The gravel fans of upper Glen Roy,Lochaber, Scotland: their importance for understanding glacial,proglacial and glaciolacustrine dynamics during the Younger Dryas cold period in an Atlantic margin setting |
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| Institution: | 1. Research Laboratory for Archaeology, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford OX1 3QY, UK;2. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK;3. UMR 5199 PACEA, Université de Bordeaux, Bâtiment B8, Allée Geoffroy Saint Hilaire, CS 50023, 33615 PESSAC CEDEX, France;1. Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, 1 South Parks Road, Oxford, OX1 3TG, UK;2. Scottish Universities Environmental Research Centre, University of Glasgow, Rankine Avenue, East Kilbride, South Lanarkshire, G75 0QF, UK;3. Isotope Climatology and Environmental Research Center (ICER), Institute for Nuclear Research, Hungarian Academy of Sciences, H-4026, Debrecen, Bem tér 18/c, Hungary;4. Eötvös Lóránd University, MTA-MTM-ELTE Research Group for Paleontology, Department of Environmental and Landscape Geography, Pázmány P. stny. 1/C, H-1117, Budapest, Hungary;5. Romanian Academy, Institute of Speleology, Clinicilor 5, 400006, Cluj-Napoca, Romania;1. Centre for Quaternary Research, Department of Geography, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK;2. Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK;3. Department of Geography, University of Lethbridge, Lethbridge, T1K 3M4, Canada |
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| Abstract: | Over the past 200 years significant research effort has gone into explaining the origin of the obvious former shorelines in Glen Roy (the so-called “Parallel Roads”). The large gravel deposit at the mouth of Glen Turret has attracted similar interest, but a solution to its origin and age remains contested: the same applies to the associated gravel fans in upper Glen Roy. This paper presents the results of systematic mapping and instrumental levelling of these features and new evidence from two previously unrecorded gravel fans in the nearby Allt Chonnal valley. Interpretation of altitudinal and lithofacies data indicates that all the fans (including the one at the mouth of Glen Turret) were deposited in a series of ice-dammed lakes during the Loch Lomond Stadial (Younger Dryas). The largest gravel fans were deposited in the shallow lake heads of the 260 m, 325 m and 350 m lakes in upper Glen Roy, infilling these areas to the extent that deposition was in part subaerial. The absence of foreset bedding from the deposits is explained by the relatively shallow depth of lake waters, which inhibited development of classic Gilbert-type deltas and encouraged Hjulström-type fans. The previous assumption that gravel deposition into the 325 m and 350 m lakes was relatively limited is shown to be erroneous. The Allt Chonnal gravel fans, deposited into these lakes, have an estimated combined volume of 6,000,000 m3 deposited in about 200 years. Significant gravel deposition into these former lakes continued at least until glaciers started to retreat in Glen Roy. When glacier retreat began, gravel deposition was reduced by over 85%. This research also concludes that the glacier which deposited the Turret fan emanated from Glen Gloy, supplied not only by ice from the south but also from ice that spilled into Glen Gloy from the adjacent Great Glen. The Loch Lomond Stadial (LLS) ice cap mapped in the Monadhliath Mountains was connected to the west Highland ice cap, which at the time filled the Great Glen. Regional equilibrium line altitude (ELA) estimates, based solely on the Monadhliath LLS ice cap evidence, may therefore be altitudinally too high. |
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| Keywords: | Glen Roy fan gravels Hjulström-type fans Instrumentally levelled profiles Lacustrine sediments Diamicton Loch Lomond Stadial glacier limits in Glen Gloy |
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