LOAD ORIGIN FOR LENTICULAR SANDSTONE BODIES IN THE GREEN RIVER FORMATION ON THE EASTERN MARGIN OF THE UINTA BASIN ALONG COTTONWOOD CANYON

The Uinta Basin, in northeastern Utah, was a Laramide structural basin that contains Eocene lacustrine deposits of the Green River Formation. Along the White River, on the Utah-Colorado border, multiple lenticular sandstone bodies occur at various stratigraphic intervals within the Douglas Creek Member of the Green River Formation. The interpretation of these sandstone bodies has significance for depositional environment, processes, and distribution of sand across the eastern margin of the basin. The examination of several sandstone bodies showed that these were developed due to loading. The lenticular sandstone bodies are sourced from the southeast and range from around 5 to 15 m in length/width and 1 to 6 m in thickness. They are filled with fine sand by either a single or multiple flows. The main facies is characterized by parallel laminations with a climbing ripple cap, to climbing ripples. The largest load features have up-dip rotated bedding (up to 45^O) with common scouring on down dip edge. One such load shows a progressive rotation and a crumpled lineation trending perpendicular to flow along the base of the bed. These lenticular sandstone bodies are commonly associated stratigraphically with broad thin (up to 0.5 m) sandstone sheet deposits that are km’s in length.

These sandstone load features indicate that the underlying mudstones were still partially fluidal in order to allow for the loading to occur. The underlying mudstones are largely terrigenously sourced with low organic content that may have resulted from more rapid deposition in a prodelta environment. The sheet-like sandstone bed morphology, thicker packages of mudstone vs. sandstone, lack of apparent subaerial exposure, and distance into the basin suggests sandstone beds may have been deposited by hyperpycnal flows in a delta front/lobe environment.