Basal till fabric and deposition at Burroughs Glacier, Glacier Bay, Alaska

Abstract

Research Article| December 01, 1994 Basal till fabric and deposition at Burroughs Glacier, Glacier Bay, Alaska NELSON R. HAM; NELSON R. HAM 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706 Search for other works by this author on: GSW Google Scholar DAVID M. MICKELSON DAVID M. MICKELSON 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1994) 106 (12): 1552–1559. https://doi.org/10.1130/0016-7606(1994)106<1552:BTFADA>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation NELSON R. HAM, DAVID M. MICKELSON; Basal till fabric and deposition at Burroughs Glacier, Glacier Bay, Alaska. GSA Bulletin 1994;; 106 (12): 1552–1559. doi: https://doi.org/10.1130/0016-7606(1994)106<1552:BTFADA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Basal till and debris-rich ice in the basal transport zone of Burroughs Glacier, southeast Alaska, were studied to develop a model for till deposition and to acquire new pebble fabric measurements from till at a modern glacier. Studies of till deposition and fabric measurements from modern glacial deposits are important for studying the genesis of Pleistocene and pre-Pleistocene glacial sediment.Basal till at Burroughs Glacier is deposited at the ice margin by the melting of basal debris-rich ice that stagnated progressively, from the bottom upward, beneath moving ice during deglaciation. The debris-rich ice is typically ∼1-3 m thick and has very high sediment content ranging from 60% to 70% by volume. The long axes of pebbles in the debris-rich ice, and in other parts of the basal transport zone of the glacier, are typically well oriented parallel to ice flow. The average S1 eigenvalue for nine fabrics measured in the basal transport zone is 0.8092 ± 0.067σ. The basal till is massive, matrix-supported, silty-sandy diamicton. Striated, lodged boulders, and crag and tails are common on the till surface. S1 eigenvalues calculated from 27 pebble fabrics measured in the till range from 0.4930 (no fabric) to 0.8261; the average value is 0.6757 ± 0.092σ. The range of values is nearly identical to that reported for fabrics from "undeformed lodgment till" by Dowdeswell and Sharp (1986).Although the final process of till deposition at Burroughs Glacier is passive melt out from stagnant, debris-rich ice, the nature and pebble fabric of the till are inherited from active ice processes, specifically the progressive stagnation of debris-rich ice beneath active ice. Evidence of differential movement (shear) within the debris-rich ice during deposition is reflected in a change in fabric azimuth with depth in the till, beveled bullet boulders, and shear surfaces. These features are typically thought to be characteristic of lodgment till or brittle deformation of subglacial sediment. The melt-out process is passive because of the very high debris content of the debris-rich ice. If the same sequence of till deposition occurred in older glacial deposits and the debris content of the basal ice was high, the final process of melt-out would not be reflected in properties of the sediment. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.