Last interglacial sediments of the Don Valley Brickyard, Toronto, Canada, and their paleoenvironmental significance

Abstract

The Don Valley Brickyard in Toronto is an internationally designated type site in recognition of diverse faunal remains in the Don Beds of last (Sangamonian) interglacial age; pollen in overlying strata record the climatic deterioration marking the onset of the last (Wisconsinan) glacial cycle. New sedimentological descriptions show that the Don Beds, about 8 m thick, were deposited in a lacustrine lower shoreface environment subject to episodic storms. Storm-deposited sand facies are interbedded with peaty muds that are extensively bioturbated. Water depths, derived from wave-formed ripples using linear wave theory, appear to have increased during deposition of the Don Beds from about 2 m to about 18 m (12–28 m above the modern lake level), a change that is recorded by an overall fining-up sequence. Increasing water depths may have been the result of isostatic recovery of the lake outlet to the east. The Don Beds overlie a thin bouldery deposit, possibly a remnant of older Illinoian glacial sediments (York Till). The interglacial beds pass up into prodelta rhythmites (Scarborough Clays) of a regionally extensive delta body, indicating continued deepening. Deepening was accompanied by steadily decreasing mean annual temperatures; upper deltaic sediments (Scarborough Sands), exposed to the east along lakeshore bluffs, were deposited in a cold-climate setting during the opening phase of the Wisconsin glaciation.