EVIDENCE FOR LATE CENOZOIC UPLIFT IN THE SOUTHERN APPALACHIAN MOUNTAINS FROM ISOLATED SEDIMENT TRAPS

The height and morphology of the present-day southern Appalachian Mountains (as defined physiographically) are attributed traditionally to Paleozoic and early Mesozoic tectonism and differences in the resistance to erosion of the various Precambrian and Paleozoic rocks that comprise the province. The present configuration of the Fall Line, combined with the occurrence of Cretaceous and younger marine deposits up to 300 m (1,000 ft) above present sea level indicate that Coastal Plain strata once covered parts of the mountain chain, which have been regionally uplifted to their present positions. Remnant Cretaceous and lower Cenozoic strata are preserved at elevations up to +685 m (+2,250 ft) in numerous fault-bounded and(or) sinkhole sediment traps as far inland as northern Georgia and Alabama, southeastern Tennessee, western Virginia, and Pennsylvania. The sediments in these traps are most likely the preserved parts of an extensive blanket of Coastal Plain strata that was derived from regional erosion. The sediment traps, which are filled with fluvial strata as much as 100 m (325 ft) thick uncommonly contain carbonaceous beds. Palynological age assignments of pollen in these beds indicate that they are correlative with Coastal Plain formations hundreds of kilometers seaward. The ages assigned to the sediments in these traps range from Late Cretaceous to middle Eocene. If the sediment trap strata are part of a regional cover that was once continuous across the southern Appalachian Mountains, then the uplift of the present-day southern Appalachians must post-date the youngest palynological age (middle Eocene). Applying minimal published erosion rates (3 m/m.y.) for the Appalachian Mountains, these deposits would have been completely eroded during the last 33 m.y. given their present thickness (< 100 m). Therefore, the fact that they exist at all indicates that: (1) they were once covered by a much thicker sedimentary cover, and(or) (2) their uplift, along with that of the Appalachians, must be considerably more recent than Eocene. This new evidence suggests the intriguing possibility that the Appalachians are not Paleozoic mountains, but rather late Cenozoic mountains comprised of Precambrian and Paleozoic rocks.