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A substantial Sangamon interglacial (isotope stage 5) and subsequent Wisconsin glacial sedimentary record is preserved at Toronto, Canada. The age of individual stratigraphic units is poorly constrained, however. An interglacial sequence records climatic deterioration from warm temperate to subarctic. The interglacial Don Beds, resting on a presumed Illinoian till, were deposited on a storm-influenced shoreface of an ancestral Lake Ontario in water depths that increased over the recorded time interval from about 2 to 20 m. Pollen and faunal analyses identify a climatic deterioration in the upper Don from warm-temperate conditions, with mean annual temperatures some 2 °C warmer than at present, to cool temperate, with temperatures lowered by about 3 °C. Continued cooling is recorded in overlying deeper-water deltaic sediments of the Scarborough Formation, but later climatic amelioration and the return of mixed forest are suggested by the pollen record and by caddisfly fauna. The youngest deltaic sediments, lying immediately below a Wisconsin glacial complex, were deposited in a subarctic setting in an ice-dammed lake, with local mean annual temperatures depressed by at least 7 °C.

This chapter identifies the likely continuity of the Don Beds and Scarborough Formation and places them in an expanded “Sangamon” interglacial possibly equivalent to the whole of stage 5 (i.e., 130–75 ka). The biological record at Toronto for this stage indicates one or more phases of cooling when continental-glacier ice may have developed in North America; this record can be favorably compared with the marine oxygen-isotope record with its evidence of increased global ice volumes during stage 5. The subsequent Wisconsin record at Toronto is not well constrained by radiometric age dating but indicates that maximum regional expansion of the Laurentide Ice Sheet in the eastern Great Lakes area occurred after 25 ka.

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