CGRG Bibliography of Canadian Geomorphology
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Author : Breckenridge, A.; and Johnson, T.C.
Date : 2005.
Title : Paleohydrology of Lake Agassiz and the upper Great Lakes from 10,700 to 8,800 CAL YBP [9,500-7,900 14C YBP].
Publication : Water, Ice, Land, And Life: The Quaternary Interface. Canadian Quaternary Association 2005 Conference June 5-8, 2005, University of Manitoba, Winnipeg, Manitoba.
Issue : Abstract Volume:
Page(s) : A7.
Abstract
Late glacial ostracode and bivalve records from Lakes Huron and Michigan are characterized by extreme d18O variations, ranging from values that reflect a source that is primarily glacial in origin (~-20 ‰ PDB) to much heavier values characteristic of a regional meteoric source (~-5 ‰ PDB). In contrast, a co-eval record from benthic ostracodes (Candona subtriangulata) from a varve sequence in Lake Superior is consistently depleted in 18O, ranging from -18 to -22 ‰ PDB, in a manner similar to a record from northern Lake Winnipeg (Agassiz) (Rodrigues and Lewis, 2000. GSC Open File 3470: 791-794). Age models from cores in Lake Huron and Michigan are re-evaluated to show a strong correlation between a sequence of thick varves and the lowest d18O values in Lake Superior between 9,400 and 9,000 cal ybp [8.4-8.1 14C ka] and negative d18O anomalies in Huron and Michigan. This negative excursion (~15 ‰ in Lake Huron) resulted from anomalously great fluxes of isotopically depleted water from Lake Superior; in Huron this event was previously prescribed to the Late Stanley lowstand (Rea et al., 1994. Can. Jour. Ear. Sci. 31(11): 1586-1605), and in Michigan the event was attributed to Lake Agassiz overflow and labeled 'A2' (Colman et al., 1994. Geology, 22: 547-550). During the 500 years prior to this period, the presence of very high d18O values in Huron strongly contrast with much lower values in Superior, which suggests Lake Superior overflow circumvented Lake Huron, and discharged through the Pic-White Otter River Valley en route to Glacial Lake Ojibway. Because glaciofluvial deltaic deposits in the Pic River Valley dated around 9,200 cal ybp [8.2 14C ka] record glacial meltwater flow towards Lake Superior (Bajc et al., 1997. Can. Jour. Ear. Sci. 34(5): 687-698), northern drainage of Lake Superior must have been blocked by ice advance at around 9,400 cal ybp [8.4 14C ka], rather than by differential uplift of a northern outlet. If this scenario is incorrect and Lake Superior never overflowed via a northern outlet, then the oxygen isotope records from benthic ostracodes in Lakes Superior and Winnipeg (Agassiz) grossly underestimate the average d18O values of the greater water bodies. During this entire period, both Lake Agassiz and glacial meltwater discharged into Lake Superior via the Nipigon inlets. Lake Agassiz and glacial meltwater fluxes into Lake Superior diminished to zero between 9,040 and 8,840 cal ybp [~8.1-7.9 14C ka].
Bibliography of Canadian Geomorphology