Geoscience and Exploration

Cosmogenic Surface Exposure Ages for Laurentide Ice Sheet Deglaciation in the Western Slave Craton

Sunday, October 21, 2018 - 16:30 to 19:00 Multiplex Gym (DND)


A.V. Reyes (Presenting)
University of Alberta

A.E. Carlson
Oregon State University

J.R. Reimink
Carnegie Institute

M. Caffee
Purdue University

The timing of northwest Laurentide ice sheet deglaciation is important for understanding how ice-sheet retreat, and associated meltwater discharge, may have been involved in abrupt climate change and rapid sea-level rise at the end of the last glaciation. However, the deglacial chronology across the western Canadian Shield is poorly understood, with only a handful of minimum-limiting radiocarbon dates constraining the timing and pattern of northwest Laurentide ice-sheet retreat. We use cosmogenic beryllium-10 surface exposure dating of glacial erratics, sampled opportunistically during bedrock mapping campaigns in the western Slave Craton, to directly date the timing of northwest Laurentide ice-sheet retreat during the last deglaciation. Five erratics sampled near the Acasta Gneiss “Discovery Site” have exposure ages between 12.8+/-0.6 and 12.2+/-0.6 thousand years ago (ka), with a weighted mean of 12.4+/-0.2 ka. Five erratics were also sampled 115 km to the east at Point Lake; four exposure ages are currently in-process, but one erratic from this site yielded an exposure age of 11.6+/-0.5 ka. When corrected for decreased atmospheric depth due to isostatic uplift since deglaciation, the data indicate that the Laurentide ice sheet retreated through this western part of the Slave Craton ~13.7-12.8 ka, or ~1000 years earlier than inferred from the canonical compilation of minimum-limiting radiocarbon dates for deglaciation. Additional exposure ages on glacial erratics across the Slave Craton will allow comprehensive testing of hypotheses related to northwest Laurentide ice-sheet retreat and its potential forcing of abrupt deglacial sea-level rise and climate change events.