Late glacial and postglacial geology in the Lake Ontario basin

Abstract

Western Lake Ontario sediments record a till–mud–till sequence over bedrock and a thick layer of partly distorted glaciolacustrine clay unconformably overlying this. Another unconformity separates this clay from younger fine (lacustrine?) deposits, which are also distorted. Modern foreset and bottomset beds of the Niagara River overlap the lacustrine and glaciolacustrine deposits.In eastern Lake Ontario, thick glaciolacustrine clays overlie bedrock and the infilling ice-marginal deposits. These glaciolacustrine clays are severely distorted, and in the deepest parts of the area patches of overlying lacustrine (?) clay are preserved. A distorted terracelike deposit is preserved at higher elevation in the St. Lawrence trough. Bedrock, lag gravels, and sandy deposits characterize shallow-water areas.We suggest that after the fall of lake levels in the Lake Ontario basin, during the post-Iroquois lake phases, glaciolacustrine clays were subject to distortion by ice action at the time of the Greatlakean stadial. This deformation was more severe at the east end of the basin. At its lowest level, the surface of early Lake Ontario following the post-Iroquois phases was below the present lakebed in much of western Lake Ontario. Ice-wedge casts formed in sediments at both ends of the basin, soon after the initiation of early Lake Ontario, and are correlated with the Algonquin (St. Narcisse) glacial phase. Whereas there are significant accumulations of modern mud in the western basin of Lake Ontario, in the Kingston basin there is little except in the St. Lawrence trough.

Regional Stratigraphic Framework of Surficial Sediments and Bedrock Beneath Lake Ontario

“…No attempt was made to include nearshore areas or areas that are locally complex, such as the offshore areas adjacent to the Niagara River, the Kingston Basin, or the westernmost part of the lake. The present compilation adds a regional context to earlier local studies off Toronto (Lewis and Sly, 1971) and in Kingston Basin and off Niagara River (Sly and Prior, 1984). It adds a vertical dimension to pioneering work on the distribution of offshore surficial sediments carried out by Lewis and McNeely (1967) and Thomas et al (1972 a, b).…”

River Incision in Relation to Post-Glacial Events in the Humber River Basin, Ontario

“…As much of the postglacial surface was characterized by a stratigraphic sequence of various glaciogenic materials, initial incision was likely associated with relatively young sediments, with potentially abundant silt and sand sized materials. In contrast, it is possible that late Holocene rivers have been eroding older, perhaps more resistant, deposits, and have suffered from a concentration of coarser et al 1961;Duckworth, 1979;Terasmae, 1980;Chapman and Putnam, 1984;Sly and Prior, 1984;Anderson and Lewis, 1985;Chapman, 1985;Eschman and Karrow, 1985;Muller and Prest, 1985;Yu et al 1997;Yu and Wright, 2001 (Karrow et al, 1961;Duckworth, 1979;Terasmae, 1980;Chapman et Putnam, 1984;Sly et Prior, 1984;Anderson et Lewis, 1985;Chapman, 1985;Eschman et Karrow, 1985;Muller et Prest 1985;Yu et al, 1997;Yu et Wright, 2001).…”

“…2) have been proposed by Sly and Prior (1984) Chapman and Putnam (1984) and Muller and Prest (1985). ORM: Oak Ridges Moraine, K: Approximate location of Lake Algonquin drainage at Kirkfield following further ice retreat.…”

“…Evidence of these proglacial lakes is recorded not only in sediments, but also in many exposed shoreline bluffs throughout the Great Lakes region (Terasmae, 1980;Chapman and Putnam, 1984;Sly and Prior, 1984;Anderson and Lewis, 1985;Muller and Prest, 1985). Interpretation of deglacial and post-glacial events is complicated by shoreline identification and radiocarbon ( 14 C) dating techniques; however, the most significant challenge is associated with the patterns and rates of isostatic rebound.…”

“…The main stage of Lake Iroquois was about 40 to 45 m above contemporary lake levels. At the west end of the basin, water levels during the falling stages of Lake Iroquois may have reached as much as 100 to 125 m below present day lake level (Sly and Prior, 1984;Anderson and Lewis, 1985). Rising water levels of early Lake Ontario between ca.…”