CRETACEOUS EROSION OF THE SOUTHERN APPALACHIANS FROM IN-SITU THERMOCHRONOMETERS, SEDIMENT PROVENANCE, AND SEDIMENT ACCUMULATION RATES IN THE EASTERN GULF OF MEXICO BASIN

Cretaceous erosion of the southern Appalachians is known from in-situ thermochronometers and the stratigraphy of the Atlantic margin from New Jersey to North Carolina. Measured apatite fission track (AFT) and (U-Th)/He ages from rocks across the southern and central Appalachian orogen are Cretaceous or older, and recent workers have argued that the data record steady exhumational cooling. In contrast, stratal volumes along the Atlantic margin indicate maxima of sediment accumulation rates in the Hauterivian-Barremian and in the Coniacian-Santonian. We attempt to better resolve the Cretaceous erosional history of the southern Appalachians using three methods.

First, a review of published AFT data shows that a broad AFT age mode from ~150-85 Ma in the deeply eroded parts of the orogen. Second, reconnaissance detrital zircon data (100 single-grain U-Pb ages from each of 13 samples) were collected for the Cenomanian lower Tuscaloosa Group, the Albian-Cenomanian Washita-Fredericksburg Groups, and the Neocomian Hosston Formation, all from Mississippi and Alabama. In the context of other recent detrital zircon-based provenance studies, these data show a persistent source-sink connection between the southern Appalachians and the eastern Gulf of Mexico. Third, in the eastern Gulf of Mexico just offshore of the western Florida Panhandle and Mobile Bay, we constructed a Cretaceous stratigraphic framework for six wells that penetrated the entire Cretaceous section. Geophysical logs, public-domain paleontological reports, and lithologic logs constrain the stratigraphy in these wells. Analysis of sediment accumulation rates between 12 Cretaceous stratigraphic datums indicates generally rapid sediment accumulation (order of ~100m/Myr) from the Berriasian to the Cenomanian, with relatively slower sediment accumulation (order of ~10 m/Myr, and predominantly carbonate deposition) thereafter. In light of the thermochronologic evidence for widespread exhumation in the Early Cretaceous and coeval relatively rapid eastern Gulf sediment accumulation from Appalachian source areas, we suggest that most of the relief in the southern Appalachians that was inherited from Paleozoic orogenesis and Triassic-Jurassic continental breakup was eroded by approximately the Cenomanian.