USE OF UAV TECHNOLOGY IN RECONSTRUCTING THE ALLUVIAL ARCHITECTURE OF CHANNEL-BELTS IN THE CEDAR MOUNTAIN FORMATION (EARLY CRETACEOUS), GREEN RIVER, UTAH

The Cretaceous Cedar Mountain Formation (Aptian) near Green River, Utah, preserves segments of fluvial channel belts. These channel belts occur as inverted topography, are up to 9 km long and allow for a top-down view of the system. This perspective presents an opportunity to utilize unmanned aerial vehicle (UAV) technology to create high resolution aerial photographs and 3-D models of the alluvial architecture. For this study we completed 13 flights using two platforms; the senseFly swinglet CAM (fixed wing) and a DJI Phantom 4 Pro (quadcopter). The senseFly swinglet CAM was used to image larger areas (17 to 24 acres) and its higher-flying altitude resulted in pixel resolutions of approximately 3 - 10 cm. The DJI Phantom 4 Pro imaged smaller areas (< 10 acres) but managed spatial resolutions of approximately 1 cm. Imagery was processed using Pix4Dmapper to generate digital surface models and stitch the aerial imagery into georeferenced mosaics. The high-resolution imagery allowed delineation of depositional, diagenetic and structural features. The aerial imagery and models were coupled with measured sections and paleocurrent data to provide a comprehensive model of the depositional system.

Channel belts are multistory and 5 to 8 m thick. Internally, the channel belts are divided into 5 to 8 fining-upward packages of conglomerate to medium sandstone. The sandstone is dominantly trough cross-bedded (5 – 20 cm sets) with no finer-grained intervals preserved. Paleocurrent vectors from trough cross-beds ranged from northeast to southeast with a mean southeasterly flow direction of 103 degrees (n = 41). The exposed tops of the channel belts, imaged with the UAV, are 15 to 80 m wide and allowed for identification and mapping of individual trough cross-bed sets, accretionary forms and patchy silcrete zones. This was supplemented with GPS locations that documented sedimentological characteristics, including additional paleocurrents.

The channel belts record deposition of primarily downstream accreting barforms within low sinuosity channels. The lack of finer-grained lithologies within the channel belts is indicative of frequent channel migration within narrowly confined channel belt systems within a broader floodplain.