LATE PLEISTOCENE DEGLACIATION OF THE CORDILLERAN ICE SHEET FROM SOUTHWEST YUKON: TIMING, RECESSION RATES, AND IMPLICATIONS

A Late Pleistocene deglacial chronology for southwest Yukon provides an opportunity to examine the style of ice retreat from the LGM and the deglacial landscape evolution along the northwest margin of the Cordilleran ice sheet. A large dataset of ¹⁰Be and ³⁶Cl chronology from erratic boulders is being assembled for the northern portion of the Cordilleran ice sheet. This deglacial record will be presented and recession rates for both early and late phase deglaciation on a portion of the Cassiar lobe will be discussed.

In the ice sheet system, it appears that initial deglaciation begins around 15 ka and is punctuated by frontal pauses and/or oscillations marked by recessional moraines and lateral meltwater channels; this is consistent with an initial slow rate of recession. Landforms in this region also include deeply incised meltwater channels and a network of moraine/ice dam-controlled lake basins that persist today. In contrast, the later phase of deglaciation appears to be controlled by a rapid warming that is linked to the Bolling-Allerod and led to an increase in retreat rate and fewer recessional moraine-building episodes. Rapid retreat was accentuated by calving into glacial lakes and stagnation in interior lowlands. This phase of rapid warming is also reflected in regional paleoenvironmental reconstructions based on lake cores.