Stratigraphy and Structure of Part of the Western Blue Ridge Foothills near Tellico Plains, Southeastern Tennessee

The Upper Proterozoic Walden Creek and Great Smoky Groups (Ocoee Supergroup) are a thick sequence of metasedimentary rocks that underlies the western Blue Ridge Foothills in southeastern Tennessee. These rocks represent synrift sedimentation along the Late Proterozoic to Early Cambrian Laurentian margin. They were subsequently deformed and metamorphosed during the Taconic orogeny (Ordovician), then brittlely deformed by northwestward thrusting during the Alleghanian orogeny (Permian). Rejected alternative interpretations suggest that the Walden Creek Group may be Middle Ordovician to Mississippian in age, and deposited in a post-Taconic successor basin, possibly during the Acadian orogeny. Those interpretations require that these rocks were metamorphosed and deformed only during the Alleghanian orogeny. Detailed geologic mapping (1:12,000 and 1:24,000) of a 191 km2 (~74 mi2) area indicates the western Blue Ridge Foothills in southeastern Tennessee consist of Chilhowee Group (Lower Cambrian), Walden Creek Group, and Great Smoky Group lithologies broken by late Paleozoic brittle faults. Rocks assigned to the Great Smoky Group are correlated with the Ammons and Dean formations, whereas rocks of the Walden Creek Group are correlated with the Wilhite and Sandsuck formations. A klippe of quartz arenite on Groundhog Mountain is correlated with the Hesse Quartzite (Chilhowee Group). The contact between the overlying Walden Creek Group (Wilhite Formation) and Great Smoky Group (Dean Formation) is conformable, thus providing an upper bound for the age of the Walden Creek Group. This contact previously has been interpreted as the southern continuation of the Greenbrier fault, as a Middle Ordovician unconformity, and more recently as conformable. The only other conformable contact between formations in the study area is between the Dean Formation and the underlying Ammons Formation (Great Smoky Group); all others are faults. In the Walden Creek Group, the Wilhite Formation is thrust (Miller Cove fault) onto the Sandsuck Formation, which is thrust (Great Smoky fault) onto Valley and Ridge units. Rocks within the study area were metamorphosed once, and cut by six regional thrust faults, and four generations of folds and cleavages. Metamorphism during the Taconic orogeny reached chlorite and biotite grade in the study area. During this orogeny, F1 folds with axial-planar slaty cleavage (S1) formed along with pressure-solution cleavage (S1a). Brittle Alleghanian deformation resulted in emplacement of the Bullet Mountain, Great Smoky, Maggies Mill, Miller Cove, Rabbit Creek and Oconaluftee faults. These faults separate the western Blue Ridge Foothills in the study area into three thrust sheets (Great Smoky, Miller Cove, and Rabbit Creek thrust sheets). The Bullet Mountain thrust sheet is located in the Valley and Ridge and is interpreted to have been transported northwestward beneath the Great Smoky thrust sheet. F2 kink folds and S2 crenulation cleavage formed as a result of this Alleghanian deformation in the Miller Cove thrust sheet. F3 folds and axial- planar slaty cleavage (S3) formed in the Great Smoky thrust sheet. Folding of these western Blue Ridge thrust sheets by duplexing of Valley and Ridge footwall units represents the F4 folding event. Strain analysis (Rf/0| and normalized Fry methods) of ten oriented sandstones from the Walden Creek Group and the Great Smoky Group in three western Blue Ridge thrust sheets yield mean strain ratios (Rxy, Rxz, Ryz) of 1.33, 1.71, 1.3 (X≥Y≥Z) and 1.61, 2.27, 1.43 (X≥Y≥Z), respectively. Strains appear to be the result of one or two western Blue Ridge deformation events. The highest strain values occur near Alleghanian brittle faults, and toward the southeast in the direction of increasing metamorphic grade and deformation. An environmental assessment for a hypothetical residential development within the Sixmile Creek and Rocky Branch watersheds in the study area indicates slope instabilities exist due to mechanical discontinuity characteristics in bedrock, recognition of previous landslides, topography, and climate. Previous landslides within this area are classified as debris slides and debris flows, and were possibly triggered by heavy rainfall events. Extensive development is not recommended in most of the assessment area