Unconformity Types and Examples

Diagram of Unconformity Types

Unconformities are breaks or gaps in the geologic record, as shown by the arrangement of sedimentary (stratigraphic) features in the rock. This gallery shows the basic unconformity types recognized by U.S. geologists plus photos of examples from outcrops. This article gives more details about unconformities.

Here are the four main unconformity types. British geologists classify the disconformity and paraconformity as nonsequences because the rock beds are conformable, that is, parallel. Learn more in this article.

Angular Unconformity, Pebble Beach, California

Strongly tilted sedimentary rocks have been eroded and covered with much younger flat-lying sediments. Wave erosion of the young layers has exhumed the old erosion surface.

Angular Unconformity, Carlin Canyon, Nevada

This famous unconformity involves two rock units of Mississippian (left) and Pennsylvanian (right) ages, both of which are now tilted.

Angular Unconformity in Conglomerate

The tilted pebbles in the lower half mark the bedding plane in this conglomerate. The erosion surface is covered by finer material laid down parallel to the photo frame. The time gap represented here may be very short.

Nonconformity, Red Rocks, Colorado

This widespread feature is known as the Great Unconformity, but the Precambrian rock on the right is gneiss overlain by Permian sandstone, making it a nonconformity. It dramatically represents a billion-year time gap.