Silurian System undivided (ILSu;0)

Silurian System undivided, includes Sexton Creek Limestone, St. Clair Limestone, and Moccasin Springs Formation in southern Illinois; includes Wilhelmi Formation, Elwood Dolomite, Kankakee Dolomite, Joliet Dolomite, Sugar Run Dolomite, and Racine Dolomite in northeastern Illinois; includes Mosalem, Tete des Morts, Blanding, Sweeney, Marcus, and Racine Dolomites in northwestern Illinois.

State	Illinois
Name	Silurian System undivided
Geologic age	Silurian (Llandovery to Pridoli)
Lithologic constituents	Major Sedimentary > Carbonate > Dolostone (Bed, Glauconitic)Dolomite can be cherty, silty, shaly or argillaceous, or glauconitic. Sedimentary > Carbonate > Limestone (Bed, Reef)Moccasin Springs Formation and Racine Dolomite contain limestone reefs. Limestone can be cherty, silty, or shaly or argillaceous. Minor Sedimentary > Clastic > Mudstone > Shale (Bed)Shale can be dolomitic.
Comments	Thickness from stratigraphic columns (listed from oldest to youngest): Bowling Green Dol (0-50'), Sexton Creek Ls (0-125’), St. Clair Ls (0-150’) (of which the seventy-Six Shale Mbr occurs at the base), Moccasin Springs Fm (0-1,000’) in southern Illinois (south of 40 degrees north latitude); Wilhelmi Fm (0-100’), Elwood Dol (0-30’), Kankakee Dol (0-50’), Joliet Dol (0-80’), Sugar Run Dol (0-30’), and Racine Dol (0-300') in northern Illinois (north of 40 degrees north latitude); Mosalem Fm (0-100’), Tete des Morts Dol (0-24’), Blanding Dol (0-50’), Sweeney Dol (0-55’), Marcus Dol (0-45’), and Racine Dol (0-300’) in northwestern Illinois. The Schweizer Mbr occurs at the base of the Wilhelmi Fm and the Birds Mbr at the top; the Kankakee Dolomite is comprised, from oldest to youngest, of the Drummond, Offerman, Troutman, and Plaines Members; and the Joliet Dolomite is comprised, from oldest to youngest, of the Brandon Bridge, Markgraf, and Romeo Members. Unit name in original GIS (Esri shapefile IL_Geologic_Units_500K_2005_Py) is 'Silurian System'; name on Legend of geologic map is 'Silurian System undivided'.
Stratigraphic units	Bowling Green Dolomite, Seventy-Six Shale Member (of the St. Clair Ls), Schweizer Member and Birds Member (of the Wilhelmi Fm), Drummond Member, Offerman Member, Troutman Member, and Plaines Member of the Kankakee Dolomite), Brandon Bridge Member, Markgraf Member, and Romeo Member (of the Joliet Dolomite)
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 - Champaign - Cook - DeKalb - Douglas - DuPage - Ford - Greene - Henry - Iroquois - Jersey - Jo Daviess - Kane - Kankakee - Kendall - Lake - Lee - McHenry - Ogle - Pike - Rock Island - Scott - Stephenson - Union - Whiteside - Will

State

Illinois

Name

Silurian System undivided

Geologic age

Silurian (Llandovery to Pridoli)

Lithologic constituents

Major

Sedimentary > Carbonate > Dolostone (Bed, Glauconitic)Dolomite can be cherty, silty, shaly or argillaceous, or glauconitic.

Sedimentary > Carbonate > Limestone (Bed, Reef)Moccasin Springs Formation and Racine Dolomite contain limestone reefs. Limestone can be cherty, silty, or shaly or argillaceous.

Minor

Sedimentary > Clastic > Mudstone > Shale (Bed)Shale can be dolomitic.

Comments

Thickness from stratigraphic columns (listed from oldest to youngest): Bowling Green Dol (0-50'), Sexton Creek Ls (0-125’), St. Clair Ls (0-150’) (of which the seventy-Six Shale Mbr occurs at the base), Moccasin Springs Fm (0-1,000’) in southern Illinois (south of 40 degrees north latitude); Wilhelmi Fm (0-100’), Elwood Dol (0-30’), Kankakee Dol (0-50’), Joliet Dol (0-80’), Sugar Run Dol (0-30’), and Racine Dol (0-300') in northern Illinois (north of 40 degrees north latitude); Mosalem Fm (0-100’), Tete des Morts Dol (0-24’), Blanding Dol (0-50’), Sweeney Dol (0-55’), Marcus Dol (0-45’), and Racine Dol (0-300’) in northwestern Illinois. The Schweizer Mbr occurs at the base of the Wilhelmi Fm and the Birds Mbr at the top; the Kankakee Dolomite is comprised, from oldest to youngest, of the Drummond, Offerman, Troutman, and Plaines Members; and the Joliet Dolomite is comprised, from oldest to youngest, of the Brandon Bridge, Markgraf, and Romeo Members. Unit name in original GIS (Esri shapefile IL_Geologic_Units_500K_2005_Py) is 'Silurian System'; name on Legend of geologic map is 'Silurian System undivided'.

Stratigraphic units

Bowling Green Dolomite, Seventy-Six Shale Member (of the St. Clair Ls), Schweizer Member and Birds Member (of the Wilhelmi Fm), Drummond Member, Offerman Member, Troutman Member, and Plaines Member of the Kankakee Dolomite), Brandon Bridge Member, Markgraf Member, and Romeo Member (of the Joliet Dolomite)

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 - Champaign - Cook - DeKalb - Douglas - DuPage - Ford - Greene - Henry - Iroquois - Jersey - Jo Daviess - Kane - Kankakee - Kendall - Lake - Lee - McHenry - Ogle - Pike - Rock Island - Scott - Stephenson - Union - Whiteside - Will