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. ...

. 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 g ...

, chiefly

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

, 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 whe ...

. 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.

Stratigraphy

The Knox lies beneath a unconformity 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 ro ...

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 in northern Arkansas through Missouri, Illinois and Indiana that dates to the middle Ordovician Period. It was named by Ulrich (1907) for exposures found around

Everton, Arkansas Everton is a town in Boone County, Arkansas, United States. The population was 133 at the 2010 census. It is part of the Harrison Micropolitan Statistical Area. Geography Everton is located at (36.154002, -92.908029). According to the United ...

. 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, which ...

s ''Paraprioniodus costatus'' and ''Leptochirognathus quadratus'' indicate Whiterockian age. Unconformities separate this formation from the underlying Powell Formation and the overlying St. Peter Sandstone Formation. The Everton Formation is composed primarily of

, and some sandstone as well as a zone of breccia. There are local thick sections of a friable sandstone. The grains are nearly identical to the overlying

St. Peter Sandstone The St. Peter Sandstone is an Ordovician geological formation. It belongs to the Chazyan stage of the Champlainian series in North American regional stratigraphy, equivalent to the late Darriwilian global stage. This sandstone originated as a sheet ...

, and may cause some confusion in identifying the different formations. The sand grains are medium grained, well rounded and are frosted. Fossils of ostracods,

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 ...

s, gastropods,

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, bival ...

, trilobites, and bryozoans are preserved within the formation.

Stratigraphy

Five named members 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, which ...

fauna. It contains dolomitic sandstones and

from just off land from the palaeocoastline. Most likely the Arbuckle

Arbuckle Group The Arbuckle Group is a geologic group in Oklahoma. It preserves fossils dating back to the Ordovician period. See also * Arbuckle Mountains * List of fossiliferous stratigraphic units in Oklahoma * Paleontology in Oklahoma * Oklahoma earthquake ...

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 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 is mined in outcrops found in Virginia. 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 cryst ...

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 deposits, sedimen ...

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

Chepultepec Formation

The Chepultepec Formation is an

-aged geological formation 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, Ca ...

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 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

formation, the earliest formation of the Ordovician 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 geologic group in the Southeastern United States. The age is from the Late Cambrian to the Early Ordovician. Predominantly, it is composed of carbonates, ch ...

of the

Beekmantown Group The Beekmantown Group is a late Cambrian to lower–middle Ordovician Group (geology), geologic group that occurs in the eastern Canada (Québec) and northeastern United States, datable from its conodont fauna. It contains Dolomite (mineral), do ...

. The formation was first described from Allgood, and has also been found in Tennessee and Virginia. 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 vaul ...

es, including Natural Tunnel in Scott County and Natural Bridge in

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 ...

Prairie du Chien Group

This group includes the Oneota Formation and the Shakopee Formation.

Oneota Formation

The Oneota Formation is a geologic formation in the upper Midwest (United States) including Minnesota, Illinois, Indiana and Wisconsin. It preserves

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

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 in ...

dating back to the Ordovician period. The Oneota Formation is a geologic formation in the upper Midwest (United States) including Minnesota, Illinois, Indiana and Wisconsin. It preserves

dating back to the Ordovician 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 is made of Oneota Dolomite.

Shakopee Formation

The Shakopee Formation is a geologic formation in Illinois, Indiana, Wisconsin, and Minnesota. It preserves

dating back to the Ordovician period. It is named after the town of Shakopee, Minnesota, 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 material that was covered by marine deposits. Facies-defining cycles are divided into grainy carbonate, muddy carbonate, sandstone, shale, and Stromatolitic– Algal 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