Evidence for Subglacial Meltwater Floods Through the Lake Ontario and Eastern Lake Erie Basins
Evidence for Subglacial Meltwater Floods Through the Lake Ontario and Eastern Lake Erie Basins
Previously Published Material: Partial results for Lake Ontario and Lake Erie separately were presented in NE Geological Society of America section meeting, 1996, Buffalo NY; Geological Society of America meeting, 1998, Toronto; and International Association of Great Lakes - Great Lakes Conference 1999, Cleveland OH. The complete interpretation of subglacial floods affecting Lake Ontario through eastern Lake Erie with connecting onshore evidence at 13.5 (16.2 cal) ka and ending at the cross-lake Norfolk Moraine is unique to this presentation. These findings and interpretation are not under review elsewhere, and have not been submitted to a scientific journal.
Abstract ID#: 34428
English 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.