Abstract

The municipality of Metropolitan Toronto (area 480 km2, population 2.15 million) is centrally located on the Late Pleistocene sedimentary infill of the Laurentian Channel, a broad bedrock low up to 115 km wide connecting the Huron and Ontario basins. This channel forms part of a relict (late Tertiary?) drainage network (the Laurentian River) modified by Pleistocene glacial erosion and infilled by over 100 m of glacial and interglacial sediments. The subsurface stratigraphy of the channel fill below Metropolitan Toronto has been established from many different data sources and is depicted, in this paper, as a series of cross sections with a total length of nearly 105 km.The subsurface stratigraphy has been divided, provisionally, into five depositional complexes, which have been mapped in the subsurface along several transects. These are (1) a glacial complex of Illinoian (?) age, (2) a lacustrine complex of Sangamon Interglacial and earliest Wisconsinan sediments (120 000 – 75 000 BP?), (3) a glaciolacustrine – lacustrine complex spanning the Early and Mid-Wisconsinan (75 000 – 30 000 BP?), (4) a Late Wisconsinan (> 30 000 BP) glacial complex, and (5) a postglacial lacustrine complex (ca. 12 000 BP).The data presented in this paper are significant for applied geological investigations in the heavily urbanized Toronto area and provide new insights into the glacial history of the Ontario Basin, in particular the regional extent of the Laurentide Ice Sheet margin prior to the Late Wisconsinan.

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