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Great Unconformity

A large regional unconformity (time gap in the rock record) that is famously exposed in the Grand Canyon, USA. The Great Unconformity developed during the early part of the Phanerozoic Eon, about half a billion years ago, and was due to the landward advance of coastline of Laurentia (North America and Greenland) in the Cambrian marine transgression. Similar unconformities developed all of the world at this time.