PALEOECOLOGY OF AN ESTUARINE SEQUENCE IN THE BREATHITT FORMATION (PENNSYLVANIAN), CENTRAL APPALACHIAN BASIN

A sequence of strata containing 24 or more ichnogenera was investigate d along the western outcrop margin of the Breathitt Formation in easte rn Kentucky. Four facies were delineated within the study interval. Da rk shales of the Carbonaceous Shale Facies (CSF) exhibit a low-diversi ty/low-abundance ichnofossil assemblage dominated by small Conostichus , Planolites, and Thalassinoides. Some interbedded siltstones exhibit greater diversity with Lockeia, Paleophycus, Monocraterion, and Rhabdo glyphus. The CSF is truncated by the Bioturbated Heterolithic Facies ( BHF), consisting of bioturbated sandstones with robust Asterosoma, Con ostichus, and Rosselia, siltstones and gray shales with abundant Plano lites and Teichichnus, and non-bioturbated sideritic claystones. The B HF is truncated by the Interbedded Sandstone and Shale Facies (ISF), w hich occurs as two sheet-form tongues of ripple-bedded sandstone and s hale with variable-diversity and variable-abundance trace fossils, inc luding Asterosoma, Curvolithus, Helminthoida, Helminthopsis, Lockeia, Monocraterion, Planolites, Olivellites, Rosselia, and Scolicia. The IS F is truncated by the Ripple Bedded Sandstone Facies (RSF), which cons ists of two ripple-dominated channel fills. Bedding within parts of th e fills is crudely rhythmic; some repetitive form sets consist of 10 t o 12 laminae couplets. Trace fossils are rare in the channel fills, bu t Beaconichnus, arthropod resting traces, and arthropod rake marks occ ur. Flaser, wavy, and lenticular bedding, bi- to polymodal current ori entations, local rhythmic sedimentation, and bioturbation indicate tha t the facies were deposited in a shallow marine- to brackish-water tid al setting with minimal wave reworking. Changes in trace fossil abunda nce, diversity, and size were caused by changes in current velocity an d possibly salinity. Scour-filling tidal facies with indications of sa linity changes and a mixed Cruziana-Skolithos Ichnofacies are interpre ted to represent estuarine infilling. The fill sequence was controlled by the accomodation space of the estuary and lateral shifting channel s. Limited accomodation space caused repetitive scouring of older fill facies and incisement of multiple channels.