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Subglacial environment inferred from bedrock-coating siltskins, Mendenhall Glacier, Alaska, U. S. A.

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Abstract:

Retreat of Mendenhall Glacier near Juneau, Alaska, U. S. A., has exposed a bedrock ridge spotted with ''siltskins'', patchy coatings of calcite-cemented clay-to sand-sized lithic grains. Coatings 0.5-20 mm thick occur in two distinct morphologies. Thin, striated siltskins coat mainly stoss faces. Thicker, corrugated siltskins on lee faces consist of parallel micro-ridges elongated downslope. Thin-section analysis shows that siltskins consist of a basal, calcite-rich layer overlain by microlaminated layers of calcite-cemented lithic grains. Scanning electron microscope (SEM) energy-dispersive spectrometer (EDS) analysis of laminae and surfaces shows laterally persistent Ca/Si differences. Isotopic values for O18and O13ranged from -19.52‰ to ^12.74‰ and -6.18‰ to -3.44‰, respectively, consistent with deposition from subglacial waters of varying isotopic composition and with derivation of carbon from inorganic sources. Corrugated siltskins are complex depositional features modified by erosional processes. Parallel micro-ridges spaced 1-10 mm apparently formed as sediment-rich water dripped down lee-slope rock faces. Ice-rock separation, flow energy and the transported sediment controlled the layering and depositional forms. Siltskins probably formed when a subglacial cavity system was active on the rock ridge and provide clues about how microscale hydrologic processes interact with larger-scale subglacial systems.

Document Type: Research Article

DOI: http://dx.doi.org/10.3189/172756503781830412

Publication date: December 1, 2003

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  • The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.
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