TIMING THE DRAINAGE OF LAKE OJIBWAY USING VARVE STRATIGRAPHY FROM FOUR REMNANT LAKES IN ONTARIO AND QUEBEC, CANADA

During the retreat of the Laurentide Ice Sheet, the Lake Ojibway varve sediments were preserved in small remnant lake basins. The stratigraphy of these individual lakes can be correlated across the large Lake Ojibway basin in order to get an overall history of Lake Ojibway. It is thought that a catastrophic drainage of Lake Ojibway inundated the North Atlantic with fresh water, altering the thermo-haline cycle and causing a cooling period known as the 8200 year event.

In order to refine this stratigraphy, sediment cores were taken from four remnant lakes within the Lake Ojibway basin: Reid Lake, Lac Montbeillard, Lac De Courval, and Lac Wawagosic. These four lakes make a northeast transect through the lake basin and join together with a northwest transect from a previous study. Subsurface seismic profiles from these four lakes were used to help determine coring locations. Temporal correlation among these basins is possible by correlating glacial varves.

There are four main units present in nearly all of the cores: a highly organic modern lacustrine unit, a laminated clay unit, pellet (consider clay pebble conglomerate) unit, and glacial varves. The age at the top of the laminated unit in Reid Lake is dated at 7780 +/- 87 Cal BP (Stroup, 2009). The conglomerate is a transitional unit, between the glacial varves and the post glacial lacustrine deposits. The drainage of Lake Ojibway happened at this transition. Varve correlations between these cores suggest that the timing of the drainage in the eastern Ojibway basin shortly post-dates the limit of the Cochrane re-advance. Why this might be and the implications are still under consideration.