Masters Theses

Date of Award

5-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Robert D. Hatcher, Jr.

Committee Members

Thomas W. Broadhead, William M. Dunne

Abstract

The Upper Proterozoic Walden Creek Group (Ocoee Supergroup) is a thick sequence of metasedimentary rocks that underlies the western Blue Ridge Foothills belt in eastern Tennessee. Traditional interpretation suggests that rocks of the Walden Creek Group represent synrift sedimentation along the Late Proterozoic Laruentian margin. These rocks were later regionally metamorphosed, cleaved, folded, and thrust westward during two Paleozoic orogenies (Taconic and Alleghanian). Recent hypotheses from uncorroborated paleontological evidence suggest that the Walden Creek Group is no older than Silurian, deposited into a post-Taconic successor basin, and subsequently metamorphosed and deformed only during the Alleghanian orogeny. Stratigraphic and structural data from this study in the Foothills belt of southern Tennessee support traditional views about the age, depositional setting, and structural chronology of the Walden Creek Group.

Detailed geologic mapping (1:12,000 and 1:24,000) of a 209 km2 (84 mi2) area indicated that the Walden Creek Group sequence in southern Tennessee is broken by the Miller Cove and Maggies Mill faults. Lithologic similarities between the footwall and hanging wall of the Maggies Mill fault provide a partially complete stratigraphic section. Mapping confirms that the middle and upper members of the Sandsuck Formation (Walden Creek Group) are conformably overlain by the Lower Cambrian Chilhowee Group, and that the Wilhite Formation (Walden Creek Group) conformably overlies rocks of the Great Smoky Group (Ocoee Supergroup). The upper conformable contact with the Chilhowee Group implies that at least the middle and upper members of the Sandsuck Formation can be no younger than Early Cambrian. The lower conformable contact with the Great Smoky Group was previously interpreted to be the southern continuation of the Greenbrier fault.

Rocks of the study are deformed by four generations of folds and cleavages, and four regional thrust faults. F1 folds are overprinted by regionally dominant F2 folds and axial-planar slaty cleavage (S2). F1 and S2 are related to regional Barrovian-type metamorphism. Pressure-solution cleavage (S2a) probably developed late in the same event that produced F2 folds and axial-planar S2 cleavage. Strain analysis (Rf/ᶲ, normalized Fry, and Flinn methods) yield values that range between 1.18 to 1.63, 1.30 to 1.73, and 2.43 to 4.92 (Rxy [X ≥ Y ≥ Z), respectively. Strain values appear to be the product of one non-coaxial western Blue Ridge event, but it is unclear whether this event occurred before or during F2 and S2 development. Crenulation cleavage (S3), spaced cleavage (S3a), F3 folds, and F4 folds may have developed during a later deformational event dominated by regional brittle faulting. These brittle faults (Great Smoky, Maggies Mill, Miller Cove, and Bullet Mountain faults) separate rocks of the study area into three western Blue Ridge frontal thrust sheets (Great Smoky, Maggies Mill, Miller Cove thrust sheets), and one Valley and Ridge thrust sheet (Bullet Mountain thrust sheet).

Stratigraphic and age relationships, and sedimentological characteristics of Great Smoky and Walden Creek Group rocks in southern Tennessee, southwestern North Carolina, and northwestern Georgia suggest that the Ocoee depositional basin at this latitude evolved during rifting of the Laurentian margin on the Late Proterozoic to Early Cambrian. Rifting was followed by stabilization of the rift basin and passive margin development during the Early Cambrian. The Wilhite Formation may be the western equivalent of the Nantahala Brasstown Formations, and the Murphy Marble in the Murphy Belt. Carbonate clasts in breccia of the lower member of the Sandsuck Formation may have been derived from the Murphy Marble as base-of-slope deposits. Structural analysis of Foothills belt rocks in the study area suggests that subsequent deformation along the Laurentian margin occurred during the Taconic orogeny with the development of regional metamorphism, F1 and F2 folds, axial-planar slaty cleavage (S2), and pressure-solution cleavage (S2a). Regional brittle thrust faults, crenulation cleavage (S3), spaced cleavage (S3a), F3 folds, and F4 folds deformed these rocks during the Alleghanian orogeny.

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