Bald Eagle Formation
| Bald Eagle Formation | |
|---|---|
| Stratigraphic range: Late Ordovician | |
| File:Bald Eagle Formation 1.jpg | |
| Type | sedimentary |
| Underlies | Juniata Formation |
| Overlies | Reedsville Formation |
| Thickness | 275 +/-25 m[1] |
| Lithology | |
| Primary | sandstone |
| Other | conglomerate, shale |
| Location | |
| Region | Appalachian Mountains |
| Extent | Pennsylvania, Maryland, West Virginia |
| Type section | |
| Named for | Bald Eagle Mountain, Pennsylvania |
| Named by | A. W. Grabau[2] |
The Ordovician Bald Eagle Formation is a mapped bedrock unit in central Pennsylvania, USA. It is a ridge-forming unit in the Appalachian Mountains.
Description
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The Bald Eagle is defined as a gray to olive-gray and grayish-red, fine to coarse-grained crossbedded sandstone or greywacke. A conglomeratic member, called the Lost Run Member, exists in some locations.[3]
Depositional environment
[edit | edit source]The depositional environment of the Bald Eagle 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 Bald Eagle Formation, and most of them are trace fossils. However, at the base of the formation is the Orthorynchula biostratigraphic marker bed, which contains abundant Orthorynchula brachiopods.
Age
[edit | edit source]Relative age dating of the Bald Eagle places it in the Upper Ordovician period, being deposited between 488.3 and 443.7 (±10) million years ago. It rests conformably atop the Reedsville Formation and conformably below the Juniata Formation.[4]
Economic Uses
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The Bald Eagle is a good source of road material, riprap and building stone.[5] However, iron pyrite inclusions may lead to acidic rainwater runoff.
References
[edit | edit source]- ^ Faill, R.T., Glover, A.D., and Way, J.H., 1989, Geology and mineral resources of the Blandburg, Tipton, Altoona, and Bellwood quadrangles, Blair, Cambria, Clearfield and Centre Counties, Pennsylvania: Pennsylvania Geological Survey Topographic and Geologic Atlas, 4th series, 86, 209 p., scale 1:24,000 and 1:48,000
- ^ Grabau, A.W., 1909, Physical and faunal evolution of North America during Ordovicic, Siluric, and Early Devonic time: Journal of Geology, v. 17, p. 209-252.
- ^ 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.
- ^ 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
- Ordovician geology of Pennsylvania
- Appalachian Mountains
- Cliff-formers
- Conglomerate formations of the United States
- Shale formations of the United States
- Northeastern United States geologic formation stubs
- Pennsylvania stubs