Knox Supergroup

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, chiefly dolomite, with some limestone. There are also cherty inclusions as well as thin beds of sandstone.

The Knox lies beneath a unconformity known as the Knox Unconformity. There is well-developed karst topography 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.

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. Fossils of Conodonts 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 dolomite, limestone, 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, and may cause some confusion in identifying the different formations. The sand grains are medium grained, well rounded and are frosted. Fossils of ostracods, cephalopods, gastropods, bivalves, trilobites, and bryozoans are preserved within the formation.

Five named members of the Everton Formation are recognized (in stratigraphic order):

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 fauna. It contains dolomitic sandstones and carbonates 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 the Beekmantown is broken down into the Bellefonte Formation at the Knox Unconformity, followed by the either the Axemann Formation or the Nittany Dolomite, with the Stonehenge Dolomite at its base. The Stonehenge is stratigraphically equitant to the Chepultepec Formation.

Zinc is mined in outcrops found in Virginia. Mostly in Augusta, Rockingham, and Shenandoah counties. The largest is the Bowers-Campbell Mine.