Shatterconed sandstone in Ontario, Canada.

Shattercones are striated conical structures in rocks formed by a powerful shock wave or pressure front moving through during an impact event. They have a three-dimensional cone-like structure, with the points of the cones directed toward the shock wave origination site. Undisturbed shatterconed rocks will have the apex of the cones pointing toward the direction of the incoming object (i.e., upward - toward space).

The host rocks here consist of ~2.3 to 2.4 billion year old fluvial sandstones of the Mississagi Formation. Notice that the shattercones are pointing downward, indicating that the impact event also overturned the beds.

This outcrop is in the Sudbury Impact Structure, the site for one of the largest impact events in Earth history. The impact structure, located in southeastern Ontario, is ovoid in shape, about 37 miles long by 19 miles wide. It was originally ~circular, but has since been laterally compressed by tectonic deformation. Before erosion and structural deformation, the structure may have been between 60 and 120 miles across. The impacting object is estimated to have been about 6 miles in size. The impact event itself occurred at 1.85 billion years ago. At that time, this part of Ontario was ocean. Computer modeling indicates that the splash wave generated by the Sudbury Impact may have reached about 30 miles high and generated a ~300 feet high megatsunami that radiated away from the target area for up to ~1800 miles. The impact punched a hole down into underlying mantle rocks.

Abundant evidence indicates that the Sudbury, Ontario area was indeed the site of an impact long ago. This includes impact breccias, shattercones, and extensive syn-formational sulfide mineralization. The sulfides are rich enough for mining to occur. In fact, the Sudbury Mining District targets the # 1 most productive nickel deposit on Earth.

This is a no-hammer outcrop.

Stratigraphy: Mississagi Formation, upper Hough Lake Group, Huronian Supergroup, Paleoproterozoic, ~2.3 to 2.4 Ga