Sediments of the Norris Glacier outwash area, upper Taku Inlet, southeastern Alaska

Abstract

An 8-square mile outwash fan, composed of gravelly sediment, extends from the terminus of Norris Glacier to the waters of upper Taku Inlet, Southeastern Alaska. Thirty-seven surface sediment samples from the tidal portion of the fan form the bulk of this study. The tidal flat is largely composed of very poorly sorted muddy sediment and relatively well sorted sand which, for the most part, overlie outwash gravel. Mixing of various modal size classes has produced a complex sediment distribution pattern as well as a complicated size-sorting relationship. The sand-size fraction of the sediments consists of feldspar, quartz, rock fragments, amphiboles, pyroxenes, micas and opaques; the clay-size fraction consists of micas, chlorite, montmorillonite, feldspar and amphibole. The sediments are the product of glacial abrasion in the Juneau Ice Field area. The sand and mud are derived largely from Norris and Taku Glacier detritus; their nature indicates valley glacier detritus may be fairly rapidly sorted when subjected to hydraulic action. Absence of quartz and presence of feldspar in the clay-size fraction may indicate the physical properties of these minerals control the size to which they can be reduced by valley-glacier abrasion.