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.
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. 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.
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 ,
Rockdale Run Formation, 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 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. Within the breccia zone
galena is extracted along with small amounts of
sphalerite and
pyrite.
Chepultepec Formation The
Chepultepec Formation is an
Early Ordovician-aged
geological formation in the
Appalachian 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 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 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
arches, including
Natural Tunnel in
Scott County and
Natural Bridge in
Rockbridge County.
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 fossils dating back to the
Ordovician period. The
Sugar Loaf 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
fossils 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 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 ==