Subdividing the Undifferentiated Eastern Uinta Mountain Group, Northeastern Utah
Rybczynski, Dan1, Carol Dehler1, and Andy Brehm2
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