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The Ordovician Period in Britain was traditionally broken into Early (Tremadocian and Arenig), Middle (Llanvirn (subdivided into Abereiddian and Llandeilian) and Llandeilo) and Late (Caradoc and Ashgill) epochs. The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column.
The Ordovician Martinsburg Formation (Om) is a mapped bedrock unit in Pennsylvania, ... It is the dominant rock formation of the Great Appalachian Valley in New ...
The Ordovician Juniata Formation is a mapped bedrock unit in Pennsylvania, West Virginia, Virginia, Tennessee, and Maryland. It is a relative slope-former occurring between the two prominent ridge-forming sandstone units: the Tuscarora Formation and the Bald Eagle Formation in the Appalachian Mountains .
The formation was named by E. O. Ulrich in 1911 for the town of Chepultepec (now Allgood). [6] The Chepultepec Formation is a primarily limestone and dolomite formation, the earliest formation of the Ordovician period in its area. Further north, it is equivalent to the Stonehenge Formation of the Beekmantown Group. [12]
The Bellevue Formation is the uppermost rock bed layer and is the youngest layer of the Ordovician period, dating to around 455-450 million years ago. This formation is the least accessible of the three formations at Maysville, requiring a steep hike up a trail located near the south end of the roadcut.
Rocks of Ordovician age are best exposed in the Northwestern part of the state, largely in the Driftless Area (see below). Ordovician rocks in the state are separated from Cambrian and Silurian rocks by unconformities. Most of the Ordovician saw continued offshore marine deposition throughout the entirety of the state; however, Southern parts ...
The St. Peter Sandstone is an Ordovician geological formation.It belongs to the Chazyan stage of the Champlainian series in North American regional stratigraphy, equivalent to the late Darriwilian global stage.
Because the rocks of the Manitou Dolomites are mostly indeterminate carbonates, the exact depositional environment is unknown. However it was likely shallow water, either lagoon or near-shore, and the many jumbled fossils of trilobite spines and brachiopods suggest that the paleoenvironment may have been prone to storms.