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1 Geology Department, University of Vermont, Burlington, Vermont 05405, USA
2 Department of Natural Sciences, Bentley College, Waltham, Massachusetts 02452, USA
3 Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94550, USA
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 10Be and 26Al 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 10Be and 26Al abundances indicate that ice filled Pangnirtung Fjord for about 15 k.y. (either continuously or intermittently) prior to 10 ka, which is compatible with 14C 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.
Key Words: Baffin Island • cosmogenic exposure dating • dating • deglaciation • Laurentide ice sheet • Last Glacial Maximum
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