Juniata Formation
| Juniata Formation | |
|---|---|
| Stratigraphic range: Late Ordovician | |
| File:Juniata Fm Blacklog.jpg 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 | 400–1,125 ft (122–343 m) |
| Lithology | |
| Primary | sandstone, siltstone, shale |
| Location | |
| Region | Appalachian Mountains |
| Extent | Maryland, Pennsylvania, Tennessee, Virginia,[1] and West Virginia |
| Type section | |
| Named for | Juniata River in Pennsylvania |
| Named by | Darton and Taff[2] |
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.
Description
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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.[3][4] The Juniata is a lateral equivalent of the Queenston Shale in western Pennsylvania.
Depositional environment
[edit | edit source]The depositional environment of the Juniata has always been interpreted as mostly terrestrial or shallow marine deposits resulting in a molasse sequence produced by the Taconic orogeny.
Fossils
[edit | edit source]Very few fossils exist in the Juniata Formation, but different types of trace fossils such as tracks and burrows can commonly be found.
Age
[edit | edit source]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,[4] and conformably below the Tuscarora Formation.[5]
Economic use
[edit | edit source]The Juniata is a good source of road material, riprap and building stone.[6]
References
[edit | edit source]- ^ Paleozoic Sedimentary Successions of the Virginia Valley & Ridge and Plateau
- ^ 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 Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
- ^ Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.
- ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
See also
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- Ordovician System of North America
- Upper Ordovician Series
- Sandstone formations of the United States
- Siltstone formations of the United States
- Shale formations of the United States
- Geologic formations of Maryland
- Geologic formations of Pennsylvania
- Geologic formations of Virginia
- Ordovician West Virginia
- Ordovician Maryland
- Ordovician geology of Pennsylvania
- Ordovician Tennessee
- Ordovician geology of Virginia
- Geologic formations of Tennessee
- Geologic formations of West Virginia
- Southern United States geologic formation stubs
- Maryland stubs