Masters Theses

Date of Award

3-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Nick Woodward

Committee Members

Don Byerly, Ken Walker

Abstract

The Wartburg Basin Is a broad area of little deformed rocks which protrudes into structurally disturbed portions of the Cumberland Plateau and northwestern Valley and Ridge. Northeast of the protrusion the Pine Mountain fault system Is characterized by a classic staircase geometry. Southeast of the Wartburg Basin the Chattanooga thrust segment of the Pine Mountain system assumed a more listric thrust shape and cut up-section to a higher stratigraphic position above the presently preserved Wartburg Basin. The two contrasting thrust shapes are joined laterally by a suite of transitional structures. Including a major lateral ramp, which Is surflcially expressed as the Jacksboro tear fault. Subsequent erosion has exposed the Wartburg Basin as the undeformed footwall to the Pine Mountain thrust system.

Classically, the evolution of lateral structures has been attributed to "along strike" changes in the distribution of structural units within a sedimentary succession. An evaluation of the stratigraphic units encountered by the Pine Mountain thrust system led to the distinction of five structural units. Unit 1 Is the basal weak layer and consists of the Rome Formation and the Conasauga Shale. Unit 2 Is dominant strong layer in the sedimentary wedge and is composed of the Maynardville Limestone, the Knox Group, and the Chickamauga Group. Unit 3 Is the primary upper-level weak unit and Includes the Reedsville Shale, Sequatchie Formation, Chattanooga Shale, and the Grainger Formation. Unit 4 Is a strong layer whose members are from the Mississippian carbonate section. Finally, unit 5 behaved as a weak unit during deformation and consists of the Pennington Shale and the lower portion of the Crab Orchard Mountain Croup.

The pronounced lateral change in structural geometries of the Pine Mountain thrust system occurred in response to the loss of the Grainger Formation, and much of the Chattanooga Shale, from structural unit 3 due to southwesterly thinning of the two shale sections. This change in the character of structural unit 3 is paralleled by a progressive change in modes of upper-level detachment. Along the central portion of the Pine Mountain fault trace extensive detachment is by sole thrusting or duplexing in the upper parts of unit 3. As the Grainger and Chattanooga thin to the southwest, duplexing becomes more prominent and the floor thrust to the detachment lowers in stratigraphic position. Southwest of the Jacksboro fault, detachment is by blind imbrication off of a poorly developed flat in the Reedsville Shale. The lack of an extensive upper-level detachment southwest of the Jacksboro fault resulted in increased fault angles, thus prompting the development of a more listric fault shape.

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