title: Green River Alan Carroll home

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Summary

My principal area of current research is the sequence stratigraphy and three-dimensional distribution of lacustrine and associated facies, primarily in the Eocene Green River Formation. The Green River Formation provides an excellent natural laboratory for such studies by virtue of its accessibility, the diversity of lake types it encompasses, and the geologic context provided by its long history of previous studies. One goal of this work will be to document the stratigraphic context, sequence-scale and basin-scale distribution, and hydrocarbon generative potential of the heterogeneous Green River Formation organic facies. In addition to stratigraphic and source-rock studies, we will also seek to quantify specific tectonic and climatic influences on the evolution of lake facies. Part of this study will involve detailed application of traditional techniques of sedimentary basin analysis, such as facies and paleocurrent analysis and sandstone petrography.

In addition, we are applying various radiogenic isotopic tools to the Green River Formation, in collaboration with UW professors Clark Johnson and Brad Singer. By examining temporal changes in 87Sr/86Sr ratios in lacustrine carbonates we are seeking to document the provenance of lake waters, which is controlled by both tectonic reorganization of drainage patterns and by climatically-induced changes in runoff and evaporation. These studies are supported by conventional provenance analyses using sandstone petrography, and by sedimentary facies and paleocurrent evidence. A unique advantage of using these different approaches is that we will be able to differentiate between the provenance of clastic sediments and the provenance of lake waters, allowing sediment supply variations to be effectively decoupled from lake level variations. High-resolution 40Ar/39Ar dating of interbedded tuffs will provide the best chronostratigraphy in any lake basin, permitting the first reliable measures of lacustrine sediment accumulation rates. This information will be useful both to tie lake types to timing of subsidence and uplift events, and to test for possible Milankovitch-scale cyclicities.

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image: Green River map

Location of the greater Green River basin.

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Stratigraphy of the greater Green River basin.


image: photo, mountain

Farson Sandstone Member, northern Green River Basin. Note the clinoforms dipping to the left (southwest) in this deltaic sandstone. Wasatch Formation underlies the sandstone. (photo: Alan Carroll)

image: photo, mountain

Wilkins Peak Member at Wilkins Peak, near Rock Springs. (photo: Alan Carroll)

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Wilkins Peak Member, White Mountain. Note strong evidence for cyclicity in lacustrine and lake-marginal mudstone. (photo: Alan Carroll)


image: photo, mountain

Sand Butte, Washakie basin. Base of exposure is the alluvial Wasatch Formation, top is volcaniclastic sandstone of the Sand Butte Bed, Laney Member. LaClede Bed of the Laney Member is partially exposed in between. (photo: Alan Carroll)

image: drawing, cross section

Simplified stratigraphic cross-section of the Laney Member at DeLaney Rim, Washakie Basin (Rhodes et al., in prep.).

image: drawing, evolution

Schematic representation of strontium isotopic evolution of lake waters during a flooding-desiccation cycle, Laney Member (Rhodes et al., in press).


Researchers

Jeff Pietras is completing his Ph.D. disseration on the stratigraphy and strontium isotope geochemistry of the Wilkins Peak Member. Meredith Rhodes is completing her Ph.D. dissertation on the Laney Member. Both of their projects involve major collaboration with Clark Johnson and Brian Beard of the UW Radiogenic Isotopes Laboratory.

Mike Smith is working on 40Ar/39Ar age determinations for tuff horizons interbedded in the Green River Formation, in collaboration with Brad Singer of the UW Rare Gas Geochronology Laboratory. He is currently completing an M.S.. His Ph.D. dissertation will continue with this work, with a goal of documenting the uplift timing of Laramide basin-bounding uplifts by dating synorogenic coarase clastic deposits that interfinger with the Green River Formation.

Ackowledgments

Financial support provided by the National Science Foundation, the Donors of the Petroleum Research Fund of the American Chemical Society, Conoco, and Texaco.


page created December 5, 2001