PALEOCLIMATE VS. SEA-LEVEL CONTROL OF COALY ZONES IN UPPER MISSISSIPPIAN STRATA OF THE CENTRAL APPALACHIAN BASIN: NEW INSIGHTS DERIVED FROM RECOGNITION OF REGIONAL TRANSGRESSIVE-REGRESSIVE CYCLES

Upper Mississippian (Serpukhovian) strata in the central Appalachian basin were deposited during the Carboniferous greenhouse-to-icehouse climate transition. Well developed paleosols and other climatically sensitive facies in this red-bed dominated succession generally record relatively dry climate conditions. In contrast, the occurrence of thin, locally developed coaly zones has sparked debate about evidence for climate cyclicity related to Gondwanan glacial episodes. A recent “climate model” suggests that coaly zones record brief shifts from seasonal-dry to humid conditions related to glacio-eustatic lowstands (glacial maxima). Alternatively, a “water-table model” proposes that coaly zones record landscape water-logging (not climate change) related to sea-level rise. Recent detailed sedimentological and sequence stratigraphic work in the outcrop belt has better constrained transgressive-regressive cyclicity in part of the succession (upper part of the Hinton Formation). In the refined stratigraphic framework, several coaly zones in the upper Hinton Formation underlie areally-extensive marine zones and are developed on fluvial or coastal facies that overlie sequence boundaries, suggesting association with transgressive events. A few coaly zones occur just above marine zones and are typically overlain by flooding surfaces, suggesting association with pulses of coastal progradation during highstand. Unequivocal evidence for coaly zones deposited during lowstand conditions seems to be absent. Although the “climate model” is appealing, we find that the “water-table” model better fits the new stratigraphic framework. If orbitally-forced climate events are recorded in the Upper Mississippian cyclothems, the evidence appears cryptic at the scale of field observations. Assuming that orbital forcing of climate occurred during Late Mississippian time, it may be productive to ask what factors contributed to the suppressed record of these cycles in the Upper Mississippian strata of the central Appalachian basin.