The Ordovician Reedsville Formation is a mapped surficial bedrock unit in Pennsylvania, Maryland, Virginia, West Virginia, and Tennessee, that extends into the subsurface of Ohio. This rock is a slope-former adjacent to the prominent ridge-forming Bald Eagle sandstone unit in the Appalachian Mountains. It is often abbreviated Or on geologic maps.
The Collier Shale is a geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. Dating from the Late Cambrian to Early Ordovician periods, the Collier Shale is the oldest stratigraphic unit exposed in Arkansas. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue assigned the type locality to the headwaters of Collier Creek in Montgomery County, Arkansas, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.
The Hale Formation is a geologic formation in northern Arkansas that dates to the Morrowan Series of the early Pennsylvanian. The Hale Formation has two named members: the Cane Hill and the Prairie Grove Members. The lower member is the Cane Hill, a primarily sandstone and shale interval that unconformably overlies the Mississippian-age Pitkin Formation. The upper member, the Prairie Grove Member, is predominately limestone and conformably underlies the Bloyd Formation.
The Bloyd Formation, or Bloyd Shale, is a geologic formation in Arkansas. It preserves fossils dating back to the Carboniferous period.
The Everton Formation is a geologic formation in northern Arkansas that dates to the middle Ordovician Period. Unconformities separate this formation from the underlying Powell Formation and the overlying St. Peter Sandstone Formation. Named for the town of Everton in Boone County, Arkansas in 1907, the Everton Formation is composed primarily of dolomite, limestone, and sandstone.
The Winslow Formation was a geologic formation in Arkansas, now abandoned and replaced by the Atoka Formation, the Hartshorne Formation, and the lower McAlester Formation. It preserves fossils dating back to the Carboniferous period.
The Johns Valley Formation is a geologic formation in Arkansas and Oklahoma. It preserves fossils dating back to the Carboniferous period.
The Tucumcari Formation is a geologic formation in New Mexico. It preserves fossils dating back to the Albian Age of the early Cretaceous period.
The Vinini Formation is a marine, deep-water, sedimentary deposit of Ordovician to Early Silurian age in Nevada, U.S.A. It is notable for its highly varied, mainly siliceous composition, its mineral deposits, and controversies surrounding both its depositional environment and structural history. The formation was named by Merriam and Anderson for an occurrence along Vinini Creek in the Roberts Mountains of central Nevada and that name is now used extensively in the State.
Cordylodus is an extinct genus of conodonts in the family of Cordylodontidae.
The Crystal Mountain Sandstone is an Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. This interval was first described in 1892, but remained unnamed until 1909 as part of a study on the Ouachita Mountains of Arkansas by Albert Homer Purdue.
The Mazarn Shale is an Early Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. This interval was first described in 1892, but remained unnamed until 1918 as part of a study by U.S. Geological Survey geologist Hugh Dinsmore Miser.
The Womble Shale is a Middle Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas, where he named this unit as part of the upper Ouachita Shale and the Stringtown Shale. In 1918, U.S. Geological Survey geologist, Hugh Dinsmore Miser, replaced Purdue's nomenclature with the Womble Shale. Miser assigned the town of Womble in Montgomery County, Arkansas as the type locality. As of 2017, a reference section for this unit has yet to be designated.
The Bigfork Chert is a Middle to Late Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue assigned the town of Big Fork in Montgomery County, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated. The Bigfork Chert is known to produce planerite, turquoise, variscite, and wavellite minerals.
The Polk Creek Shale is a Late Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue assigned Polk Creek in Montgomery County, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.
The Blaylock Sandstone is a Silurian geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue assigned the Blaylock Mountain in Montgomery County, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.
The Missouri Mountain Shale is a Silurian geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue assigned the Missouri Mountains in Polk and Montgomery counties, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.
The Stanley Shale, or Stanley Group, is a Mississippian stratigraphic unit in the Ouachita Mountains of Arkansas and Oklahoma. First described in Arkansas in 1892, this unit was not named until 1902 by J.A. Taff in his study of the Ouachita Mountains of Oklahoma. Taff assigned the town of Stanley in Pushmataha County, Oklahoma as the type locality, but did not designate a stratotype. After introduction into Arkansas in 1909 by Albert Homer Purdue, the unit was redefined in 1918, when the formation known as the Fork Mountain Slate was abandoned and partially combined into the Stanley Shale. As of 2017, a reference section for the Stanley Shale has yet to be designated.
The Savanna Sandstone or Savanna Formation is a Pennsylvanian geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. Early descriptions of this unit have considered it to be part of the Coal Measures, part of the Upper or Western Coal Bearing Division, part of the Sebastian Stage, and part of the Cavaniol Group. In 1899, J.A. Taff introduced the Savanna Formation name in his study of the Ouachita Mountains of Oklahoma. The name was introduced into Arkansas in 1907, although in 1950, the interval was renamed the Boggy Formation, while the name "Savanna Formation" replaced the underlying interval consisting of the upper Fort Smith Formation and the lower Paris Shale. The Savanna Formation is informally recognized with two named sub-units in Arkansas: the Charleston and Paris coal beds. Taff assigned the type area to the towns of McAlester and Savanna in Pittsburg County, Oklahoma, however he did not state whether the town of Savanna is the origin of the name. Taff did not designate a stratotype, however, a reference section was designated in 1995 in Pittsburg County, Oklahoma.
The Joachim Dolomite is a Middle Ordovician geologic formation in Arkansas, Illinois, and Missouri. The name was first introduced in 1894 by Arthur Winslow in his study of the geology of Missouri. Winslow designated a stratotype along Plattin Creek, which was misidentified as Joachim Creek, in Jefferson County. The name was introduced into Arkansas in 1911, replacing part of the, now abandoned, Izard Limestone.
