A study of Keweenawan and Cambrian sediments in the Lake Superior region indicates that major structural trends in the basement rocks exerted a prolonged and profound influence upon sedimentation and the development of post-depositional structural features. The major structural elements trend east-west throughout most of northern Michigan, northeast throughout Minnesota and western Ontario, and north-south and east-west near the eastern shore of Lake Superior. Paleocurrent directions show that the outline of the Keweenawan sedimentary basin was essentially parallel with these structural trends. Source areas were near the margins of the present Lake Superior. Subsidence of the basin permitted a great thickness of lava and clastic sediment to accumulate with little or no va iation in the regional slope. Structural contours and isopach lines of the Keweenawan sequence are parallel with paleoslope contours of the Keweenawan basin, indicating that subsidence parallel with basement structural trends was a controlling factor for dispersal patterns and sediment accumulation. Basement control of sedimentation continued throughout most of Cambrian time.

Post-depositional structural features such as the Lake Superior syncline and the Keweenaw fault, as well as the present Lake Superior basin, also parallel basement structural trends.

It is concluded that resurgent tectonics have been active in the Lake Superior region since pre-Keweenawan time and have exerted a significant effect upon the area to the present.