MINIMUM BE-10 EXPOSURE AGES OF EARLY PLIOCENE FOR THE TABLE-MOUNTAIN-PLATEAU AND THE SIRIUS GROUP AT MOUNT-FLEMING, DRY-VALLEYS, ANTARCTICA

Using accelerator mass spectrometry (AMS), we have measured Be-10 and Al-26 in, quartz from granites and sandstones from Table Mountain and Mount Fleming, Antarctica. Our data show that the plateau surface at T able Mountain had formed by early Pliocene time at the latest. Granite s fringing but within the Sirius Group at Table Mountain give a minimu m exposure age of 2.6 Ma for this deposit. A sandstone clast on the Fe rrar dolerite surface just outside and below and thus postdating, the Sirius Group has a minimum age of 2.9 Ma. Two samples from the Sirius Group at Mount Fleming have Be-10 concentrations that have reached sec ular equilibrium. This deposit is at least 4.8 m.y. old. The Sirius Gr oup at Mount Fleming cannot have been deposited after 3.0 -2.5 Ma, as implied by biostratigraphic data. Our dates contradict the hypothesis that in the Pliocene East Antarctica was deglaciated and the climate w as significantly warmer and wetter. The preservation of these surfaces indicates a continuous cold desert in the dry valleys since the begin ning of the Pliocene. The high Be-10 concentrations we have measured c annot be reconciled with uplift of the Transantarctic Mountains at a r ate of 1 km/m.y. during the past 3 m.y.