Surface that represents a break in the geologic record.

The rock unit(s) immediately above the break is/are much younger than that/those below.

Usually represent buried erosional surfaces – parcel of geology is missing!

Three types:

DISCONFORMITY: unconformity is parallel to layering, but there is a gap in the geologic record.

Typically erosional and hard to spot. Can be non-erosional also.

Look for weathering surfaces, boulders/pebbles of older rock in younger.

Disconformities require deposition, uplift and erosion without tilting, followed by more deposition.

ANGULAR UNCONFORMITY: Younger strata overly older rocks that were tilted/folded.

Angular Unconformities require deposition, uplift and erosion with tilting, followed by submergence and more deposition.

First recgnized in the NW highlands of Scotland by Hutton - Hutton's Unconformity.

NONCONFORMITY: A contact in which an erosional surface on a plutonic or metamorphic rock has been covered by younger sediments or volcanic rocks (i.e., unconformity separates different rock types).
Nonconformities represent a considerable time-gap.