Permian System
| The Section below shows the general stratigraphy for the Permian of Southwestern Pennsylvania. The red boxes to the right represent the section exposed at each outcrop site. Click on the box to visit the page for that site. |
KEY: Gray is shale, blue is limestone, black is coal, and yellow is sandstone.
Dunkard Group (the following is paraphrased from http://www.dep.state.pa.us/dep/deputate/minres/districts/cmdp/Chap08-1.html)
The Dunkard Group is found only in the most southwestern corner of Pennsylvania in Greene and Washington Counties. It is made up of Waynesburg, Washington and Greene Formations (Berryhill et al., 1971). The Dunkard reaches a maximum thickness of about 1120 ft (340 m) in Greene County and the upper surface is the modern day erosional surface. The lower boundary of the Dunkard Group is defined as the base of the Waynesburg coal, which is the only coal routinely mined in the Dunkard.
The Dunkard is generally composed of fine-grained clastics which are frequently calcareous. Thick lacustrine limestones are especially prevalent in the Washington Formation. The only significant interval with sandstone is above the Waynesburg coal. This sandstone is often, but not always, calcareous. A comparison of this data with the study by Berryhill et al. (1971) for Washington County shows some differences in abundance of lithologies. For example Berryhill et al. show that 33% of the Group is limestone, whereas this study found only 6.2% limestone. This is probably largely attributable to a facies change between Washington and Greene Counties. The Upper Washington and Lower Washington Limestones, which are thick in Washington County are barely present in Greene County.
As mentioned, the only coal routinely mined in the Dunkard is the Waynesburg.
References
Berryhill, H.L., Jr., S.P. Schweinfurth, and B.H. Kent, 1971. Coal-bearing Upper Pennsylvanian and Lower Permian Rocks, Washington Area, Pennsylvania. USGS Prof. Paper 621.
Edmunds, W.E., V.W. Skema, and N.K. Flint, 1998. Pennsylvanian. Part II. Stratigraphy and Sedimentary Tectonics. Geology of Pennsylvania, pp. 149-169.
Skema, V.W., C.H. Dodge and J.R. Shaulis, 1991. Lithologic character and correlation of marine units in the Conemaugh Group (Upper Pennsylvanian), western Pennsylvania (abstract). Geol. Soc. of America, Northeastern and Southeastern Section Meeting, v. 23, no. 1, p. 128.
Williams, E.G., 1960. Marine and fresh water fossiliferous beds in the Pottsville and Allegheny Groups of western Pennsylvania. Jour. of Paleontology, v. 34, pp. 908-922.