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Particle Size Sorting in Subglacial Eskers: Abstract
Glaciofluvial deposits in subglacial eskers consist of two groups, those deposited during (1) free-surface flow and (2) full-pipe flow. Hydraulic sorting during free-surface flow is no different from that in open-channel eskers, and consequently structural assemblages are similar. Under full-pipe flow there are only minor differences in primary structures and size sorting in sand sizes. Thus, ripple, dune and plane bed attributes are found in both supraglacial and subglacial environments during free-surface flow and during subglacial, full-pipe flow.
Near and above the limit deposit condition, at Froude numbers ranging from about 3 to 10, particle sorting becomes distinctively different under full-pipe flow than in free-surface flow. At a velocity slightly less than the limit deposit velocity, the whole bed slides along the invert of a pipe. Inside this sliding bed, particle sorting is probably restricted to that produced by particle collisions and dilation of the sediment mix caused by strong seepage flow through the bed. At flow velocities higher than the limit deposit velocity, heterogeneous and homogeneous suspension occur, but all of the sediment in the pipe is in suspension and no bed forms can be preserved. A poorly sorted sand and gravel facies of probable sliding bed origin is abundant in several eskers near Guelph and Orangeville, Southern Ontario. Beyond the inferred exits of these eskers. more effective size sorting has produced well-defined bedding in fans and deltas.
Acknowledgments and Associated Footnotes
1 Department of Geography, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5
Copyright © 2009 by the Canadian Society of Petroleum Geologists