The

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

Bald Eagle Formation is a mapped bedrock unit in central

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

, USA. It is a ridge-forming unit in the

Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. The ...

Description

The Bald Eagle is defined as a gray to olive-gray and grayish-red, fine to coarse-grained

crossbedded In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...

. 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 The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the Unit ...

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

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 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 t ...

.Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.

Economic Uses

The Bald Eagle is a good source of road material, riprap and building stone. However,

iron pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue gi ...

inclusions may lead to acidic rainwater runoff.

Description

Depositional environment

Fossils

Age

Economic Uses

References

See also