Juniata Formation
| Juniata Formation Stratigraphic range: Ordovician |
|
|---|---|
 Outcrop on U.S. Route 522 at Blacklog Narrows southeast of Orbisonia, Pennsylvania. |
|
| Type | sedimentary |
| Underlies | Tuscarora Formation |
| Overlies | Bald Eagle Formation |
| Thickness | 400 to 1125 ft |
| Lithology | |
| Primary | sandstone, siltstone, shale |
| Location | |
| Named for | Juniata River in Pennsylvania |
| Named by | Darton and Taff[1] |
| Region | Appalachian Mountains |
| Extent | Pennsylvania, Maryland, Virginia, West Virginia, and eastern Tennessee |
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.
Contents |
[edit] Description
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.[2][3] The Juniata is a lateral equivalent of the Queenston Shale in western Pennsylvania.
[edit] Depositional environment
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.
[edit] Fossils
Very few fossils exist in the Juniata Formation, but different types of trace fossils such as tracks and burrows can commonly be found.
[edit] Age
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,[3] and conformably below the Tuscarora Formation.[4]
[edit] Economic Uses
The Juniata is a good source of road material, riprap and building stone.[5]
[edit] References
- ^ Darton, N.H., and Taff, J.A., 1896, Description of the Piedmont sheet (West Virginia-Maryland): U.S. Geological Survey Geologic Atlas of the United States, Piedmont folio, no. 28, 6 p.
- ^ 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.
- ^ a b "Allegheny Plateau and Valley and Ridge". Geologic Map of Maryland. Maryland Geological Survey. 1968. http://www.mgs.md.gov/esic/geo/lgdalleg.html. Retrieved 2008-01-26.
- ^ Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.
- ^ Doden, Arnold G. and Gold, David P. (2008) (pdf). Bedrock Geologic Map of The Mc Alevys Fort Quadrangle, Huntingdon, Centre, and Mifflin Counties, Pennsylvania. Pennsylvania Geological Survey. http://www.dcnr.state.pa.us/topogeo/openfile/mcalevysfort.pdf.
[edit] See also
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