Cosmogenic 10Be and 26Al ages for the Last Glacial Maximum, eastern Baffin Island, Arctic Canada

Abstract

A chronology for the Last Glacial Maximum based on cosmogenic exposure dating in the Pangnirtung Fjord area, eastern Baffin Island, Arctic Canada, is at odds with many decades of land-based, glacial stratigraphic research. Most previous chronologies focused primarily on relative weathering criteria and suggested that ice extent was restricted during the late Wisconsinan (ca. 24–8 ka). In contrast, by directly dating glacial features, we conclude that late Wisconsinan ice was far more extensive than previously believed. There are 36 gneissic boulders and 8 samples of ice-molded gneissic bedrock that yield late Wisconsinan 10 Be and 26 Al exposure ages for the last glaciation of Pangnirtung Fjord. The prominent Duval moraines, which were previously interpreted to represent a significant early Wisconsinan (100–60 ka) ice advance on southern Cumberland Peninsula, were actually deposited between 24 and 9 ka. Two boulders from a raised glaciomarine delta, stratigraphically related to the Duval moraines, date to about 10 ka. Two recessional moraines and striated bedrock along Pangnirtung Fjord, as well as erratics on the floor of the Kolik River valley, a tributary to Pangnirtung Fjord, indicate that deglaciation began between 12 and 9 ka. In situ produced 10 Be and 26 Al abundances indicate that ice filled Pangnirtung Fjord for about 15 k.y. (either continuously or intermittently) prior to 10 ka, which is compatible with 14 C chronologies for adjacent Cumberland Sound. Thus, our data support other recent studies that suggest the northern and southern margins of the Laurentide ice sheet were generally in phase during the latest Wisconsinan, contrary to earlier interpretations.