HR: 1340h
AN: T23D-1631    [Abstracts]
TI: Strontium isotopic evidence of shifting inflows to Eocene Lake Uinta in the Laramide foreland of Utah
AU: * Davis, S J
EM: sjdavis@stanford.edu
AF: Stanford University Geological and Environmental Sciences, 450 Serra Mall, Stanford, CA 94305, United States
AU: Wiegand, B A
EM: bwiegand@pangea.stanford.edu
AF: Stanford University Geological and Environmental Sciences, 450 Serra Mall, Stanford, CA 94305, United States
AU: Chamberlain, C P
EM: chamb@pangea.stanford.edu
AF: Stanford University Geological and Environmental Sciences, 450 Serra Mall, Stanford, CA 94305, United States
AB: Isotopic records from the Uinta basin in Utah are evidence of an evolving landscape during the early Cenozoic. Combined with studies of provenance and paleoflow, oxygen and carbon isotopic results have recently been interpreted to reflect changes in hydrology and catchment hypsometry as the basin responded to developing relief in the foreland. We now present strontium isotope data from lacustrine limestones indicating significant and rapid (< 1 my) shifts in the source of inflowing surface waters. Provenance of Eocene sediments has been used to argue that water spilling south from an overfilled Lake Gosiute in the Greater Green River basin caused a highstand of the lake in the Piceance Creek basin, which in turn overtopped the Douglas Creek Arch and connected with Lake Uinta in the Uinta basin. The lake highstand was extremely productive, and resulted in the deposition of the rich "Mahogany zone" oil shales. New data shows that the ⁸⁷Sr/⁸⁶Sr ratio of lacustrine limestones collected in the Uinta basin is generally low (< 0.7105) for most of the Eocene, but spikes higher (to 0.7122) in samples of the Main Body of the Green River Formation near and within the Mahogany zone. We interpret this data to reflect a period of input of water from Lake Gosiute, where that lake's catchments included exposed basement that was much more radiogenic. The strontium data further supports the interpretation that intraforeland basin development in the central North American Cordillera was largely controlled by shifting drainage patterns as the landscape responded to ongoing Laramide tectonism.
DE: 1040 Radiogenic isotope geochemistry
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4239 Limnology (0458, 1845, 4942)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting