Locality SL 6533—The Brush Creek limestone in Parks Township, PA

My first experience with any marine limestone comes from Locality SL 6533, numbered after I donated the first gastropod specimen from it to the Carnegie Museum of Natural History. The locality sits on the unglaciated Allegheny Plateau. As the plateau lifted, rivers and tributaries cut into the Pennsylvanian-aged sediments. Eventually, these cut deep enough to expose the marine limestones discussed in this book.

Guffy Run and its tributaries carved out the valley here on personal property and private farmland. With permission from various neighbors, I collected the one-foot-thick Brush Creek limestone from a wide swath of the valley where the eroded bedrock allowed the limestone to crop out.

The sources of Guffy Run start in the Casselman Formation. Guffy Run cuts through the Glenshaw Formation and spends considerable time cutting through the top of the Allegheny Group before emptying into the Kiskiminetas River. Forming the southwestern border of Parks Township, the Kiskiminetas River sits in the Allegheny Group. Guffy Run unnamed tributaries cut through the Brush Creek limestone in two viewable locations. One cut is to the East—off a private right-of-way; the other is to the West. Both of these sit at the bottom of deep incised valleys.

The valley floodplain is the widest in places where it runs North to South. The floodplain is consistently 160–210 feet wide from this location until it reaches the Kiskiminetas floodplain. The point where Guffy Run cuts through the Brush Creek limestone is unapparent and buried in the floodplain. Several float blocks of the limestone likely sit hidden in floodplain sediments. Guffy Run has a washed-out massive shale floor that produces expansive fern fossils in places. The floodplain deposit is roughly three feet (91.4 cm) thick based on the stream-exposed bedrock.

Distinct plant-producing layers exist below the Brush Creek limestone in Parks Township. The shales contain remains of ferns (Marattiaceae), Calamities (Calamitaceae), and woody material. The ferns can appear as impressions and a deep-black carbon film on many specimens.

Fig. 1.—A generalized stratigraphic map of Parks Township formations. The Brush Creek limestone occurs in the lower to middle Glenshaw Formation.

Historical Paleontology Reports

The first modern paleontology report from Parks Township came from Burke in 1958 when he named the Carnahan Shale for exposures along alternative PA Route 66 in Parks Township. Burke noted the calcareous shale was five feet thick, fossiliferous, contained tiny flecks of mica, and had a dark grey color. In addition, he wrote that there were 347 feet of bedrock between the Freeport Coal and the Ames Limestone at the type locality. Later, Wells (1983) found that Burke’s Carnahan Run shale belonged to the Woods Run limestone.

Hughes (1933) reported on the geology of the Freeport Quadrangle, a 15-minute (one-fourth of a degree of latitude) wide section in Western Pennsylvania. The Eastern Section Meeting of the American Association of Petroleum Geologists (Busch & Brezinski, 1984) added a geological exposure stop in North Vandergrift, Parks Township, along Kepple Ave. They reported Dunbarella, Worthenia tabulata, and plant fragments from the Brush Creek marine zone.

On the Pinnids of SL 6533

Yancey (2024) reported on a species of Pinnid from SL 6533 using a large cache of material I collected over a few years. The holotype (CM 54677, formerly CG-0112) sits in the Carnegie Museum of Natural History. Pinnid fossils are common in the Brush Creek limestone at Parks Township. I find most of the specimens in life position. In life, pinnids bury their narrow end into sediment using a byssus—a bundle of anchoring filaments. The anterior anchored part of the shell is thick and hardened with a pearly nacreous layer. The top posterior end is flimsy in comparison and rarely survives burial. The pinnids appear as pointed oval shapes in the limestone, aligned perpendicular to the lateral limestone layer.
The Field Conference of Pennsylvania Geologists (DATE?) added an exposure stop in North Vandergrift, located behind the Parks Township Administration Building.

References

Burke, J. J., 1958. New Marine Horizon in the Conemaugh Formation, Science. p. 302
Busch, R. M., and Rollins, H. B., 1984. Correlation of Carboniferous strata using a hierarchy of transgressive–regressive units: Geology, v. 12, p. 471-474.
Harper, J. A., 2016. Some geological considerations of the marine rocks of the Glenshaw Formation (Upper Pennsylvanian, Conemaugh Group), in Anthony, R., ed., Energy and environments: Geology in the “Nether World” of Indiana County, Pennsylvania. Guidebook, 81st Annual Field Conference of Pennsylvania Geologists, Indiana, PA, p. 47-62.
Heckel, P. H., Barrick, J.E., and Rosscoe, S.J., 2011. Conodont-based correlation of marine units in lower Conemaugh Group (Late Pennsylvanian) in Northern Appalachian Basin: Stratigraphy, v. 8, p. 253-269.
Hughes, H.H, 1933. No. 36 Freeport Quadrangle, Topographical and Geologic Atlas of Pennsylvania.
Yancey, T.E., 2024. Revision of Late Paleozoic Pinnid Genera and North American Species of Bivalve Family Pinnidae, Paleontological Research Institution, 84 p.
Wells, J. W., 1966. Paleontological evidence of the rate of the Earth’s rotation. pp. 70-81, in: B. G. Marsden and A. G. W. Cameron (eds.), The Earth-Moon System, Springer.
White, I. C., 1878. Report of progress in the Beaver River district of the bituminous coal fields of western Pennsylvania. Middletown: Pennsylvania Geological Survey. 2nd Series, Report Q, 337 p.