CGRG Bibliography of Canadian Geomorphology
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Author : Allard, G.; Roy, M.; Ghaleb, B.; Veillette, J.; Parent, M.; Larouche, A.; Richard, P.; and Lacroix, C.
Date : 2007.
Title : Paleoecological content and chronology of a subtill organic-bearing deposit in the James Bay of Québec.
Publication : CANQUA Ottawa 2007. Canadian Quaternary Association Conference, June 4-8, 2007. Carleton University, Ottawa, Ontario, Canada.
Issue :
Page(s) :
Abstract
The main rivers of the James Bay lowlands expose an extensive record of late Pleistocene deposits. The sedimentary sequences of this region are generally characterized by several glacial units interbedded in places with nonglacial sediments. There are, however, scarce geological data on the glacial sequences exposed along the rivers of Quebec, in particular on the paleoecological content and age of subtill organic-bearing deposits. Here we characterize the pollen and plant macro-remain content of a subtill organic-bearing deposit outcropping at the base of thick (>20 m) startigraphic sections exposed along the Nottaway River, ~40 km south of Waskaganish, Québec. The nonglacial unit investigated lies below several glacial (tills) and deglacial (varves) sediments, and consists primarily of an accumulation of abundant compressed wood fragments and organic-rich clays of about 5 meters in thickness. Detailed sampling at 10-cm intervals was carried out throughout the unit for pollen analyses while plant macro-remains analyses were done on the organic-rich horizons. Preliminary results of plant macro-remains reveal the occurrence of Picea mariana, Scirpus type validus, Menyanthes trifoliata, Scorpidium scorpioides, Potamogeton sp., Calliergon cordifolium and Cenococcum graniforme. In addition, preliminary results of pollen analyses reveal the presence of Picea mariana, Pinus banksiana, Betula sp., Tilia sp., Alnus sp., Larix laricina, Cyperaceae, Ericaceae, Polypodiaceae, Tubuliflorae, Menyanthes trifoliata and Pediastrum spp.. The paleoecological content of this unit is thus composed of species that are found in the modern environments of the James Bay region, and is thus indicative of a warm climate, roughly similar to the one of today. The organic-bearing unit shows several similarities with the well-known Missinaibi Formation described along the Moose River in Ontario. Taken together, the stratigraphic context and the paleoecological data suggest that this unit was deposited during the last (Sangamonian) interglacial. This is in agreement with U/Th dating of a wood log retrieved from the unit, which yielded an age of 107 ± 2 ka. Radiocarbon dating of the same tree gave an infinite age of >55.2 ka. The organic-bearing unit also lies on a massive (marine?) clay unit that is currently being investigated for its pollen and micro-fossil (dinoflagellate, foraminifera) contents. Further characterizing the pollen and macro-organic rest content of this nonglacial sequence will help to define the vegetation and climate of the last interglacial (LIG) in James Bay lowlands. These results will also contribute to the establishment of a chrono-stratigraphic framework for the Hudson and James Bay lowlands in Canada, and will help to understand the transition from interglacial to glacial environments.
Bibliography of Canadian Geomorphology