Paleogeography of Paleocene Wind River basin
The Paleocene Fort Union Formation in the Wind River basin was deposited in response to Laramide deformation between south-verging faults to the north (Owl Creek and Casper thrusts) and south (Wind River and Granite thrusts). Exposures in this asymmetric basin include a lower fluvial member overlain by the Waltman (lacustrine) and time-equivalent Shotgun (fluvial) members in the northeast and a single fluvial unit in the southeast. In the northeast, low sinuosity, ribbon channel sandstones (northwest paleoflow, about 40 m thick) are overlain by sheet-sand deposits interspersed with channel sandstones (southwest paleoflow, about 700 m thick), which are in turn overlain by the Waltman Member. The basal channel sands are wide (about 100 m perpendicular to flow), thick (5 to 10 m), and trough cross-bedded. The sheet-sand deposits consist of upward-fixing cycles 1 to 10 m thick. These facies are interpreted to be the product of longitudinal drainage flowing parallel to the Casper thrust, overlain by fan-delta sediments prograding perpendicular to the thrust. Palynology suggests a nearly complete Paleocene record for this sequence. To the south along the Rattlesnake Hills, trough cross-bedded sheet sandstones and gravel channel deposits (northward, 140 m thick) are overlain by layered mudstones and siltstones (180 m thick). The top of these high-energy braided-stream deposits and overlying low-energy delta-plain sediments are equivalent in age to the Waltman Member. A topographic low paralleled the Casper arch thrust during the earliest Paleocene. Prograding alluvial-fan sedimentation gradually shifted this topographic low away from the Casper thrust. Southern exposures record drainage toward, and ponding in, the topographic low.
- Research Organization:
- Cornell Univ., Ithaca, NY
- OSTI ID:
- 7230389
- Report Number(s):
- CONF-8609129-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 70:8; Conference: AAPG Rocky Mountain Section meeting, Casper, WY, USA, 7 Sep 1986
- Country of Publication:
- United States
- Language:
- English
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