From Saline to Freshwater: The Diversity of Western Lakes in Space and Time
Beginning with the nineteenth-century territorial surveys, the lakes and lacustrine deposits in what is now the western United States were recognized for their economic value to the expanding nation. In the latter half of the twentieth century, these systems have been acknowledged as outstanding examples of depositional systems serving as models for energy exploration and environmental analysis, many with global applications in the twenty-first century. The localities presented in this volume extend from exposures of the Eocene Green River Formation in Utah and Florissant Formation in Colorado, through the Pleistocene and Holocene lakes of the Great Basin to lakes along the California and Oregon coast. The chapters explore environmental variability, sedimentary processes, fire history, the impact of lakes on crustal flexure, and abrupt climate events in arid regions, often through the application of new tools and proxies.
Interpretation of mouth-bar and related lacustrine and fluvial sand bodies from the middle Green River Formation (Eocene), southern Uinta Basin, Utah
-
Published:August 12, 2021
-
CiteCitation
Dave Keighley, Øystein Spinnangr, John Howell, Stephen Flint, 2021. "Interpretation of mouth-bar and related lacustrine and fluvial sand bodies from the middle Green River Formation (Eocene), southern Uinta Basin, Utah", From Saline to Freshwater: The Diversity of Western Lakes in Space and Time, Scott W. Starratt, Michael R. Rosen
Download citation file:
- Share
ABSTRACT
The Uinta Basin of eastern Utah is an intermontane basin that contains an ~2-km-thick succession of mostly carbonate-rich mudrock assigned to the Eocene Green River Formation. In the southwest part of the basin, along Nine Mile Canyon and its tributary canyons, the middle member of the Green River Formation contains numerous interbedded sand bodies. Previous researchers have interpreted these sand bodies variably as lacustrine deltaic mouth bars, terminal fluvial distributary bars, and various types of fluvial (delta plain/floodplain/braid plain) bar.
Using some modern western U.S. lakes as partial analogues, and taking into account the overall lacustrine basin context of a widely fluctuating, wave-influenced, alkaline-lake shoreline, we again interpret many of the sand bodies to be fluvial in origin. Several sand bodies both truncate and are capped by brown to red-maroon and variegated weak to noncalcareous mudstone with root and desiccation structures, indicating terrestrial deposition well away from the lake shoreline. Others display steep cutbanks from which noncalcareous, inclined heterolithic stratification laterally accreted as fluvial side bars. Utilizing helicopter-based light detection and ranging (LiDAR) data, we investigated additional sand bodies that may be better examples of deltaic mouth bars. In contrast to the more commonly documented highstand progradational mouth bars of marine and open lake settings, these sand bodies are interpreted to have originated as late-lowstand or transgressive system tract fluvial channels that were then flooded and modified by waves following lake transgression. These examples illustrate that any large-scale sandy bed form present in the general vicinity of a closed basin’s fluctuating lake shore may be expected to have formed under more than one set of environmental conditions. A revised set of guidelines is therefore presented to aid in the interpretation of lacustrine deltaic mouth bars.
- bars
- basins
- bedforms
- calcareous composition
- Cenozoic
- channels
- clastic rocks
- deltas
- Eocene
- floodplains
- fluvial features
- Green River Formation
- highstands
- intermontane basins
- interpretation
- lacustrine features
- laser methods
- lidar methods
- lowstands
- mudstone
- Paleogene
- planar bedding structures
- progradation
- red beds
- sand bodies
- sandstone
- sea-level changes
- sedimentary rocks
- sedimentary structures
- shorelines
- succession
- Tertiary
- transgression
- tributaries
- Uinta Basin
- United States
- Utah
- Western U.S.
- Nine Mile Canyon
- mouth bars