IDENTIFYING THE STRATIGRAPHIC POSITION AND PALEOENVIRONMENTAL SIGNATURE OF THE CARBONIFEROUS-PERMIAN TRANSITION IN THE TERRESTRIAL SEQUENCES OF CENTRAL APPALACHIA, EASTERN NORTH AMERICA

In central Appalachia (Pennsylvania, Ohio, West Virginia) the Late Paleozoic is represented by Carboniferous-Permian (C-P) sediments that are preserved within the Dunkard Basin. These sediments are characterized by terrestrial sandstones, mudstones, and paleosols in the southwest and similar lithologies interbedded with thick coals and lacustrine limestone accumulated to the northeast. However, the lateral facies changes, as well as few indicator fossils, radiometrically datable horizons and paleomagnetic reversals, make it challenging to identify the stratigraphic position of the C-P transition, contributing to conflicting chronostratigraphic allocation of the basin-fill sediments and uncertainties with assessing the global climate effects on terrestrial environmental change. To address these problems, we studied ~32.5 m of Monongahela and Dunkard group outcrops exposed in southeast Ohio, examining rock magnetism and hematite concentrations of paleosols. Magnetic susceptibility is low (0.38 to 0.73 x 10^-7 kg/m²) for Monongahela samples but increases greatly in the Dunkard Group (0.39 to 9.6 x 10^-7 kg/m²). Similarly, ARM values show an increase by two orders of magnitude in Dunkard paleosols. Spectral analysis indicates the rock magnetic stratigraphic variations recur in ~20-30 cm cycles that in combination with chronostratigraphic evidence may represent orbital precession (~20 kyr) forcing of monsoonal rainfall. The increase in susceptibility may be indicative of paleoclimate change associated with the C-P transition, which evidently resulted in increasingly favorable conditions for single-domain magnetic particles. These observations may suggest the Dunkard Group is a Permian unit, in agreement with tetrapod body fossils, footprint evidence, and insect biostratigraphy. We evaluate these results by comparing the competing chronostratigraphic interpretations and evidence from previous documented geochemical records of rainfall, paleosol types, and ichnofacies. Finally, the rock magnetic stratigraphy and paleoenvironment of the Paradox Basin contrasts with central Appalachia, perhaps indicating some regions of eastern equatorial Laurentia may have not experienced the Permian aridity characteristic of the end of the Late Paleozoic Ice Age.