Late Carboniferous Fossils from the Glenshaw Formation in Armstrong County, Pennsylvania » The Armstrong County Localities

Armstrong County is one of 67 counties in the state of Pennsylvania. The counties’ administrative borders were organized in 1800—named after the Revolutionary War Major General John Armstrong (Betts 2012)—35 years before the first report of Pennsylvanian-aged marine fossils in the United States.

This book focuses on fossils from two localities, two different Glenshaw Formation limestones. Both have a unique paleoenvironment. The Brush Creek limestone at Parks Township (SL 6533) features embedded pinnid fossils, brachiopods, large bivalves, and limited gastropod and crinoid material. The Pine Creek limestone at Manor Township (SL 6445) has abundant gastropods, horn corals, and bivalves. Both locations have abundant cephalopods and preserve occasional chondrichthyan (cartilaginous fish) teeth.

Another difference is the condition of the limestone at each location. The Brush Creek limestone at Parks Township is a rigid, brittle rock. Fossils are difficult to recover in good condition. You’ll often get steinkerns with only bits of fossilized shell material stuck. In comparison, the Pine Creek limestone at Manor Township is fissile, usually allowing the recovery of complete fossils. Gastropods come with a coating of calcitic mud that I brush away with a steel brush and hot water.

Last, it’s important to note how well-studied each locality is. The 81st Annual Field Conference of Pennsylvania Geologists featured the Manor Township location as a stop during their field trip. Harper and Bragonier (2016) authored a section in the trip field guide to expand on the location’s geology, paleobiology, and the Pine Creek limestone. It is a public right-of-way that sits alongside a highway on-and-off ramp. In contrast, pre-2024 literature has never featured the Parks Township location; it is represented only by adjacent drill records published in a state report of the Freeport Quadrangle by Hughes (1933). These drill records can only partially correlate the geology at the Parks Location site. The majority of the land at the Parks Township location is private property.

Locality SL 6533

The Brush Creek limestone
Parks Township, Pennsylvania, USA

Locality SL 6445

The Pine Creek limestone
Manor Township, Pennsylvania, USA

• Locality SL 6445—The Pine Creek limestone in Manor Township, PA
• Locality SL 6533—The Brush Creek limestone in Parks Township, PA

References

• Betts, W. W. (2012). Rank and gravity, the life of General John Armstrong of Carlisle. Heritage Books.
• Hughes, H.H, 1933, No. 36 Freeport Quadrangle, Topographical and Geologic Atlas of Pennsylvania
• 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.