EXPLORING THE STRUCTURAL AND STRATIGRAPHIC ARCHITECTURE OF THE PELL CITY THRUST SHEET WITHIN THE ANNISTON TRANSVERSE ZONE OF THE SOUTHERN APPALACHIANS

The Pell City fault is an ~ 120-km long, northeast-striking, southeast-dipping thrust that truncates footwall structures, thus indicating an out-of-sequence development in the southern Appalachian Valley and Ridge. Across the Anniston transverse zone, the Pell City fault exhibits two 90-degree bends in strike and the detachment changes stratigraphic level from the Cambrian Rome Formation to the Cambrian-Ordovician Knox Group, defining the location of hanging-wall and footwall lateral ramps. At the Reads Mill offset, in the footwall of the Pell City fault, a structurally complex shale-dominated sequence contains both Mississippian Floyd Shale and Ordovician Athens Shale, similar to rocks within the Fort McClellan window to the southeast. The Pell City thrust sheet is truncated by the Jacksonville fault to the southeast and dips northwestward in the footwall, indicating a synclinal structure. Retrodeformation of the Jacksonville thrust sheet restores to a basal detachment surface near the trailing part of the foreland sequence. Restoring the Pell City thrust sheet proves more difficult, especially because of the out-of-sequence deformation. The Pell City thrust sheet may represent a regional-scale klippe or a foreland-directed ramp advancement of the decollement. Another possible structural solution is that footwall strata may be material that the advancing Pell City fault decapitated along a ramp or at a ramp-flat transition and then passively translated ahead of thrust sheet displacement. We explore these structural solutions to advance understanding of the stratigraphic architecture, thrust sheet geometry, and sequence of deformation for the Pell City fault and the evolution of thrust belt development in the southernmost Appalachians.