 to 180 meters), and finally the present lake stages (Leverett and Taylor, 1915; Bretz, 1939; Farrand and Eschman, 1974). POST-PLEISTOCENE HISTORY As the ice of the Lake Michigan Lobe began to recede from Allegan County, kettle lakes began to develop in 40 depressions that formed from the melting of buried masses of ice. Several of the kettle lakes remain, scattered throughout the county, while many have since drained, or have become filled with organic matter and form the many swamps and marshes that occur in the county. Kettle lakes and marshes are especially common within the Valparaiso Morainic System and associated till plains and outwash de- posits, within the kamic deposits along the eastern border of the county, and in the southern portion of the lake plain that lies between the Lake Border Morainic System and the Inner Valparaiso Moraine. Marshes also occur in the flood- plains of rivers and streams throughout the county. With the retreat of the Lake Michigan Ice Lobe out of southwestern Michigan and the drop of the level of Lake Chicago from the Glenwood Stage, the present drainage pattern in Allegan County began to develop. The Kalamazoo River most likely began to occupy its present course west of the city of Otsego as the ice margin began to retreat from the Inner Valparaiso Moraine, and probably breached Covert Ridge of the Lake Border Morainic System when the level of Lake Chicago dropped to the Calumet Stage. It attained its present course to Lake Michigan as the lake dropped to the Toleston, Nippissing, Algoma, and present levels. The Kalamazoo River and its major tributaries, the Rabbit River and the Gun River, drain most of the area comprising Allegan County. The extreme northwest corner of the county, north of the northern portion of Covert Ridge, is drained by the Black River, which discharges into Lake Macatawa in 41 southwestern Ottawa County. The southwest corner of Allegan County is drained by the Black River, which discharges into Lake Michigan at South Haven in Van Buren County. Following the drop of Lake Chicago to either the Toleston Stage (605 feet - 184 meters), or a later lower level, shore- line dunes began to form along the present Lake Michigan shoreline. Some of these dunes stand more than 200 feet (61 meters) higher than the surrounding region, and form a belt that is generally .5 to .75 miles (.8 to 1.2 kilometers) wide. Many of these dunes possess a well-developed forest cover. The vegetation on some of the dunes, however, has been destroyed by wave action, disease, fire, or by man, thus subjecting these dunes to the effects of wind erosion. Just a small break in the vegetative cover on the windward side of a dune can cause a major blowout and dune migration - a situation that has occurred with several dunes in Allegan County, most notably the Goshorn Dune, which occurs just north of the Kalamazoo River near the town of Saugatuck. This dune has migrated rapidly eastward, and now extends as much as 1.5 miles (2.4 kilometers) inland from the Lake Michigan shoreline (Reinking and Gephart, 1978). PART II: DIFFERENTIATION AND CORRELATION OF TILLS O O USING 7A/lOA DIFFRACTION RATIOS OF THE CLAY-SIZE FRACTION OF TILL In order to determine whether or not semi—quantitative mineralogic analyses of the clay-size fraction of tills can be used to successfully differentiate and/or correlate till units associated with the Lake Michigan Ice Lobe in south- western Michigan, a reference section was chosen and then sampled extensively in an effort to characterize the clay mineralogy of each till unit exposed. The Glenn Shores sec- tion (figures 3 and 5) was used as the reference section not only because it is one of the best exposures of multiple till units in Allegan County, but also because it is the only lo- cation in the county where three tills are exposed. In ad- dition, the occurence of organic material between the lowest till unit (the Glenn Shores Till) and the middle till unit (the Ganges Till) makes this section one of the most impor- tant in the Lake Michigan basin since very little is known about the Early and Middle Wisconsinan in this area. Till that comprises the moraines that occur inland in Allegan County (the Lake Border, Inner Valparaiso, and Outer Valparaiso moraines) was then sampled, and the clay—size fraction analyzed in an attempt to correlate the moraines with the till units exposed in the Glenn Shores section. 43 4 4 SAMPLING PROCEDURE A total of 63 samples were collected from the three till units that are exposed at the Glenn Shores section — 25 sam- ples from the upper (Saugatuck) till (samples UT 100 - UT 124); 30 from the middle (Ganges) till (samples MT 1 - MT 30); and 8 from the lower (Glenn Shores) till (samples LT 300 - LT 307). In addition, 9 samples of the middle till (samples MT 500 - MT 508) were collected approximately 0.4 miles (0.6 kilometers) south of the Glenn Shores section, and 5 (LT 250 - LT 254) and 8 (LT 200 - LT 207) samples of the lower till unit were collected about 900 feet (274 meters) and about 1400 feet (426 meters), respectively, north of the section (see figure 5). Also,10 samples (samples 620 - 629) were collected along the shoreline about 1.8 miles (3 kilometers) south of the Glenn Shores section, where Covert Ridge of the Lake ‘Border Morainic System intersects the shoreline. These samples (620 - 629) were collected from a 15 to 20 feet (4.6 meter) thick unit of till near the top of the exposure — presumably the crest of the moraine. All samples collected along the shoreline were taken from fresh exposures of till, and all were unoxidized and unleached. A total of 35 samples were collected from till that com- prises the moraines in Allegan County — 21 samples (LBm l - LBm 21) from the Lake (Border Morainic System; 9 samples (IVm l - IVm 9) from the Inner Valparaiso Moraine; and 5 samples (OVm l - OVm 5) from the Outer Valparaiso Moraine. 45 Rnw mew ; : TZN : LT 200-205 ' \ 3| : LT 250-254—9 E l I I I ---------------------- 4r---1 : I 6 : I i I I I 1 TIN ----------------------- :ou--.( I I I 7 I =====Fri ..'§ . ‘ _ _fiEMUO 0 . 00 In! E—I—I-é—u—r—lqfio I‘IIOMCIQI Figure 5: Shoreline sampling locations. 46 Sampling locations are shown in figure 6. Oxidized, unleached samples were taken generally 5 to 10 feet (1.5 to 3 meters) below the surface in roadcut exposurs, using a hand soil auger. SAMPLE PREPARATION AND X-RAY PROCEDURES Methods described by Jackson (1958) were used to qual- itatively determine which clay minerals are present in the tills that occur in Allegan County. This method of analysis employs several pre-treatments that remove soluble salts, free calcium carbonates, organic matter, and free iron oxides from the sample. The clay-size fraction (<12 microns) is separated out by gravity fractionation and then deposited on a porous porcelain plate by vacuum suction, thus producing an oriented sample ready for x-ray analysis. Three samples (UT 104, MT 24, and LT 301) were pretreated using the above methods, and were analyzed by x—ray diffraction after each of the following treatments: 1) Mg saturated and glycerol solvated; 2) K saturated and dried at room temperature; 3) K saturated and heated to 3000 C; and 4) K saturated and heated to 5500 C. Illite is the only common clay mineral that produces a 10: peak, and is not affected by the chemical or heat treat- ments. Kaolinite will produce a 7; peak that will disappear after heating the sample to 5500 C. Vermiculite and chlorite 0 both produce 14A peaks after Mg saturation and glycerol 47 .mGOADMOOH mcHHmEMm ocflmnoz "w whomflm “IO-h‘xa it; o max—<26! >223". z ‘ r 1 v r v t I I fl 0 2 HI 2 m5- EM Inner Valparaiso mean .69 u. dov. .14 3. 2. l- —..LJJIJ._.L. .I. . . -- Lake Border mean .59 otdov. .11 l .40 .50 .60 .70 .0'0 .9'0 100 1T0 L20 1530 1.10 I30 0 C 7A/10A RATIO 0 0 Figure 9: Histogram showing 7A/10A ratio values for till collected from moraines in Allegan County. 59 have a mean 72/102 of 0.69 and a standard deviation of 0.14; and samples collected from the Outer Valparaiso Moraine have a mean 72/10: ratio of 0.58 and a standard deviation of 0.07. Histograms representing this data are shown in figure 9. The 72/10: ratios for samples 620 - 629, collected south of the Glenn Shores section where Covert Ridge intersects the Lake Michigan shoreline (figure 6), are listed in table 7 and are represented as a histogram in figure 7. The mean 72/102 ratio value for these samples is 0.63 and the standard deviation is 0.04. To determine the variability involved in the preparation and analysis of a till sample, a series of reproducibility tests were performed on three samples (UT 107; MT 25; LT 303) and the coefficient of variability (V) was calculated for each test. To determine the machine variability (Vm) (var- iability of the x-ray diffractometer and the variability in- volved in establishing the baseline for peak height measure- ments), the clay slide was left in the sample holder of the goniometer and x-rayed five times. The variability due to the orientation of clay minerals (Vr) within a prepared sample was determined by rotating a clay slide four times(900 ro- tations), x-raying the sample after each rotation. The var- iability involved in the preparation of a till sample (Vp) was determined by splitting a particular sample into five samples, preparing each separately, and x-raying each of these 0 O twice (180o rotations). The 7A/10A ratios were then calcu- ated for each test. 60 Based on the three till samples tested, Vm was deter- mined to be 3%-4%, Vr to be 3%-6%, and Vp to be 8%-10%. Obviously, sample preparation produced the largest coeffi- cient of variability in the 72/102 peak height ratios for each particular sample. VP' however, incorporates both Vm and Vr since each sample is x-rayed 10 times (incorporating Vm) at 10 different orientations (incorporating Vr)' Since Vp is by far the most important to consider, it was calculated for several additional till samples. The mean Vp values for each of the three till units exposed at the Glenn Shores section are: Upper (Saugatuck) Till 9.5% Middle (Ganges) Till 8.25% Lower (Glenn Shores) Till 14.0% DISCUSSION 0 o The 7A/10A peak height ratio values for the three till units eXposed in the Glenn Shores section show that semi- quantitative clay mineral analyses can indeed be used success- fully to differentiate multiple till units eXposed in strat- igraphic section in southwestern Michigan. Since the upper- most till unit exposed in the Glenn Shores section (the Saugatuck Till) can be physically traced southward to the Lake Border Morainic System (Covert Ridge), a distance of 1.8 miles ( 3 kilometers), this till unit provides a good 61 test of whether semi-quantitative clay mineral analyses can also be used to correlate till sheets to till that comprises moraines. A comparison of the 72/10: ratio values for the Saugatuck Till with the ratio values calculated for the till that comprises the Lake Border Morainic System (figures 8 and 9) shows that there is no significant difference between these tills; this is supported by the application of the t-test. o o A comparison of the 7A/10A peak height ratios for the samples collected from the three till units eXposed in the Glenn Shores section with the values for those samples col- lected from the Inner and Outer Valparaiso moraines in Allegan County (figures 8 and 9) clearly shows that the clay mineral content of the till that comprises these moraines is also most similar to that of the uppermost till at the Glenn Shores section (the Saugatuck Till). In fact, application of the t-test shows that there is no significant difference between samples collected from the Lake Border Morainic System, the Outer Valparaiso Moraine, and the Saugatuck Till. The t-test shows, however, that samples collected from the Inner Valparaiso Moraine are significantly different from the upper— most (Saugatuck) till, but are clearly more closely associated with this till than with the other two tills exposed at Glenn Shores. If the two anomolously high ratio values are excluded from the Inner Valparaiso Moraine values, the mean 72/1og ratio value for this till is lowered to 0.63 - very close to that of the Saugatuck Till. 62 It is not surprising that the clay mineral composition of the tills that comprise the Outer Valparaiso Moraine, Inner Valparaiso Moraine, Lake Border Morainic System, and the Saugatuck (upper) Till are similar. This is because the Inner and Outer Valparaiso moraines, the Lake Border Morainic System, and the Saugatuck Till were all formed after the Erie Interstade during a progressive retreat of the ice. The clay mineral composition of the till that comprises these moraines and the uppermost till unit at Glenn Shores would be expected to change significantly only if this progressive retreat were interupted by a later interstade. If the middle (Ganges) till is also Late Wisconsinin in age, it may correlate to older, pre-Erie Interstade moraines of the Lake Michigan Lobe. For example, if the lacustrine sand deposits that separate the Saugatuck and Ganges tills represent an Open lake in the Lake Michigan basin during the Erie Interstade, then the Ganges Till may correlate to either or both the Kalamazoo and Tekonsha moraines. If the Erie Interstade began as a retreat from the Tekonsha Moraine and ended with a readvance to the Kalamazoo Moraine, then the till comprising the Tekonsha Moraine may correlate to the Ganges Till and the till comprising the Kalamazoo Moraine would most likely correlate to the Saugatuck. If, however, the Erie Interstade began as a retreat from the Kalamazoo Moraine and ended with a readvance to the Outer Valparaiso Moraine, then the till comprising both the Tekonsha and Kalamazoo moraines should correlate to the Ganges (middle) Till. If either of the above correlations can be made in 63 future clay mineralogy studies, the Erie Interstade could be well defined for the Lake Michigan Ice Lobe, a significant contribution to the Pleistocene history of the Great Lakes region. The reason for the difference in the clay mineral comp- ositions of the three tills eXposed in the Glenn Shores sec- tion is not known with any certainty, but appears to be re— lated to significant glacial retreats. This is suggested by the occurence of lacustrine sediments between the till units. In fact, the retreat of the ice following the deposition of the Ganges Till was great enough to allow northward and east- ward drainage through the Straits of Mackinac or the Indian River lowlands (Gephart, et al., 1982). Each time one of these lakes develOped in the Lake Michigan basin, sediment from different source areas may have been washed in and de- posited on the lake bottom. Each subsequent advance of the ice margin would then have incorporated these lake sediments into the ice and re-deposited them as till with a unique clay mineral composition. Another possibility is that the lower two tills exposed at the Glenn Shores section were deposited from either the Saginaw or Huron-Erie lobes, rather than from the Lake Michigan Lobe. Since the ice would have advanced over different source areas,the composition of the lower and middle tills might be expected to differ significantly from the uppermost till unit at the section, derived from the Lake Michigan Lobe. This eXplanation can only be tested by independent provenence 64 indicators (i.e. strontium/rubidium ratio of feldspars and/ or heavy mineral assembleges). Also, the difference in the clay mineral compositions of the three tills exposed in the Glenn Shores section may be the result of some sort of pedogenic or weathering effect. For example, kaolinite has been produced in the laboratory by dissolving aluminosilicate minerals, mainly labradorite, microline,and augite, in organic acids. Silica and aluminum dissolves into solution, then re-combines to form kaolinite (Huang and Keller, 1970; Linares and Huertas, 1971; Hem and Lind, 1974). This explanation for the clay mineral differences in tills at the Glenn Shores section is unlikely, however, because of the short time intervals in which these processes could have taken place. Also, the till units at the Glenn Shores section are composed of dense clay-rich till, and are as much as 20 feet (6 meters) thick, making weathering through- out the till unlikely. In addition, vertical sampling of each till unit has shown no consistant vertical change or trend in the clay mineral composition with a particular till sheet that would suggest pedogenic clay mineral alteration. SUMMARY AND CONCLUS IONS The surficial deposits in Allegan County, Michigan are comprised mostly of drift associated with the progressive Late Wisconsinin retreat of the Lake Michigan Ice Lobe. The deglaciation of the county occured during the approximate period 14,800 to 13,800‘ years BP (Farrand and Eschman, 1974), and resulted in the formation of four moraines in Allegan County - the Outer and Inner Valparaiso moraines, and Covert Ridge and Zeeland Ridge of the Lake Border Morainic System, all of which roughly parallel the present Lake Michigan shoreline. Outwash deposits, lacustrine sediments, and till plains separate these moraines. Pre-Late Wisconsinin drift deposits are not exposed at the surface in Allegan County, but can be observed along the Lake Michigan shoreline in the southern part of the county. A sequence of tills and lacustrine sediments exposed in the Glenn Shores section about one mile (1.6 kilometers) south- west of the village of Glenn record several fluctuations of glacial ice during the Wisconsinin. The three till units exposed in the Glenn Shores section were sampled in order to determine whether or not these tills can be differentiated on the basis of clay mineral composition. 65 66 Till that comprises the moraines that occur further inland was also sampled, in order to determine if the till sheets exposed at Glenn Shores can be correlated to the moraines on the basis of clay mineral composition. Based on semi- quantitative clay mineral analyses of these till samples, the following conclusions have been determined: 1) 2) 3) 4) The dominant clay minerals that comprise the three till units eXposed in the Glenn Shores section are illite and kaolinite. Chlorite and vermiculite occur in much lesser amounts and do not significantly affect the 7: peaks. The illite content of the till increases with respect to kaolinite, from the lowermost till unit at Glenn Shores (Glenn Shores Till) to the uppermost till unit (Saugatuck Till). The three till units eXposed in the Glenn Shores section can be differentiated on the basis of 72/102 peak height ratios. Application of the t-test shows that the three till units are significantly different, based on their clay mineral composition, to the 99.9% confidence level. The mean 72/10: ratios for the three tills exposed at Glenn Shores are: Upper (Saugatuck) Till: 0.58 Middle (Ganges) Till: 0.85 Lower (Glenn Shores) Till: ' 1.22 The Saugatuck Till can be traced laterally for a distance of 1.8 miles (3 kilometers) to a shoreline exposure 5) 67 of the Lake Boarder Moraine, using semi—quantitative clay mineral analyses. The clay mineral compositions of till that comprise all of the moraines that occur in Allegan County (the Lake Boarder Morainic System, the Inner Valparaiso ' Moraine, and the Outer Valparaiso Moraine) are all most similar to that of the Saugatuck (upper) Till at Glenn Shores. The Saugatuck Till is therefore related to each of the moraines in Allegan County - a situation that would be expected with a progressive retreat of glacial ice. REFERENCES REFERENCES Black, R.F., 1978, Comment on"Great1akean Substage": A replacement for Valderan Substage in the Lake Michigan basin: by Evenson, E.B., and others, Quaternary Research, v.9, p.119—123. 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Willman, H.B., Glass, H.D. and Frye, J.C., 1963, Mineralogy of glacial tills and their weathering profiles in Illinois, Part I, Glacial Tills: Illinois State Geol. Surv., Circ. 347. HICHIGQN srnre UNIV. LIBRARIES ll)1111111HINUIWWIWI“INHIIINIIIWUIH1| 31293104117092