GEOL Thesis Defense - John ChesleyWednesday, March 29, 2017 - 1:00pm
Title: Integrating Structure-from-Motion photogrammetry and Unmanned aerial vehicles to characterize variability in fluvial deposits from the Salt Wash Member of the Morrison Formation, east-central Utah
Abstract: Modern fluvial systems are highly variable, often containing the entire spectrum of fluvial styles (e.g., braided to meandering). This variability is difficult to capture in ancient fluvial deposits due to limited 1- and 2-dimesional exposures, which provide only a snapshot of the depositional history at one location. As a result, researchers are forced to interpolate between exposures and develop regional scale models that often underestimate the complexity and variability seen in modern environments. Outcrops of the Upper Jurassic Salt Wash Member of the Morrison Formation in east-central Utah, USA provide a relatively unique opportunity to examine ancient fluvial sandstone bodies in planview. However, capturing the 3-dimensional nature of these outcrops is problematic in that field-based observations are too specific to delineate larger-scale trends, and existing aerial imagery does not have the resolution to distinguish important details. This thesis outlines the workflow and results of a study that utilizes unmanned aerial vehicles (UAV) and structure-from-motion (SfM) photogrammetry to produce sub-meter-scale outcrop reconstructions in 3-D. Overall, average values of sandstone body characteristics (width, orientation, paleocurrent, etc.) in the Salt Wash Member are consistent with existing models. However, within this spectrum are four distinct types of fluvial deposits, each with its own characteristics. Very narrow sandstone bodies (4-6 m wide) occur in groups, are less than 2 m thick and heavily bioturbated. Narrow sandstone bodies (15 to 45 m wide) are straight to sinuous, contain evidence of lateral migration, and were deposited by east-northeast flowing fluvial systems. Medium sandstone bodies (75 to 105 m wide) are straight, and were deposited by non-migrating, east-flowing fluvial systems. Sheet/other sandstone bodies consist of both sheet-like sandstones whose edges are not visible and eroded sandstones bodies that cannot be reconstructed. The succession is consistent with a distributive fluvial system model (DFS) previously proposed for the Salt Wash Member. However, the variability of sandstone bodies and orientations in this area suggest these deposits may be more variable at local scales (e.g. 10km2) than what would be predicted by existing DFS models.