Abstract

Continental sequence stratigraphy in upstream fluvial environments can be complex due to the interplay of source tectonics, local and global climate change, and topography. The Tertiary Duchesne River Formation, Utah, U.S.A., represents the last stage of intermontane basin fill in the Uinta Basin. It is surrounded by sediment source mountain ranges of the Uinta Mountains to the north and the Sevier Fold-Thrust Belt (FTB) to the west. Excellent basin-scale exposure of the Duchesne River Formation allows the vertical and lateral characterization of facies architectures in the upstream environments.

The four members of the Duchesne River Formation are distinctive lithological units. The lower three members comprise a typical upward-fining unconformity-bounded fluvial sequence from the basal coarse-grained unit into the overlying fine-grained units. The fourth uppermost coarse-grained member records the onset of another upward-fining cycle. The sequence stratigraphy of these unconformity-bounded upward-fining cycle(s) was primarily tectonics-driven due to uplift of the Uinta Mountains.

The Duchesne River Formation records a distinct change in fluvial–lacustrine styles between the western and eastern part of the basin, demonstrating the variable allogenic controls of tectonic subsidence and discharge related to the local climate and source-terrain input within the basin. Specifically, the western degradational fluvial system with a high net-sandstone-to-gross-thickness ratio of the basal member was controlled by high discharge due to a wet climate and two source-terrain inputs (i.e., Uinta Mountains and Sevier Fold-Thrust Belt), whereas the eastern aggradational fluvial system with a low net-sandstone-to-gross-thickness ratio was controlled by low discharge due to a dry climate and single source terrain input (i.e., Uinta Mountains). The development of local lacustrine environments on the alluvial plain of the third member, present in the western Uinta Basin, was controlled by differential tectonic subsidence in the basin. The Duchesne River Formation preserves a valuable example of an upstream fluvial sequence, and demonstrates how internal facies architectures at the basin scale were dictated by allogenic controls.