The Knox Supergroup, also known as the Knox Group and the Knox Formation, is a widespread geologic group in the Southeastern United States. The age is from the

Late Cambrian The Furongian is the fourth and final Epoch (geology), epoch and Series (stratigraphy), series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocia ...

to the

Early Ordovician The Early Ordovician is the first epoch (geology), epoch of the Ordovician period, corresponding to the Lower Ordovician series (stratigraphy), series of the Ordovician system. It began after the Cambrian Stage 10, Age 10 of the Furongian epoch o ...

. Predominantly, it is composed of

carbonates A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group . ...

, chiefly dolomite, with some

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) ...

. There are also

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 ...

y inclusions as well as thin beds of

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

Stratigraphy

The Knox lies beneath a

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

known as the Knox Unconformity. There is well-developed

karst topography Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

at the top of the Knox Supergroup. This demonstrates a prolonged period of erosion. This has modern economic impact because of forming reservoirs for hydrocarbons as well as some mineral deposits.

Everton Formation

The Everton Formation is a

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 northern

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 ...

through

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 ...

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

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 ...

that dates to the middle

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 ...

Period. It was named by Ulrich (1907) for exposures found around Everton, Arkansas. Fossils of

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 ''Paraprioniodus costatus'' and ''Leptochirognathus quadratus'' indicate Whiterockian age.

Unconformities An unconformity is a buried erosion surface, erosional or non-depositional surface separating two Rock (geology), rock masses or Stratum, strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer ...

separate this formation from the underlying Powell Formation and the overlying St. Peter Sandstone Formation. The Everton Formation is composed primarily of dolomite,

, and some

as well as a zone of

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

. There are local thick sections of a friable sandstone. The grains are nearly identical to the overlying St. Peter Sandstone, and may cause some confusion in identifying the different formations. The sand grains are medium grained, well rounded and are frosted. Fossils of

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

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 ...

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

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 ...

s, and

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

ns are preserved within the formation.

Stratigraphy

Five named

members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

of the Everton Formation are recognized (in stratigraphic order): * Jasper Limestone Member * Newton Sandstone Member * Calico Rock Sandstone Member * Kings River Sandstone Member * Sneeds Limestone Lentil

Beekmantown Group

The Beekmantown Group is the upper unit of the Knox Supergroup. It is a late Cambrian to lower–middle Ordovician geologic group that occurs in the eastern Canada (Québec) and northeastern United States, datable from its

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 ...

fauna. It contains dolomitic

s and

from just off land from the palaeocoastline. Most likely the Arbuckle Arbuckle Group of Oklahoma, and Ellenburger Group of Texas are equlivant to the Beekmantown. The usage of the term is diverse and depends on the state or region in question, and the group encompasses different formations in different regions. In some states it is considered a formation rather than a group, but the lithology varies by region. In

Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...

the Beekmantown is broken down into the Bellefonte Formation at the Knox Unconformity, followed by the either the Axemann Formation or the

Nittany Dolomite The Knox Supergroup, also known as the Knox Group and the Knox Formation, is a widespread geologic group in the Southeastern United States. The age is from the Late Cambrian to the Early Ordovician. Predominantly, it is composed of carbonates, c ...

, with the Stonehenge Dolomite at its base. The Stonehenge is stratigraphically equitant to the Chepultepec Formation.

Mining and Industrial materials

Zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

is mined in outcrops found in

Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

. Mostly in Augusta, Rockingham, and Shenandoah counties. The largest is the Bowers-Campbell Mine. Within the breccia zone

galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It crysta ...

is extracted along with small amounts of

sphalerite Sphalerite is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimentary exhalative, Carbonate-hoste ...

and

pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

. The Beekmantown is quarried in many locations for aggregate and rock.

Chepultepec Formation

The Chepultepec Formation is an

-aged

geological 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 expo ...

in the

Appalachia Appalachia ( ) is a geographic region located in the Appalachian Mountains#Regions, central and southern sections of the Appalachian Mountains in the east of North America. In the north, its boundaries stretch from the western Catskill Mountai ...

n regions of Eastern North America. Also known as the Chepultepec Dolomite, it is a unit of the Upper Knox Group, overlying the

Copper Ridge Dolomite The Copper Ridge Dolomite is a geologic formation in Alabama. It preserves fossils dating back to the Cambrian Period. See also * List of fossiliferous stratigraphic units in Alabama * Paleontology in Alabama Paleontology in Alabama refers ...

and underlying the Longview-Kingsport-Mascot sequence. The formation was named by E. O. Ulrich in 1911 for the town of Chepultepec (now Allgood). The Chepultepec Formation is a primarily

and dolomite formation, the earliest formation of the

period in its area. Further north, it is equivalent to the

Stonehenge Formation The Knox Supergroup, also known as the Knox Group and the Knox Formation, is a widespread Group (geology), geologic group in the Southeastern United States. The age is from the Cambrian, Late Cambrian to the Ordovician, Early Ordovician. Predomin ...

of the Beekmantown Group. The formation was first described from Allgood, and has also been found in

Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

and

. In Virginia, the Chepultepec Formation has a habit of forming large natural

arch An arch is a curved vertical structure spanning an open space underneath it. Arches may support the load above them, or they may perform a purely decorative role. As a decorative element, the arch dates back to the 4th millennium BC, but stru ...

es, including Natural Tunnel in Scott County and

Natural Bridge A natural arch, natural bridge, or (less commonly) rock arch is a natural landform where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion fro ...

in Rockbridge County.

Prairie du Chien Group

This group includes the Oneota Formation and the Shakopee Formation.

Oneota Formation

The Oneota Formation is a

in the upper Midwest (United States) including

Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...

and

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 ...

. It preserves marine

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the

period. The Sugar Loaf landmark located in

Winona, Minnesota Winona ( ) is a city in and the county seat of Winona County, Minnesota, United States. Located in bluff country on the Mississippi River, its most noticeable physical landmark is Sugar Loaf (Winona, Minnesota), Sugar Loaf. The population was 2 ...

is made of Oneota Dolomite.

Shakopee Formation

The Shakopee Formation is a

, and

. It preserves

dating back to the

period. It is named after the town of

Shakopee, Minnesota Shakopee ( ) is a city in and the county seat of Scott County, Minnesota, United States. It is southwest of Minneapolis. Sited on the south bank bend of the Minnesota River, Shakopee and nearby suburbs comprise the southwest portion of Minneap ...

, where the formation can be seen in bluffs along the

Minnesota River The Minnesota River () is a tributary of the Mississippi River, approximately 332 miles (534 km) long, in the U.S. state of Minnesota. It drains a watershed of in Minnesota and about in South Dakota and Iowa. It rises in southwestern ...

. The formation is broken up into two members, the New Richmond and Willow River Members. The Shakopee was deposited in a peritidal setting and is divided by an unconformity. The unconformity left river valleys that were filled with

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclastic rock types include mudrock, sandstone Sandstone is a Clastic ...

material that was covered by marine deposits. Facies-defining cycles are divided into grainy carbonate, muddy carbonate, sandstone, shale, and Stromatolitic–

Algal Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, s ...

mat Boundstones. Stromatolite reefs are a common occurrence in the Shakopee and are well documented throughout. Some of the recognized species of stromatolites are ''cryptozoon minnesotense, cryptozoon liberta and cryptozoon rosemontensis.''

= Fossils

= * Mollusk ** ''Murchisonia artemesia'' ** ''Pleurotomaria canadensis'' ** ''Lophospira cassina'' ** ''Cameroceras stillwaterense'' ** ''Cotteroceras compressum'' ** ''Cyptendoceras ruedemanni''

References

{{Chronostratigraphy of West Virginia Ordovician geology of Pennsylvania Ordovician geology of New York (state) Ordovician Tennessee Ordovician southern paleotemperate deposits Ordovician Indiana Ordovician Illinois Ordovician Arkansas Ordovician Kentucky Ordovician West Virginia Ordovician Wisconsin Ordovician Minnesota Ordovician geology of Virginia Dolomite groups Limestone groups of the United States Sandstone groups of the United States