RECONSTRUCTING REGIONAL GLACIAL AND CLIMATE HISTORIES OF THE SEVIER AND WASATCH PLATEAUS OF CENTRAL UTAH

The Sevier and Wasatch Plateaus of Central Utah present a unique opportunity to study regional climate change, due in large part to the region's unique glacial histories. Within the Wasatch Plateau, glaciers and ice fields have carved the plateau into recognizable geomorphic features that have been well documented. South of the Wasatch Plateau, the Sevier Plateau exhibits evidence of less-extensive cirque glaciers. However, recent field work suggests that some of these glaciers were larger than previously thought. Improved constraints on the timing and size of this glacial advance would offer needed insight into the paleoclimate of the region.

Preliminary mapping of glacial deposits and equilibrium line altitudes (ELAs) shows a distinct pattern in glacial advances in Central Utah. In particular, ELAs changes (present day minus glacial maximum) decrease from north to south across the Wasatch Mountains and Plateau and then rapidly increase over the Sevier Plateau. The variation in climate required to explain this pattern in regional ELAs is examined through glacier mass balance models, general circulation models, and modern analogs of climate variability. Such interpretations of the regional climate history from the glacial history are severely hindered, however, by the lack of absolute numerical ages of the glacial deposits; very few absolute ages have been reported for the Wasatch Plateau, and no absolute ages have been published for the Sevier Plateau. Moreover, absolute dating in this area is somewhat problematic due to the complex geomorphology and lithology of the region. Landslides and other mass wasting processes in particular make identifying glacial deposits and obtaining accurate numerical ages of these deposits difficult. Moreover, much of the lithology of the Sevier Plateau is dacite, a large proportion of which is unusable devitrified glass and Fe-Ti oxides. Preliminary sample preparation does suggest the potential for measurement of cosmogenic Cl-36 in plagioclase within the dacite, but isolating measurable amounts of the isotope remains difficult.

In summary, while the pattern of regional glacial and climate histories in Central Utah is intriguing, reliable absolute ages need to be acquired before the glacial record can be placed into context with other regional and hemispheric paleoclimate records.