CGRG Bibliography of Canadian Geomorphology
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Author : Brennand, T.A.; and Shaw, J.
Date : 2003.
Title : Ice sheet sediment transfer inferred from the geomorphic and sedimentary record.
Publication : Canadian Geophysical Union. Annual Meeting, May 10 -14, 2003. Banff Centre, Banff, Alberta.
Issue :
Page(s) :
Abstract
Understanding sediment transport by ice sheets may be approached from two directions. First, we may consider the ice-sheet motion, assume certain sediment transport characteristics and devise models for the transport system. Such glaciological modeling is usually sophisticated and quantitative, though highly dependent on physical assumptions. An alternative, geological approach is to work backwards from the transported and deposited sediment to draw conclusions on the actual processes of its entrainment, transport and deposition. These two approaches are essential and complementary; one informs the other. Here, we derive an integrative model of sediment transfer for an ice sheet segment in time and space. The geological approach, together with simplistic glaciological analysis, is used here to point the way towards a clearer understanding of sediment transport by ice. Three cases are based on the sedimentological evidence: (1) steady state flow with deposition by lodgement; (2) steady state flow over a deforming bed; and (3) accretion/melt-out phases alternating with transport phases. Cases 1 and 3 require accretion of debris and englacial debris transport in a basal layer. The role of supercooled water is emphasized in the process of accretion. The debris load of the ice is estimated from the rate and duration of accretion. The sediment transport rate is estimated from the ice velocity, the debris load and the rate of deposition with respect to distance. A similar approach informs our understanding of sediment transfer by meltwater. Five cases are based on the geomorphological evidence: (1) plano-concave sorted sediment stringers in lodgement till indicate sediment transport in Nye channels; (2) sorted sediment stringers in meltout till indicate sediment transport in a network of low Röthlisberger channels; (3) sorted sediment beds alternating with diamicton beds indicate sediment deposition in extensive subglacial cavities; (4) extensive esker networks indicate sediment transport in large Röthlisberger channels; and (5) subglacial bedforms and tunnel channels indicate sediment transport by catastrophic underbursts. Sediment transport rates in conduits and broad flows are estimated from sediment characteristics and geomorphology.
Bibliography of Canadian Geomorphology