RECENT DEFORMATION IN THE BOTTOM SEDIMENTS OF WESTERN AND SOUTHEASTERN LAKE-ONTARIO AND ITS ASSOCIATION WITH MAJOR STRUCTURES AND SEISMICITY

Geophysical surveys, undertaken in the Toronto-Burlington corridor of western Lake Ontario and in the Rochester Basin of southeastern Lake O ntario, revealed the presence of features affecting the young lake-bot tom sediments. In the western part of the lake, they include inferred pop-ups in bedrock, and plumose structures, dark linear patterns, and linear belts of circular to elliptical signatures in the modern mud. I n southeastern Lake Ontario the glacial and post-glacial sediments dis play vertical separations of on the order of 10-15 m. Pop-ups are tect onically-induced structures. The features in the modern mud commonly p arallel the orientation of P-stresses measured in Paleozoic rocks near by and, along with the pop-ups, are spatially related to an aeromagnet ic lineament. Furthermore, all of these features occur within a seismi cally active belt. The vertical displacements of the layered glacial a nd post-glacial sediments, within the Rochester Basin, are located alo ng the southern margin of the postulated WSW extension of the seismica lly active St. Lawrence rift system and are interpreted to be due to f aulting. The geologically young age of the sediments affected by the v arious deformational features, along with the characteristics of the f eatures themselves, suggest that the lake-bottom sediments surveyed in this study may have recorded the effects of neotectonic processes.