THE EFFECT OF THE CAROLINA PROMONTORY ON THE PARTITIONING OF THE APPALACHIAN BASIN IN THE MIDDLE TO LATE PENNSYLVANIAN

Zircons extracted from fluvial sandstones of the Conemaugh and Monongahela Groups in southeastern Ohio were analyzed by laser ablation-ICPMS for U-Pb geochronology. The goals of the study were to determine if fluvial styles contained different zircon populations and if the transition between groups in the Late Pennsylvanian reflected changes in provenance. Thin section point counts show that the meandering, anastomosing, and braided fluvial deposits vary slightly in grain composition with grain size but fall within the recycled orogenic field, as expected. However, all samples have essentially identical zircon age populations with a moderate ~420 Ma (Acadian) population and a much larger population from 1000-1200 Ma (Grenville). These data, which are similar to those previously reported from both older and younger strata in this portion of the central Appalachian basin, indicate that the controls on fluvial style do not reflect source rock variations and that there was no resolvable change in provenance from the Middle Pennsylvanian through to the Early Permian(?).

A spatial and temporal comparison of detrital zircon age spectra from this and other modern geochronologic studies along the length of central and southern Appalachians shows that there are three distinct zircon age signatures present. Type A lacks a Paleozoic zircon population, Type B has few, if any, zircons older than 1600 Ma but has a Paleozoic signal, and Type C has zircons that range in age from the Archean to Early Paleozoic. All types have a strong 1100 Ma Grenville component and there appears to be no stratigraphic trend related to unroofing of the orogen. However, the spatial distribution is significant: Type B is present only in samples north of a NW-trending lineament that is coincident with the northern margin of the Carolina Promontory. This major tectonic feature appears to have partitioned sediment provenance within the Appalachian basin throughout the Alleghenian Orogeny