s G£0l0GfCAl f' 14.GS: ILUMOtS CIR 528 SURVEY LIBRARY c.4 OSTRATIGRAPHY ----er AND DEPOSITIONAL ENVIRONMENTS OF THE MAQUOKETA GROUP (ORDOVICIAN) IN NORTHERN ILLINOIS Dennis R. Kolata and Anne M. Graese Illinois Department of Energy and Natural Resources CIRCULAR 528 STATE GEOLOG ICAL SURVEY DIVISION 1983 Cover photo: Slab of Brainard dolomite from near Pearl City, Stephenson County, Illinois (locality 6), containing numerous specimens of St rophomena sp. PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS/1983/3000 Kolata, Dennis R. Lithostratigraphy and depositional environments of the Maquo­ keta Group (Ordovician) in northern Illinois Dennis R. Kolata I and Anne M. Graese. - Champaign, IL : Illinois State Geological Survey, 1983. 49 p. ; 28 cm. - (Circular Illinois State Geological Survey I Division ; 528) 1. Maquoketa Group-Illinois. Geology, Stratigraphic-Ordovician. 2. I. Graese, Anne M. Title. Series. 11. 111. Illustrator: Craig Ronto Editor: St enzel £. W. LITHOSTRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE MAQUOKETA GROUP (ORDOVICIAN) IN NORTHERN ILLINOIS Dennis R. Kolata and Anne M. Graese l.LBNots GfOlOGBCA1 SURVEY lU:JRAAY CIRCULAR ILLINOIS STATE GEOLOG ICAL SURVEY 528 Robert E. Bergstrom, Chief 1983 Natural Resources Building East Peabody Drive 615 Champaign, Illinois 61820 CONTENTS ABSTRACT FIGU RES ACKNOWLEDGMENTS 1 1. Thickness of the Maquoketa Group in the Midcontinent 2 INTRODUCTION 2 2. Wells and outcrops used in this study 3 METHODS OF STU DY 3 3. General stratigraphic relations of the Maquoketa Group in northern Illinois 4 LITHOST RAT IGRAPHY OF THE MAQUOKETA GROUP 4 4. Classification of the Ordovician System in Illinois 5 Distribution and Thickness 5 5. Structure map of the top of the Franconia Formation 6 Age and Correlation 5 6. Cross section of the Maquoketa Group from Rock Island County to Kankakee County, Illinois 8 STRUCTU RAL FRAMEWORK OF NORTHERN ILLINOIS 6 7. Scales Formation type section 9 8. Cross section shows correlations between key basal SCA LES FORMATION Maquoketa outcrops in northwestern linois 10 7 11 Lithology 11 9. Cross section of the Maquoketa Group from Milwaukee Distribution and Thickness 13 County, Wisconsin, to Kankakee County, Illinois 10 Stratigraphic Relations 14 10. X-ray diffraction pattern of clay fraction in Scales shale 12 Geophysical Log Characteristics 14 11. Radiograph of Scales shale 12 Faunal Characteristics 18 12. Lithofacies interpretation of the Scales Formation 13 Argo-Fay Bed 18 13. Scales Mound Northeast Section 14 14. Mt. Carroll Southwest Section 15 FORT AT KINSON FORMATION 18 15. Cross section of the Maquoketa Group from Cook County, Lithology 18 Illinois, to Parker County, Indiana 15 Distribution and Thickness 20 16. Characteristic fossils of the Maquoketa Group 16 Stratigraphic Relations 20 17. Characteristic fossils of the Maquoketa Group 17 Geophysical Log Characteristics 22 18. Lithofacies interpretation of the Fort Atkinson Faunal Characteristics 22 Formation 19 19. Photomicrograph of crinoid-bryozoan lime grainstone BRAINARD FORMAT ION 22 from Fort Atkinson Formation 20 Lithology 22 20. Fort Atkinson Formation at the Divine Section 21 Distribution and Thickness 24 21. Fort Atkinson strata along Du Page River 21 Stratigraphic Relations 25 22. Cross section of the Maquoketa Group from De Kalb Geophysical Log Characteristics 25 County to Cook County, Illinois 22 Faunal Characteristics 26 23. X-ray diffraction pattern of clay fraction in Brainard shale 23 NEDA FORMATION 27 24. Maquoketa Group in Hillside Quarry, Cook County 24 Lithology 29 25. Lithofacies interpretation of the Brainard Formation 25 Distribution and Thickness 29 26. Wacker Southeast Section 26 . Stratigraphic Relations 30 27. Angular unconformity in Hillside Quarry, Cook County 27 Geophysical Log Characteristics 31 28. Radiograph of Brainard dolomite 28 Age and Correlation 31 29. Radiograph of Brainard shale 28 30. Radiograph of Neda shale 29 DEPOSIT IONAL ENVI RONMENTS 31 31. Photomicrograph of dolomitic Neda shale 30 Scales Formation 31 32. Distribution of Neda Formation 30 Fort Atkinson Formation 32 Brainard Formation 32 PLATES Neda Formation 32 1a. Thickness of the Maquoketa Group in northern Illinois 1 b. Thickness of the Scales Formation REFERENCES 34 1c. Thickness of the Fort Atkinson Formation APPENDIX A. Geologic sections of selected outcrops 36 1d. Thickness of the Brainard and Neda Formations APPENDIX B. Well records 39 2. Fence diagram of the Maquoketa Group LITHOSTRA TIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE MAQUOKETA GROUP (ORDOVICIAN) IN NORTHERN ILLINOIS Dennis R. Kolata and Anne M. Graese ABSTRACT Neda Formation-a blackish red to very dusky­ The Cincinnatian (late Ordovician) Maquoketa Group in red, silty, hematitic shale containing flattened, the 25-county area of northern Illinois consists primarily concentrically layered, iron-oxide spheroids about of olive -gray and greenish gray shale and some dolomite 0.50 millimeters in diameter. and limestone; the group is generally about 200 feet (60 m) thick. Due to post-Silurian erosion, the Maquoketa is In northwestern Illinois, where the Fort Atkinson For­ missing in north - central Illinois. It rests disconformably mation grades to shale, the entire stratigraphic section is on the Galena Dolomite Group and is disconformably referred to as the Maquoketa Group undifferentiated. overlain by Silurian strata, which locally truncate the The Maquoketa was deposited on a broad shelf in a upper part of the Maquoketa. Where the Silurian was widespread epicontinental sea. Most Scales sediments removed by erosion, the Maquoketa is overlain by strata accumulated in relatively deep, oxygen-poor water that of Pennsylvanian or Pleistocene age. was infrequently mixed. Local deposits of phosphorite The Maquoketa Group is divided into four formations were probably formed by upwelling of phosphate-rich in northern Illinois, in ascending order: water at the continental margin. Near the end of Scales deposition, there was a gradual shallowing of the sea in Scales Formation-a mainly light olive-gray to northern Illinois and a reduced influx of terrigenous material. olive- black, silty, calcareous, laminated to intensely The relatively pure, fossiliferous carbonates of the suc­ bioturbated shale, locally containing biogenic ceeding Fort Atkinson Formation were deposited in shal­ carbonates and phosphorite. The Argo-Fay Bed low, well aerated water of normal marine salinity. The (new stratigraphic unit) is a 1 to 2 foot (0.3 to Brainard Formation records two depositional environments: 0.6 m) bed of hard, brownish black to black, the base largely marks a change to predominantly shale carbonaceous, fissile clayshale that occurs in the deposition in a relatively deep, oxygen-poor environment; lower part of the Sca les in northwestern llinois. while in the upper Brainard, the locally abundant and 1 diverse fauna indicate shallower, more aerated conditions. Fort Atkinson Formation-a light olive-gray to The Neda appears to be, in part, a product of lateritic olive-gray and yellowish brown to dark yellowish weathering during the Richmondian (late Ordovician) brown, pure to argillaceous, crinoid-bryozoan­ glacio-eustatic drop in sea level. brachiopod lime or dolomite packstone and grainstone, and to a lesser extent, wackestone. ACKNOWLEDGMENTS We thank H. B. Willman, T. C. Buschbach, Elwood Ather­ Brainard Formation-a mainly greenish gray to ton, Robert B. Votaw, and John B. Droste for suggestions dark greenish gray, silty, fossiliferous, calcareous during this investigation. Mary H. Barrows conducted the shale with interbeds of dolomite or limestone. reflected light analyses and assisted with the field work. THE MAQUOKETA GROUP IN ILLINOIS INTRODUCT ION As the general characteristics of the Maquoketa rocks The Cincinnatian (late Ordovician) Maquoketa Group, a in northern Illinois factor into many geologic and engi­ body of predominantly olive- gray and greenish gray shale, neering problems, detailed lithologic and stratigraphic and lesser amounts of limestone and dolomite, is distributed information is essential. For example, groundwater move­ over a large part of the Midcontinent, including Illinois ment is greatly influenced by local stratigraphic variations (fig. 1 ). The Maquoketa is part of a wedge of terrigenous of the Maquoketa. Because of its generally low hydraulic elastic rocks that thicken eastward toward the Appalachian conductivity, the Maquoketa limits the vertical movement region. In the 23-county study area of northernmost Illinois of groundwater, and as a result, is the main confining (fig. 2). the Maquoketa is approximately 200 feet (60 m) stratigraphic unit in the area. Its effectiveness as an aqui­ thick and occurs at or shortly below the bedrock surface, tard, however, is largely related to variations in lithology, except in the north-central part of the state where erosion thickness, and distribution of the formations that compose has removed part or all of it. The Maquoketa covers approx­ the Maquoketa. In engineering projects such as excavations 2 imately 9,000 square miles (23,400 km ) and has a volume for foundations, highways, dams, and tunnels, the physical of about 350 cubic miles of strata in these counties (fig. 2). properties of the Maquoketa area a major consideration. NOR TH DAKOTA (I \ - -- -- - -- - / ! ( \ MINNESOTA I I SOUTH DA KOTA � ' ---- MISSOURI K KENTUC Y / - - --- -- -- ____ jI / I ---- - � -- OKLAHOMA TENNESSEE I j/. I/,......./ ISGS 1982 Figure Thickness of the Maquoketa and equivalent strata in the Midcontinent,