Reevaluation of the Age and Provenance of the GiantPalmichnium kosinskiorumEurypterid Trackway, from Elk County, Pennsylvania

Abstract

Palmichnium kosinskiorum Briggs and Rolfe, 1983, is a fossil trackway recovered from sandstones of the purported marine Shenango Formation along the banks of Spring Creek, in Elk County, Pennsylvania. Discovered in 1948, the type specimen is interpreted as a trail made by a lower Mississippian eurypterid. Recent field work has disclosed that the trackway of P. kosinskiorum was recovered from an allocthonous block of pebbly sandstone inconsistent with the character of the surrounding Shenango Formation. The P. kosinskiorum block is one of more than a dozen out-of-place giant boulders that train up the valley wall. These boulders can be traced back to an outcrop of the Pennsylvanian Pottsville Group located several hundred feet up the side of the Spring Creek Valley. Thus, it can be demonstrated that P. kosinskiorum originated from lower Pennsylvanian, not lower Mississippian bedrock.Palmichnium kosinskiorum was recovered from the top of a trough cross-bedded conglomeratic sequence, indicating that it was deposited in a high-energy fluvial environment of the Olean Conglomerate, a formation of the Pottsville Group. This purported depositional environment is consistent with other Upper Carboniferous eurypterid discoveries.