The St. Clair Limestone is a geologic unit in

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the Osage ...

, and Oklahoma. It is classified as a Geologic Member in Indiana and Missouri. It dates back to the Middle of

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

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 Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ma ...

, and manganese deposits are mined as well. The St Clair is designated as a member of the Bainbridge Group in the State of

Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...

. In

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...

Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...

and

Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...

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 The Tippecanoe sequence was the cratonic sequence--that is, the marine transgression--that followed the Sauk sequence; it extended from roughly the Middle Ordovician to the Early Devonian. Sedimentary characteristics After the regression of the ...

. 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 The Illinois Basin is a Paleozoic depositional and structural basin in the United States, centered in and underlying most of the state of Illinois, and extending into southwestern Indiana and western Kentucky. The basin is elongate, extending app ...

. At its northernmost reaches where it grades in to the Joliet and

Racine Formation The Hunton Megagroup also Hunton Super Group, Hunton Group, Hunton Formation and Hunton Limestone is predominantly composed of carbonate rock, deposited between the Silurian and early to mid Devonian periods. In many States it acts as a reservoir ...

s 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 Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

. 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

* '' Ancillotoechia'' : ''A. marginata'' * '' Antirhynchonella'' : ''A. thomasi'' * ''

Atrypa ''Atrypa'' is a genus of brachiopod with shells round to short egg-shaped, covered with many fine radial ridges (or costae), that split further out and growth lines perpendicular to the costae and 2-3 times wider spaced. The pedunculate valve is ...

'' * '' Atrypina'' : ''A. erugata'' * '' Boucotides'' : ''B. barrandei'' * '' Brachymimulus'' : ''B. americanus'' : ''B. elongatus'' * '' Cymostrophia'' * '' Dicamaropsis'' : ''D. parva'' * '' Dicoelosia'' : ''D. bilobella'' * '' Dolrorthis'' : ''D. nanella'' * ''

Eospirifer ''Eospirifer'' is a genus of extinct brachiopod in the class Rhynchonellata (Articulata) and the order Spiriferida. Their fossils occur most commonly in marine calcareous, microbialitic mudstones with extensive mudcracks or shelly packstones, ge ...

'' : ''E. acutolineatus acutolineatus'' :''E. acutolineatus pentagonus'' * '' Hircinisca'' : ''H. havliceki'' * '' Homoeospirella'' : ''H. costatula arkansana'' : ''H. pygmaea'' * '' Howellella'' : ''H. splendens'' * '' Kozlowskiellina'' : ''K. vaningeni'' * '' Leangella'' : ''L. (Opikella) dissiticostella'' * ''

Leptaena ''Leptaena'' is an extinct genus of mid-sized brachiopod that existed from the Dariwilian epoch to the Emsian epoch, though some specimens have been found in strata as late in age as the Tournasian epoch. Like some other Strophomenids, ''Lept ...

'' * '' Lissostrophia'' * '' Meristina'' : ''M. clairensis'' * '' Nanospira'' : ''N. clairensis'' * '' Nucleospira'' : ''N. raritas'' * '' Onychotreta'' : ''O. angustata'' : ''O. lenta'' : ''O. (Eilotreta) miseri'' : ''O. multiplicata'' : ''O. (Lissotreta) plicata'' * '' Orthostrophella'' : ''O. clairensis'' * '' Oxoplecia'' : ''O. infrequens'' * '' Parastrophinella'' : ''P. lepida'' * '' Placotriplesia'' : ''P. juvenis'' : ''P. praecipta'' * '' Plectatrypa'' : ''P. arctoimbricata'' * ''

Plectodonta ''Plectodonta'' is an extinct genus of brachiopods which existed during the Devonian to Silurian of the United States, Australia, Canada, China, the Czech Republic, Czechoslovakia, Germany, Kazakhstan, Morocco, Poland, Spain, Ukraine, Argentina, ...

'' * '' Plicocyrtia'' : ''P. arkansana'' * '' Resserella'' * '' Shaleria'' * '' Streptis'' : ''S. glomerata'' * '' Virginiata'' : ''V. arkansana''

Conodont Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...
s

* ''

Acodus ''Acodus'' is an extinct genus of conodonts. Species * ''A. acutus'' * ''A. campanula'' * ''A. crassus'' * ''A. delicatus'' * ''A. deltatus'' * ''A. erectus'' * ''A. firmus'' * ''A. jonesi'' * ''A. kechikaensis'' * ''A. neodeltatus'' * ''A. ...

'' : ''A. inornatus'' : ''A. unicostatus'' * '' Ambalodus'' : ''A. triangularis'' * '' Belodella'' : ''B. flexa'' * '' Belodina'' : ''B. inclinata'' * '' Carniodus'' : ''C. carnulus'' : ''C. carnus'' * '' Cordylodus'' : ''C. delicatus'' : ''C. flexuosus'' * '' Distacodus'' : ''D. mehli'' : ''D. posterocostatus''> : ''D. procerus'' * ''

Distomodus ''Distomodus'' is an extinct genus of conodont Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were kno ...

'' : ''D. kentuckyensis'' * '' Drepanodus'' : ''D. homocurvatus'' * '' Hadrognathus'' : ''H. staurognathoides'' * '' Hindeodella'' : ''H. equidentata'' * '' Ligonodina'' : ''L. egregia'' : ''L. silurica'' * '' Neoprioniodus'' : ''N. costatus'' : ''N. excavatus'' : ''N. multiformis'' : ''N. subcarnus'' * '' Oistodus'' : ''O. inclinatus'' * '' Ozarkodina'' : ''O. gaertneri'' : ''O. inclinata'' : ''O. media'' : ''O. ziegleri'' * '' Paltodus'' : ''P. multicostatus'' : ''P. trigonius'' * '' Panderodus'' : ''P. gracilis'' : ''P. simplex'' : ''P. unicostatus'' * '' Plectospathodus'' : ''P. extensus'' * '' Pterospathodus'' : ''P. amorphognathoides'' * ''

Spathognathodus ''Spathognathodus'' is an extinct conodont genus in the family Spathognathodontidae. It is a non-Platform conodont, from the Pennsylvanian (Carboniferous).Pennsylvanian Nonplatform Conodont Genera, I: Spathognathodus. Glen K. Merrill, Journal o ...

'' : ''S. ranuliformis'' : ''S. rhenanus'' : ''S. wolfordi'' * '' Trichonodella'' : ''T. brassfieldensis'' : ''T. carinata'' : ''T. exacta'' : ''T. variflexa''

Trilobites

* ''

Ananaspis ''Ananaspis'' is a genus of trilobite in the order Phacopida, which existed in what is now the Czech Republic. It was described by Campbell in 1967, and the type species is ''Ananaspis fecundis'', which was originally described as ''Phacops fecu ...

'' * ''

Balizoma ''Balizoma'' is a genus of trilobites from the family Encrinuridae established by David J. Holloway in 1980. It has only been found in rocks of Silurian age. Its type species, ''B. variolaris'' (Brongniart, 1822), is currently the only named sp ...

'' * ''

Cheirurus ''Cheirurus'' (from Greek ''χείρ, cheir'' meaning "hand" and ''ουρά, oura'' meaning "tail") is a genus of phacopid trilobites that lived from the Ordovician to the Devonian. Its remains have been found in Africa, Asia, Australia, Euro ...

'' : ''C. phollikodes'' : ''C. prolixus'' * '' Cornuporoetus'' : ''C. kyphora'' * ''

Dalmanites ''Dalmanites'' is a genus of trilobite in the order Phacopida. They lived from the Late Ordovician to Middle Devonian. The trilobites of this genus have slightly convex exoskeletons with an average length of . The cephalon is semicircular or pa ...

'' : ''D. howelli'' : ''D. ptyktorhion'' * '' Decoroproetus'' : ''D. anaglyptus'' : ''D. corycoeus'' * ''

Deiphon ''Deiphon'' is a distinctive genus of Silurian phacopid trilobites of the family Cheiruridae found in Western and Central Europe, and in Central and Eastern United States. The type species, ''D. forbesi'', from England, Bohemia, and Sweden, was ...

'' : ''D. longifrons'' * '' Delops'' * ''

Diacalymene ''Diacalymene'' is a genus of trilobite from the order Phacopida, suborder Calymenina. It includes the species ''D. ouzregui'', ''D. clavicula'', ''D. diademata'' and ''D. gabrielsi''. It lived in the Ordovician and Silurian periods. Distributi ...

'' : ''D. altirostris'' * ''

Encrinurus ''Encrinurus'' is a long-lived genus of phacopid trilobites that lived in what are now Africa, Asia, Australia, Europe, North America, and South America from the middle Ordovician to the early Devonian from 472 to 412.3 mya, existing for appr ...

'' : ''E. egani'' * '' Eophacops'' : ''E. fontana'' * '' Harpidella'' : ''H. butorus'' : ''H. spinulocervix'' * '' Lepidoproetus'' : ''L. (Dipharangus) xeo'' * ''

Proetidae Proetidae is a family of proetid trilobites. The first species appeared in the Upper Ordovician, and the last genera survived until the Middle Permian. However, if the closely related family Phillipsiidae is actually a subfamily of Proetidae, t ...

'' * '' Proetus'' : ''P. vaningeni'' * '' Radnoria'' * '' Raphiophorus'' : ''R. niagarensis'' * '' Sphaerexochus'' : ''S. glaber'' * '' Staurocephalus'' : ''S. lagena'' : ''S. oarion'' * '' Sthenarocalymene'' : ''S. scutula'' * '' Tropidocoryphinae''

References

{{Chronostratigraphy of Indiana Silurian Arkansas Silurian Illinois Silurian Indiana Silurian Missouri