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 Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

to the

Early Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. Th ...

. Predominantly, it is composed of

carbonates A carbonate is a salt of carbonic acid (H2CO3), 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 ...

, chiefly dolomite, with some

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

. 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 ...

y inclusions as well as thin beds of

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

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 o ...

known as the Knox Unconformity. There is well-developed

karst topography Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ...

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 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 ...

through

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 ...

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

and

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 ...

that dates to the middle

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

Period. It was named by Ulrich (1907) for exposures found around Everton, Arkansas. Fossils 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 known only from their tooth-like oral elements, w ...

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

Unconformities 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 ...

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 rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...

. 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 of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

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

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

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s, and

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

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 ( 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, w ...

fauna. It contains

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dol ...

s and

from just off land from the palaeocoastline. Most likely the Arbuckle Arbuckle Group of Oklahoma, and

Ellenburger Group The Ellenburger Group is a geologic group in Texas. It preserves 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, shel ...

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 (; (Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Ma ...

the Beekmantown is broken down into the

Bellefonte Formation The Ordovician Bellefonte Formation is a mapped bedrock unit in central Pennsylvania. It is the uppermost unit of the Beekmantown Group. The top of the Bellefonte is marked by the Knox Unconformity. Description The Bellefonte is defined as a m ...

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, ...

, 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 with the symbol Zn and atomic number 30. Zinc 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 t ...

is mined in outcrops found in

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the East Coast of the United States, Atlantic Coast and the Appalachian Mountains. The geography an ...

. 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 cry ...

is extracted along with small amounts of

sphalerite Sphalerite (sometimes spelled sphaelerite) 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, Mississippi-Va ...

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 giv ...

. 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 cultural region in the Eastern United States that stretches from the Southern Tier of New York State to northern Alabama and Georgia. While the Appalachian Mountains stretch from Belle Isle in Newfoundland and Labrador, ...

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

Knox Group The Knox Group is a widespread geologic group in the Southeastern United States. Though not commonly fossiliferous, it preserves fossils dating back to the Cambrian period. Typical lithologies include thick-bedded cherty dolomites and limeston ...

, 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 This article contains a list of fossil-bearing stratigraph ...

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 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 state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to ...

and

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

arch An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it. Arches may be synonymous with vau ...

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 f ...

Rockbridge County Rockbridge County is a county in the Shenandoah Valley on the western edge of the Commonwealth of Virginia. As of the 2020 census, the population was 22,650. Its county seat is the city of Lexington. Rockbridge County completely surrounds the i ...

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) The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of the United States. I ...

including

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the List of U.S. states and territories by population, 22nd most populous, with over 5.75 million residents. Minne ...

and

Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...

. 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 Oneota Formation is a

in the upper

including

and

. It preserves marine

dating back to the

period. The

Sugar Loaf A sugarloaf was the usual form in which refined sugar was produced and sold until the late 19th century, when granulated and cube sugars were introduced. A tall cone with a rounded top was the end product of a process in which dark molasses, a r ...

landmark located in

Winona, Minnesota Winona is a city in and the county seat of Winona County, in the state of Minnesota. Located in bluff country on the Mississippi River, its most noticeable physical landmark is Sugar Loaf. The city is named after legendary figure Winona, who s ...

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 located southwest of Minneapolis. Sited on the south bank bend of the Minnesota River, Shakopee and nearby suburbs comprise the southwest portion of ...

, where the formation can be seen in bluffs along the

Minnesota River The Minnesota River ( dak, Mnísota Wakpá) 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 ris ...

. 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. Siliciclasic rock types include mudrock, sandstone, and conglomerate Conglome ...

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

Algal Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from un ...

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 geology of Tennessee Ordovician southern paleotemperate deposits Ordovician Indiana Ordovician Illinois Ordovician Arkansas Ordovician Kentucky Ordovician West Virginia Ordovician geology of Wisconsin Ordovician Minnesota Ordovician geology of Virginia