CGRG Bibliography of Canadian Geomorphology
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Author : Duhamel, D.; and Allard, M. Centre d’études nordiques,
Date : 2004.
Title : Deglaciation and Holocene evolution of the valleys flowing into Lac Guillaumedelisle, northern Québec.
Publication : Arctic Net. First Annual Scientific Meeting, Palace Royal, Quebec City. December 5-8, 2004. Program.
Issue :
Page(s) : 28.
Abstract
This study presents a paleo-environmental reconstruction of the deglaciation dynamics, Quaternary deposits and the sedimentary evolution of the valleys east of Lac Guillaume-Delisle (GD). Numerous evidences of glacial erosion indicate that the glacial recession in the region occurred on a warm base where meltwater flow was dynamic. Glacial and glaciomarine accumulations suggest an eastward glacial recession interrupted by three short halts until it the glacier front reached the maximum marine limit (MML) of the Tyrrell Sea in the valleys. MML is made conspicuous by considerable deltaic deposits and raised beaches, often associated with kettle holes or outwash plains. Three short series of De Geer moraines found in the region made it possible to estimate an annual retreat rate of about 80 to 90 m/yr. Also, the emplacement of moraines at regular intervals made it possible to estimate that the last MML dates back to around 7420 yr BP. The measured retreat rate is slightly slower than those estimated to the north (Nastapoka River) and south (James Bay lowlands) of the study area, probably because of the more rugged and irregular physiography of the region. Fossils shells found in the deep water sediments of the Tyrrell Sea made it possible to estimate that the postglacial marine sediments were deposited by 7120 ± 60 yr BP at the very least. These massive marine deposits (> 50% clay) filled valley of Rivière à l’eau-Claire up to 15 km inland and reach thicknesses of more than 80 m in some places. Further to the east, shell fragments recovered from stratified marine deposits (fine sand) in two different valleys have been dated back to 6500 yr BP. These dates demonstrate that sediment deposition occurred synchronously in neibourghing valleys. It is likely that the glacial recession did so as well. Following the marine transgression, the fast glacio-isostatic rebound resulted in the emergence of the sediments. Unstable sediments were quickly eroded, transported away, and stored downstream in Holocene deltas. Seismic reflection surveys taken in the GD, at the mouth of the rivers, enabled observation of a signifiant prodeltaic sediment deposition of at least 30 m in thickness. Carbon-14 dating indicates a strong decrease over time of sediment erosion in the valleys. Nowadays only sporadic landslides ensure continuing – but weak – sediment recycling
Bibliography of Canadian Geomorphology