The origin of the Great Unconformity

What is it about?

Researchers found that across the scale of North America, about 3–5 km (2–3 miles) of erosion coincided with Snowball Earth glaciations at about 700–650 million years ago when the planet is believed to have been nearly covered in massive ice sheets. This suggests the Great Unconformity—which is an erosion surface that represents a mysterious period of “missing time” of up to a billion years or more (i.e., the rocks are gone!)—was primarily formed during the time of these glacial ice sheets.

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Photo by Lorenzo Castagnone on Unsplash

Photo by Lorenzo Castagnone on Unsplash

Why is it important?

The Great Unconformity involves a common gap of hundreds of millions to billions of years in the geologic record. The cause of this missing time has long eluded explanation, but recently two opposing hypotheses claim either a glacial or a plate tectonic origin in the Neoproterozoic. We provide thermochronologic evidence of rock cooling and multiple kilometers of exhumation in the Cryogenian Period in support of a glacial origin for erosion contributing to the composite basement nonconformity found across the North American interior. The broad synchronicity of this cooling signal at the continental scale can only be readily explained by glacial denudation.

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