Wills Creek Formation is a mapped Silurian bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.
Description The Wills Creek is defined as a moderately well bedded greenish-gray shale containing local limestone and sandstone zones, or more specifically as an olive to yellowish-gray, thin-bedded sandstone, calcareous shale, dolomite, argillaceous limestone, and sandstone. Red shale and siltstone occur in the lower part of the formation. The formation has a thickness between 450 feet and 600 feet in Maryland and 445 to 620 feet in Pennsylvania.
The Wills Creek forms the bedrock of the valley around and to the east of Lewistown, Pennsylvania.
Fossils The Wills Creek Limestone contain fossils from the Pridoli to the Ludlow epoch, or 422.9 to 418.1 Ma.
Dean et al. (1985) describe the Wills Creek as sparsely fossiliferous.Dean, S.L., Kulander, B.R., and Lessing, Peter, 1985, Geology of the Capon Springs, Mountain Falls, Wardensville, Woodstock, and Yellow Springs quadrangles, Hampshire and Hardy Counties, West Virginia: West Virginia Geological and Economic Survey Map, 26, 1 sheet, scale 1:24,000
Conodonts have been identified in the Wills Creek in Virginia (Ozarkodina snajdri crispa Zone).Harris, A.G., Stamm, N.R., Weary, D.J., Repetski, J.E., Stamm, R.G., and Parker, R.A., 1994, Conodont color alteration index (CAI) map and conodont-based age determinations for the Winchester 30' x 60' quadrangle and adjacent area, Virginia, West Virginia, and Maryland: U.S. Geological Survey Miscellaneous Field Studies Map, MF-2239, 40 p., 1 sheet, scale 1:100,000
Notable outcrops Type section at Wills Creek at Cumberland, Allegany County, Maryland Roundtop Hill, Maryland, along railroad grade
Age Relative age dating of the Wills Creek places it in the Silurian period. It rests conformably a top the Bloomsburg Formation and below the Tonoloway Formation.
Economic use The Wills Creek is a poor source of construction material and is only suitable as common fill.
See also Geology of Pennsylvania
References