High-resolution reconstruction of the last ice sheet in NW Scotland |
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| Authors: | Ballantyne McCarroll Nesje Dahl Stone & Fifield |
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| Institution: | School of Geography and Geosciences, University of St Andrews, Fife KY16 9ST, Scotland, UK.; Department of Geography, University of Wales, Swansea, Singleton Park, Swansea SA2 8PP, Wales, UK.; Department of Geology, University of Bergen, Allégaten 41, N-5007, Bergen, Norway.; Department of Geography, University of Bergen, Breiviken 2, N-5035 Bergen-Sandviken, Norway.; Quaternary Research Center, University of Washington, Box 351360, Seattle, WA 98195–1360, USA.; Research School of Physics and Engineering, Australian National University, Canberra ACT 0200, Australia. |
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| Abstract: | Reconstructions of the last (late Devensian) British ice sheet have hitherto been based on assumptions regarding its extent and form. Here we employ observational evidence for the maximum altitude of glacial erosion (trimlines) on mountains that protruded through the ice (palaeonunataks) to reconstruct the form of the ice sheet over ≈ 10 000 km2 of NW Scotland. Contrasts in the clay mineralogy of soils and exposure ages of rock surfaces above and below these trimlines confirm that they represent the upper limit of late Devensian glacial erosion. The reconstruction yields realistic values of basal shear stress and is consistent with independent evidence of ice movement directions. The ice sheet reached ≈ 950 m altitude over the present N–S watershed, descended northwards and north-westwards, was deflected around an ice dome on Skye and an independent Outer Hebrides ice cap, and probably extended across the adjacent shelf on a bed of deforming sediments. |
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