From the Proceedings of the Entomological Society of Ontario, Vol. 99, 1968

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1 From the Proceedings of the Entomological Society of Ontario, Vol. 99, 1968 GLACIAL HISTORY OF THE UPPER GREAT LAKES S. C. ZOLTAI Canada Department of Fisheries and Forestry, Winnipeg, Manitoba Glaciation was perhaps the most significant event in the recent history of central Canada. Huge ice sheets, estimated as being one to three miles thick, advanced from the north, displacing the existing fauna and flora, reshaping the physiography and rearranging the drainage systems. Loose material froze into the mass of this ice and was dragged along for hundreds of miles, abrading the underlying bedrock. Oceans shrank as water was withdrawn from them and concentrated on the land as ice or lake water. The weight of this ice depressed the crust of the earth by as much as 400 feet in the upper Great Lakes area. The story of glaciation in North America is slowly emerging after about seven decades of painstaking work. The clues for this gigantic detective work are the deposits of the glaciers and the lakes impounded by them. In this review I have drawn freely on the results of studies by many workers, as well as my own work. This paper will describe the events in various lake basins and attempt to correlate them with those of Lake Agassiz during its easterly drainage. Before examining the glacial history of this area, we might clarify a few general concepts. Continental glaciers flow because of the slope of the ice dome. The great weight of the ice renders it plastic and it flows as highly viscous fluid. The glacier advances if ice is accumulating (or invading) faster than the available heat can melt it. The ice front is said to be stationary when the rate of melting just balances the rate of forward movement. The ice sheet is waning when wastage exceeds the increment of ice. The waning of an ice sheet is often incorrectly visualized as an orderly, progressive uncovering of land. In fact, the waning of ice sheets was often interrupted by minor readvances and halts, when the temperature regime or the increased nourishment of the glacier resulted in renewed activity. I suspect that the general advancing of ice sheets was similarly interrupted by periods of stagnation or increased melting. The gathering ground of the North American continental glaciers is identified as the Hudson Bay area, as indicated by the greatest depression of the earth's crust by the weight of ice (Farrand and Gajda, 1962). Following the melting of ice the land surface rebounded, rapidly at first, then more slowly. Because the depression was the greatest in the Hudson Bay area, the uplift was also the greatest there and progressively less farther south. It is believed that eastern Canada was covered by a large ice sheet, the Laurentide ice sheet (Prest, 1963), radiating from the Hudson Bay area. Movement in all parts of this large ice sheet was not synchronous, as some of its sections could move independently of others. Thus the Labradorean ice mass would be inactive while the Patrician mass was advancing, or the Keewatin ice mass was retreating. We also know that, at least during the waning stages of glaciation, there were local centers of outflow, such as in the Superior basin and in the Ontario basin, and west and east of Hudson, Bay (Figure 1). The sequence of glaciation and deglaciation is derived from the examination of glacial and associated lacustrine deposits. Radiocarbon dates of organic materials buried in, or deposited on, these deposits afford an approximation of absolute chronology. In the following account radiocarbon dates are used when available and are correlated to glacial features in areas lacking such dates. The dating of various events shown in the figures is tentative and should be used with caution. A convenient starting point for this review of the glacial history of the upper 15

2 FIGURE 1. Generalized direction of ice flow during the waning stages of glaciation. (Modified after Prest 1963.) Great Lakes is the latest general ice advance during the late-wisconsin stage, some 28;000 years ago (Goldthwait et at., 1965). For the next 15,000 years ice covered the Great Lakes region, extending well into the United States. As the following deglaciation proceeded, the southern part of the Great Lakes basin became free of ice and proglacial lakes were initiated in the ice-free portions of the basin. Thus Lake Chicago was dammed at the southern tip of the Michigan basin, and a succession of lakes (Lakes Maumee, Arkona, Whittlesey and Warren) were formed in the southern part of the Huron and in the western part of the Erie basin (Hough, 1963). As the waning of the ice mass continued, Lake Lundy was established in the Huron-Erie basins, and Lake Chicago in part of the Michigan basin (Figure 2a). Both lakes drained south into the Mississippi River through the Chicago outlet (Hough, 1963). Lake Iroquois, draining to the Hudson River, occupied all of the Ontario basin. Lake Duluth was formed at the tip of the Superior basin by the coalescence of smaller proglacial lakes. Lake Duluth drained to the south into the Mississippi system through the St. Croix outlet. The ice border stood in the west at the Steep Rock moraine (ZoItai, 1965). Lake Agassiz covered large areas of the Canadian prairies. Further retreat of the ice front allowed the establishment of Early Lake Algonquin (Hough, 1963) in parts of the Huron and Erie basins (Figure 2b). Lake Duluth was still dammed by ice in part of the Superior basin, but the ice front retreated to the Eagle-Finlayson moraine. Later the Kirkfield outlet of Lake Algon- 16

3 Fig.2a STEEP ROCK Fig.2b. EAGLE-FI LAYSON Fig.2c. HARTMANN L -DOG L-MARKS Fig.2d. WISKEY LAKE F l EUL and CHAPLEAU FIGURE 2. Various stages of deglaciation and the glacial Great Lakes. quin (Chapman and Putnam, 1966) became free of ice, lowering the water level and draining the lake into Lake Iroquois of the Ontario basin. The Valders readvance which occurred about 11,500 years ago (Broecker and Farrand, 1963) affected mainly the Michigan basin, restricting Lake Chicago to a smaller area. In the west a small marginal lake, Lake Kaministikwia, was dammed by ice standing at the Hartmann-Dog Lake-Marks morainic system. This lake drained westward into Lake Agassiz (Figure 2c). The Kirkfield outlet of Lake Algonquin was maintained at this time. Further shrinkage of ice opened an outlet through the Huron mountains to the Michigan basin (Figure 2d), draining Lake Washburn, which occupied part of the Superior basin (Farrand, 1960). Lake Algonquin in the Huron-Michigan basins 17

4 was still largely bordered by ice standing at the Whiskey Lake moraine (Boissonneau, 1968 ) and drained through the Kirkfield outiet into Lake Iroquois. However, uplift of the land caused by the reduction of the weight of ice, gradually tilted the ba in to the south. This resulted in a series of lower standlines in the north and in progressive flooding of the shores in the south. As the ice receded further, a lower outlet was opened at Fossmill (Figure 2e), lowering the level of the post-algonquin lakes by as much as 160 feet (Chapman, 1954). The ice margin stood probably at the Cartier moraine north of the Huron basin (Boissonneau, 1968). Ice had disappeared from most of the Superior basin, and Lake Minong, having probably the same level as the post-algonquin lake in the Michigan-Huron basins, was created (Farrand, 1960). The removal of much of thl? ice load from the land resulted in rapid uplift and further tilting of the lake basins to the south, again modifying the lake levels in the Huron-Michigan and the Superior basins. Finally the tilt was sufficient to return the drainage of the post Algonquin lake to the Chicago and St. Clair River outlets. Further melting of the ice uncovered a lower col to the Ottawa River valley about 10,000 years ago and the Algonquin-Nipissing transitional lakes were initiated in the Huron basin, draining eastward through the North Bay outlet (Chapman and Putnam, 1966). The ice front was at the Chapleau moraine, and Lake Barlow w&s established in the Timiskaming area (Figure 20. Lake Minong occupied the Superior basin while the ice front was stationary at the Lac Seul moraine (Zoltai, 1965). The Algonquin-Nipissing transitional lakes in the Michigan-Huron basins continued to drain eastward through the North Bay outiet, but the basin was still s,trongly depressed to the north by the weight of ice, exposing large areas which are now in Lake Huron and Michigan. Differential uplift was tilting the basins southward, however, resulting in a series of transitional lakes exposing more land in the north and inundating land in the south. In the west, the Kaiashk outlet of Lake Agassiz reached Lake Minong in the Superior basin (Figure 3a) while the ice front was stationary at the Nipigon moraine (Zoltai, 1967a). Lake Barlow-Ojibway occupied the low-lying areas south of the melting ice sheet in northeastern Ontario (Boissonneau 1966). Melting ice uncovered lower outlets from Lake Agassiz into Lake Kelvin in the Nipigon basin (Zoltai, 1967a) while the ice stood at the Whitewater-Crescent moraines (Figure 3b). This water reached a post-minong Lake in the Superior basin, draining through St. Mary's River. The Algonquin-Nipissing transitional lake in the Huron basin was draining east through North Bay. Further shrinkage of the ice sheet allowed Lake Agassiz to drain into a narrow ice marginal lake, Lake Nakina (Figure 3c) while the ice front was stationary at the Nakina moraine (Zoltai, 1967b). This lake was a temporary extension of the post-minong lake which occupied the Superior basin. Lake Barlow-Ojibway covered large areas in the north and drained through the Timiskaming trench. The lake in the Huron basin was draining eastward through the North Bay outlet. Continued retreat of the ice front allowed the expansion of Lake Barlow-Ojibway in northern Ontario. Lake Houghton, a relatively low-level lake, was established in the Superior basin (Farrand, 1960), draining through the St. Mary's River (Figure 3d). About 8,275 years ago (Hughes, 1965) a readvance of ice, the Cochrane (Figure 3e), covered the greater part of the former bed of Lake Barlow-Ojibway (Boissonneau, 1966). Rapid melting of the ice followed and all glacial ice disappeared from the region about 7,800 years ago. Differential uplift was still continuing as the earth's mantie adjusted to the removal of the ice burden. Uplift gradually tilted the Great Lakes basin to the south and the Nipissing Great Lakes were established about 6,000 years ago as water drained through the Chicago and St. Clair River outlets, as well as through the North Bay outlet (Figure 30. The uplift continued and the North Bay outlet was 18

5 fig.3b. WHITEWATER-CRESCENT Fig.3f. NIPISSING GREAT LAKES yea,s B.P. FIGURE 3. Various stages of deglaciation and the glacial Great Lakes. finally abandoned. The St. Clair channel was deepened by erosion and became the only outlet (Hough, 1963). This terminated the Nipissing stage about 4,000 years ago. The succeeding stage, Lake Algoma, still covered the three upper lakes, but it terminated some 3,200 years ago as its outlet at St. Clair River was further eroded. The modern Great Lakes emerged from this complex series of glacial and postglacial lakes only about 3,000 years ago. Glacier ice offered a very inhospitable environment to all life forms, destroying the existing flora and fauna. The biota later had to invade the areas which became free of ice, as no part of the area escaped glaciation. The glacial lakes formed barriers to migration as some areas which are now dry land were under water and 19

6 others which are now under water were dry land. These barriers were not insurmountable for most plants or animals, as many of the lakes existed for a short time and their outline changed frequently. The northern sections of the Great Lakes were studded with islands which offered migration routes. Lakes may have been barriers to some plants or animals, but for other organisms they provided a means of dispersion. The direct connection with Lake Agassiz in the west probably facilitated the mixing of hardy aquatic life forms. The his t ory of deglaciation depicts a situation of great fluidity. Ice sheets came and went, lakes flooded areas only to disappear later, great rivers drained these lakes and then dwindled to mere trickles. A great variety of environment was available to colonizing plants and their animal suite: rubble fields, sand flats, former lake beds. Pioneer plants and highly mobile animals were favored in the initial invasion of these areas, but they suffered setbacks by flooding or readvances of ice. This delayed the establishment of organisms that require a stable community for best development. Relative stability returned to the Great Lakes area some 7,000 years ago, permitting the unhampered establishment of an ecologically suitable biota. The readjustment of the biota to the postglacial environment is not complete. Some remnants of arctic flora are stili found in suitable environments far south of their normal range (Soper and Maycock, 1963). It is possible that slowly migrating organisms have not yet occupied their potential range and the native biota is still adjusting to the environment left by the departing ice. Literature Cited BOISSONNEAU, A. N Glacial history of northeastern Ontario 1. The Cochrane-Hearst area. Can ad. Jour. Earth Sci. 3 : BOISSONNEAU, A. N Glacial history of northeastern Ontario II. The Timiskaming-Algoma area. Can. Jour. Earth Sci. 5: BROECKER, W. S. and W. R. FARRAND Radiocarbon age of the Two Creeks forest bed, Wisconsin. Bull. Geo!. Soc. Am. 74: CHAPMAN, L. J An outlet of Lake Algonquin at Fossmill, Ontario. Proc. Geo!. Assoc. Can. 6: CHAPMAN, L. J. and D. F. PUTNAM The physiography of southern Ontario. 2nd ed. University of Toronto Press, 386 p. FARRAND, W. R Former shorelines in western and northern Lake Superior basin. Unpub!. Ph.D. thesis, Univ. of Michigan, Ann Arbor, Mich. FARRAND, W. R. and R. T. GAJDA Isobases on the Wisconsin marine limit in Canada. Geogr. Bull. 17:5-22. GOLDTHWAIT, R. P., A. DREIMANIS, J. L. FORSYTH, P. F. KARROW and G. W. WHITE Pleistocene deposits of the Erie lobe, p In H. E. Wright Jr. and D. G. Frey (ed.) The quaternary of the United States. Princeton University Press, Princeton, N.J. HOUGH, J. L The prehistoric Great Lakes of North America. Am. Sci. 51: HUGHES, O. L Surficial geology of part of the Cochrane District, Ontario, Canada. In H. E. Wright, Jr. and D. G. Frey (ed.) International studies on the Quaternary. Geo!. Soc. Am., Special Paper 84, p PREST, V. K Pleistocene geology and surficial deposits. In C. H. Stockwell (ed.) Geology and economic minerals of Canada. Geo!. Surv. Can., Econ. Geo!. Ser. 1, 4th ed., p SOPER, J. H. and P. F. MAYCOCK A community of arctic-alpine plants on the east shore of Lake Superior. Canad. Jour. Bot. 41: ZOLTAl, S. C Glacial features of Quetico-Nipigon area, Ontario. Can. Jour. Earth Sci. 2: a Eastern outlets of Lake Agassiz, p In W. J. Mayer-Oakes (ed.) Life, land and water. University of Manitoba Press, Winnipeg, Man b. Glacial features of the north-central Lake Superior region, Ontario. Can. Jour. Earth Sci. 4: (Accepted for publication: December 16,1968) 20

CARD #1 The Shape of the Land: Effects of Crustal Tilting

CARD #1 The Shape of the Land: Effects of Crustal Tilting When we look at a birds-eye view of the Great Lakes, it is easy to assume the lakes are all at a similar elevation, but viewed in this way, we