Timing of Postglacial Cirque Reoccupation in the Northern Uinta Mountains, Northeastern Utah, U.S.A.

Abstract

Radiocarbon-dated organics from lacustrine cores and colluvial basins, combined with measurements of lichens growing on moraines previously interpreted as Neoglacial in age, argue that the extent of post-Pleistocene ice in the northern Uinta Mountains was limited. An AMS date of 12,190 ± 120 14C yr BP on basal organic sediment from a tarn indicates that deglaciation was locally complete by ~14 ka BP. Additional radiocarbon ages of ~10 ka BP from two colluvial basins behind end moraines suggest that these moraines date to the latest Pleistocene. Cross-cutting moraines from a fourth site indicate that an active cirque-glacier system was present at some point after the terminal Pleistocene deglaciation. Maximum diameters of Rhizocarpon geographicum lichens on these moraines, however, suggest they may predate Little Ice Age deposits in the Wind River Range and Sierra Nevada. The convergence of evidence suggests that glaciers in the northern Uintas during the Holocene were extremely limited in extent, and restricted to the middle Neoglacial period. This preliminary conclusion contradicts some previous interpretations of the upper subalpine geomorphology of the range, which postulated widespread post-Pinedale glaciation, and multiple stades of Holocene Neoglaciation.