Abstract

Three distinctive volcanic ash layers are present in the postglacial sediments at Banff National Park, Alberta. The chemical and mineralogical composition of the ash deposits, together with the radiocarbon age of associated charcoal, indicate the presence of Bridge River ash, whose source area is approximately located in the heart of the southern Coast Mountains, British Columbia, and Mazama ash, derived from Mount Mazama at Crater Lake, Oregon. A maximal age for Bridge River ash is 2 670 ± 140 years B.P. (GSC-531); a minimal age is 2 120 ± 150 years B.P, (G5C-577). Mazama ash is established as being about 6 600 years old, although a slightly younger date of 6 020 ± 90 years B.P. (S-191) was obtained on organic matter associated with this ash at Banff National Park. The source and age of the third ash deposit is not definitely known, but the presence of cummingtonite suggests that it might be St. Helens Y ash, derived from Mount St. Helens, Washington.

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