Postglacial development of a marl and peat complex on the Precambrian Shield of northwestern Ontario |
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| Authors: | S H McIntyre H C Duthie B C Warner |
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| Institution: | (1) Department of Biology, University of Waterloo, N2L 3G1 Waterloo, Ontario, Canada;(2) Quaternary Sciences Institute, University of Waterloo, N2L 3G1 Waterloo, Ontario, Canada;(3) Department of Geography, University of Waterloo, N2L 3G1 Waterloo, Ontario, Canada;(4) Quaternary Sciences Institute, University of Waterloo, N2L 3G1 Waterloo, Ontario, Canada |
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| Abstract: | This paper presents the first paleolimnological study of the postglacial development of a marl and peat complex on the Canadian Precambrian Shield. Ring Lake (48° 46 N, 85° 51 W), situated within the carbonate glacial drift area of northwestern Ontario, originated about 9000 BP in a basin exposed by the retreating waters of proglacial Lake Superior. The development of Ring Lake was interpreted from pollen and diatom analysis of one sediment core from the littoral zone and another core from near the lake centre.The sequence of postglacial vegetation development parallels published accounts of forest history in northern Ontario. The predominant diatom throughout the littoral core was the alkaliphilous Cymbella diluviana. The central core was dominated by circumneutral and alkaliphilous species of Achnanthes Navicula, Fragilaria, and Cymbella, except in recent samples where acidophilous species of Anomoeoneis were common.Diatom-inferred (DI) pH shows that the early lake was alkaline because of drainage from base-rich tills. The presence of marl in the littoral core indicates deposition of calcareous materials until the site dried out during the Hypsithermal period. There is evidence that beaver activity around 5000 BP caused a temporary change in lake hydrology. A decline in DI pH over much of the postglacial reflects gradual exhaustion of carbonates in the drainage area. An increase in acidophilous diatoms in samples representing the past 3500 y is consistent with gradual acidification of the system and development of a littoral peatland in a cooler neoglacial climate. |
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| Keywords: | marl lakes paleolimnology diatom-inferred pH palynology Hypsithermal wetlands |
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