USING UNMANNED AERIAL VEHICLE (UAV) PHOTOGRAMMETRY TO REVISIT A CLASSIC OUTCROP: SHELBURNE BOAT ACCESS, WEST-CENTRAL VERMONT

A ~50 m long x ~25 m wide outcrop of well-bedded, weakly-metamorphosed, ferruginous quartzite from the Early Cambrian Monkton Formation extends northward into Shelburne Bay from the Vermont state boat launch. These quartzites lie in the hanging wall of the Champlain Thrust and were emplaced over the Stony Point Shale during the Ordovician Taconian Orogeny. To build on the work of Stanley (1974), we used a UAV to survey the outcrop from an elevation of ~11m, assembled a photo mosaic using Photoscan, and analyzed structures from the composite image in GIS. In addition, the attitudes of all structures (bedding, fractures, faults, and veins) were measured in the field and detailed meter-scale photo mosaics were constructed at key locations. The goal of this study is to integrate 1:83 scale aerial imagery with ground-based measurements to discriminate different structural generations.

Stanley proposed two generations of structures; the first including ~E-W striking fractures, steeply-dipping wrench faults and en echelon vein arrays, and a younger ~N-S striking secondary generation, including fractures and wrench faults. Generation 2 offsets generation 1. The proposed mechanism for generation 1 is the Devonian Acadian Orogeny, while the origin of generation 2 is unknown. Our photogrammetry investigation produced a more extensive and detailed map of the study area than was previously possible. A preliminary statistical analysis, conducted by integrating field measurements with UAV data, defines three generations of structures, but recognizes that relative age relationships are ambiguous in some locations.

Further investigation will include: a detailed statistical analysis of the azimuths and lengths of all digitized lineaments on the UAV mosaic, a Mohr circle analysis of field data, and a 3D block model of the outcrop. To search for correlative structures in areas adjacent to the field area, we highlighted large-scale lineaments by varying illumination angles on digital elevation models developed from LiDAR data. Beyond the local setting, we will also assess how these three generations of structures fit into the Paleozoic-Mesozoic tectonic history of the northeastern Appalachians. We developed a structural framework that is useful for characterizing the complex fractured rock aquifers in this area.