PUSHING THE MARGINS: UTILIZING ARCHIVED ROCK SAMPLES TO DELINEATE LACUSTRINE SOURCE ROCK DEPOSITIONAL TRENDS IN THE UTELAND BUTTE MEMBER, GREEN RIVER FORMATION, UINTA BASIN, UTAH

The Uteland Butte member (UB) of the Green River Formation is a regionally correlative lacustrine sequence that records freshwater deposition during one of the initial transgressions of Lake Uinta into the Uinta Basin. Previous studies have delineated a succession of lacustrine depositional environments within the UB that extend from outcrops along the southern margin of the basin to subsurface cores and logs collected to the north near the southern flank of the Uinta Mountains. This succession records the transition from distal lacustrine environments in the north, where profundal mudstones and sublittoral carbonate wackestones dominate the rock record, to shallower environments where proximal deltaic sandstones and littoral carbonate grainstones become commonplace in the outcrops of Willow Creek, Minnie Maud Creek and Kyune Creek. The northern extent of this lacustrine sequence is delineated by an influx of coarse-grained clastic rocks of the alluvial Wasatch Wash; however, limited work has been published regarding the lithologic character of the UB and other Green River Formation lacustrine units through this transition.

This study presents new research that utilizes detailed lithologic characterization from archived core and drill cutting samples stored at the Utah Geological Survey’s Utah Core Research Center in Salt Lake City, UT and the U.S. Geological Survey Core Research Center in Lakewood, CO, in concert with geophysical logs to evaluate changes in UB depositional environment in close proximity to the Wasatch Wash. Log interpretations from the northern Uinta Basin demonstrate that carbonate content within the UB decreases with increased proximity to the Wasatch Wash. Furthermore, log property maps suggest that a zone of enhanced organic-richness may exist where carbonate content decreases. Analytical samples were selected along two well traverses for analytical characterization utilizing X-ray fluorescence spectroscopy (XRF) and programmed pyrolysis to investigate changing mineralogy and organic richness within these zones. Both XRF and programmed pyrolysis delineate sharp transitions that correlate to distinct boundaries identified from geophysical mapping. These results provide a refined look at a fundamental margin within the UB in the northern Uinta Basin.