SEDIMENTOLOGICAL ANALYSIS OF LATE QUATERNARY SEDIMENTS EXPOSED ALONG THE NORTH SHORE OF LAKE ONTARIO, CANADA

Quaternary aged sediments are well exposed along the north shore of Lake Ontario at Bowmanville and provide a record of changing depositional conditions along the southern margin of the Laurentide Ice Sheet (LIS) during the Wisconsin glaciations. Detailed sedimentological analysis of over 4km of lakeshore bluffs in the Bowmanville area identified five main facies types in the Quaternary sediments; silt-rich and sand-rich diamicts, sands, fines and gravels. Documentation of the vertical and lateral arrangement of these five facies types along the bluffs also allowed four stratigraphic units to be identified. The lowermost unit (Unit 1) consists of deformed laminated silts and clays and is interpreted as a slumped glaciolacustrine deposit. This is overlain by silt-rich diamict (Unit 2) that records relatively deep water, ice-contact glaciolacustrine conditions in the Ontario basin. Unit 3 consists of interbedded sands, fines and gravels and represents a glaciolacustrine deltaic complex that documents the progradation of a delta into the basin during an episode of reduced water levels and limited ice influence. The uppermost stratigraphic unit (Unit 4) consists of a sand-rich diamict interpreted as a subglacial deformation till that records the advance of ice, likely the southern margin of the LIS, over the lake basin during the late Wisconsin. These four stratigraphic units can be tentatively correlated with the sediments documented in the Greater Toronto Area. Unit 1 shows similar characteristics to the Sunnybrook, Units 2 and 3 are similar to the Thorncliffe Formation and the subglacial deformation tills of Unit 4 have similar characteristics to both the Northern and the Halton tills of the Toronto region.