| Wills Creek Formation | |
| Type: | sedimentary |
| Age: | Silurian |
| Period: | Silurian |
| Prilithology: | Sandstone, shale |
| Otherlithology: | Siltstone, limestone, dolomite |
| Namedfor: | Wills Creek at Cumberland, Allegany County, Maryland |
| Namedby: | P. R. Uhler, 1905[1] |
| Region: | Appalachian Mountains |
| Underlies: | Tonoloway Formation |
| Overlies: | Bloomsburg Formation and Williamsport Formation |
| Extent: | Pennsylvania, Maryland, Virginia, West Virginia |
Wills Creek Formation is a mapped Silurian bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.
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.[2]
The Wills Creek forms the bedrock of the valley around and to the east of Lewistown, Pennsylvania.[3]
The Wills Creek Limestone contain fossils from the Pridoli to the Ludlow epoch, or 422.9 to 418.1 Ma.[4]
Dean et al. (1985) describe the Wills Creek as sparsely fossiliferous.[5]
Conodonts have been identified in the Wills Creek in Virginia (Ozarkodina snajdri crispa Zone).[6]
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.[7]
The Wills Creek is a poor source of construction material and is only suitable as common fill.[8]