Abstract

Due to its low input of coarse sediment, Upper Waterfowl Lake, in Banff Park, Alberta, has developed a delta atypical of lacustrine deltas in this high mountain region: lack of foresets, vertically aggrading stable distributary channels, and a surface composed of mostly fine-grained floodplain materials. Deltaic progradation has outrun the supply of coarse sediment, resulting in entrapment of all gravel and coarse sand in proximal channels.Data provided by auger samples, including stratigraphic positions of Mazama and Bridge River volcanic ashes, suggest the lake was formed about 8800 years ago when deposition of a large alluvial fan blocked the Mistaya River at the upper end of Lower Waterfowl Lake. The delta has undergone two progradations, one beginning at the lake's time of origin, the other following a renewed lake level rise some 2300 years ago. Mean aggradation rates since Mazama time (6600 y BP) have been approximately steady at about.05 cm/y. Pre-Mazama lake sediments, however, were deposited more than twice as fast as a result of accelerated sedimentation rates that accompanied deglaciation.

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