Reexamination of the Sevier-Blountian Basin Through Detailed Geologic Mapping, Structural and Stratigraphic Analysis: Bays Mountain Synclinorium, Northeastern Tennessee

Bultman, John G., Robert D. Hatcher, Jr., and Neil E. Whitmer
Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN

One key to understanding the development of the Middle Ordovician southern Appalachain Sevier-Blountian basin lies in detailed geologic mapping. Key subdivisions have been identified that permit more accurate estimates for the thickness of the Sevier Shale. New detrital zircon and existing sedimentological data suggest the Sevier-Blountian basin is a back-bulge basin. Detrital zircon analyses from Ordovician to Pennsylvanian foreland clastics reveal few Paleozoic zircon cores until the Devonian and Carboniferous, indicating late Paleozoic unroofing of the southern and central Appalachians. Palinspastic reconstructions of the Alleghanian foreland fold-thrust belt require the Sevier-Blountian basin to be formed as much as 300 km inboard from the Middle Ordovician Laurentian margin. Furthermore, easterly derived conglomerate in the lower third of the section on the eastern flank of the basin is composed predominantly of Cambrian-Ordovician platform carbonates, and includes fewer 1.1 Ga basement and Cambrian rifted-margin and platform clasts. Regional isopachs and previously unidentified structural features in the basin may identify locations and migrations of the palinspastically restored forebulge and back-bulge basin. Isopach maps and 2-D backstripping curves would provide additional evidence for timing, possible depocenter migration, and subsidence rates for the basin. Facies and thickness information from new detailed geologic mapping helps define the role the back-bulge played in tectonic loading and deposition rates. A new model for Sevier-Blountian basin dynamics has been formulated based on our new data that better delineates thickness and facies variations.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004