COMBINING GEOLOGICAL MAPPING AND LIDAR DATA TO ANALYZE THE CONTRIBUTION OF "LOCAL" VERSUS "REGIONAL" BEDROCK FRACTURE SETS IN WESTERN NORTH CAROLINA
Mapping in areas of best exposure (~6 km2) indicates Panthertown valley follows the axis of a NE-trending, upright, km-scale open antiform of felsic gneiss overlain by micaceous gneiss, gently refolded about a subvertical axis. Bedrock along the fold core is incised by two sets of topographic lineaments, one following the arcuate fold axis and others in a NW-trending cross-joint geometry. A kinematic model for fracture formation during folding predicts that steeply dipping, NE and NW trending, joint fracture sets are responsible for the valley lineament sets.
Bedrock exposure is very limited on the fold limbs and along the valley axis. A LiDAR ground model (~83 km2) was used to look for lineaments indicating predicted, and possible superimposed regional, fracture sets. Despite a 1 pt/2 m2 spatial resolution, fracture trace lineaments are easily identifiable and penetrative. Most lineaments have azimuths predicted by the kinematic model. To assess contribution from superimposed regional fracture sets, adjacent LiDAR tiles were added (~664 km2) and resampled to artificially lower resolution. Lineaments visible at the lowest resolution (analogous to topographic map resolution) are considered 1st order. Those only visible at the original LiDAR resolution are considered 3rd order; those at intermediate resolution, 2nd order. Two 3rd order sets are statistically parallel to the 1st order sets and can be considered part of "regional" lineament sets. Traces not parallel to 1st order sets are focused in the Panthertown fold area.
Geological mapping is often limited by exposure but permits development of a kinematic model relating fracture sets in 3D. LiDAR is limited by largely 2D fracture information, but permits mapping of fracture traces regardless of bedrock exposure. Therefore, their combination is a powerful way to characterize bedrock fractures at scales needed for land use planning.