Lakes of the Huron basin: their record of runoff from the laurentide ice sheet

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The 189,000 km2 Huron basin is central in the catchment area of the present Laurentian Great Lakes that now drain via the St. Lawrence River to the North Atlantic Ocean. During deglaciation from 21-7.5 ka BP, and owing to the interactions of ice margin positions, crustal rebound and regional topography, this basin was much more widely connected hydrologically, draining by various routes to the Gulf of Mexico and Atlantic Ocean, and receiving overflows from lakes impounded north and west of the Great Lakes-Hudson Bay drainage divide.Early ice-marginal lakes formed by impoundment between the Laurentide Ice Sheet and the southern margin of the basin during recessions to interstadial positions at 15.5 and 13.2 ka BP. In each of these recessions, lake drainage was initially southward to the Mississippi River and Gulf of Mexico. In the first recession, drainage subsequently switched eastward along the ice margin to the North Atlantic Ocean. In the second recession, drainage continued southward through the Michigan basin, and later, eastward via the Ontario basin and Mohawk River valley to the North Atlantic Ocean. During the final retreat of ice in the Huron basin from 13 to 10 ka BP, proglacial lake drainage switched twice from the Michigan basin and the Mississippi River system to the North Atlantic via the Ontario basin and Mohawk River valley, finally diverting to the Champlain Sea in the St. Lawrence River valley at about 11.6 ka BP.New seismo- and litho-stratigraphic information with ostracode data from the offshore lacustrine sediments were integrated with the traditional data of shorelines, uplift histories of outlets, and radio-carbon-dated shallow-water evidence of transgressions and regressions to reconstruct the water level history and paleolimnological record for the northern Huron basin for the 11-7 ka BP period. Negative excursions in the δ18O isotopic composition of ostracodes and bivalves in southern Lake Michigan, southwestern Lake Huron and eastern Lake Erie indicate an influx of water from ice-marginal Lake Agassiz in central North America about 11 ka BP. A major decline in water levels of the Huron basin after 10.5 ka BP followed the high-level Main Lake Algonquin phase as ice receded and drainage was established through the North Bay area to Ottawa River valley. During the subsequent Mattawa-Stanley phase, the lake level history was dominated by fluctuations of tens of meters. Highstands of the earliest oscillations, whose origin is not clear, might be related to some of the well known Post Algonquin shorelines. After 9.6 ka BP, it is suggested that large inflows from Lake Agassiz and hydraulic damming in downstream outlets were the likely cause of the Lake Mattawa highstands. A lowstand at 9.3–9.1 ka BP occurred when these inflows were diverted, or impeded by an ice advance in the Nipigon basin area, while undiluted meltwater continued to enter the Huron basin. Assemblages and isotopic composition of the ostracode fauna indicate very dilute meltwater during the lowstands as late as 7.5 ka BP, and precipitation runoff with comparatively higher dissolved solids during the highstands. We speculate that the water composition of the Lake Mattawa highstands was dominated by the Agassiz inflows; by that time, much of Lake Agassiz was remote from ice-marginal environments, and the inflows were drawn from surface water of the southern sector of the lake, which was largely supplied by runoff and dissolved solids from the exposed land area of western Canada. Major inflows apparently ended about 8 ka BP, but northern proglacial lakes apparently continued as meltwater persisted in the Huron basin until about 7.5 ka BP. The cessation of major inflows initiated the final lowstand in the Huron basin and the present hydrological regime of local runoff.