The Rove Formation[1] is a sedimentary rock formation of Middle Precambrian age underlying the upper northeastern part of Cook County, Minnesota, United States, and extending into Ontario, Canada. It is the youngest of the many layers of sedimentary rocks which constitute the Animikie Group.
Before the Rove sediments were laid down, during the Archean Eon, the Algoman orogeny added landmass along a border from South Dakota to the Lake Huron region; this boundary is the Great Lakes tectonic zone. Several million years later a thin layer of hypervelocity impact ejecta from the Sudbury impact event was deposited on the older, underlying, Gunflint Iron Formation, and the Rove was then deposited on top of the ejecta; it is estimated that at ground zero the earthquake generated by the meteor impact would have registered 10.2 on the Richter scale.
During the Middle Precambrian a shallow inland sea covered much of the Lake Superior region and formed the Animikie Group of sedimentary rocks overlying 2700-million-year-old Archean rocks.
After the Rove Formation sediments were deposited, the Penokean orogeny added more land mass by accretion that occurred from the south. A few hundred million years later the proto-North American continent nearly split in half along the Midcontinent Rift, which is a bow-shaped rift extending from northeast Kansas, arcing through the present-day Lake Superior Basin and then angling southeast through Michigan. Then came a period of advancing and retreating glaciers. The more resistant diabase sills and dikes remained, while the softer shales were bulldozed away by the glaciers. The north path of glaciation is transverse to the general trend on the valleys and ridges.
As a result of erosion of sandstone and the erosion-resistant sills and dikes, the topography in Minnesota has repeated parallel hills and valleys. The tightly packed lakes in the narrow valleys are long and narrow, and they orient from the east to west. The cliffs in these narrow valleys are the habitat to several rare plants which prefer living in narrow cliff areas in a sub-Arctic climate. In Ontario the Rove Formation is overlain by a thick diabase cap.