DEPOSITIONAL FACIES OF THE TETRAPOD FOOTPRINT ASSEMBLAGE FROM THE MISSISSIPPIAN MAUCH CHUNK FORMATION, SCHUYLKILL COUNTY, PENNSYLVANIA

Vertebrate footprints were first reported in 1850 by Isaac Lea from the Mississippian Mauch Chunk Formation at Mount Carbon, Schuylkill County, Pennsylvania and are among the oldest known tetrapod tracks from the United States. Numerous Mauch Chunk footprints were collected near Lea's locality during the early 20th century and are now housed at the Reading Public Museum, Pennsylvania. These earlier discoveries supplemented with recent collecting by the authors, have developed an extensive-low diversity footprint assemblage from the Mauch Chunk Formation.

Tracks in the assemblage are preserved as two facies, the most common, mud-draped ripple laminated with the less common, flat-bedded sandstone. In the mud-draped ripple laminated facies, mudstone drapes preserved current ripple bedforms and rare wave-ripple bedforms. Mudstone drapes serve as a parting surface for the slabs, allowing the identification of a spectrum of tracks and undertracks as extramorphological variants of Paleosauropus primaevus. Rare incipient shrinkage cracks and more commonly, raindrop impressions are found on the mudstone drapes. The flat-bedded sandstone preserves tracks and undertracks and has rare mudstone drapes. Tool marks are present on some slabs. Both facies were developed in fluvial channels with highly variable discharge in which velocity rapidly dropped shifting from bedload transport of sand to suspension settling of mud, most likely in the shallower parts of the channel.

Because of the mudstone drapes these tracks preserved in channel deposits reflect an important but difficult to recognize taphonomic window into Mississippian tetrapod diversity. This Mississippian tetrapod footprint assemblage that was preserved in fluvial channel sediments contrasts significantly with later Paleozoic track bearing red beds that developed either in tidal flats or in overbank ephemeral fluvial deposits where mudcracks and tracks are coincidental. In order to resolve ichnofaunal relationships with overbank deposits more systematic collection of finer-grained units of the Mauch Chunk Formation is warranted