PRECISE COSMOGENIC BE-10 MEASUREMENTS IN WESTERN NORTH-AMERICA - SUPPORT FOR A GLOBAL YOUNGER DRYAS COOLING EVENT

The Inner Titcomb Lakes moraine in the Wind River Mountains, Wyoming, has been dated with a precision of 5% using accelerator mass spectrome tric measurements of cosmogenic Be-10 in surface samples from nine bou lders resting on its crest. The age of this moraine is 11.4 +/- 0.5 to 13.8 +/- 0.6 ka; the range in age is due to the uncertainty in the Be -10 production rate and uncertainties in rock erosion rate and shieldi ng of cosmic rays by snow. Additional exposure ages on bedrock and bou lder surfaces that are stratigraphically younger and older than the In ner Titcomb Lakes moraine conform with this age. The exposure ages of the Inner Titcomb Lakes moraine overlap the North Atlantic Younger Dry as event, 12.8 +/- 0.2 to 11.5 +/- 0.3 ka.