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 chemical precipitate or a diagenetic replacement, as in petrified wood.
In geology and related fields, a stratum is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as either bedding surfaces or bedding planes. Prior to the publication of the International Stratigraphic Guide, older publications have defined a stratum as either being either equivalent to a single bed or composed of a number of beds; as a layer greater than 1 cm in thickness and constituting a part of a bed; or a general term that includes both bed and lamina.
The Highland Rim is a geographic term for the area in Tennessee surrounding the Central Basin. Nashville is largely surrounded by higher terrain in all directions.
The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group in south-east England. The name is derived from the district known as the Isle of Purbeck in Dorset where the strata are exposed in the cliffs west of Swanage.
Type locality, also called type area, is the locality where a particular rock type, stratigraphic unit or mineral species is first identified. If the stratigraphic unit in a locality is layered, it is called a stratotype, whereas the standard of reference for unlayered rocks is the type locality.
The Ste. Genevieve Limestone is a geologic formation named for Ste. Genevieve, Missouri where it is exposed and was first described. It is a thick-bedded limestone that overlies the St. Louis Limestone. Both are Mississippian in age. The St. Louis Limestone is Meramecian and the Ste. Genevieve is the base of the Chesterian series.
The Fort Payne Formation, or Fort Payne Chert, is a geologic formation found in the southeastern region of the United States. It is a Mississippian Period cherty limestone, that overlies the Chattanooga Shale, and underlies the St. Louis Limestone. To the north, it grades into the siltstone Borden Formation. It preserves fossils dating back to the Carboniferous period.
The Pennsylvanian Pottsville Formation is a mapped bedrock unit in Pennsylvania, western Maryland, West Virginia, Ohio, and Alabama. It is a major ridge-former in the Ridge-and-Valley Appalachians of the eastern United States. The Pottsville Formation is conspicuous at many sites along the Allegheny Front, the eastern escarpment of the Allegheny or Appalachian Plateau.
The Rundle Group is a stratigraphical unit of Mississippian age in the Western Canadian Sedimentary Basin.
The Devonian Old Port Formation is a mapped bedrock unit in Pennsylvania, USA. Details of the type section and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database. Current nomenclature usage by U.S. Geological Survey restricts the name Old Port Formation to Pennsylvania, but correlative units are present in adjacent states.
The Phosphoria Formation of the western United States is a geological formation of Early Permian age. It represents some 15 million years of sedimentation, reaches a thickness of 420 metres (1,380 ft) and covers an area of 350,000 square kilometres (140,000 sq mi).
The Ogallala Formation is a Miocene to early Pliocene geologic formation in the central High Plains of the western United States and the location of the Ogallala Aquifer. In Nebraska and South Dakota it is also classified as the Ogallala Group. Notably, it records the North American Land Mammal Ages (NALMAs) Hemphillian, Clarendonian, and Barstovian. It also includes an excellent record of grass seeds and other plant seeds, which can be used for biostratigraphic dating within the formation. The Ogallala Formation outcrops of Lake Meredith National Recreation Area preserve fish fossils. Similar specimens from the same unit are found at Alibates Flint Quarries National Monument in Texas.
The Boone Formation a discrete and definable unit of cherty limestone rock strata located in northwest Arkansas and northeast Oklahoma.
The Chattanooga Shale is a geologic formation in Alabama, Arkansas, Kentucky, Missouri and Tennessee. It preserves conodont fossils dating to the Devonian Period. It occurs mostly as a subsurface geologic formation composed of layers of shale. It is located in Eastern Tennessee and also extends into southeastern Kentucky, northeastern Georgia, and northern Alabama. This part of Alabama is part of the Black Warrior Basin.
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.
The Flume Formation is a geologic formation in the Western Canada Sedimentary Basin in Alberta, Canada. It was deposited as an extensive carbonate platform along the western edge of the basin during Late Devonian (Frasnian) time and the reefs of the Cairn Formation subsequently developed on it.
The Beaverfoot Formation is a stratigraphic unit of Late Ordovician to Early Silurian (Llandovery) age. It is present on the western edge of the Western Canada Sedimentary Basin in the Rocky Mountains of British Columbia and Alberta, and the Purcell Mountains of British Columbia. It consists of carbonate rocks, and was named for the Beaverfoot Range at Pedley Pass southeast of Golden, British Columbia by L.D. Burling in 1922.
The Huntersville Chert or Huntersville Formation is a Devonian geologic formation in the Appalachian region of the United States. It is primarily composed of mottled white, yellow, and dark grey chert, and is separated from the underlying Oriskany Sandstone by an unconformity. The Huntersville Chert is laterally equivalent to the Needmore Shale, which lies north of the New River. It is also laterally equivalent to a sandy limestone unit which is often equated with the Onondaga Limestone. These formations are placed in the Onesquethaw Stage of Appalachian chronostratigraphy, roughly equivalent to the Emsian and Eifelian stages of the broader Devonian system.
The Kananaskis Formation is a geologic formation that is present on the western edge of the Western Canada Sedimentary Basin in the southern Canadian Rockies of western Alberta. Named after the Kananaskis Range near Banff, it was deposited during the Late Pennsylvanian sub-period of the Carboniferous period. Some of its strata host fossils of marine invertebrates.
![<span class="mw-page-title-main">Douglas Lake Member</span> Geologic formation in [[Tennessee]], United States](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Casterlorum_crispum_slab.jpg/320px-Casterlorum_crispum_slab.jpg)
The Douglas Lake Member is a geologic unit of member rank of the Lenoir Limestone that overlies the Mascot Dolomite and underlies typical nodular member of the Lenoir Limestone in Douglas Lake, Tennessee, region. It fills depressions that are part of a regional unconformity at the base of Middle Ordovician strata, locally the Lenoir Limestone, that separates them from the underlying Lower Ordovician strata, locally the Knox Group.
