The Ordovician Reedsville Formation is a mapped surficial bedrock unit in Pennsylvania, Maryland, Virginia, West Virginia, and Tennessee, that extends into the subsurface of Ohio. This rock is a slope-former adjacent to (and stratigraphically below) the prominent ridge-forming Bald Eagle sandstone unit in the Appalachian Mountains. It is often abbreviated Or on geologic maps.
Description The Reedsville Formation is an olive-gray to dark-gray siltstone, shale, and fine-grained sandstone.Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000. In Central Pennsylvania along the Nittany Arch, and extending into the subsurface of northern West Virginia, the base of the Reedsville formation includes the black calcareous Antes Shale formation.
Type section The type locality is at Reedsville, Pennsylvania.
Age Relative age dating of the Reedsville places it in the Upper Ordovician. It rests conformably atop the Upper Ordovician Coburn Formation at the top of the Trenton Group limestone and conformably below the Bald Eagle Formation.
Isotopic dating of shale mylonite in Pennsylvania reveals a K-Ar age of 372+/-8 Ma.Lapham, D.M., and Root, S.I., 1971, Summary of isotopic age determinations in Pennsylvania: Pennsylvania Geological Survey Information Circular, 4th series, no. 70, 29 p.
Economic uses The Reedsville is quarried locally in borrow pits for road material and fill.
Palaeontology Taxa Class Description Images Kionoceras Cephalopod
References
See also Geology of Pennsylvania