COSMOGENIC NUCLIDE EXPOSURE AGES AND GLACIAL HISTORY OF LATE QUATERNARY ROSS SEA DRIFT IN MCMURDO SOUND, ANTARCTICA

He-3, Be-10 and Al-26 surface exposure ages were determined for rock s amples from late Quaternary drift sheets deposited on the coast of McM urdo Sound, Antarctica, by the Ross Sea Ice Sheet. The youngest drift, previously believed to be Late Wisconsin in age, has exposure ages of 8-106 kyr (19 samples). These results suggest that the apparent 'Late Wisconsin' ice margin may represent a number of ice sheet advances du ring the last glacial period. He-3 exposure ages from analogous, strat igraphically older drift range from 104 to 567 kyr (seven samples), an d clearly distinguish the youngest drift from older deposits. Comparis on of Be-10 and He-3 concentrations in Ross Sea Drift quartz samples i ndicates significant He-3 loss in only one sample, suggesting that cos mogenic He-3 is generally retained in young Antarctic quartz samples ( exposure age < 100 kyr) of appropriate grain size. In two of the five quartz samples analyzed, significant excesses of Al-26 relative to Be- 10 preclude meaningful Al-26 exposure age calculations. These excesses may be due to nucleogenic Al-26 produced as a byproduct of uranium an d thorium decay.