Research Interests
Research interests:
Quaternary history of the U.S. cordillera. Specialty in the history
and dynamics of glaciation in the southern and middle Rocky Mountains,
the greater Yellowstone region and the Wind River Range of Wyoming.
Much of my research involves combining
relative-age techniques [soil
development, lichenometry, hornblende weathering, moraine morphology, and
boulder weathering parameters]with
numeric age analyses to solve
problems of glacial stratigraphy. An ongoing theme of my work also
involves describing the variability of soils developed across different-aged
glacial landscapes as an attempt to refine the use of soil development
as a relative-age technique.
Recent
Work
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Recently funded work: (NSF) involves collaboration
with Jon Harbor (Purdue University) & Derek Fabel of the Purdue
Rare Isotope Measurement Lab (PRIME
Lab) & University of Melbourne and Dr. Allan James (University
of South Carolina) to reconstruct spatial patterns of glacial erosion using
cosmogenic radionuclide exposure ages. Field work in the Wind River
Range of Wyoming and the northwestern Sierra Nevada of California provides
bedrock samples across a series of glaciated valley sections. Cosmogenic
radionuclide concentration determinations will evaluate how field patterns
of cosmogenic radionuclide concentrations compare with theoretical predictions
based on scenarios for the spatial pattern and relative amount of glacial
erosion. All fieldwork has been completed, and initial results from
seven samples collected in Wyoming are very encouraging. In the center
of the glaciated valley the cosmogenic radionuclide concentrations give
exposure ages relating to the last glaciation. Towards the margin
of glaciation, concentrations increase dramatically to levels indicative
of exposure ages relating to the penultimate glaciation. However,
these elevated radionuclide concentrations occur within the last glacial
limit, suggesting that they include some remnant isotope concentration.
This is precisely what we predicted for cases of declining erosion rates
towards the glacial margin. Our empirical results to date are consistent
with our theoretical predictions for a pattern of erosion that declines
from a maximum toward the center of the valley to a minimum at the margin.
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Continuing work: to refine and test
the cosmogenic nuclide exposure technique, where type localities in the
Wind River Range, Wyoming and the Sierra Nevada, California, have been
intensively dated using cosmogenic radionuclides (e.g. Gosse et al., 1995a-b,
Phillips et al., 1990, 1997). However, before widespread use of this
approach can be recommended, it is necessary to develop pilot studies demonstrating
the value and limitations of extending this technique from type localities,
which generally have excellent moraine preservation but are located on
the piedmont, to alpine valleys with less preservation of glacial features
and potential gaps in the stratigraphic sequence. I have mapped glacial
deposits and collected boulder and bedrock samples to determine the glacial
chronology while working on the above project designed to reconstruct spatial
patterns of valley scale glacial. In the Wind River Range, I have
samples from the cirques to the piedmont outlet of the Middle Popo Agie
valley, providing a spatially continuous glacial stratigraphy that can
be correlated with nearby type localities.
Related interests: soil morphology
and development across Quaternary landscapes. Recent work involve
studies of soil variability along catenas developed on moraine slopes of
Pinedale and Bull Lake-age glaciations of the Wind River Range; hornblende
and feldspar weathering with age in soils of glacial landscapes; and weathering
relationships (in-situ vs. eolian addition) along catena slopes of different-age
glacial landscapes using the total chemical analyses (XRF) of sand, silt,
and clay separates.
