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The Rove Formation is located in the upper northeastern part of Cook County, Minnesota, United States, and extends into Ontario, Canada. It is the youngest of the many Animikie layers, a layer of sedimentary rocks. 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, layers of sedimentary rocks overlying 2700-million-year-old Archean rocks. The Rove Formation is the youngest of the many Animikie layers. After the Rove 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 zone, 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. ==Location== The Rove Formation is in the Arrowhead Region of northeastern Minnesota, U.S., and extends into Ontario, Canada. In Minnesota it occurs along the U.S.-Ontario border from Gunflint Lake to Pigeon Point (both in northeastern Cook County) and northward into Canada. Pigeon Point is the most eastern part of Minnesota; it is a diabase sill about thick.〔 Both the north and south coasts of the point expose Rove slates under and over the sill.〔 Within the sill, rates of cooling and gravity have created an interesting distribution of rock types.〔 The visible formation is in Minnesota and contains many east-west oriented ridges and valleys. Many lakes in this wide band along the Canadian border are in the elongated east-west valleys; included are Caribou, Clearwater, Crocodile, Daniels, Duncan, Dunn, Hungry Jack, Iron, Loon, Moose, Pine, Portage and South. In Ontario the Rove Formation is overlaid by a thick diabase sill. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「History of the Rove Formation」の詳細全文を読む スポンサード リンク
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