ORDER IN CHAOS: QUANTIFYING FLUVIAL CHANNEL DISTRIBUTION IN THE LATE CRETACEOUS CASTLEGATE SANDSTONE

The Castlegate Sandstone and underlying Blackhawk Formation of central Utah record the dynamic fluvial processes which transported sediment from the Sevier Orogenic Belt to the Cretaceous Interior Seaway. These geologic formations have been an integral part of past studies focused on understanding allogenic processes (e.g., climate, tectonics, and eustacy) and in building nonmarine sequence stratigraphic models of the Late Cretaceous. Recently, statistical methods have been developed to relate the randomness of fluvial channel distribution in outcrop to allogenic drivers. Regional, high-quality outcrops of the Castlegate Sandstone and Blackhawk Formation are ideal for applying these quantitative methods.

In this study, we quantify and statistically analyze the spatial distribution of fluvial channels in the Castlegate Sandstone and Blackhawk Formation. A photogrammetric model of a multi-kilometer series of outcrops near Orangeville, Utah was generated using Agisoft Metashape, from which the precise locations of channel centers were identified and exported as spatial data. A custom Python script projects the channel centers onto a plane perpendicular to the paleoflow direction, after which a K function is applied to the data and to random distributions are generated via Monte Carlo trials. This approach can quantify the degree of randomness of the spatial distribution.

Preliminary results suggest consistent clustering of channels during basin aggradation by nonrandom, autogenic channel avulsion, rather than clustering driven by allogenic boundary conditions. Further work will solidify or refute this interpretation, helping to build a predictive understanding of the drivers that lead to channel element organization in this and other fluvial systems.