CGRG Bibliography of Canadian Geomorphology
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Author : Brooks, G.R.; and Medioli, B.E.
Date : 2007.
Title : Sub-bottom profiling and coring from the lower French River, Ontario; evidence supporting temporary closure of the ancient outlet of the upper Great Lakes at 9.0 ka cal BP.
Publication : CANQUA Ottawa 2007. Canadian Quaternary Association Conference, June 4-8, 2007. Carleton University, Ottawa, Ontario, Canada.
Issue :
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Abstract
In the late Pleistocene-early Holocene, the ancient outlet of the upper Great Lakes flowed from the northeastern shore of (present day) Georgian Bay towards the east-northeast along the French River-Lake Nipissing-North Bay corridor, down the Mattawa and Ottawa valleys, and into the St. Lawrence Lowland. Sub-bottom profiling and shallow coring were undertaken in eight sub-basins of the lower French River, Ontario, to test the hypothesis that flow through the ancient outlet ceased temporarily during the last Stanley-Hough lake stage in the early Holocene, as inferred from offshore evidence in the Lake Huron-Georgian Bay basins. The sub-bottom profiling revealed a suite of deposits preserved in the French River sub-basins. Six sub-bottom profile facies are identified: four facies (I to IV) represent late Quaternary sediments, the fifth facies represents areas of poorly-penetrated facies I and/or II, and the sixth is bedrock. Based on ten cores that provide compositional control, facies I consists of glacio-lacustrine deposits interpreted to have aggraded within glacial Lake Algonquin during the late Pleistocene. Facies II deposits are composed of lacustrine gyttja deposits with one or two internal sand beds, 0.015 to 0.6 m thick. Radiocarbon dating of detrital organic materials contained within some of the sand beds indicate that facies II deposits aggraded in the early Holocene. Facies III and IV deposits are both composed entirely of lacustrine gyttja. Radiocarbon-dated detrital organic samples revealed that the facies III deposits aggraded in the mid-Holocene while the facies IV deposits are inferred to have aggraded in the mid- to late Holocene. Radiocarbon ages between 7870 ± 80 to 8280 ± 25 yr BP (about 8.7 to 9.3 ka cal BP) allow correlation of a sand bed, underlain by facies II gyttja, between five cores extracted from Muskrat, Deep and Crombie bays, indicating that a marked change in depositional environment occurred in the lower French River area at about 9.0 ka cal BP years ago. By this time, the sill controlling the Stanley-Hough lake level stages had shifted eastwards from the Dalles Rapids area toward modern Lake Nipissing due to regional differential uplift. This caused Great Lake water levels to transgress over the lower French River, imposing lacustrine conditions within a previously fluvial environment. The occurrence of the 9.0 ka cal BP-aged sand bed, and in particular examples in the two Muskrat Bay cores that contain abundant detrital organic materials, seem indicative of shallow rather than deep water conditions. Such an interpretation is consistent with a marked drop in water levels at the ancient outlet, supporting the notion that the Stanley-Hough water surface fell below the level of the outlet sill causing the upper Great Lakes to enter a temporary, closed basin stage.
Bibliography of Canadian Geomorphology