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The St. Clair Limestone is a geologic unit in Arkansas, and Oklahoma. It is classified as a Geologic Member in Indiana and Missouri. It dates back to the Middle of Silurian period. It is high density, high magnesium dolomitic limestone. It was originally classified as a marble in Oklahoma due to the fact that it would hold a high polish, hence Marble City. It is sold in slabs and as tiles, in a similar manner as marble would be. This unit has many economic uses in Arkansas and Oklahoma. It is used as a construction material, manufacture of quicklime, and manganese deposits are mined as well. The St Clair is designated as a member of the Bainbridge Group in the State of Indiana. In Illinois, Missouri, Arkansas and Oklahoma it is part of the Hunton Megagroup. The St. Clair is the Basal member of the Niagaran Series, making it part of the Tippecanoe sequence. Throughout most of the Southern extent the unit is roughly 10 to 20' thick. Moving northward it thickens to approximately 80 to 100' thick in the Illinois Basin. At its northernmost reaches where it grades in to the Joliet and Racine Formations it is about 150' thick.

Appearance

The St. Clair is composed of course calcite grains to fine grains. It may contain partings of claystone or Mudstone. It can range in color from light-gray to chocolate brown, or even or purplish-black. Beds of pink crinoid remains are also found with in this unit, mostly toward the base.

Physical characteristics

Paleofauna

Brachiopods

Conodonts

Trilobites

See also

• List of fossiliferous stratigraphic units in Arkansas
• Paleontology in Arkansas

References

1. Penrose Jr., R.A.F. (1891). "Manganese: its uses, ores, and deposits". Annual Report of the Geological Survey of Arkansas for 1890. 1: 101–102, 112–114, 124–128, 166–203, 214–215.
2. Schrenk, Steven (September 2017). "The Grey American Limestone that Acts Like a Marble". The Slippery Rock Gazette: 36, 37.
3. "Saint Clair Limestone - Grey Limestone - StoneContact.com". www.stonecontact.com. Retrieved 2023-12-19.
4. Ham, W.E.; Dott, R.H.; Burwell, A.L.; Oakes, M.C. (1943). "GEOLOGY AND CHEMICAL COMPOSITION OF THE ST. CLAIR LIMESTONE NEAR MARBLE CITY OKLAHOMA" (PDF). Oklahoma Geological Survey. Retrieved 18 December 2023.
5. Willman, H. B.; Atherton, Elwood (1975). "Handbook of Illinois Stratigraphy: Illinois State Geological Survey". Handbook of Illinois Stratigraphy: Illinois State Geological Survey. Bulletin 95: 261.
6. "Saint Clair Linear | Polycor | Natural Stone | North America | Limestone". Polycor. Retrieved 2017-10-13.
7. Amsden, Thomas W. (1968). "Articulate Brachiopods of the St. Clair Limestone (Silurian), Arkansas, and the Clarita Formation (Silurian), Oklahoma". Memoir (The Paleontological Society). 1: i–117. JSTOR 1315506.
8. Craig, William (1968). The stratigraphy and conodont paleontology of Ordovician and Silurian strata, Batesville district, Independence and Izard counties, Arkansas (PhD). The University of Texas.
9. Holloway, David J. (January 1980). "Middle Silurian trilobites from Arkansas and Oklahoma, USA., Part I". Palaeontographica Abteilung A. 170: 1–85.

• Silurian Arkansas
• Silurian Illinois
• Silurian Indiana
• Silurian Missouri