Keyser Formation

Keyser Formation Stratigraphic range: Late Silurian to Early Devonian
Outcrop of the Keyser Formation on U.S. Route 522 in Fulton County, Pennsylvania north of Warfordsburg.
Type	sedimentary
Unit of	Helderberg Group
Sub-units	Byers Island, Jersey Shore, La Vale
Underlies	Old Port Formation
Overlies	Tonoloway Formation
Thickness	33 m at Allegheny Furnace
Lithology
Primary	limestone
Location
Region	Appalachian Mountains
Extent	Pennsylvania, Maryland, Virginia, West Virginia
Type section
Named for	Keyser, West Virginia
Named by	E. O. Ulrich, 1911

The Late Silurian to Early Devonian Keyser Formation is a mapped limestone bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.

The Keyser is a nodular limestone overlain by thick- and thin-bedded limestone and laminated limestone at its type locality in Keyser, West Virginia.

In central Pennsylvania, the basal "calico" limestone is a fossiliferous, medium-light- to medium-gray very thick bedded calcilutite containing numerous small irregular patches of clear calcite. The abundantly fossiliferous, nodular limestone at the base overlies the "calico". Overlying this is 5 to 6 m of fragmental calcarenite containing abundant crinoid columnals. Above the calcarenite is 6 m of fossiliferous, banded calcisiltite. The uppermost 15 m is a sequence alternating between laminated, stromatolitic calcisiltite, and calcilutite and calcisiltite that are argillaceous and fossiliferous.

The depositional environment of the Keyser is interpreted as shallow marine and tidal flats, occurring in cycles.

Contact with Tonoloway Formation is probably conformable, but sharp enough to suggest an unconformity. Upper contact with the Old Port Formation is conformable.

The Keyser was divided into three members by J. W. Head in 1972. These are, from lowest to highest, the Byers Island Member, Jersey Shore Member, and La Vale Member. The type locality of the Byers Island Member is at Selinsgrove, Pennsylvania, where it is 93 feet thick. The type locality of the Jersey Shore Member is at Jersey Shore, Lycoming County, Pennsylvania. The type locality of the La Vale Member is at the Corriganville quarry, Allegany County, Maryland, and is named from nearby town of La Vale. This nomenclature is accepted by the USGS.