MARGINAL-MARINE FACIES OF THE CATSKILL FORMATION (UPPER DEVONIAN), TIOGA COUNTY, PENNSYLVANIA

Nearly the entire thickness of the Catskill Formation (Upper Devonian) is exposed in roadcuts along US-15 near Tioga and Blossburg, Pennsylvania. The Tioga outcrop records the intertonguing relationship between drab marine mudrocks and sheet sandstones of the underlying Lock Haven Formation and terrestrial redbeds in the lower ~60% of the Catskill Formation. Terrestrial redbeds at this location are composed of red mudrock (~50%) with abundant, immature paleosols and scattered thin channel bodies. Thin, transitional redbed intervals at the contact between terrestrial and marine facies contain articulate brachiopods, Lingula, and vertical, Skolithos-like trace fossils. Although obvious indicators of tidal influence are lacking, sheet and channel sandstones exhibit bimodal (N-S) paleoflow indicators, suggesting a subtle tidal influence. The Blossburg outcrop contains the upper 75% of the Catskill Formation and lacks marine bands and transitional intervals present at Tioga. The Blossburg section is largely composed of red mudrock with abundant, immature paleosols – some of which contain mudcracks and pedogenic slickensides. Sandstone channel bodies become increasingly common upsection and progressively take on the gray coloration typical of the overlying Huntley Mountain Formation.

Exposures of the Catskill Formation near Tioga were deposited in a muddy, lower delta plain that prograded into a relatively calm, shallow marine environment. Transitional redbed intervals with marine body fossils and Skolithos-like trace fossils may represent a muddy tidal flat at the terrestrial-marine interface. Although the mud-dominated exposures at Blossburg represent much of the same stratigraphic interval, the lack of marine indicators suggests deposition in an upper delta plain slightly inland/updip from Tioga. While the majority of the Catskill Formation is exposed at these locations, they differ from exposures a few kilometers to the south, which contain abundant calcareous paleosols, and thick, multistorey channel bodies which record northeasterly paleoflow.