Bellefonte Formation
| Bellefonte Formation | |
|---|---|
| Stratigraphic range: Lower Ordivician | |
| File:Road Cut of Bellefonte Formation.jpg Bellefonte Formation outcrop Mackeyville, PA | |
| Type | Formation |
| Unit of | Beekmantown Group |
| Sub-units |
|
| Underlies | Loysburg Formation |
| Overlies | Axeman Formation |
| Thickness | 50' - 2,145' |
| Lithology | |
| Primary | Dolomite, Limestone |
| Other | Sandstone, Chert |
| Location | |
| Region | Maryland, Pennsylvania, Virginia |
| Country | United States |
| Type section | |
| Named for | Bellefonte, Pennsylvania |
The Ordovician Bellefonte Formation is a mapped bedrock unit in central Pennsylvania. It is the uppermost unit of the Beekmantown Group. The top of the Bellefonte is marked by the Knox Unconformity.
Description
[edit | edit source]The Bellefonte is defined as a medium-gray, brownish-weathering, medium-bedded dolomite and minor sandstone. The very fine grained Tea Creek Member lies above, and the crystalline Coffee Run Member lies below.[1] The Tea Creek Member is a medium gray argillaceous limestone. While still a limestone it does have a high magnesium content. Mostly devoid of fossils. Beds of Chert maybe found about a third of the way through the Tea Creek Member.[2]
Depositional environment
[edit | edit source]Deposition of formations such as the Bellefonte Dolomite occurred in environments equivalent to the modern Bahama lagoons, east of Miami.[3]
Age
[edit | edit source]Relative age dating places it in the Ordovician period. It rests atop the Axemann Formation,[1] or the Nittany Formation. An example of this, is between Tyrone and Water Street, Pennsylvania. Here the Axemann is missing, and the Loysburg Formation conformably overlies the Bellefonte Formation.[4]
Fossils
[edit | edit source]Fossils are scarce in the Bellefonte. A few specimens have been found. Shells of a Hormotoma artemesia have been identified in the Bellefonte. [5]
See also
[edit | edit source]References
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