Abstract

Twenty lake sediment cores extracted upstream from Last Glacial Maximum terminal moraines constrain the timing of the glacial-interglacial transition in the Uinta Mountains, Utah (USA). The stratigraphy observed in the cores, and accelerator mass spectrometry 14C dating of inorganic silty clay beneath gyttja, temporally constrain local deglaciation. The majority of basal ages fall within the Bølling-Allerød interval, with strong overlap at ca. 12.7 cal. (calibrated) kyr B.P. This convergence matches regional evidence of rising temperatures, increasing aridity, falling pluvial lake levels, and glacial retreat near the end of the last glacial-interglacial transition. Normalized estimates of glacier terminus retreat and elevation rise in the Uinta Mountains and elsewhere in the Rocky Mountains derived from consideration of cosmogenic ages on terminal moraines consistently average ∼10%/k.y. between ca. 20 and 13 ka, implying a regionally uniform climate forcing during deglaciation. Minor variations between these rates likely reflect hypsometric effects during deglaciation. Seven lakes dammed by cirque-floor moraines have basal ages within, or slightly younger than, the Younger Dryas interval, suggesting advances of favorably located cirque glaciers before the glacial-interglacial transition was complete.

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