EXPLORING THE RELATIONSHIP BETWEEN LATERAL RAMPS AND AN ORTHOGONAL BEND IN THE PELL CITY FAULT, JACKSONVILLE WEST 7.5-MINUTE QUADRANGLE, APPALACHIAN THRUST BELT, ALABAMA

We explore the relationship between surficial structural geometry of the Pell City fault and lateral ramps by presenting a 1:24,000-scale bedrock geologic map and cross sections of the Jacksonville West 7.5-minute quadrangle, northeast Alabama. The quadrangle is along the Anniston transverse zone, which is defined as an ~40-km-wide, cross-strike, northwest-southeast trending alignment of lateral ramps, displacement-transfer zones, and terminations of multiple large-scale structures. Regionally, the northwest-directed Pell City fault places Cambrian-Ordovician strata above Mississippian strata, trends northeast-southwest, dips to the southeast, and is traced for ~120 km along strike. In the Jacksonville West quadrangle, the Pell City fault truncates pre-existing upper-level footwall structures. The hanging-wall detachment cuts up section southwestward along strike from lower Cambrian Rome Formation to Cambrian-Ordovician Knox Group strata, indicating an up-to-southwest hanging-wall lateral ramp. The trace of the Pell City fault bends abruptly from regional northeast-southwest to local northwest-southeast strike, outlining a dextral offset of approximately six miles, defining the geometry and location of a subsurface footwall lateral ramp. Emplacement of the hanging-wall lateral ramp of the Pell City thrust sheet over the footwall lateral ramp characterizes the Anniston transverse zone. In the footwall of the Pell City fault, a structurally complex shale-dominated sequence contains both Mississippian strata and Ordovician Athens Shale, similar to other parts of the Coosa deformed belt to the southwest and to rocks within the Fort McClellan window to the southeast. Understanding the similarities and relationships between these structures has direct implications for local and regional structural geometry and emplacement history.