Quaternary features beneath Lake Simcoe,Ontario, Canada: drumlins,tunnel channels,and records of proglacial to postglacial closed and overflowing lakes |
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| Authors: | Brian J Todd C F Michael Lewis Thane W Anderson |
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| Institution: | (1) Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, Natural Resources Canada, Box 1006, Dartmouth, NS, Canada, B2Y 4A2;(2) 25 Dexter Drive, Ottawa, ON, Canada, K2H 5W3 |
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| Abstract: | Lake Simcoe is a large lake 45 km across and in places over 30 m deep, located between Lake Huron and Lake Ontario, in the
glaciated terrain of southern Ontario, Canada. Seismostratigraphic analysis of high-resolution seismic reflection profiles,
together with lakebed sediment sampling and pollen study, revealed distinctive sequences in the sediments beneath Lake Simcoe,
Ontario. A surface unit (Blue Sequence) of soft Holocene mud (low-amplitude surface reflection, discontinuous parallel internal
reflections) lies in the deeper basins of the lake. The underlying unit (Green Sequence) is characterized by high-amplitude
parallel internal reflections; basal sediments of this sequence consist of clay rhythmites with dropstones. The Green Sequence
was deposited by lacustrine sedimentation in proglacial Lake Algonquin; sedimentation persisted until the basin was isolated
from other glacial lakes at about 10 14C ka at the Penetang post-Algonquin phase. Subsequent erosion of the uppermost portion of the Green Sequence is attributed
to wave action in a low-level early Holocene lake, possibly closed hydrologically and coeval with closed lowstands in the
Huron and Georgian Bay basins. Two sequences with high-amplitude surface reflections and chaotic internal reflections (Purple
and Red Sequences) lie below the Green Sequence. Northeast-southwest trending ridges, tens of metres in height, on the Red
Sequence (the lowermost of these two units) are interpreted to be drumlins. An erosion surface descends into narrow valleys
50–80 m deep beneath the lake in bays to the west and south of the main lake basin. These depressions are interpreted as subglacial
tunnel channels cut by rapid flows of meltwater. The sediments of Purple Sequence are interpreted as channel-fill sediments
rapidly deposited during waning stages of the meltwater drainage. The Red Sequence is correlated with the Newmarket Till of
the last glacial maximum identified beneath the Oak Ridges Moraine to the south. |
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| Keywords: | Lake Simcoe Lake Algonquin Seismostratigraphy Glacial sediment Tunnel channel Closed lake |
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