Mysterious 'gap' in Grand Canyon's violent quakes when ancient supercontinent Rodinia broke apart

"The Great Unconformity" has perplexed geologists since it was first described nearly 150 years ago. It is an erosion surface found worldwide, but best exposed at the bottom of the Grand Canyon, where the 500-million-year-old Paleozoic Tapeats Sandstone is directly overlying the 1.4 to 1.8 billion-year-old Proterozoic Vishnu Schist, representing a gap between 100 million and 1 billion years long in Earth's rock record.

A new study coauthored by University of Colorado Boulder researchers reveals the complex history behind this gap of missing time, suggesting that the break up of an ancient supercontinent, causing tectonic uplift of some areas and erosion in others, may be to blame.

"Think of the red bluffs and cliffs of the Grand Canyon as Earth's history textbook," explained Barra Peak, lead author of the new study and a graduate student in geological sciences at CU Boulder. "If you scale down the canyon's rock faces, you can jump back almost 2 billion years into the planet's past. But that textbook is also missing pages: In some areas, more than 1 billion years' worth of rocks have disappeared from the Grand Canyon without a trace."

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"The Great Unconformity is one of the first well-documented geologic features in North America," Peak said. "But until recently, we didn't have a lot of constraints on when or how it occurred."

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