Juniata Formation

Juniata Formation Stratigraphic range: Late Ordovician
Outcrop on U.S. Route 522 at Blacklog Narrows southeast of Orbisonia, Pennsylvania.
Type	sedimentary
Underlies	Oswego Formation and Tuscarora Formation
Overlies	Bald Eagle Formation
Thickness	400 to 1125 ft
Lithology
Primary	sandstone, siltstone, shale
Location
Region	Appalachian Mountains
Extent	Pennsylvania, Maryland, Virginia, West Virginia, and eastern Tennessee
Type section
Named for	Juniata River in Pennsylvania
Named by	Darton and Taff

The Ordovician Juniata Formation is a mapped bedrock unit in Pennsylvania 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 Juniata is defined as a grayish-red to greenish-gray, thin- to thick-bedded siltstone, shale, and very fine to medium-grained crossbedded sandstone or subgraywacke and protoquartzite with interbedded conglomerate. The Juniata is a lateral equivalent of the Queenston Shale in western Pennsylvania.

The depositional environment of the Juniata has always been intrepreted as mostly terrestrial or shallow marine deposits resulting in a molasse sequence produced by the Taconic orogeny.

Very few fossils exist in the Juniata Formation, but different types of trace fossils such as tracks and burrows can commonly be found.

Relative age dating of the Juniata places it in the Upper Ordovician period, being deposited between 488.3 and 443.7 (±10) million years ago. It rests conformably atop the Bald Eagle Formation in Pennsylvania and the Martinsburg Formation in Maryland, and conformably below the Tuscarora Formation.