Abstract

The Uinta Mountain Group in the eastern Uinta Mountains was recently subdivided into three broadly defined map units. The Jesse Ewing Canyon Formation represents the basal formation of the Uinta Mountain Group. An unnamed unit overlies the Jesse Ewing Canyon Formation and comprises the bulk of the Uinta Mountain Group. The uppermost map unit is the Red Pine Shale.

Samples collected from shale beds within each of these formations yielded rich assemblages of cyanobacteria and/or algae. The organisms in the lower part of the Uinta Mountain Group (Jesse Ewing Canyon Formation) consist of simple leiospheres and carbonaceous filaments that likely lived in freshwater to tidal-flat environments. The number and complexity of organisms increases stratigraphically upward in the unnamed unit. These more complex organisms likely lived in marine to marginal-marine environments. The organisms recovered from the Red Pine Shale show an even higher degree of complexity and likely lived in marine environments. These apparent stratigraphic changes in assemblages may reflect evolutionary changes, or they may only indicate varied environmental conditions or degree of effective preservation. The microfossils and their level of diversity indicate that the age of the Uinta Mountain Group is early to middle Neoproterozoic.

Kerogens recovered from these samples are well preserved and not significantly altered. They have a thermal alteration index (TAI) that ranges from 2.5 to 2.8. This thermal maturity of the organic matter is equivalent to 0.6% to 1.0% vitrinite reflectance (R₀) and indicates that maximum burial of the Uinta Mountain Group has remained within the oil window.