Bellefonte Formation

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.

Bellefonte Formation
Stratigraphic range: Lower Ordivician
Bellefonte Formation outcrop Mackeyville, PA
Type	Formation
Unit of	Beekmantown Group
Sub-units	Tea Creek Mbr Coffee Run Mbr
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

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 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

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

• Geology of Pennsylvania