Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Robert D. Hatcher

Committee Members

Don W. Byerly, Steven G. Driese, William M. Dunne

Abstract

The western Blue Ridge in southeastern Tennessee is underlain principally by metasedimentary rocks of the Walden Creek and Great Smoky Groups (Ocoee Supergroup). These rocks have traditionally been interpreted as turbiditic synrift sediments deposited along the Late Proterozoic to Early Cambrian southeastern Laurentian margin, which were subsequently metamorphosed and deformed during an early Paleozoic (Taconic) orogeny, then brittlely deformed and thrust westward during a late Paleozoic (Alleghanian) orogeny. More recent hypotheses suggest that at least part of the Walden Creek Group was deposited above the regional Middle Ordovician unconformity in post-Taconic successor basins, and deformed and metamorphosed only during a later Paleozoic event. Data gathered for this study in southeastern Tennessee support traditional interpretations of the age, stratigraphic relationships, and structural history of this portion of the Ocoee Supergroup.

First generation detailed (1:12,000-scale) geologic mapping of a 175 km2 (68 mi2) area in the Foothills and Mountain belts between Tellico River and Citico Creek, southeastern Tennessee, indicates that the contact between the Great Smoky Group and the overlying Walden Creek Group is conformable. This contact has previously been interpreted as the southern extension of the Greenbrier fault (a major premetamorphic tectonic boundary in the Great Smoky Mountains northeast of the study area), as a candidate for the Middle Ordovician unconformity, or as conformable. Rocks assigned to the Great Smoky Group are correlated with the Ammons and Dean Formations, and rocks assigned to the Walden Creek Group are correlated with the Wilhite Formation. These units are offset by the Rabbit Creek and Oconaluftee-Greenbrier faults.

Rocks within the study area were metamorphosed once, developed three foliations, displaced twice by thrust faults, and develolped four generations of folds. Metamorphism reached chlorite and biotite grades in the Taconic orogeny, during which regionally dominant F1 folds with axial-planar slaty cleavage (S1) were formed. Pressure-solution cleavage (S1a) also formed during this event. The Rabbit Creek and Oconaluftee-Greenbrier faults are Taconic structures that were reactivated in the Alleghanian orogeny, during which the entire predeformed package was thrust westward over unmetamorphosed Paleozoic platform rocks. Crenulation cleavage (S2) and F2 folds were probably also formed during this event. In the waning stages of the Alleghanian orogeny, F3 folds formed as the result of footwall duplexing in the Paleozoic rocks.

The Oconaluftee-Greenbrier thrust sheet is comprised of upper Great Smoky Group units and lower Walden Creek Group units, and contains the southwest-plunging Epperson synclinorium, which is analogous to the Murphy synclinorium on the west limb of the Ducktown anticlinorium. This simplified regional structure permits correlation of units within the study area with lithostratigraphically similar units in the Murphy belt to the east.

The Rabbit Creek thrust sheet is comprised of rocks previously assigned to the Cades Sandstone and contains southwest-plunging structure and a stratigraphic assemblage equivalent to that observed in the Oconaluftee-Greenbrier thrust sheet. The Rabbit Creek thrust sheet is here interpreted as containing the entire suite of Great Smoky Group formations. The name "Cades Sandstone," then, should be abandoned as a formation name.

The Alleghanian Foothills duplex produced the antiform that was eroded to breach the Great Smoky fault and form the windows in the Great Smoky Mountains National Park. Seismic evidence suggests this structure exists beneath the present study area. Other evidence includes a fold interference pattern, deflection of the biotite isograd, geomorphic anomalies, and rotation of bedding and cleavage.

An environmental site assessment for a hypothetical road construction project in the study area suggests that northeast- and south-facing slopes are the best candidates for planar or wedge failures, and that finer-grained lithologies crossed by the road have the most potential for producing acidic drainage. Further detailed study of these slopes and encapsulation of pyrititic materials would diminish or mitigate environmental damage.

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