Bellefonte Formation
| Bellefonte Formation | |
|---|---|
| Stratigraphic range: Lower Ordivician | |
| 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 | |
| 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]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]Deposition of formations such as the Bellefonte Dolomite occurred in environments equivalent to the modern Bahama lagoons, east of Miami.[3]
Age
[edit]Relative age dating of the Bald Eagle 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]
See also
[edit]References
[edit]- ^ a b "Explanation of Geologic Units" (PDF). Pennsylvania Geological Survey. Archived from the original (PDF) on April 22, 2003. Retrieved 2008-01-26.
- ^ ULRICH, E. O. (1911-01-01). "Revision of the Paleozoic systems". Geological Society of America Bulletin. 22 (1): 281–680. doi:10.1130/gsab-22-281. ISSN 0016-7606.
- ^ "Structures of The Appalachian Foreland Fold-Thrust Belt: Fold-Thrust Geometries of the Juniata Culmination (State College and Environs), Central Appalachians of Pennsylvania". Pennsylvania State University Department of Geosciences. Archived from the original on December 13, 2000. Retrieved 2008-01-27.
- ^ "Trenton Black River Carbonates: Stop 3". Trenton and Black River Carbonates in the Union Furnace Area of Blair and Huntingdon Counties, Pennsylvania. Pennsylvania Geological Survey. Archived from the original on 27 December 2007. Retrieved 2008-01-27.