Trace Fossils Indicating Estuarine Deposystems for the Devonian-Mississippian Cloyd Conglomerate Member, Price Formation, Central Appalachians

Abstract

The use of ichnologic data is crucial to the understanding of some paleoenvironmental regimes. The Cloyd Conglomerate Member of the Price Formation has been interpreted as entirely fluvial, partly fluvial and partly marine bar, and entirely marine bar. Trace fossils provide data to resolve these divergent opinions. The Cloyd preserves a thin sedimentary wedge composed of a lower, regressive nonmarine phase and an upper, transgressive marine phase bearing trace fossils and a restricted marine fauna. Massive, quartz-pebble conglomerates of the lower Cloyd were deposited in fluvio-distributaty systems during a regression near the Devonian-Mississippian boundaty. Regressive channel systems became estuaries during a subsequent transgression. Trace fossils in the upper Cloyd constitute a mixed Skolithos-Cruziana Ichnofacies of suspension-feeding sand dwellers and depositfeeding mud dwellers. Though not abundant, trace fossils occur most commonly in the uppermost sandstone beds of fining-upward, estuary pointbar deposits. A point-bar assemblage includes large, deep Skolithos and Cylindrichnus suspension feeders that inhabited bar slip faces. Deep burrowing behavior suggests that point-bar trace makers sought to moderate environmental extremes, e.g., salinity and temperature fluctuation and possible subaerial exposure of bar surfaces. The Teichichnus trace maker inhabited lower-energy, submerged sand flats on point-bar surfaces, possibly following channel abandonment. Tidal-flat facies composed of organic-rich silty shales with interbedded siltstones and sandstones overlie point-bar sandstones. Well-circulated tidal-flat facies are dominated by shallow-burrowing suspension feeders in sandstone interbeds. The trace assemblage includes Arenicolites, Diplocraterion, Monocraterion, Planolites, Rusophycus?, and shallow Skolithos. A backwater assemblage includes Chondrites and Planolites deposit feeders that inhabited organic-rich, black