The St. Clair Limestone is a geologic unit in

Arkansas Arkansas ( ) is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma ...

, 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 23.5 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 third and shortest period of t ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

. 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 (formula: Ca O), 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-containin ...

, 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, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the s ...

. In

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') 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 border ...

and

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

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 or the marine transgression following the Sauk sequence; it extended from roughly the Middle Ordovician to the Early Devonian. The Tippecanoe is bound by two Unconformities, at the base by the Knox ...

. 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 a ...

. 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 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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

. It can range in color from light-gray to chocolate brown, or even or purplish-black. Beds of pink

crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

remains are also found with in this unit, mostly toward the base.

Physical characteristics

Paleofauna

Brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...
s

* '' Ancillotoechia'' : ''A. marginata'' * '' Antirhynchonella'' : ''A. thomasi'' * '' Atrypa'' * '' 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'' * '' 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'' * '' Plicocyrtia'' : ''P. arkansana'' * '' Resserella'' * '' Shaleria'' * '' Streptis'' : ''S. glomerata'' * '' Virginiata'' : ''V. arkansana''

Conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...
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 ''Cordylodus'' is an extinct genus of conodonts in the family Cordylodontidae. Use in stratigraphy It is suggested that ''Cordylodus andresi'' can be a marker of the Cambrian Stage 10. Distribution Fossils of ''Cordylodus'' have been found ...

'' : ''C. delicatus'' : ''C. flexuosus'' * '' Distacodus'' : ''D. mehli'' : ''D. posterocostatus''> : ''D. procerus'' * '' Distomodus'' : ''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 ''Ozarkodina'' is an extinct genus of conodonts in the family Spathognathodontidae. Use in stratigraphy ''Ozarkodina snajdri'' forms a subdivision of the '' Pseudomonoclimacis'' latilobus graptolite zone in the Burgsvik beds Silurian format ...

'' : ''O. gaertneri'' : ''O. inclinata'' : ''O. media'' : ''O. ziegleri'' * '' Paltodus'' : ''P. multicostatus'' : ''P. trigonius'' * '' Panderodus'' : ''P. gracilis'' : ''P. simplex'' : ''P. unicostatus'' * '' Plectospathodus'' : ''P. extensus'' * ''

Pterospathodus ''Pterospathodus'' is an extinct genus of conodont from the Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the ...

'' : ''P. amorphognathoides'' * '' Spathognathodus'' : ''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 fecun ...

'' * '' Balizoma'' * ''

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, Europe, ...

'' : ''C. phollikodes'' : ''C. prolixus'' * '' Cornuporoetus'' : ''C. kyphora'' * '' Dalmanites'' : ''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 ''Delops'' is a trilobite in the order Phacopida, that existed during the upper Silurian in what is now England. It was described by Rickards in 1964, and the type species is ''Delops obtusicaudatus'', which was originally described under the ge ...

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

Proetidae Proetidae is a family (biology), family of Proetida, 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 ...

'' * ''

Proetus In Greek mythology, Proetus (; Ancient Greek: Προῖτος ''Proitos'') may refer to the following personages: * Proetus, king of Argos and Tiryns, son of Abas and twin brother of Acrisius. *Proetus, a prince of Corinth as the son of Prince ...

'' : ''P. vaningeni'' * '' Radnoria'' * ''

Raphiophorus ''Raphiophorus'' is a genus of the family Raphiophoridae in the Ordovician and Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the ...

'' : ''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 Limestone formations of the United States Dolomite formations of the United States Geologic formations of Arkansas Geologic formations of Illinois Geologic formations of Indiana Geologic formations of Missouri Geologic formations of Oklahoma