Ice readvance from the southern Sperrin Mountains during the last deglaciation

Abstract

Abstract:Sedimentary exposures near Mullaghcarn in the southern Sperrin Mountains, north-central Ireland, overlie planated bedrock platforms and comprise interbedded sequences of bedrock-derived diamictic breccias, rock rafts and glaciotectonic shears. At Murrinmaguiggan, bedrock rafts are located between glacial outwash sediments that were deposited alternately from Sperrin ice to the north and Omagh Basin ice to the south-west. Flow indicators, including erratic carriage and the dip direction of rock rafts, glaciotectonic shears and outwash sediments, show that Sperrin ice advanced from north to south into terrain that had been vacated by Omagh Basin ice, which then readvanced following Sperrin ice retreat. This geomorphic and sedimentary evidence suggests that Sperrin ice was active during early deglacial stages and that oscillations of its ice margin were not synchronous with oscillations of Omagh Basin ice. Changes in climate and ice mass balance may have controlled ice mass activity.