QUATERNARY HISTORY IN THE ISKUT REGION, BRITISH COLUMBIA, CANADA

The geomorphology of British Columbia (BC) has been strongly affected by multiple glaciations of the Cordilleran Ice Sheet. Although the nature and timing of many of these glaciations are well understood for parts of BC, little work has been done in the northwestern portion of the province. We address this knowledge gap by reporting on the pattern of glaciation and deglaciation: migration of the local ice divide; development of extensive advance and retreat glacial lakes; and geochronology provided by radiocarbon ages.

The study area is located near the town of Iskut and the Red Chris Mine on the traditional territories of the Tahltan Nation in Northwestern BC. The area is rugged with a series of deep, interconnected valleys containing thick valley fill sequences separated by high plateaus and mountains. A surficial geology map was created using a LiDAR derived digital elevation model paired with orthoimagery. The mapping was combined with field observations including ice flow measurements, stratigraphic analysis, and radiocarbon dating to reconstruct the late Quaternary history of the area.

The oldest sediments are recorded in drill cores and include a glaciolacustrine sequence that yielded a radiocarbon age of > 54 ka (UCIAMS-271934). Above this are glaciolacustrine sediments capped by till attributed to advance MIS 2. The subsequent ice flow in the region was complex. Initially, ice accumulated in the Coast Mountains and flowed to the northeast. As the glaciation progressed, the ice divide migrated to the east, resulting in flow towards the northwest. Geomorphic analysis suggests that during deglaciation the equilibrium line rose rapidly, causing the ice sheet to thin. Ice retreat is characterized by a complex combination of active retreat and ice stagnation. A large ice-dammed lake formed in the major valleys with a minimum of four distinct, lowering lake stands. The MIS 2 glaciation affected drainage patterns in the area, resulting in relocation of drainage divides pre- and post-glaciation.

This research expands our understanding of the Cordilleran Ice Sheet and allows us to validate models of glaciation and deglaciation that have been developed for the southern portions of the ice sheet.