CGRG Bibliography of Canadian Geomorphology
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Author : Atkinson, N.; and Andriashek, L.
Date : 2007.
Title : Buried tunnel valleys in northeast Alberta: 3-D morphology and evolution.
Publication : CANQUA Ottawa 2007. Canadian Quaternary Association Conference, June 4-8, 2007. Carleton University, Ottawa, Ontario, Canada.
Issue :
Page(s) :
Abstract
Tunnel valleys are large elongated depressions eroded into unconsolidated sediments and bedrock. Tunnel valleys are believed to have been efficient subglacial drainage pathways for large volumes of meltwater, and reflect the interplay between groundwater flow and variations in the hydraulic conductivity of the substrate, and basal meltwater production and associated water pressure variations at the ice/bed interface. Tunnel valleys are therefore an important component of the subglacial hydrological system. Three-dimensional modeling of newly acquired geophysical and lithological data from the Athabasca oilsands mining area has revealed numerous buried tunnel valleys eroded into the pre-Quaternary bedrock unconformity in northeast Alberta. Due to the very high data density used in this study, it is possible to delineate the outline, orientation and sedimentary architecture of a number of tunnel valleys eroded beneath the western Laurentide Ice Sheet. The northeast Alberta buried tunnel valleys are similar to the open tunnel valleys described along the margins of the southern Laurentide Ice Sheet. They have high depth to width ratios, with undulating, low gradient longitudinal profiles. Many valleys start and end abruptly, and typically occur as individual, straight to slightly sinuous incisions, or form widespread anastomosing networks. They are between 0.5 and 3 km wide and 10 and 30 m deep, although the depth of incision along some thalwegs exceeds 75 m. Several valleys are up to 60 km long, but most are between 10 and 30 km long. The bedrock unconformity is overlain by a succession of Quaternary sediment of variable thickness (0 to 200 m). Valley fills comprise a range of lithofacies, including stacked sequences of till, glaciofluvial sand and gravel and glaciolacustrine silt and clay. Displaced bedrock, presumably of glaciotectonic origin also occurs within several anastomosing valleys. Sedimentary sequences exposed along sections through a number of valleys reveal a series of cut-and-fill structures. The 3-D morphology of the northeast Alberta tunnel valleys, combined with the sedimentology of their associated deposits, suggest they the entire tunnel valley system developed progressively during repeated cycles of increased basal meltwater discharge and subglacial erosion, followed by periods of low meltwater discharge, concomitant with localized modification by glacial ice. Basal meltwater is inferred to have been released as episodic jökulhlaups, which at times re-used existing valley systems, which were relatively stable features in terms of both lateral migration and temporal continuity, and at other times incised new valleys.
Bibliography of Canadian Geomorphology