Types of Geologic Unconformities

Geologic unconformities explained with the use of block models.

Posted February 28, 2012

Law of Unconformities
Surfaces called unconformities represent gaps in the geologic record that formed wherever layers were not deposited for a time or else layers were removed by erosion.

Surfaces or contacts between rock layers called unconformities represent periods of time where deposition was paused. Depositional pauses result in gaps (missing layers) in the geologic record. These gaps can be caused by erosion. Unconformities are important when interpreting the sequence (chronology) of geologic events.

There are three types of unconformities, and they are described below. Select each block model to view larger image.


Disconformity

A disconformity is an unconformity between relatively parallel rock layers.

Disconformity Block Model: A disconformity is an unconformity between relatively parallel rock layers.


Angular unconformity

An angular unconformity is an unconformity between rock layers which are not parallel.

Angular Unconformity Block Model: An angular unconformity is an unconformity between rock layers which are not parallel.


Nonconformity

A nonconformity is an unconformity between younger sedimentary rocks and crystalline rocks (metamorphic or igneous types).

Angular Unconformity Block Model: An angular unconformity is an unconformity between rock layers which are not parallel.


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