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Surface observations along the southern margin of the Wind River Range in Fremont County, Wyoming, indicate that early motion along the Wind River and Continental faults controlled depositional patterns and lithologic characteristics of the local syntectonic sediments, and that the latest motion on a segment of the Wind River fault between Oregon and Pacific buttes folded some of these same sediments into a monocline. The stratigraphic sequence exposed in the monocline consists (in ascending order) of a lower distal fan or alluvial plain unit (main body of the Wasatch Formation), a lake margin unit (Tipton Tongue of the Green River Formation), a fluvial and deltaic sandbody (Tipton Sandstone), and an alluvial fan unit (Cathedral Bluffs Tongue of the Wasatch Formation). Cu rent direction, clast composition, and clast-size data indicate that a granitic and mafic distal source to the east and a proximal granitic source to the north supplied sediment. Subsequent movement on the Wind River fault warped this sequence into a monocline 2 mi long. This structure dies out in both a northwest and southeast direction along the inferred trace of the Wind River fault and is overlain by undeformed middle Eocene sediments.
Other syntectonic units (e.g., Fort Union, Ice Point, White River, Arikaree, and South Pass conglomerates) occur in patches along the Wind River and Continental faults in this area. Each deposit is of local extent, exhibits rapid thickness and petrofacies changes, and probably represents proximal alluvial fan deposition. These characteristics are typical of syntectonic sediments in transcurrent-faulted terrains, and we are investigating the possibility of such faulting in this area.
Tectonic implications of these interpretations are: (1) early motion on the Wind River fault controlled the margin of Eocene Lake Gosiute and generated a distal sediment source to the east; (2) late early Eocene uplift of the north side of the Continental fault provided a proximal source for pegmatitic and granitic boulders to the north; (3) last motion on the Wind River fault was latest early Eocene or earliest middle Eocene between Oregon and Pacific buttes; (4) the Wind River fault consists of several segments which moved separately rather than as one, long continuous zone of concurrent faulting; (5) while the Wind River Range was being thrust to the southwest it may have been uncoupled from the basins to the south by a zone of transcurrent faulting; (6) Pliocene or younger recurre t motion along the Continental fault was opposite to that in the Eocene.
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