INTEGRATED SEDIMENTOLOGICAL, PALEONTOLOGICAL, AND GEOCHEMICAL DATA FROM UPPER DEVONIAN STRATA, NORTH-CENTRAL PENNSYLVANIA (U.S.A): IMPLICATIONS FOR RECONSTRUCTING PALEOENVIRONMENTS THAT HOSTED THE FIN-TO-LIMB TRANSFORMATION

Upper Devonian strata (Catskill and upper Lock Haven Formations) in north-central Pennsylvania preserve abundant sedimentary features, trace fossils, palynomorphs, and body fossils, including fishes and tetrapodomorphs, making this region ideal for reconstructing paleoenvironments that hosted the fin-to-limb transition. Recent research from outcrops and cores yielded late Famennian palynomorph assemblages and three main lithofacies associations: (1) cross-stratified sandstone bodies, red mudrocks, sharp-based sandstones, and bedded shales interpreted as fluvial channels-bars, floodplain paleosols, crevasse splay channels and lobes, and ponds and lakes, respectively; (2) heterolithic mudstone, sandstone, and coquinite with flaser-wavy-lenticular bedding attributed to tidal channels, bars, and flats in transitional environments; and (3) mudrock, shale, and sandstone interpreted as shoreface and prodelta environments. Fluvial deposits preserve diverse floral remains and trace fossils constructed by soil-dwelling and aquatic organisms, including decapods, scorpions, other arthropods, lungfish, and bivalves. Transitional and shallow marine deposits yield body fossils of acritarchs, brachiopods, bivalves, bryozoa, crinoids, nautiloids, and aquatic trace fossils attributable to fishes, sea-stars, horseshoe crabs, trilobites, gastropods, and bivalves, among others. Fluvial and transitional deposits preserve diverse vertebrates, including “placoderms”, acanthodians, and sarcopterygians, indicating these taxa inhabited a spectrum of brackish to freshwater habitats. However, actinopterygians occur only in fluvial deposits, indicating they were restricted to freshwater habitats. Shallow marine deposits pass vertically into transitional and fluvial deposits, consistent with westward alluvial plain progradation. However, smaller-scale stratigraphic variations reveal relative sea-level fluctuations and lateral complexities in shoreline environments that warrant further study. Decapod burrows constructed in pedogenically modified floodplain deposits to the depth of the water table, as well as bulk (XRF) geochemical signature of Catskill Formation strata, record evidence of wet-dry (precipitation) seasonality in the late Devonian climate system.