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Reconstructing Fluvial Meander-Belt Morphodynamics in a UAV Structure-From-Motion Digital Outcrop Model

Abstract

Three dimensional mapping and reconstruction of fluvial architecture in outcrop is inherently challenging due to limited exposures, rapid facies transitions, and complexity of the internal stratigraphic architecture. To address these limitations, we utilize Unmanned Aerial Vehicle (UAV) Structure-from-Motion (SfM) photogrammetry to generate a 3D digital outcrop model (DOM) of fluvial deposits exposed at Dinosaur Provincial Park (DPP). High-resolution DOMs provide location data (x, y, z), colour information (RGB), and 3D topography that can be utilized for bed-scale mapping, detailed correlation, and facies classification. The “badlands” style topography at DPP provides a unique perspective of ~50 m of late Cretaceous fluvial meander-belt and floodplain deposits. We combine classic field-based data collection methods with extensive stratigraphic surface mapping in the DOM to reconstruct meander-belt morphodynamics at the belt, bar, and bed scale. The resulting DOM is 2.5 km2 at 0.027 m resolution. To test the utility of DOMs for facies classification, we collocated 10 field-based sedimentary logs in the DOM and measured digital sedimentary logs; results estimated facies with similar conviction to field-based methods (+/- 4.9%). Stratigraphic surfaces were digitally traced within the DOM, enabling measurements of accretion direction, width-to-depth ratios, and stacking patterns, which are nearly impossible to obtain accurately in the field. Results indicate that measurements derived from the UAV-SfM DOM were commensurate with conventional ground-based mapping techniques, with the added advantage of increased lateral continuity and time efficiency. Results of multi-scale DOM stratigraphic mapping improve our understanding of meander-belt morphodynamics. At the belt scale, we characterize meander-belt distribution and stacking patterns for 8-10 m thick stories. At the bar scale, projecting mapped accretion surfaces characterizes detailed bar evolution. A counter-point-bar deposit interpretation is confirmed by demonstrating concave accretion surfaces and their relationship to the meander-belt edge. At the bed scale, bed-by-bed correlations between measured sections provide realistic internal stratigraphic architecture. Overall, we provide a high-resolution DOM of Cretaceous fluvial deposits, compare field-based data collection to digital mapping/classification, and utilize accurate 3D relationships to improve reconstructions of meander-belt morphodynamics.