NEW 10BE EXPOSURE AGES FOR PLEISTOCENE GLACIAL STRATIGRAPHY, SOUTHERN WIND RIVER RANGE, WYOMING, USA

New ¹⁰Be boulder exposure ages from the southern Wind River Range, Wyoming, more tightly constrain the ages of Early, Middle, and Late Pleistocene glacial allostratigraphic units here that previously were estimated from relative age-data. Our results from Sinks Canyon, North Fork Canyon, Stough Basin, and Cirque of the Towers assign numeric ages to previously described deposits and also suggest differences from earlier age estimates:

• The age of the diamicton previously described from Table Mountain as Pre-Sacagawea Ridge-1 appears to be >2Ma;

• A boulder exposure age of ca. 600-700 ka indicates the previously-described Pre-Sacagawea Ridge-2 unit above Sinks Canyon should now be considered as a Sacagawea Ridge unit that;

• The Pinedale advance reached its terminus in North Fork Canyon ca. 23 ka and, by extrapolation, no later than 22 ka in Sinks Canyon;

• New ages from the Alice Lake and Temple Lake allostratigraphic units -- previously described in Stough Basin and Cirque of the Towers as “Neoglacial’ and ‘Younger Dryas’ apparently correspond more closely to, respectively, the IACP-Younger Dryas (13.7 – 11.3 ka) and Oldest Dryas (16.0 – 14.3) cooling events of the Lateglacial period.

These results suggest that (1) evidence of Early Pleistocene glacial activity exists above and outside the present canyons along the eastern flank of the Wind River Range that revives the earlier discussion of a ‘pre-canyon’ chapter of glacial activity here and that (2) numeric age-evidence from cirque moraines indicates that post-LGM ice advances here probably correspond to regional and global patterns of Lateglacial climate cooling.