DETAILED GROWTH-STRATA MAPPING AND FACIES ANALYSIS OF UPPER CRETACEOUS TO PALEOGENE STRATA,TABBY MOUNTAIN, UT: INSIGHT INTO KINEMATICS OF THE UINTA MOUNTAIN UPLIFT

The Uinta Mountains form a unique, east-west-oriented mountain range in the North American Cordillera. The exact timing and kinematics of this uplift is not well constrained. Recently discovered growth strata provide insight into the relative timing, kinematics, and depositional response to the uplift. This study presents new stratigraphic profiles and detailed geologic mapping (1:14,000 scale about 25 sq km) of the growth strata to determine the number of uplift events and depositional response. Fieldwork involved the collection of strike and dip measurements at nearly 100 outcrop locations. Two syn-tectonic unconformities were identified suggesting at least two distinct phases of uplift- one within the Cretaceous upper Mesaverde Group (upper fluvial interval) and one in the Paleocene Current Creek Formation. The syn-tectonic unconformities are marked by dip discordances of approximately 5-8 degrees. Five distinct facies associations were recorded in two stratigraphic profiles within the growth-strata section: 1) a pre-growth, marginal marine interval within the upper Mesaverde Group, 2) a marginal marine to fluvial interval within the largely fluvial section of the upper Mesaverde Group, 3) a mixed sandstone-conglomerate fluvial section within the lower Current Creek Formation, 4) a distinct succession of sandstone and conglomerates interbedded with thin, red mudstone and sandstone beds with root traces and insect burrows (i.e., stacked paleosols) and 5) a massive, clast- to matrix-supported, cobble to pebble conglomerate within the upper Current Creek Formation. Overall, these facies highlight a transition from marine to proximal alluvial fan environments that correspond to phases of uplift in the Uinta Mountains. In conclusion, this study documented two distinct syn-tectonic unconformities that indicate two distinct phases of uplift, and a transition in depositional systems from marginal marine to alluvial fan, where the majority of motion occurred within the fluvial to alluvial fan section. The exact dating of these unconformities remains uncertain; however, future work employing detrital zircon geochronology and/or paleomagnetic dating techniques will better constrain this.