Investigating the glacial history of the northern sector of the Cordilleran Ice Sheet with cosmogenic 10Be concentrations in quartz

Exposure durations of glacial landforms in widely separated areas of central Yukon Territory affected bythe northern sector of the Cordilleran Ice Sheet (CIS) and alpine glaciers have been determined usingcosmogenic 10Be in quartz. The aim of our research is to test previous reconstructions of glacial historyand to begin to address the paucity of chronological control for the lateral and vertical extent of thenorthern CIS. Chronological evidence for CIS expansion predating the Last Glacial Maximum comes fromminimum surface exposure durations of c 100 ka for two bedrock samples within the Reid glacial limit,indicating a possible marine Oxygen Isotope Stage (OIS) 6 age for this event, and from minimumexposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatakwithin the McConnell glacial limit (OIS 2), indicating a possible OIS 4 age. High elevation minimumsurface exposure durations within the McConnell limit indicate that some areas formerly mapped asnunataks were covered by cold-based ice prior to 30 ka. Montane glaciation in the Mackenzie Mountains,outside the McConnell glacial limit, was contemporaneous with nearby CIS advance at 17 ka, with CISretreat by 15 ka. Deglaciation of the Tintina Trench, a major ice discharge route, was completed by 12 ka.At this time ice in an adjacent discharge route to the south was still entering higher-elevation valleys inthe Pelly Mountains. A Lateglacial readvance may have peaked at ca 10 ka in the Ogilvie Mountains.Considerable variation in ages from individual landforms, and possible complex histories, requireadditional cosmogenic nuclide measurements to confirm interpretations.
Our research was funded by Swedish Research Council grant VR 2005-4972 to APS and benefited from post-doctoral employment of ATC by the Department of Physical Geography and Quaternary Geology,Stockholm University, through APS