Bald Eagle Formation
{{Infobox rockunit
| name = Bald Eagle Formation
| image = Bald Eagle Formation 1.jpg
| caption = Outcrop of Bald Eagle Formation, where Rt. 164 crosses Tussey Mountain, Blair County, Pennsylvania
| type = sedimentary
| age = Late Ordovician
| period = Late Ordovician
| prilithology = sandstone
| otherlithology = conglomerate, shale
| namedfor = Bald Eagle Mountain, Pennsylvania
| namedby = A. W. GrabauGrabau, 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.
| region = Appalachian Mountains
| country =
| coordinates =
| unitof =
| subunits =
| underlies = Juniata Formation
| overlies = Reedsville Formation
| extent = Pennsylvania, Maryland, West Virginia
| area =
| map =
| map_caption =
}}
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
Image:Bald Eagle Formation 2.jpg crosses Tussey Mountain, Blair County, Pennsylvania. Note prominent crossbedding and lens cap for scale.]]
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.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.
=Depositional environment=
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=
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
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.Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.
Economic Uses
Image:Bald Eagle Formation Pyrite.jpg in the Bald Eagle Formation, from the Skytop Roadcut where I-99 crosses Bald Eagle Mountain, Centre County, Pennsylvania. Scale bar is 1 cm.]]
Image:Bald Eagle 522 Shade Gap.jpg west of Shade Gap, Huntingdon County, Pennsylvania]]
The Bald Eagle is a good source of road material, riprap and building stone.{{cite journal|url=http://www.dcnr.state.pa.us/topogeo/openfile/mcalevysfort.pdf|archive-url=https://web.archive.org/web/20110609185124/http://www.dcnr.state.pa.us/topogeo/openfile/mcalevysfort.pdf|url-status=dead|archive-date=June 9, 2011|author1=Doden, Arnold G. |author2=Gold, David P. |name-list-style=amp |year=2008|title=Bedrock Geologic Map of The Mc Alevys Fort Quadrangle, Huntingdon, Centre, and Mifflin Counties, Pennsylvania|publisher=Pennsylvania Geological Survey}} However, iron pyrite inclusions may lead to acidic rainwater runoff.
References
{{Reflist}}
See also
{{wide image|BaldEagleFm_narrows.jpg|1000px|A panorama of the Bald Eagle portion of the Narrows roadcut in Bedford County for the Pennsylvania Turnpike. Stratigraphic up is to the left, and thus the beds are overturned. The beds are highly folded and faulted at right. February 2001.}}
Category:Ordovician System of North America
Category:Upper Ordovician Series
Category:Sandstone formations of the United States
Category:Ordovician geology of Pennsylvania
Category:Appalachian Mountains
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