Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record |
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| Authors: | Sarah L Greenwood Chris D Clark |
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| Institution: | 1. Department of Physical Geography & Quaternary Geology, Stockholm University, 10691 Stockholm, Sweden;2. Department of Geography, University of Sheffield, Winter Street, Sheffield S10 2TN UK;1. Department of Geography, Durham University, Durham DH1 3LE, UK;2. School of Geosciences, University of Aberdeen, UK;3. Department of Geography, University of Sheffield, UK;4. Department of Geography, University of the Fraser Valley, Abbotsford, B.C., Canada;1. British Geological Survey, Murchison House, West Mains Road, Edinburgh EH93LA, UK;2. Department of Geographical and Earth Sciences, University of Glasgow, Glasgow G128QQ, UK;3. Institute of Geography, University of Edinburgh, Drummond Street, Edinburgh EH89XP, UK;1. Department of Geography and Geology, University of Turku, FI-20014 Turku, Finland;2. Geological Survey of Finland, P.O. Box 96 (Betonimiehenkuja 4), FI-02151 Espoo, Finland;1. Department of Geology, University of Tromsø, N-9037 Tromsø, Norway;2. DONG Energy E&P Norge AS, Roald Amundsens Plass 1, N-9257 Tromsø, Norway |
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| Abstract: | The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one ‘flowsets’ comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset cross-cutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative ‘age-stack’ of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset – its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, ‘smudged’ landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories. The flowsets and their palaeo-glaciological significance that we derive for Ireland provide a regional framework and context for interpreting results from local scale fieldwork, provide major flow events for testing numerical ice sheet models, and underpin a data-driven reconstruction of the Irish Ice Sheet that we present in an accompanying paper – Part 2. |
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