GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 143-4
Presentation Time: 2:25 PM


NORRIS, Sophie Louise, MARGOLD, Martin and FROESE, Duane, Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada,

The Interior Plains of northern Alberta and Saskatchewan hosted the Laurentide-Cordilleran ice saddle and the south-western slopes of the Keewatin Ice Dome at the peak of the Late Wisconsinan glaciation. Subsequently, the western margin of the Laurentide Ice Sheet passed over this region during the deglaciation, opening the north-western drainage route for Lake Agassiz. The north-western Agassiz outlet and the associated flooding event(s) have received great attention and continue to be a subject of debate. However, the detailed ice dynamics in the region, the understanding of which is crucial for inferences of meltwater drainage, is still poorly understood. This applies both for the ice sheet geometry at the Last Glacial Maximum (LGM) and for the pattern of ice margin retreat.

We focus on a 26, 680 km2 region of northeast Alberta and northwest Saskatchewan centered on the Clearwater-Athabasca Spillway, the assumed north-western Agassiz outlet. Using mapping from high-resolution digital elevation data, we reconstruct the glacial landform record comprising attenuated bedforms, eskers, moraines and meltwater channels. These data permit the classification of 62 flowsets that indicate multiple cross cutting ice flow directions. We tie the reconstructed ice flow direction with moraines and meltwater landforms to derive the ice margin configuration. Based on this mapping we present a preliminary five-stage model of ice sheet evolution in the form of palaeo-geographic maps spanning from the LGM through to deglaciation (~21-9.5 cal ka BP). This reconstruction reveals three major changes in ice stream configuration and indicates that margin retreat was complex and dominated by the dynamic spatial and temporal evolution of ice streams. In the next stage, we will date the reconstructed ice margin positions with cosmogenic exposure dating and use our model in combination with 3-D investigation of regional till architecture to link individual till layers to each of the five identified stages of ice stream operation. Overall, our projects aim to improve the knowledge of one of the focal points of the last North American deglaciation.