| Title | Evidence for subglacial meltwater floods through the Lake Ontario and eastern Lake Erie basins |
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| Author | Lewis, C F M ;
Todd, B J |
| Source | Joint Assembly, AGU-GAC-MAC-CGU, 2015, abstracts listing; Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Programs with Abstracts 2015, 2015 p. 336  Open Access |
| Links | Online - En ligne (complete
volume - volume complet, PDF, 10.7 MB)
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| Image |  |
| Year | 2015 |
| Alt Series | Earth Sciences Sector, Contribution Series 20150183 |
| Publisher | American Geophysical Union |
| Meeting | Joint Assembly (Geological Association of Canada/ Mineralogical Association of Canada, Canadian geophysical Union, American Geophysical Union); Montreal, QC; CA; May 3-7, 2015 |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf (Adobe® Reader®) |
| Program | GSC Atlantic Division |
| Released | 2015 05 01 |
| Abstract | Lakebed relief in deep water of eastern Lake Ontario, portrayed in conventional hydrographic charts, is dominated by linear WSW-trending ridges. The ridges had been interpreted variously in the early
1990s as Holocene fault scarps, and as streamlined glacial landforms. A multibeam sonar survey confirmed the trend of lakefloor relief, but showed that individual ridge features were not as long or as continuous as previously thought. The features
are distinct, long (up to 6 km), narrow (100s m wide), subparallel ridges which stand up to 30 m above the surrounding lakefloor, and closely resemble erosional drumlins. Seismic reflection profiles indicated the ridge material is characterized by
incoherent internal reflections and rests on a continuous unfaulted bedrock reflector. A piston core recovered stony, sandy diamicton (till), confirming the glacial origin of the relief-forming drumlins, and showed that they are draped with
glaciolacustrine and postglacial lake sediments. The till is absent in places between ridges, suggesting the drumlins were formed by erosion from a former till sheet, and were probably sculpted by erosive subglacial flows of meltwater. Onshore
digital elevation models reveal drumlins in the same orientation, suggesting the erosive meltwater flows continued WSW into the northern part of the eastern Lake Erie basin where seismic profiles and a borehole reveal an absence of till, except for
thin remnants, and glaciolacustrine sediments resting directly on bedrock. This unconformable sequence terminates westward at the cross-lake Norfolk Moraine. An extensive cover of till remains atop a 45m-high bedrock escarpment in the southern part
of the eastern Erie basin suggesting an ice cover was pinned there during the subglacial flows. Constraining chronological data indicate that these subglacial meltwater flows, which were effective agents in shaping lake bathymetry and land
topography, occurred about 13.5 (~16.2 cal) ka. |
| Summary | (Plain Language Summary, not published)
This abstract describes erosional drumlins (elongated ridges kilometres long by a few 100s of m wide) deposited at the base of a glacier over bedrock in
eastern Lake Ontario, and an absence of glacier deposits (indicating their removal) over bedrock in eastern Lake Erie while an ice sheet was present, all overlain with glacial lake deposits. Age constraints and the observed sediment/landform
relations suggest the region was eroded by fast-flowing meltwater beneath the Laurentide Ice Sheet about 13,500 years ago, giving rise to much of the present lake bathymetry and onshore topography. |
| GEOSCAN ID | 296878 |
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