Insights on the events surrounding the final drainage of Lake Ojibway based on James Bay stratigraphic sequences |
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| Authors: | M Roy F Dell’Oste JJ Veillette A de Vernal J-F Hélie M Parent |
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| Institution: | 1. Department of Earth and Atmospheric Sciences, and GEOTOP Research Center, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montréal, QC H3C 3P8, Canada;2. Geological Survey of Canada, 601 Booth st., Ottawa, ON K1A 0E8, Canada;3. Geological Survey of Canada, 490 de la Couronne, Québec City, QC G1K 9A9, Canada;1. Dept. of Environmental and Earth Sciences, University of Milano-Bicocca, Piazza della Scienza 1, 20126 Milano, Italy;2. CNR-Institute for the Dynamics of Environmental Processes, Lab. of Palynology and Palaeoecology, Piazza della Scienza 1, 20126 Milano, Italy;3. Dept. of Material Sciences, University of Milano-Bicocca, Piazza della Scienza 4, 20126 Milano, Italy;4. CNR-Institute of Atmospheric Sciences and Climate, Via Gobetti 101, 40129 Bologna, Italy;1. Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, NS, Canada B2Y;2. Physical Sciences Department, Rhode Island College, Providence, RI 02908, USA;3. Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882-1197, USA;1. Département de géographie, Université Laval, 2405 rue de la Terrasse, Québec, QC G1V 0A6, Canada;2. Direction des inventaires forestiers, Ministère des Forêts, de la Faune et des Parcs, Gouvernement du Québec, 5700 4e av. ouest, Québec, QC G1H 6R1, Canada;3. Département de biologie and Centre d’études nordiques, Université Laval, 1045 av. de la Médecine, Québec, QC G1V 0A6, Canada;4. Département de géographie and Centre d’études nordiques, 2405 rue de la Terrasse, Québec, QC G1V 0A6, Canada |
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| Abstract: | Deglaciation of the James Bay region was highly dynamic, with the occurrence of ice (Cochrane) readvances into glacial Lake Ojibway around final deglaciation time, which culminated with the drainage of Ojibway waters into Hudson Bay and subsequent incursion of the Tyrrell Sea at ～8 ka. Renewed interest on these events comes from the possible link between the drainage of the ice-dammed Lake Agassiz-Ojibway and a major climate deterioration known as the 8.2-ka cooling event. Recent glaciological modeling suggests that this drainage may have occurred subglacially, a mechanism that can accommodate more than one lake discharge, as suggested by marine records. The exact number and timing of drainage events, as well as location of the lake discharge pathway(s) remain, however, largely unconstrained. Here we focus on the events that led to the drainage of Lake Ojibway by documenting late-glacial sedimentary sequences located east of James Bay. Our investigations indicate that the deglacial sequence consists of a readvance till, extensive Ojibway rhythmites, and thick marine sediments. The glaciolacustrine and marine units are separated by a 60 cm-thick horizon composed of laminated silt beds containing rounded clay balls and disseminated clasts resulting from the abrupt drainage of the lake. Radiocarbon dating of marine fossils lying above the drainage horizon indicates that the glaciolacustrine episode ended around 8128–8282 cal yr BP. Micropaleontological analyses reveal that freshwater ostracods (Candona sp.) and marine microfossils (foraminifers, dinocysts) occur together in the upper part of the Ojibway sediments. Analysis of oxygen isotopes (δ18O) of ostracods and foraminifers originating from the same stratigraphic position show highly contrasting values that suggest possible subglacial exchanges between Lake Ojibway and Tyrrell Sea waters prior to the final drainage event. The complexity of the deglacial events is further indicated by radiocarbon dating of marine shells retrieved from a Cochrane till that suggests that the last ice readvance occurred almost simultaneously with the final lake discharge. These results bring additional constraints on the drainage mechanism of the coalesced Lake Agassiz-Ojibway and indicate that the James Bay region formed an important drainage pathway for meltwaters at the end of the last deglaciation. |
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