Bellefonte Formation
Stratigraphic range: Lower Ordivician
TypeFormation
Unit ofBeekmantown Group
Sub-units
  • Tea Creek Mbr
  • Coffee Run Mbr
UnderliesLoysburg Formation
OverliesAxeman Formation
Thickness50' - 2,145'
Lithology
PrimaryDolomite, Limestone
OtherSandstone, Chert
Location
Region
CountryUnited States
Type section
Named forBellefonte, 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

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

Deposition of formations such as the Bellefonte Dolomite occurred in environments equivalent to the modern Bahama lagoons, east of Miami.[3]

Age

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

References

  1. 1 2 "Explanation of Geologic Units" (PDF). Pennsylvania Geological Survey. Archived from the original (PDF) on April 22, 2003. Retrieved 2008-01-26.
  2. ↑ 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.
  3. ↑ "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.
  4. ↑ "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.


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