ANTIPODAL TERRESTRIAL DEGLACIAL EVENTS FROM IRELAND AND TASMANIA

Major phases of ice retreat and readvance since the LGM have been studied in Ireland and Tasmania. In Ireland, glacial deposits from the Leinster and Mourne Mts were dated using in-situ cosmogenic 10Be, 26Al, and OSL, and in Tasmania, using 10Be and 26Al. Our aim was two-fold; first, to map and date the LGM limits and, second, the timing and mode of subsequent younger deglaciation events. We compare these glacial chronologies from quite similar oceanic mid-latitude regions in opposite hemispheres for synchronicity and amplitude. The Midland ice that formed the South Ireland End Moraine and Glacial Lake Blessington was coeval with maximum ice advance at Athdown in the Leinster Mts. Two OSL dates from Athdown suggest a maximum age of 30-25 ka BP for this LGM ice limit. Ice retreated through the Irish Sea Basin to the Plain of Mourne by 21 ka BP though glaciers still occupied Mourne mountain valleys. Readvance of Midland ice, associated with drumlins, formed moraines on the southern Plain of Mourne at 17-16 ka BP. Several, undated, retreat valley glacier stages occurred in the mountain valleys before a final cirque glaciation at 10-12 ka BP in both Leinster and Mourne. In western Tasmania, we studied three glacial valley sites exhibiting moraine sequences of the last deglaciation cycle. Our data suggests that valley glaciers of Stage 2 were formed by 25 ka BP, but a prominent extent of ice associated with sharp-crested moraines in valleys and cirques occurred at 18-20 ka BP. Episodic retreat occurred from 18-15 ka BP and by 14 ka BP the highest cirques were ice-free. Comparisons with North Atlantic cores and GRIP delta-18O records indicate glacial advances in Ireland at H3(?), H1 and HO times. Evidence for H2 is not clear. In Tasmania, valley and cirque glaciers attained recent maxima at 18-19 ka BP during H2 time, as did minima in delta-18O records of adjacent marine and Antarctic ice cores. There is no evidence for ice during the ACR or YD periods. Although not exhaustive, our set of cosmogenic ages is sufficient to show a distinct lack of correlation between Ireland in the North East Atlantic with Tasmania in the South West Pacific.