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Simon Cook, Aberystwyth University (United Kingdom)
David Graham, Loughborough University (United Kingdom)
Darrel Swift, Sheffield University (United Kingdom)
Nicholas Midgley, Nottingham Trent University (United Kingdom)
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Glaciohydraulic supercooling is potentially an important mechanism of glacial debris entrainment in both modern and former glacial environments. Recent work has suggested that the distinctive nature of basal ice formed by supercooled freeze-on can be preserved in ice-marginal sediments and landforms through in situ melt-out, and also that such sediments and landforms can be used to identify the influence of supercooling in formerly glaciated regions. However, this suggestion remains largely untested.
This study aims to assess the extent to which basal ice characteristics of facies formed by glaciohydraulic supercooling are preserved in ice-marginal sediments, and whether these characteristics are significantly different from melt-out sediments from basal ice of non-supercooling origin. Thus we assess whether there are sediment facies that can be used to diagnose the influence of glaciohydraulic supercooling in the sedimentary record.
We present a detailed study of the sedimentary characteristics and architecture of melt-out products from Svínafellsjökull, SE Iceland. The basal ice layer of this glacier has been described previously and includes two ice facies found to be formed by glaciohydraulic supercooling that have very distinctive physical and sedimentological characteristics. Our results suggest that there are some broad differences between melt-out sediments from supercool and non-supercool basal ice (including sedimentary architecture and particle size, shape and roundness), but that the supercooling signature is spatially variable around the margin. We suggest that spatial and temporal variations in sediment supply likely play a role in determining these differences in sediment characteristics around the glacier margin, a factor that has hitherto been ignored. Thus the identification of supercooling-influenced landscapes of the past likely requires information not only of the nature of supercooled freeze-on and deposition from the basal ice, but also of the nature of local sediment supply.
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