REFINING FLUVIAL MODELS USING UNMANNED AERIAL VEHICLES AND STRUCTURE-FROM-MOTION PHOTOGRAMMETRY: THE SALT WASH DFS OF THE MORRISON FORMATION, EAST-CENTRAL UTAH

The Salt Wash Member of the Jurassic Morrison Formation is interpreted as an ancient, north-northeast prograding distributive fluvial system (DFS) that extended across parts of Utah, Colorado, Arizona, and New Mexico. This study maps and characterizes 3-D outcrop exposures of the Salt Wash Member south of Green River, Utah using unmanned aerial vehicles (UAV), structure-from-motion (SfM) photogrammetry, and outcrop observations to test and refine the stratigraphic model of medial-to-distal deposits of DFSs. Current models predict that medial-to-distal deposits of DFSs are composed exclusively of distributive fluvial channels with no interaction with axial river systems. However, our observations indicate these portions of DFSs are the product of a more complicated depositional history. Plan-view widths and orientations of fluvial channel bodies in the study area are highly variable. Preliminary measurements of plan-view widths indicate three general groups of fluvial channel bodies are present: very narrow (1m-3m), narrow (15m-80m), and wide (85m-115m). The very narrow sandstone bodies are typically less than 1m thick, straight to possibly dendritic in plan-view, bioturbated, and interpreted as crevasse splay channel deposits. The narrow sandstone bodies are typically 2m thick or less, straight to sinuous in plan-view, and are generally oriented to the north and northeast with similarly directed paleocurrents. The wide sandstone bodies are typically 4m thick or more, straight in plan-view, and are oriented to the east and southeast with similarly directed paleocurrent indicators. We interpret the narrow and wide fluvial channel bodies to have been deposited by different fluvial systems. The narrow fluvial deposits are consistent with distributive channels on the DFS, whereas the wide fluvial channel bodies are more consistent with an axial system in the basin. The interaction between northeast-trending distributive channels and east-trending axial channels was likely controlled by changes in sediment influx to this part of the DFS and basin subsidence.