Penokean orogeny

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The Penokean orogeny was a mountain-building episode that occurred in the early Proterozoic about 1.85 billion years ago, in the area of North America that would eventually become Minnesota, Wisconsin, Michigan, and Ontario. It was a major event in the formation of the North American continent, and happened during a world-wide period of mountain building and continent formation.

Before this episode the area was occupied by a shallow sea, which created large sedimentary deposits including the banded iron formations of the Iron Ranges.

Hundreds of millions of years later, the Keweenawan rift occurred in the same area, creating the basin that would eventually become Lake Superior. The remains of this orogeny can be seen today as the Iron Ranges of Minnesota and Ontario, as well as in the Northern Highlands of Wisconsin and the Upper Peninsula of Michigan.