AAPG Foundation 2019 Grants-in-Aid Projects

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Anatomy of an Ancient Avulsion: Sedimentology and Stratigraphy of Exhumed Fluvial Channel-Belt Deposits of the Cedar Mountain Formation, Eastern Utah


Fluvial reservoir characterization requires knowledge of heterogeneities that exist at scales below seismic resolution limits. Because heterogeneity is a product of fluvial process, quantifying process-based variability is crucial for reservoir characterization. Avulsions are important mechanisms for sediment dispersal within filling alluvial basins. Although the processes of fluvial avulsion, abandonment, and reoccupation are often interpreted from the stratigraphic record, the third dimension and a well-defined context are often missing, complicating understanding of the avulsion process. Topographically inverted fluvial channel-belt deposits of the Cretaceous Cedar Mountain Formation in eastern Utah offer three-dimensional exposures of fluvial stratigraphy. This study will characterize the stratigraphic architecture of these deposits and relate it to the geomorphological and sedimentological processes involved in their deposition and preservation. Primary focus will be on two channel-belt segments that are likely to represent an avulsion event; this is a unique opportunity to characterize the stratigraphy of a fluvial avulsion in three dimensions. Digital outcrop models developed from Unmanned Aerial Vehicle (UAV) photogrammetry provide a three-dimensional framework for characterizing the architecture and spatiotemporal evolution of this uniquely exposed site. UAV-derived basemaps, stratigraphic sections, measured paleocurrent and accretion surface dip directions, and extensive field mapping enable correlation between lateral and vertical lithofacies trends and key bounding surfaces. The relationship between planform evolution of the geomorphic channels and the resultant channel-belt deposit architecture will be studied using field measurements and a simple numerical model for river meandering. This project will improve understanding of fluvial avulsions and associated stratigraphy and will provide a detailed outcrop analog for fluvial channel-belts which links seismic-scale changes in planform morphology to sub-seismic scale distributions of heterogeneity in facies across a channel-belt.