Reconstruction and 36Cl based geochronology of the deglaciation of central Ireland

This paper presents geomorphological and geochronological evidence for ice sheet oscillations during the deglaciation of the last Irish Ice Sheet. Cosmogenic exposure age results (36Cl ages; n = 18) demonstrate that the ice margin had retreated into central Ireland by c. 19 ka, with ice restricted to the uplands west of the River Shannon by c. 16.7 ka. These dates are consistent with dated ice margins on the east coast of Ireland. The geomorphological evidence points to streaming ice draining eastward within the Irish interior and a transition from streaming to surging ice dynamics during recession, as the ice sheet split into separate lobes. Up to four substantial, non-synchronous readvances of individual lobes over several kilometres are observed. These were in part caused by surging behaviour in the ice sheet, indicating the role of internal disequilibria in local to regional-scale advances. Despite the existence of an extensive proglacial ice-contact lake, Palaeolake Riada, which formed at the ice margin during retreat into the Shannon drainage basin, cosmogenic exposure age results demonstrate that water submersion did not affect surface exposure ages obtained from glacial boulders, indicating that the ice contact lake existed for too short a time span to have had an effect on boulder exposure ages. A key finding is that the ice retreat into central Ireland was earlier than in some parts of Britain, such as eastern Scotland, and highlights the complexity of the glacial record across Great Britain and Ireland.