Unconformity

Unconformity

A surface of erosion or non-deposition separating younger strata from older rocks, along which there is evidence of subaerial erosional truncation (and, in some areas, correlative submarine erosion) or subaerial exposure, with a significant hiatus indicated. Exxon group modified this definition to "a surface separating younger from older strata, along which there is evidence of subaerial erosional truncation (and, in some areas, correlative submarine erosion) or subaerial exposure, with a significant hiatus indicated.

Angular conformity: younger sediments rest upon the eroded surface of tilted or folded older rocks.

Disconformity: contact between younger and older beds is marked by a visible, irregular or uneven erosional surface.

Paraconformity: beds above and below the unconformity are parallel and no erosional surface is evident; but can be recognized based on the gap in the rock record.

Nonconformity: develops between sedimentary rock and older igneous or metamorphic rock that has been exposed to erosion.