Subglacial environment inferred from bedrock-coating siltskins, Mendenhall Glacier, Alaska, U. S. A.
Authors: Carter, Carissa L.; Dethier, David P.; Newton, Robert L.
Source: Journal of Glaciology, Volume 49, Number 167, December 2003 , pp. 568-576(9)
Publisher: International Glaciological Society
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
Publication date: December 1, 2003
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