Date of Award:

2007

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Carol M. Dehler

Abstract

Detailed analysis of the basal unit of the Uinta Mountain Group, the Jesse Ewing Canyon Formation, of northeastern Utah and northwestern Colorado, expands on previous work by further documenting the character of the unit and proposing a revision of the description of the formation and interpretation. The Jesse Ewing Canyon Formation is -s1 ,000 meters thick as opposed to s225 meters thick, and the dominant lithology is not conglomerate, but rather finer-grained facies. The Jesse Ewing Canyon Formation reveals multiple alluvial fan point sources feeding a shallow body of water in an active rift basin at-781 Ma. Stratigraphic mapping, measured sections, and facies analysis of the Jesse Ewing Canyon Formation have allowed the designation of two members defined by changes in lithology. The coarse-grained Head of Cottonwood member (-0-200 meters thick) represents alluvial fan deposition along the basin bounding faults to the north. The fine-grained Willow Creek member (-150-1,000 meters thick) represents distal alluvial fan, braided stream, fan delta, and nearshore deposition and records the complex interaction of transverse and longitudinal alluvial systems with an intermittent shallow body of water. The stratigraphy and distribution of the two members of the Jesse Ewing Canyon Formation suggest sedimentation along the basin-bounding east-west trending fault system was dominated by alluvial fans that graded laterally into finer sediments basinward. Changes in thickness and (or) lithology across Laramide and younger structures are attributed to synextensional deposition. A crude, overall fining-upward trend within the Willow Creek member suggests alluvial fan retrogradation that was likely controlled by coincident northward transition in fault slip along related structures. Preliminary subdivisions were made within the overlying Uinta Mountain Group based on the presence of a middle shale and conglomeratic unit. The designation of the lower, middle, and upper Uinta Mountain Group establishes a stratigraphic framework for the correlation between the northern and southern margins of Browns Park, and ultimately the eastern and western domes of the Uinta Mountains. Repetition of the lithostratigraphic units in the overlying undifferentiated Uinta Mountain Group may be due to a blind thrust fault as opposed to deposition.

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