GEOLOGIC MAP OF THE JACKSONVILLE EAST 7.5–MINUTE QUADRANGLE, ALABAMA VALLEY AND RIDGE PROVINCE

The Jacksonville East 7.5–minute quadrangle is located in the eastern portion of Calhoun County and westernmost Cleburne County in NE Alabama. The study area is located on the boundary between the Southern Appalachian Valley and Ridge province and the Piedmont province. The area is dominated by two linear ridges, Choccolocco Mountain and Dugger Mountain.

Within the Valley and Ridge portion of the area, Early Cambrian through Pennsylvanian rocks are exposed in the study area and include the Nichols Formation, Wilson Ridge Formation, and the Wiesner Formation of the Chilhowee Group; Shady Dolomite; Rome Formation; Conasauga Formation; and Parkwood Formation. Internally, these rocks are deformed by numerous, north-south striking, east-dipping thrust faults that dissect Cambrian strata. The boundary between the Valley and Ridge and Piedmont, the Talladega-Cartersville fault, runs southwest-northeast through the southeastern portion of the mapping area and carries metamorphic rocks of the Lay Dam Formation and Heflin Phyllite in the hanging wall on top of Valley and Ridge sedimentary rocks in the footwall.

U-Pb detrital zircon geochronology from samples collected within the study area records Cambrian drainage systems in the southeastern U.S. The Chilhowee Group contains zircon with U-Pb ages that are compatible with being sourced dominantly from the mid-continental Granite and Rhyolite Province (1300-1500 Ma), with minor contribution from the Canadian Shield (>2500 Ma). This suggests that sedimentation in the southeastern U.S. during the Early Cambrian were fed by a large river system emptying into a passive margin basin. (U-Th)/He zircon thermochronology from the Chilhowee Group sampled were all thermally reset giving ages of 332, 287, 282, and 253 Ma respectively (N=1; n=4). Zircon samples taken from post-Cambrian samples the north of the area yield detrital (U-Th)/He ages (i.e. older than depositional age of the sample) and are, therefore, not reset. The restricted nature of thermally reset zircon to the Early Cambrian strata suggests that only rocks beneath the Cambrian regional detachment layer were heated to conditions (>200 °C) capable of resetting zircon Cooling recorded in this strata represents the earliest phases of uplift in the Valley and Ridge.