The Bluestone Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

West Virginia West Virginia is a mountainous U.S. state, state in the Southern United States, Southern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States.The United States Census Bureau, Census Bureau and the Association of American ...

. It is the youngest unit of the Upper Mississippian-age Mauch Chunk Group. A pronounced

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

separates the upper boundary of the Bluestone Formation from

sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains, cemented together by another mineral. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed o ...

of the overlying Pennsylvanian-age Pocahontas Formation.

Fossils

Two formally named subunits of the Bluestone Formation, the Bramwell and Pride Shale Members, are quite fossiliferous. Plant fossils allow the top of the Bluestone Formation to be correlated with the

Namurian The Namurian is a stage in the regional stratigraphy of northwest Europe, with an age between roughly 331 and 319 Ma (million years ago). It is a subdivision of the Carboniferous system or period, as well as the regional Silesian series. The Na ...

A-Namurian B boundary, the European equivalent of the Mississippian-Pennsylvanian boundary.

Conodonts Conodonts, are an extinct group of marine jawless vertebrates belonging to the Class (biology), class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning "cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known ...

belonging to the '' Adetognathus unicornis'' or lower '' Rhachistognathus muricatus'' conodont zones have been found in the Bramwell Member. This would make the Bluestone Formation the youngest occurrence of Mississippian-type conodonts in eastern North America. A diverse

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

fauna was present in both the Bluestone Formation and the older Hinton Formation.

Brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the fron ...

were also fairly diverse, though not as dominant in the ecosystem as bivalves. Among the most abundant fossils were fossilized tubes of '' Microconchus hintonensis'', a microconchid. The Pride Shale Member has produced '' Tanypterichthys pridensis'', an endemic species of deep-bodied palaeonisciform fish.

Deposition

The Pride Shale Member of the Bluestone Formation preserves

interbedded In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedimen ...

variations in sediment coarseness. This variation is cyclical at multiple scales, with cycles from smaller than a millimeter to up to several meters in thickness. The smallest-scale cycles likely represent sediments settling out during daily

tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

. The largest-scale cycles are tied to changes in the tides influenced by the 18.6-year lunar nodal cycle. Cycles are also observed at half-year, monthly, and half-month scales. These correspond to seasonal changes, perigee/apogee tidal variation, and neap/spring tidal variation, respectively. Together, the different cycles reconstruct a deltaic environment near the equator which was heavily influenced by tides and a monsoonal climate. Modern equivalents would be the deltas of the

Amazon Amazon most often refers to: * Amazon River, in South America * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon (company), an American multinational technology company * Amazons, a tribe of female warriors in Greek myth ...

Ganges The Ganges ( ; in India: Ganga, ; in Bangladesh: Padma, ). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international which goes through India, Bangladesh, Nepal and China." is a trans-boundary rive ...

Brahmaputra The Brahmaputra is a trans-boundary river which flows through Southwestern China, Northeastern India, and Bangladesh. It is known as Brahmaputra or Luit in Assamese, Yarlung Tsangpo in Tibetan, the Siang/Dihang River in Arunachali, and ...

, and Fly rivers. During glacial periods, the monsoonal climate would have mellowed out into a less seasonal tropical climate in equatorial regions.

References

Carboniferous West Virginia Carboniferous geology of Virginia Carboniferous southern paleotropical deposits Serpukhovian {{Carboniferous-stub

Fossils

Deposition

See also

References