The Hunton Megagroup also Hunton Super Group, Hunton Group, Hunton Formation and Hunton Limestone is predominantly composed of

carbonate rock Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and Dolomite (rock), dolomite rock (also kn ...

, deposited between 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 Devonian Period, Mya. The Silurian is the third and shortest period of t ...

and early to mid

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

periods. In many States it acts as a reservoir for both hydrocarbons and water.

Stratigraphy

Clifty Limestone

The Clifty Limestone is a Middle

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

in the

Ozark Plateau The Ozarks, also known as the Ozark Mountains, Ozark Highlands or Ozark Plateau, is a physiographic region in the U.S. states of Missouri, Arkansas, and Oklahoma, as well as a small area in the southeastern corner of Kansas. The Ozarks cov ...

s of

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 ...

. This thin formation can but up to 4 feet thick. The name was introduced in 1916 by Albert Homer Purdue and Hugh Dinsmore Miser in their study of northern Arkansas. They designated a

stratotype In geology, a stratotype or type section is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the ...

along the East Fork of Little Clifty Creek in Benton County, Arkansas. The Clifty Limestone is very sandy, light blue to bluish grey.

Penters Chert

The Penters Chert is a

in the

s of

. Its thickness ranges up to 90'. The name was introduced in 1921 by Hugh Dinsmore Miser in his study of Arkansas. Miser designated a type locality near the old Penters Bluff railroad station in Izard County, Arkansas, however, he did not assign a

. As of 2017, a reference section has not been designated for this unit.

Bailey Limestone

The Bailey Limestone was first described by Ulrich, Buckley and Buehler, 1904, p. 110. It was named for the now abandoned town of Bailey's Landing near the village of Grand Eddy, on the

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

. The formation is gray to greenish gray, silty with chert inclusions, thin-bedded, very hard limestone.

Lafferty Limestone

The Lafferty Limestone is a Middle to Late

in the

s of

. The name was introduced in 1921 by Hugh Dinsmore Miser in his study of Arkansas, replacing part of the upper St. Clair Limestone. Miser designated a type locality at Tate Spring, located 1.25 miles north of the site of the old Penters Bluff railroad station in Izard County, Arkansas, however, he did not assign a

. As of 2017, a reference section has not been designated for this unit.

Paleofauna

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'' * '' Belodella'' : ''B. triangularis'' * '' Distacodus'' : ''D. mehli'' : ''D. posterocostatus'' : ''D. procerus'' * '' Hindeodella'' : ''H. equidentata'' * '' Ligonodina'' : ''L. silurica'' * '' Lonchodina'' : ''L. cristagalli'' : ''L. walliseri'' * '' Neoprioniodus'' : ''N. excavatus'' : ''N. multiformis'' * '' Ozarkodina'' : ''O. fundamentata'' : ''O. media'' : ''O. ziegleri'' * '' Paltodus'' : ''P. multicostatus'' : ''P. trigonius'' * '' Panderodus'' : ''P. gracilis'' : ''P. simplex'' : ''P. unicostatus'' * '' Plectospathodus'' : ''P. extensus'' : ''P. flexuosus'' * '' Polygnathoides'' : ''P. siluricus'' * ''

Polygnathus ''Polygnathus'' is an extinct genus of conodonts. Species * †''Polygnathus acrinodosus'' Aboussalam 2003 * †''Polygnathus alkhovikovae'' Baranov, Slavík & Blodgett 2014 in paleontology, 2014 * †''Polygnathus angustipennatus'' Bischof ...

'' : ''P. lignuiformis'' * '' Spathognathodus'' : ''S. hemiexpansis'' : ''S. primus'' * '' Trichonodella'' : ''T. excavata'' : ''T. inconstans''

Racine Formation

The Racine Formation or Racine Dolomite is found from

Wisconsin Wisconsin ( ) is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest of the United States. It borders Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michig ...

south through

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 ...

and

Iowa Iowa ( ) is a U.S. state, state in the upper Midwestern United States, Midwestern region of the United States. It borders the Mississippi River to the east and the Missouri River and Big Sioux River to the west; Wisconsin to the northeast, Ill ...

. Its age is from 423 to 427 million years old. It contains fossils of many species of

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

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 ...

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 ...

gastropods Gastropods (), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and from the land. Ther ...

among others This formation is found in

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

. The Racine is estimated to contain over 7 million barrels of oil in Illinois.

Moccasin Springs Formation

The Moccasin Springs Formation is found in

and

Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...

. It is also recognized in

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 ...

. This formation was first described by Becker (1974). The Moccasin Springs contains

reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...

facies that are more common at its base. These are pure

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

(

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

). These reefs also make up the Terre Haute Bank on the eastern flank of 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 ...

. The top of the formation is mostly dark-gray to black dolomitic shale. This is occasionally interbedded very fine grained limestone, that is mostly dark-greenish-gray. Below is dense to fine grained limestone. It tends to be somewhat argillaceous. The colors range from pastel shades of pink, green, yellow, tan, and gray to saturated dark-gray and red to purple colors. These colors may be mottled as well.

St. Clair Limestone

The St. Clair Limestone is a geologic unit in

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

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

. In

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. 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

. At its northernmost reaches where it grades in to the Joliet and Racine Formations it is about 150' thick. 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

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

Sexton Creek Limestone

The Sexton Creek Limestone is

in age 443 - 441 Ma. Named by (Savage, 1909, p. 518) revised by (Ulrich, 1911). It was named for Sexton Creek in

Alexander County, Illinois Alexander County is the southernmost county in the U.S. state of Illinois. As of the 2020 census, the population was 5,240. Its county seat is Cairo and its western boundary is formed by the Mississippi River. Alexander County is part of the ...

. The Sexton Creek is composed of

Limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

, Dolomite and

Chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

. In parts of the unit there may be as much as 60% chert. In Indiana the Sexton Creek unconformably overlies

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

aged rock. Further west it overlies the Edgewood Formation. In exposures the following fossils have been found; Distacodus obliquicostatus, Pterospathodus amorphognathoides, Kockelella ranuliformis.

References

{{Silurian footer, state=expanded Silurian Iowa Silurian geology of Wisconsin Devonian Iowa Devonian Arkansas Devonian Missouri Devonian Illinois Silurian Arkansas Silurian Indiana Silurian Illinois Silurian Missouri Carbonate rocks Limestone formations of the United States Dolomite groups Chert groups

Stratigraphy

Clifty Limestone

Penters Chert

Bailey Limestone

Lafferty Limestone

Paleofauna

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

Racine Formation

Moccasin Springs Formation

St. Clair Limestone

Sexton Creek Limestone

References

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