Sequence Stratigraphy of the Chinle Formation in the Uinta and Piceance Basins of Northeast Utah and Northwest Colorado, United States

Ryan Erickson, University of Minnesota-Duluth, Dept. of Geological Sciences, Duluth, Minnesota, [email protected]

The Uinta and Piceance basins of Northwest Colorado and Northeast Utah, in the Dinosaur National Monument region, form one of two Late Triassic Chinle Formation depositional centers. This succession is composed of terrestrially deposited fluvial and lacustrine sediments which preserve a unique record of the regions evolving paleoenvironments, paleoclimate, tectonics, and biota. For this project, methods of sequence stratigraphy will be used in the Uinta and Piceance basins to better define and understand the evolution of these paleoenvironnments and paleoecosystems. This research will in turn lead to a better and broader understanding of the Pangaean supercontinents Late Triassic geologic, environmental, and biologic systems.

In this study, detailed descriptions of the Gartra Member, an incised-valley fill succession that is the basal member of the Chinle, were completed. Previous lithostratigraphic work on the Gartra in this region has defines it as a single fining-upward conglomeratic sandstone unit. In this study, detailed fieldwork and sequence stratigraphic correlations have identified 3 unique packages of fluvial deposits (G1-G3) within the Gartra and related mottled member. These packages represent different stages of valley fill beginning with low-sinuosity alluvial facies (G1) being deposited in a constrained system and culminating with high-sinuosity alluvial facies deposition (mottled member and G3) when the system overlaps the valley margins and spreads across an unconstrained landscape.