ABSTRACT: Laurentide meltwater systems: geomorphic and sedimentary evidence.

CGRG Bibliography of Canadian Geomorphology
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By understanding the genesis of individual glacial landforms informed reconstructions of ice-sheet dynamics can be made; models must be constrained by geomorphic and sedimentary evidence. This thesis investigates Laurentide tunnel channel and esker genesis on Victoria Island, Northwest Territories, in south-central Ontario, and in Quebec by combined consideration of landform associations, morphology, sedimentology and glacial hydrologic theory. Associated streamlined fields have been interpreted as the products of erosion by turbulent separated flows within catastrophically released subglacial meltwater sheets. Recent theoretical modelling of ice-sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet. A geometric model is presented of the interaction of rough ice base and bed surfaces with inferred meltwater flow paths. Late-stage sheet flow scours, megachannels and tunnel channels are identified, described and interpreted as evidence of such progressive channelization and flow diversion processes, governed by the geometric interactions between the recoupling ice base and bed and the thermodynamic feedbacks within an increasingly discontinuous meltwater sheet. Subglacial or grounding-line sedimentary environments are inferred for all of the Laurentide eskers investigated, based on their association with tunnel channels, upslope flow paths, minimal postdeformational disturbance of their sediments, down-esker trends in clast roundness, and low variability in paleoflow direction estimates. Sand-gravel couplets and fine-grained rhythmites record pulsed flows which may have been seasonal. Results from an architectural approach to esker sedimentology suggest unsteady flows down nonuniform conduits, with the style of sedimentation controlled by conduit geometry. Fans, beads, and extended, hummocky zones associated with subglacial eskers record high discharge events which caused localized floatation to capture adjacent cavities or allow localized sheet-flow events. Traditionally interpreted as an interlobate moraine, the Harricana glaciofluvial complex is inferred to be a large subglacial esker. Probable changes from cold-based to warm-based or polythermal ice conditions, and from catastrophic to seasonally-controlled meltwater systems are inferred for the Laurentide Ice Sheet from landform associations, geomorphic and sedimentary evidence. Regional ice stagnation or stagnation zone retreat is inferred during esker sedimentation. The conventionally interpreted genesis of so-called interlobate moraines is questioned. Geographic differences and temporal changes in the Laurentide meltwater system, and its implications for ice-sheet behaviour, must be accounted for in future ice-sheet models.

Bibliography of Canadian Geomorphology