CONFESSIONS OF A RODINIAN INTRACRATONIC BASIN: ANALYZING THE UNDIVIDED EASTERN UINTA MOUNTAIN GROUP, NORTHEASTERN UTAH

Previous work on the western Uinta Mountain Group (UMG) has resulted in the recognition of six formations, however, detailed studies of eastern UMG strata are limited; only the basal, ≤1000 m-thick Jesse Ewing Canyon Formation (JECF) has been formally addressed, leaving ~4 to 7 km of strata undivided. Detailed geologic mapping, paleocurrent analysis, sedimentary petrography, and detrital zircon analyses are being applied to subdivide and correlate the undivided, Neoproterozoic (~765 Ma; Fanning and Dehler, 2005) UMG along the margins of Browns Park, northeastern Utah.

The eastern UMG is characterized by sandstone with subordinate shale and conglomerate. Common sedimentary structures include a diversity of crossbedding, pebble lags, symmetric and asymmetric ripplemarks, mudcracks, and soft-sediment deformation. Paleoflow directions are radially distributed (n=313) with dominant southwesterly flow, yet a subordinate northerly flow direction is also indicated. These data suggest a mixing of depositional systems that are, in part, possibly marine influenced.

Two stacked shale marker intervals of comparable thickness (~70 m) exist along the southwestern margin of Browns Park, where they are offset by previously unmapped faults related to the collapse of the Browns Park graben; one interval was previously mapped in the Swallow Canyon quadrangle as the formation of Outlaw Trail (fOT). Both intervals contain significant amounts of organic-rich shale intercalated with thin to thick-bedded micaceous arkose and quartz arenite. Their stratigraphic position is likely <2 km from the base. Their lateral extent is currently being evaluated northwestward (towards Goslin Mountain) and northward across the Browns Park graben (Willow Creek Butte quadrangle) to aid in regional correlation, refining previous thickness estimates and paleoenvironmental and paleogeographic interpretations.

Detrital zircon analysis of a JECF sandstone sample yielded age populations identical to populations from a fOT sandstone. This suggests that either the fOT is a lateral equivalent to the JECF, or that both formations shared identical sediment sources. Furthermore, if a significant population of ~765 Ma zircons can be found in the JECF, this will constrain all but the lowest 400 m of the UMG to the middle Neoproterozoic.