RECONSTRUCTION OF POST-IROQUOIS SHORELINE EVOLUTION IN WESTERN LAKE-ONTARIO

When Lake Iroquois drained between 11.7 and 11.4 ka BP, lake Level in the Ontario basin fell from a high of more than 40 m above present lak e level to a minimum close to the then-existing sea level, which was a pproximately 40 m below present sea level. Since that time, lake level . has been rising at an exponentially decreasing rate in the western p ortion of the basin as a result of postglacial and neotectonic uplift of the outlet near Kingston, at the eastern end. The published lake le vel history has been combined with other less well-known parameters (t he post-Iroquois regional topography, erosion-deposition rates, and di stribution of resistive shore materials) to reconstruct the evolution of the western Lake Ontario shoreline. Borehole, long piston core, and other subsurface data sources, primarily from the western portion of the lake near Hamilton Harbour, provide most of the physical constrain ts. Time references were provided by radiocarbon dates on shallow-wate r organics in the subsurface sediments. A computer program was designe d to calculate and contour the changing elevations of the rebounding p ost-Iroquois topographic surface, allowing the time-dependent water-pl ane elevation to be superimposed. Semiquantitative allowance was made for differential erosion and deposition along the advancing shoreline. The reconstruction provides a perspective on past and future shorelin e evolution in the basin and possibly on the location of potentially c ommercial offshore deposits of aggregate.