Unconformities are a type of geologic contact—a boundary between rocks—caused by a period of erosion or a pause in sediment accumulation, followed by the deposition of sediments anew. Danish scientist Nicolas Steno first sketched an unconformity in the year 1669.

When did the Great Unconformity occur?

In a new study in Proceedings of the National Academy of Sciences of the United States of America, researchers make the case that large-scale glaciation during parts of the Neoproterozoic era, between 720 million and 635 million years ago, led to extensive erosion of Earth's crust, causing the Great Unconformity.

Where is unconformity found?

Unconformities are gaps in the geologic record that may indicate episodes of crustal deformation, erosion, and sea level variations. They are a characteristic of stratified rocks and are thus usually found in sediments (but can also be found in stratified volcanics).