DECIPHERING THE MID-CARBONIFEROUS EUSTATIC EVENT IN THE CENTRAL APPALACHIAN REGION

The mid-Carboniferous eustatic event (MCEE), an interregional unconformity that marks the major onset of the Late Carboniferous ice age in the Euramerican paleoequatorial belt, is used to demark the boundary between the Mississippian and Pennsylvanian (Miss-Penn) Subsystems. Although a Miss-Penn unconformity is recognized throughout most of the central Appalachian foreland basin, the record of the MCEE in the structurally deepest part of the basin has been controversial. Models based on formation-scale lithostratigraphy hypothesize that the MCEE is marked by a disconformity at the base the Pineville Sandstone (New River Fm). However, paleofloral data indicate the sub-Pineville unconformity marks an intra-Westphalian (Langsettian) event that post-dates the intra-Namurian (Chokierian-Yeadonian) MCEE. Previous Miss-Penn boundary models in the foreland trough have postulated a conformable contact within a prograding deltaic succession. However, new biostratigraphic data and stratal relationships based on detailed mapping and sequence stratigraphic analysis refute these models and suggest the boundary is disconformable. The sum of biostratigraphic data supports an early Pennsylvanian hiatus (middle and late Namurian) that corresponds to the MCEE. The presence of a deeply incised paleovalley filled with basal Pennsylvanian strata is now confirmed. Along its thalweg, this paleovalley truncates a latest Mississippian marine zone capped by previously-recognized thick paleosols. The new depositional model for the Miss-Penn boundary in the foreland trough recognizes a prominent sequence boundary related to the MCEE. Therefore, major onset of the Carboniferous-Permian ice age is recorded as a mid-Namurian event in the central Appalachian region. This new model also suggests that the abrupt climate shift from relatively dry to relatively wet conditions across the Miss-Penn boundary in the may only appear abrupt due to the duration of the early Pennsylvanian hiatus.