ANALYSIS OF MESOSCALE STRUCTURES IN PALEOZOIC STRATA ON THE WESTERN HIGHLAND RIM, TENNESSEE, WITH IMPLICATIONS FOR APPALACHIAN AND OUACHITA TECTONICS

The western Highland Rim of Tennessee exposes Paleozoic strata along the Tennessee River valley that record far-field effects of multiple tectonic events attributed to the Appalachian and Ouachita orogens. Recently obtained fracture data from drill core confirm continuity of structures with depth and suggest the orientation of regional Paleozoic tectonic stress changed through time. The few exposed faults and inferred faults mainly follow SE-NW to E-W or S-N to SSW-NNE trends, but numerous open folds are observed in the Mississippian Fort Payne and Silurian Decatur formations. Fold axes are typically horizontal and oriented either WNW verging NNE or NE and verging NW. Beds generally dip at <10˚. Fractures are commonly systematic and vertical to subvertical. Compilation of 1,560 fracture measurements in the study area yields 2 prominent sets with maxima centered at ~035 – 040˚ and ~300 – 305˚ with a less prominent set at ~072 - 082˚. A SW-NE trending zone of few fractures (ZOFF) extends through the study area, across which the SW-NE fractures are invariant, but SE-NW fracture maxima vary from 299˚ NW of the ZOFF clockwise to 305˚ SE of the ZOFF. Formation microscanner fracture analysis of core from two boreholes drilled to bedrock indicate prominent subvertical fracture sets oriented SW-NE and less prominent SE-NW and E-W fracture sets, with migration of the SW-NE set to the SSW-NNE and S-N from Ordovician to Mississippian time. A stream linearity analysis shows statistical consistence with the SW-NE trending fractures, but no correspondence to other fracture maxima. The results support prominence of Ouachita orogen deformation overprinting less prominent Appalachian deformation trends.