Maquoketa Formation or Group (ILOm;0)

Maquoketa Formation or Group, includes Cape Limestone, Cape La Croix Shale, Thebes Sandstone, Orchard Creek Shale, Girardeau Limestone, and Leemon Formation in southern Illinois; includes Scales Shale, Fort Atkinson Limestone, Brainard Shale, and Neda Formation in northern Illinois; includes Noix Oolite in western Illinois.

State	Illinois
Name	Maquoketa Formation or Group
Geologic age	Upper Ordovician (Stage 6 to Hirnatian)
Lithologic constituents	Major Sedimentary > Clastic > Mudstone > Shale (Bed, Calcareous)Shale can be silty, dolomitic, or calcareous. Sedimentary > Carbonate > Limestone (Bed)Limestone can be oolitic, bioclastic, or shaly or argillaceous. Minor Sedimentary > Clastic > Sandstone (Bed, Calcareous)Sandstone can be shaly or argillaceous, or calcareous. Sedimentary > Carbonate > Dolostone (Bed)Dolomite can be bioclastic.
Comments	Thickness from stratigraphic columns: Cape Ls (0-8’), Maquoketa Fm (0-325’), Leemon Fm (0-25’) in southern Illinois (south of 40 degrees north latitude); Scales Sh (0-135’), Ft. Atkinson Ls (0-60’), Brainard Sh (0-100’), and Neda Fm (0-15’) in northern Illinois (north of 40 degrees north latitude). The Maquoketa Fm is comprised, from oldest to youngest, of the Cape La Croix Shale, Thebes Sandstone, Orchard Creek Shale, Girardeau Limestone, and Noix Oolite in southern Illinois (south of 40 degrees north latitude); the Maquoketa Group is comprised, from oldest to youngest, of the Scales Shale, Fort Atkinson Limestone, Brainard Shale, and Neda Formation in northern Illinois (north of 40 degrees north latitude). Unit name in original GIS (Esri shapefile IL_Geologic_Units_500K_2005_Py) is 'Maquoketa Shale Group'; name on Legend of geologic map is 'Maquoketa Formation or Group'.
References	Kolata, D.R., comp., 2005, Bedrock Geology of Illinois: Champaign, Ill., Illinois State Geological Survey, Illinois Map Series 14, scale 1:500,000.
NGMDB product	NGMDB product page for 87181
Counties	Alexander - Boone - Bureau - Calhoun - Carroll - Cook - DeKalb - DuPage - Greene - Grundy - Iroquois - Jersey - Jo Daviess - Kane - Kankakee - Kendall - Lake - La Salle - Lee - McHenry - Monroe - Ogle - Pike - Stephenson - Union - Whiteside - Will

State

Illinois

Name

Maquoketa Formation or Group

Geologic age

Upper Ordovician (Stage 6 to Hirnatian)

Lithologic constituents

Major

Sedimentary > Clastic > Mudstone > Shale (Bed, Calcareous)Shale can be silty, dolomitic, or calcareous.

Sedimentary > Carbonate > Limestone (Bed)Limestone can be oolitic, bioclastic, or shaly or argillaceous.

Minor

Sedimentary > Clastic > Sandstone (Bed, Calcareous)Sandstone can be shaly or argillaceous, or calcareous.

Sedimentary > Carbonate > Dolostone (Bed)Dolomite can be bioclastic.

Comments

Thickness from stratigraphic columns: Cape Ls (0-8’), Maquoketa Fm (0-325’), Leemon Fm (0-25’) in southern Illinois (south of 40 degrees north latitude); Scales Sh (0-135’), Ft. Atkinson Ls (0-60’), Brainard Sh (0-100’), and Neda Fm (0-15’) in northern Illinois (north of 40 degrees north latitude). The Maquoketa Fm is comprised, from oldest to youngest, of the Cape La Croix Shale, Thebes Sandstone, Orchard Creek Shale, Girardeau Limestone, and Noix Oolite in southern Illinois (south of 40 degrees north latitude); the Maquoketa Group is comprised, from oldest to youngest, of the Scales Shale, Fort Atkinson Limestone, Brainard Shale, and Neda Formation in northern Illinois (north of 40 degrees north latitude). Unit name in original GIS (Esri shapefile IL_Geologic_Units_500K_2005_Py) is 'Maquoketa Shale Group'; name on Legend of geologic map is 'Maquoketa Formation or Group'.

References

Kolata, D.R., comp., 2005, Bedrock Geology of Illinois: Champaign, Ill., Illinois State Geological Survey, Illinois Map Series 14, scale 1:500,000.

NGMDB product

NGMDB product page for 87181

Counties

Alexander - Boone - Bureau - Calhoun - Carroll - Cook - DeKalb - DuPage - Greene - Grundy - Iroquois - Jersey - Jo Daviess - Kane - Kankakee - Kendall - Lake - La Salle - Lee - McHenry - Monroe - Ogle - Pike - Stephenson - Union - Whiteside - Will