Subdividing the Undifferentiated Eastern Uinta Mountain Group, Northeastern Utah

Rybczynski, Dan¹, Carol Dehler¹, and Andy Brehm^2
1Utah State University, Logan, UT
²Anadarko, Woodland Hills, TX

     Although geologists recognize six separate formations throughout the western Uinta Mountain Group (UMG), only the basal unit of the eastern UMG has been formally named (Jesse Ewing Canyon Formation), leaving close to 95% of eastern UMG undivided. Detailed geologic mapping (1:12,000 scale) is underway to subdivide and correlate the seemingly homogenous, 4 to 7 km-thick Neoproterozoic (~770-780 Ma) eastern UMG along the margins of Browns Park, northeastern Utah. The eastern UMG consists of dominantly sandstone interbedded 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 range from south-southwest in some facies, to bimodal (northwest and southeast) in others.
     Preliminary divisions within the Swallow Canyon quadrangle (eastern Uintas) include a ≤ 70 m-thick shale interval, termed the formation of Outlaw Trail (fOT; De Grey, 2005). The lateral extent of this interval 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. Preliminary field and air photo interpretation show previously unmapped northwest-trending normal faulting along the western margin of Browns Park may offset the fOT at several locations. Furthermore, one or more of these structures may juxtapose the fOT with a thick shale interval (~100's of meters) from another yet unknown part of the UMG. Geologic mapping in conjunction with measured sections, petrography, and paleocurrent analysis are being applied to resolve these problems.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah