DETAILED GEOLOGIC MAPPING: GEOLOGICAL ACUMEN FOR SEVIER-BLOUNTIAN BASIN DYNAMICS: BAYS MOUNTIAN SYNCLINORIUM, NORTHEASTERN TENNESSEE

In the Appalachian orogenic belt, many aspects of 4-D basin evolution, structural and stratigraphic relationships, and foreland-fold thrust belt (FFTB) kinematics have yet to be determined. Existing palinspastic reconstructions of the Alleghanian FFTB require that the Llanvirn-Llandeilo Sevier-Blountian basin was ~300 km inboard from the rifted Laurentian margin. Results of our geologic mapping combined with new detrital zircon and existing sedimentological data suggest the Sevier-Blountian basin is a back-bulge basin. 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 with fewer 1.1 Ga basement and Cambrian rifted-margin platform clasts. The Bays Mountain synclinorium and surrounding area in the Tennessee Valley and Ridge provides critical facies data to address Sevier-Blountian basin dynamics. This area preserves the Middle Ordovician post-Knox unconformity, the Sevier-Blountian basin depositional sequence, overlying Bays Formation quartz arenite-redbed sequence, and the base of the overlying Caradocian Martinsburg clastic wedge. Detailed geologic mapping has identified key marker units used to divide the Sevier Shale into three members: a lower thin-bedded, dark gray-black graptolite-bearing shale overlain by dark gray-black micritic limestone, a middle silty-sandy limestone interbedded with light-gray silty shale overlain by calcareous sandstone, and an upper thick-bedded light gray shale grading upward into massive fossil-bearing sandy limestone. Faulting and folding within the Sevier Shale is responsible for previous thickness estimates as large as 10,000 ft (3,048 m). Instead we propose a maximum thickness of 5,000 ft (1,524 m) near the edge of the basin and a maximum basin thickness estimate of 7,500 ft (2286 m). Compilation and reanalysis of previous work, as well as new detailed geologic mapping better delineate 4-D basin evolution and FFTB kinematics providing insight for future studies.