Facies analysis of a pumiceous terrace beside klutlan Glacier, Yukon Territory

Dacitic pumice forms discontinuous terraces along both sides of Klutlan Glacier, which emanates from Mount Churchill, Alaska. Mount Churchill is the eruptive source of the White River Ash, an extensive tephra deposit accumulated ~1200 and 1900 BP during two plinian eruptions. Composition, texture, primary structures, and lack of induration suggest that, apart from a locally preserved cover of air-fall tephra, the Klutlan pumice deposits are resedimented proximal equivalents of the White River Ash. The pumice terraces display large-scale crossbedding, normal and inverse graded bedding, channels, and both linguoid and climbing ripples, all sedimentary structures characteristic of subaqueous deposition. In addition, many of the pyroclasts are subround and show a wide variation in sorting from bed to bed, in contrast to the uniformly angular to subangular texture of well-sorted pyroclasts in an air-fall ash layer that caps the terraces. This uppermost tephra unit, up to 1 m thick, is attributed to the last ma...