USGS Home
Contact USGS
Search USGS

Mineral Resources > Online Spatial Data > Geology > by state > Illinois Geology

Geologic units in Illinois (state in United States)

[Additional scientific data in this geographic area]

Carbondale Formation (Pennsylvanian) at surface, covers 16 % of this area

Carbondale Formation

Lithology: shale; limestone; clay or mud; sandstone; coal; black shale

Lower Devonian (Devonian) at surface, covers 0.3 % of this area

Lower Devonian

Lithology: limestone; chert; dolostone (dolomite)

Lime Creek Formation (Phanerozoic | Paleozoic | Devonian-Late) at surface, covers < 0.1 % of this area

Fossiliferous limestone or dolomite in upper part with local stromatoporoid biostromes in north-central Iowa; extremely fossiliferous gray shale and argillaceous limestone in middle; gray shale in lower part with spore carps toward base.

Lithology: limestone; dolostone (dolomite); shale

Lower Valmeyeran (Keokuk-Sedalia) Series (Mississippian) at surface, covers 3 % of this area

Lower Valmeyeran (Keokuk-Sedalia) Series

Lithology: limestone; shale

Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series (Mississippian) at surface, covers 3 % of this area

Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series

Lithology: limestone; siltstone; shale

Middle Devonian (Devonian) at surface, covers 1 % of this area

Middle Devonian

Lithology: limestone; shale; dolostone (dolomite); sandstone; evaporite; sedimentary breccia;

Raccoon Creek Group (Pennsylvanian) at surface, covers < 0.1 % of this area

Raccoon Creek Group - Mostly shale and sandstone; also includes thin beds of limestone, clay, and coal. B, Buffaloville Coal Member; LB, Lower Block Coal Member

Lithology: shale; sandstone; limestone; clay or mud; coal

Bond Formation (Pennsylvanian) at surface, covers 12 % of this area

Bond Formation

Lithology: limestone; shale; sandstone; clay or mud; coal; black shale

Upper Valmeyeran (Aux Vases, Ste. Genevieve, St. Louis) Series (Mississippian) at surface, covers 2 % of this area

Upper Valmeyeran (Aux Vases, Ste. Genevieve, St. Louis) Series

Lithology: limestone; sandstone; dolostone (dolomite); sedimentary breccia; chert

Abbott Formation (Pennsylvanian) at surface, covers 2 % of this area

Abbott Formation

Lithology: sandstone; shale; clay or mud; coal

Silurian (Silurian) at surface, covers 10 % of this area

Silurian

Lithology: dolostone (dolomite); limestone; coral

Modesto Formation (Pennsylvanian) at surface, covers 13 % of this area

Modesto Formation

Lithology: shale; sandstone; limestone; clay or mud; coal; black shale

Maquoketa Group (Ordovician) at surface, covers 4 % of this area

Maquoketa Group

Lithology: shale; limestone; siltstone

Meramec Series (Phanerozoic | Paleozoic | Carboniferous Mississippian-Late) at surface, covers < 0.1 % of this area

Ste. Genevieve Limestone- fossiliferous limestone and red and green shale. Approx. thickness 50 ft. St. Louis Limestone- limestone and dolomite, sandstone locally perdominant; locally contains chert. Spergen Formation- sandy micaceous dolomite.

Lithology: limestone; dolostone (dolomite); shale; sandstone; chert

Silurian, undivided (Silurian) at surface, covers < 0.1 % of this area

Silurian, undivided - Dolomite, undivided; includes Cayugan, Niagaran, and Alexandrian series

Lithology: dolostone (dolomite)

Mattoon Formation (Pennsylvanian) at surface, covers 13 % of this area

Mattoon Formation

Lithology: shale; sandstone; limestone; coal; black shale

Cambrian (Cambrian) at surface, covers 0.2 % of this area

Cambrian

Lithology: sandstone; dolostone (dolomite); shale; siltstone

Upper Chesterian (Grove Church - Tar Springs) Series (Mississippian) at surface, covers 0.8 % of this area

Upper Chesterian (Grove Church - Tar Springs) Series

Lithology: sandstone; shale; limestone; chert; coal

Spoon Formation (Pennsylvanian) at surface, covers 6 % of this area

Spoon (includes Pa in northeast)

Lithology: shale; sandstone; clay or mud; limestone; coal; black shale

HOLOCENE SERIES (Phanerozoic | Cenozoic | Quaternary | Holocene) at surface, covers < 0.1 % of this area

HOLOCENE SERIES - Alluvium - clay, silt, sand, and gravel

Lithology: clay or mud; silt; sand; gravel

Mattoon Formation (Pennsylvanian) at surface, covers < 0.1 % of this area

Mattoon Formation - Mostly shale and sandstone; also includes thin beds of coal

Lithology: shale; sandstone; coal

Kinderhookian Series (Mississippian) at surface, covers 0.7 % of this area

Kinderhookian Series

Lithology: limestone; shale; siltstone

Galena-Platteville Groups (Ordovician) at surface, covers 6 % of this area

Galena-Platteville Groups

Lithology: limestone; dolostone (dolomite); shale

Cedar Valley Limestone (Phanerozoic | Paleozoic | Devonian-Middle) at surface, covers < 0.1 % of this area

Finely crystalline and clastic limestone in upper part with coral and stromatoporoid-rich zones; brown, dolomitic limestone with biostromes of corals and stromatoporoids in middle part; gray argillaceous, fossiliferous limestone in lower part; dominantly dolomite with intervals of gypsum in the subsurface of central and southwestern Iowa.

Lithology: limestone; dolostone (dolomite)

Cretaceous (Cretaceous) at surface, covers 0.7 % of this area

Cretaceous

Lithology: sandstone; clay or mud; gravel; siltstone

Upper Devonian (Devonian) at surface, covers 1 % of this area

Upper Devonian

Lithology: shale; black shale; limestone; sandstone

Lower Chesterian (Glen Dean - Renault) Series (Mississippian) at surface, covers 1 % of this area

Lower Chersterian (Glen Dean - Renault) Series

Lithology: limestone; shale ; sandstone; coal; chert

Bond Formation (Pennsylvanian) at surface, covers < 0.1 % of this area

Bond Formation - Mostly shale and sandstone; also includes thin beds of limestone and coal

Lithology: shale; sandstone; limestone; coal

Caseyville Formation (Pennsylvanian) at surface, covers 0.7 % of this area

Caseyville

Lithology: sandstone; shale; coal; claystone; gravel

Ancell Group (Ordovician) at surface, covers 1 % of this area

Ancell Group

Lithology: sandstone; dolostone (dolomite); limestone; evaporite

Maquoketa Formation (Phanerozoic | Paleozoic | Ordovician-Late [Cincinnatian]) at surface, covers < 0.1 % of this area

Predominantly grayish-green shale in east-central area; predominantly brown dolomite and chert in the subsurface of north-central and western areas; red shale with limonite or hematite pellets (Neda) occurs locally at top.

Lithology: shale; dolostone (dolomite); chert

Prairie du Chien Group (Ordovician) at surface, covers 0.7 % of this area

Prairie du Chien Group

Lithology: dolostone (dolomite); sandstone

Wapsipinicon Formation (Phanerozoic | Paleozoic | Devonian-Middle) at surface, covers < 0.1 % of this area

In descending order, finely crystalline limestone; brown dolomite with gypsum; gray, sandy shale and argillcceous limestone; and massive, finely crystalline, dolomitic limestone and pale-orange dolomite.

Lithology: dolostone (dolomite); limestone; shale; evaporite

Carbondale Group (Pennsylvanian) at surface, covers < 0.1 % of this area

Carbondale Group - Mostly shale and sandstone; also includes thin beds of limestone, clay, and coal. S, Springfield Coal Member

Lithology: shale; sandstone; limestone; clay or mud; coal

Kinderhook Series (Phanerozoic | Paleozoic | Carboniferous Mississippian-Early) at surface, covers < 0.1 % of this area

Gilmore City Limestone- light gray fossiliferous limestone, commonly oolitic. Approx thickness 155 ft. Hampton Formation- limestone and dolomite; fossiliferous gray chert in lower portion. Approx. thickness 150 ft. Starrs Cave Formation- bio-fragmental limestone; oolitic in part. Approx thickness 15 ft. Prospect Hill Formation- greenish-gray siltstone. Approx thickness 90 ft. McCraney Limestone- very pale orange to pale yellowish-brown sublithographic limestone and brown dolomite. Approx thickness 65 ft.

Lithology: limestone; dolostone (dolomite); siltstone; chert

Sinnipee Group (Ordovician) at surface, covers < 0.1 % of this area

Sinnipee Group - Dolomite with some limestone and shale; includes Galena, Decorah, and Platteville Formations

Lithology: dolostone (dolomite); limestone; shale

Maquoketa Formation (Ordovician) at surface, covers < 0.1 % of this area

Maquoketa Formation - Shale, dolomitic shale and dolomite; includes overlying Neda Formation (age uncertain) consisting of oolitic iron oxides and shale

Lithology: shale; dolostone (dolomite)

Borden Group (Mississippian) at surface, covers < 0.1 % of this area

Borden Group - Mostly siltstone; lenses of crinodial limestone in upper part. Much cherty and silty limestone and dolomite in northwest. NP, top of New Providence Shale

Lithology: siltstone; limestone; dolostone (dolomite); chert

Patoka and Shelburn Formations (Pennsylvanian) at surface, covers < 0.1 % of this area

Patoka and Shelburn Formations - Mostly shale and sandstone; also includes thin beds of limestone and coal. WF, top of West Franklin member

Lithology: shale; sandstone; limestone; coal

Cherokee Group (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Middle [Des Moines]) at surface, covers < 0.1 % of this area

Cyclic deposits with carbonaceous shale, clay, siltstone, with lesser sandstone, and thick coal beds; minor but persistent limestone beds; may include parts of Atoka or Morrow Series.

Lithology: shale; claystone; siltstone; sandstone; coal; limestone

Yellow Spring Group (Phanerozoic | Paleozoic | Devonian-Late) at surface, covers < 0.1 % of this area

English River Formation- gray siltstone; southeastern Iowa; locally in north-central Iowa. Approx thickness 23 ft. Maple Mill Shale- greenish-gray shale, silty in upper part; contains spore carps; discoidal, concentrically laminated limonite pellets at top in the subsurface of central and southwestern Iowa. Approx thickness 300 ft. Aplington Formation- argillaceous, silty dolomite and minor chert; quartz geodes. Approx thickness 40 ft. Sheffield Formation- greenish-gray shale in central Iowa and in the subsurface of southwestern Iowa; in decending order, dusky yellowish-brown shale followed by greenish-gray shale, very light olive-gray shale, and dark olive-gray shale in the subsurface of southeastern Iowa. Approx thickness 95 ft.

Lithology: shale; dolostone (dolomite); siltstone

Galena-Decorah-Platteville Formations (Phanerozoic | Paleozoic | Ordovician-Middle [Mohawkian]) at surface, covers < 0.1 % of this area

Galena FM- dolomite, minor limestone; chert in lower half. Approx thickness 230 ft. Decorah FM- brown limestone and dolomite; gray-green and brown shales at top and base. Approx thickness 60 ft. Platteville FM- fossiliferous gray limestone and brown dolomite; grayish-green shale at base (Glenwood). Fine- to medium-grained sandstone occurs above the Glenwood in the subsurface of southeastern Iowa. Approx thickness 110 ft

Lithology: dolostone (dolomite); limestone; shale; sandstone; chert

Tertiary - Paleocene, Eocene (Tertiary) at surface, covers 0.2 % of this area

Tertiary - Paleocene, Eocene

Lithology: sandstone; clay or mud; gravel; silt

Cambrian, undivided (Cambrian) at surface, covers < 0.1 % of this area

Cambrian, undivided - Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Lithology: sandstone; dolostone (dolomite); shale

Wabash Formation (Silurian) at surface, covers < 0.1 % of this area

Wabash Formation - Limestone, dolomite, and argillaceous dolomite

Lithology: limestone; dolostone (dolomite)

Alexandrian Series (Phanerozoic | Paleozoic | Silurian) at surface, covers < 0.1 % of this area

Kankakee Formation- light colored dolomite; contains much interbedded chert. Approx thickness 155 ft. Englewood Dolomite- gray, sandy, silty, argillaceous dolomite. Approx thickness 55 ft

Lithology: dolostone (dolomite); chert

Ancell Group (Ordovician) at surface, covers < 0.1 % of this area

Ancell Group - Orthoquartzitic sandstone with minor limestone, shale and conglomerate; includes Glenwood and St. Peter Formations

Lithology: sandstone; limestone; shale; conglomerate

Niagaran Series (Phanerozoic | Paleozoic | Silurian) at surface, covers < 0.1 % of this area

Gower Dolomite- LeClaire (reef phase) tough, greenish-blue dolomite; Anamosa (inner-reef) soft, yellowish-brown, thin-bedded dolomite. Hopkinton Dolomite- light colored dolomite with nodular chert.

Lithology: dolostone (dolomite); chert

Prairie du Chien Group (Ordovician) at surface, covers < 0.1 % of this area

Prairie du Chien Group - Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Lithology: dolostone (dolomite); sandstone; shale

St. Peter Sandstone (Phanerozoic | Paleozoic | Ordovician-Early [Chazyan]) at surface, covers < 0.1 % of this area

Coarse to fine, rounded, frosted sand grains; minor green shale stringers.

Lithology: sandstone; shale

Osage Series (Phanerozoic | Paleozoic | Carboniferous Mississippian-Early) at surface, covers < 0.1 % of this area

Warsaw Formation- gray, dolomitic shale and argillaceous dolomite; chalcedonic chert. Locally contains many geodes.Approx thickness 85 ft. Keokuk Limestone- fossiliferous, gray or brown limestone and dolomite; gray and brown chert with white spicules, locally predominant in lower portion; minor brown or gray shale. Approx thickness 90 ft. Burlington Limestone- gray, fossiliferous limestone and darker gray dolomite; white and gray mottled fossiliferous chert, locally contains dolomite crystals; two widespread glauconite zones; basal sandstone locally in southeastern Iowa. Approx thickness 80 ft.

Lithology: dolostone (dolomite); limestone; shale; chert; sandstone