The buried Paleozoic bedrock surface of southern Ontario is dissected by an interconnected system of valleys. These buried valleys are infilled with thick successions of glacial, interglacial, and fluvial sediments that contain a lengthy record of changing environmental conditions during the late Quaternary. Detailed logging of over 500 m of sediment recovered from 11 continuously cored boreholes provides the basis for this study. The boreholes were drilled within two poorly defined bedrock valleys located east of the Niagara Escarpment in southern Ontario as part of a groundwater exploration program. Six distinct facies types were identified within the cores: sand, gravel, fine-grained sediment, and sand-rich, mud-rich, and clast-rich diamict. Textural characteristics of the cored sediments and vertical changes in facies types were used to identify six stratigraphic units (SU I through SU VI) within the valley-infill deposits. These units are interpreted to record fluvial or colluvial (SU I), lacustrine (SU II), fluvial, glaciofluvial or deltaic (SU III), subglacial (SU IV), glaciofluvial (SU V) and subglacial or ice marginal (SU VI) conditions. Sediment characteristics and stratigraphic relationships allow tentative correlation with known surficial deposits. Analysis of the subsurface characteristics and geometries of this stacked succession of coarse- and fine-grained stratigraphic units also allows identification of the geometry of potential aquifers.

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