Dept. of Geology


University of Tennessee at Chattanooga

Place of Publication

Chattanooga (Tenn.)


Several exposures of deformed middle Paleozoic rocks in the westernmost Valley and Ridge Physiographic Province, near Chattanooga, TN, reveal a variety of structures. These include centimeter-scale ellipsoidal to lensshaped masses of sandstone in the Mississippian to Devonian Chattanooga Shale. Fissility in the carbonaceous shale is intensified adjacent to these lenses and conforms to their biconvex shapes. Slickensides on rinds of highly polished shale trend northwest. The walnut- to fist-size masses are composed of fine- to medium-grained ferruginous quartz sandstone. Thin-section study reveals that the quartz grains retain detrital characteristics, but that many are broken and displaced; cataclastic deformation is particularly evident in microbreccia zones. X-ray diffraction studies confirm the mineralogy determined petrographically, but proved to be of little value in establishing a relationship between the lenses and other sandstones. The sandstone lenses occur low in the Chattanooga Shale, near its contact with the underlying Silurian Rockwood Formation, which consists of alternating centimeter-scale layers of mudstone and ferruginous sandstone. Where sandstone lenses are found in the Chattanooga Shale, the Rockwood Formation is complexly folded; hinge lines trend northeast. In a particularly spectacular exposure that contains numerous sandstone lenses, the uppermost sandstone layer in the Rockwood Formation is locally duplexed with meter-scale horses. Elsewhere in this same outcrop, this sandstone layer displays boudinage necking or is entirely absent. The sandstone lenses have not been observed where Chattanooga Shale and adjacent units are not deformed. Based on their shape, surface features, internal characteristics, structural and stratigraphic distribution, circumstances of their occurrence, and associated fabrics in surrounding shale, it is interpreted that the sandstone lenses are tectonic intercalations derived from sandstone layers near the top of the underlying Rockwood Formation. Boudinage of these layers may have resulted in centimeter-scale ellipsoidal to lens-shaped masses of sandstone that became entrained in the Chattanooga Shale and continued to deform during subsequent flow of the shale. Observations near Fort Payne, AL, are suggestive of an alternative mechanism, whereby joint-bounded blocks of the sandstone layers are entrained in Chattanooga Shale and are geometrically modified during subsequent flow. In either case, cataclastic flow has resulted in apparent mesoscopic ductile behavior.


B. S.; An honors thesis submitted to the faculty of the University of Tennessee at Chattanooga in partial fulfillment of the requirements of the degree of Bachelor of Science.







Document Type



xi, 48 leaves





Call Number

LB2369.7 .P66 2002


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