Refining the pattern and style of Cordilleran Ice Sheet retreat: palaeogeography, evolution and implications of lateglacial ice‐dammed lake systems on the southern Fraser Plateau, British Columbia, Canada

• Published in: Boreas
• Main Authors: Perkins, Andrew J., Brennand, Tracy A.
• Other Authors: Natural Sciences and Engineering Research Council of Canada, Geological Society of America
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: British Columbia; Canada; Dammed Lake; Glacial Lake; Marginal Lake; Ice Sheet
• Online Access: http://dx.doi.org/10.1111/bor.12100; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fbor.12100; https://onlinelibrary.wiley.com/doi/pdf/10.1111/bor.12100

Decay of the last C ordilleran I ce S heet ( CIS ) near its geographical centre has been conceptualized as being dominated by passive downwasting (stagnation), in part because of the lack of large recessional moraines. Yet, multiple lines of evidence, including reconstructions of glacio‐isostatic rebound from palaeoglacial lake shoreline deformation suggest a sloping ice surface and a more systematic pattern of ice‐margin retreat. Here we reconstructed ice‐marginal lake evolution across the subdued topography of the southern Fraser Plateau in order to elucidate the pattern and style of lateglacial CIS decay. Lake stage extent was reconstructed using primary and secondary palaeo‐water‐plane indicators: deltas, spillways, ice‐marginal channels, subaqueous fans and lake‐bottom sediments identified from aerial photograph and digital elevation model interpretation combined with field observations of geomorphology and sedimentology, and ground‐penetrating radar surveys. Ice‐contact indicators, such as ice‐marginal channels, and grounding‐line moraines were used to refine and constrain ice‐margin positions. The results show that ice‐dammed lakes were extensive (average 27 km 2 max. 116 km 2 ) and relatively shallow (average 18 m). Within basins successive lake stages appear to have evolved by expansion, decanting or drainage (glacial lake outburst flood, outburst flood or lake maintenance) from southeast to northwest, implicating a systematic northwestward retreating ice margin (rather than chaotic stagnation) back toward the C oast M ountains, similar in style and pattern to that proposed for the F ennoscandian I ce S heet. This pattern is confirmed by cross‐cutting drainage networks between lake basins and is in agreement with numerical models of N orth A merican ice‐sheet retreat and recent hypotheses on lateglacial CIS reorganization during decay. Reconstructed lake systems are dynamic and transitory and probably had significant effects on the dynamics of ice‐marginal retreat, the importance of which is currently ...