Juniata Formation

Juniata Formation

The Ordovician Juniata Formation (Oj) 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.Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000.] cite web |url=http://www.mgs.md.gov/esic/geo/lgdalleg.html |title=Allegheny Plateau and Valley and Ridge | work = Geologic Map of Maryland | year = 1968 | publisher=Maryland Geological Survey|accessdate=2008-01-26 |format= |work=] The Juniata is a lateral equivalent of the Queenston Shale in western Pennsylvania.

=Depositional Environment=

The Juniata has always been intrepreted as molasse resulting from the Taconic orogeny.


Very few fossils exist in the Juniata Formation.


Relative age dating of the Juniata places it in the Upper Ordovician period, being deposited between 488.3 to 443.7 (±10) million years ago. It rests conformably atop the Bald Eagle Formation in Pennsylvania and the Martinsburg Formation in Maryland,cite web |url=http://www.mgs.md.gov/esic/geo/lgdalleg.html |title=Geologic Maps of Maryland: |accessdate=2008-01-26 |format= |work=] and conformably below the Tuscarora Formation. [Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.]

Economic Uses

The Juniata is a good source of road material, riprap and building stone.cite paper|url=http://www.dcnr.state.pa.us/topogeo/openfile/mcalevysfort.pdf|format=pdf|author= Doden, Arnold G. and Gold, David P.|year=2008|title=Bedrock Geologic Map of The Mc Alevys Fort Quadrangle, Huntingdon, Centre, and Mifflin Counties, Pennsylvania|publisher=Pennsylvania Geological Survey]


ee also

*Geology of Pennsylvania

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