| Description |
The stratigraphy preserved in the Eocene Green River Formation provides key insights into the evolution of ancient Lake Uinta and the controls influencing sediment deposition and facies distribution. This study characterizes the stratigraphy of the middle to upper Green River Formation (transitional interval to the R8) in Gate Canyon, southcentral Uinta Basin, and Willow Creek/Indian Canyon, western Uinta Basin. The examined sections were deposited during and after early Eocene hyperthermal events that followed the Paleocene-Eocene Thermal Maximum, allowing specific investigation of the transition between a pulsed, hyperthermal climate regime during the Early Eocene Climatic Optimum to a period of climatic stability. Detailed outcrop and core descriptions along with paleocurrent data, thin sections, and X-ray fluorescence data reveal distinct suites of facies both spatially and temporally. Three evolutionary lake phases are suggested by the stratigraphy, from an overfilled basin (C1-Si.3), to a balanced-fill basin (C4-middle R8), to an underfilled basin (middle R8-saline facies). The facies of the first phase record a highly fluctuating lake with alternating carbonate and siliciclastic dominated packages that may be associated with Eocene hyperthermal events. The central portion of the basin contains a large proportion of coarser grained sandstone bodies, coarser grained carbonates, and microbialites whereas the western portion of the basin contains minor sandstone bodies, and abundant fine grained siliciclastic material and muddy carbonate units. The change in grain size from east to west represents a transition off the main depositional axis of a major deltaic system in the central portion of the basin to a more low energy, shallow lake margin setting. The stratigraphy of the second lake phase consists of organic-rich and poor carbonate mudstone, tuffs, and siltstone. These facies record a deep lacustrine environment, suggesting lake transgression as a result of the shift from a pulsed, hyperthermal climate regime to a period of climatic stability. The stratigraphy of the final lake phase consists of organic-rich and poor carbonate mudstone, tuffs, siltstone, minor sandstone, and saline deposits. These observations indicate lake regression and the eventual closing of Lake Uinta. Overall, this study seeks to link these regions to provide a more comprehensive understanding of the evolution of Lake Uinta. |
