LOWER AND LOWER MIDDLE PENNSYLVANIAN FLUVIAL TO ESTUARINE DEPOSITION,CENTRAL APPALACHIAN BASIN - EFFECTS OF EUSTASY, TECTONICS, AND CLIMATE

Interpretations of Pennsylvanian sedimentation and peat accumulation c ommonly use examples from the Appalachian basin because of the excelle nt outcrops and large reserve of coal (>100 billion metric tons) in th e region, Particularly controversial is the origin of Lower and lower Pennsylvanian quartzose sand-stones; beach-barrier, marine-bar, tidal- strait, and fluvial models all have been applied to a series of sand b odies along the western outcrop margin of the basin, Interpretations o f these sand stones and the inferred lateral relationships are critica l for understanding the relative degree of eustatic, tectonic, and cli matic controls on Early Pennsylvanian sedimentation. Cross sections ut ilizing >1000 subsurface records and detailed sedimentological analysi s of the Livingston Conglomerate, Rockcastle Sandstone, Corbin Sandsto ne, and Pine Creek sandstone (an informal member) of the Breathitt Gro up were used to show that each of the principal quartzose sandstones o n the margin of the central Appalachian basin contains both fluvial an d marginal marine facies. The four sandstones are fluvially dominated and are inferred to represent successive bed-load trunk systems of the Appalachian foreland, Base-level rise and an associated decrease in e xtra-basinal sediment at the end of each fluvial episode led to the de velopment of local estuaries and marine reworking of the tops of the s and belts, Each of the sand belts is capped locally by a coal, regardl ess of whether the upper surfaces of the sand belts are of fluvial or estuarine origin, suggesting allocyclic controls on deposition. Feats were controlled by a tropical ever-wet climate, which also influenced sandstone composition through weathering of stored sands in slowly ag- grading braidplains. Recurrent stacking of thick, coarse-grained, fluv ial deposits with extra-basinal quartz pebbles; dominance of bed-load fluvial-lowstand deposits over mixed-load, estuarine-transgressive dep osits; thinning of sand belts around tectonic highs and along faults; cratonward shift and amalgamation of successive sand belts on the marg in of the basin; and truncation of successive sand belts toward the fa ult-bound margin of the basin are interpreted as regional responses to Alleghenian tectonism, inferred to have been the dominant control on accommodation space and sediment flux in the Early Pennsylvanian basin ,