Wills Creek Formation

{{Infobox rockunit

| name = Wills Creek Formation

| image = Wills Creek Fm fold.jpg

| caption = Tight anticlinal fold in the Wills Creek Formation, along Route 22, Neff, Huntingdon County, Pennsylvania

| 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, 1905Uhler, P.R., 1905, The Niagara period and its associates near Cumberland, Maryland: Maryland Academy of Science Transactions, v. 2, p. 19-26.

| region = Appalachian Mountains

| country =

| coordinates =

| unitof =

| subunits =

| underlies = Tonoloway Formation

| overlies = Bloomsburg Formation and Williamsport Formation

| thickness =

| extent = Pennsylvania, Maryland, Virginia, West Virginia

| area =

| map =

| map_caption =

}}

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.{{cite web | url = http://www.geosc.psu.edu/news/features/gold/Final%20report%20%20Gold%20&%20Doden/Final%20Tables/Table%201%20Strat%20section.pdf| title = Table 1. Paleozoic Stratigraphic Section in Central Pennsylvania | work = Geological Report On The Skytop Road Cuts| publisher = Pennsylvania State University Department of Geosciences | year = 2004}}

The Wills Creek forms the bedrock of the valley around and to the east of Lewistown, Pennsylvania.{{cite map|url=http://www.dcnr.state.pa.us/topogeo/openfile/lewistown.pdf|archive-url=https://web.archive.org/web/20060328102026/http://www.dcnr.state.pa.us/topogeo/openfile/lewistown.pdf|url-status=dead|archive-date=March 28, 2006|format=pfd|title=Bedrock Geologic Map of the Lewistown Quadrangle, Mifflin and Juniata Counties, Pennsylvania| author = McElroy, Thomas A.| year = 2004 | publisher = Pennsylvania Geological Survey}}

= Fossils =

The Wills Creek Limestone contain fossils from the Pridoli to the Ludlow epoch, or 422.9 to 418.1 Ma.{{cite web |url=https://paleodb.org/cgi-bin/bridge.pl?action=displayStrata&group_hint=&group_formation_member=Wills%20Creek%20Limestone |title= Wills Creek Limestone Formation| publisher= Advisory Board of the Paleobiology Database | work= The Paleobiology Database| access-date=2008-01-26 }}

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 [http://ngmdb.usgs.gov/Prodesc/proddesc_294.htm]

= 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.{{cite web |url=http://www.mgs.md.gov/esic/geo/lgdalleg.html |title=Allegheny Plateau and Valley and Ridge | work = Geologic Map of Maryland | year = 1968 | publisher=Maryland Geological Survey|access-date=2008-01-26 }}

Economic use

The Wills Creek is a poor source of construction material and is only suitable as common fill.{{cite journal|url=http://www.dcnr.state.pa.us/topogeo/openfile/mcalevysfort.pdf|archive-url=https://web.archive.org/web/20110609185124/http://www.dcnr.state.pa.us/topogeo/openfile/mcalevysfort.pdf|url-status=dead|archive-date=June 9, 2011|author1=Doden, Arnold G. |author2=Gold, David P. |name-list-style=amp |year=2008|title=Bedrock Geologic Map of The Mc Alevys Fort Quadrangle, Huntingdon, Centre, and Mifflin Counties, Pennsylvania|publisher=Pennsylvania Geological Survey}}