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unconformity

1. n. [Geology]

A geological surface separating older from younger rocks and representing a gap in the geologic record. Such a surface might result from a hiatus in deposition of sediments, possibly in combination with erosion, or deformation such as faulting. An angular unconformity separates younger strata from eroded, dipping older strata. A disconformity represents a time of nondeposition, possibly combined with erosion, and can be difficult to distinguish within a series of parallel strata. A nonconformity separates overlying strata from eroded, older igneous or metamorphic rocks. The study and interpretation of unconformities locally, regionally and globally is the basis of sequence stratigraphy.

See: angular unconformitybasementconformablehiatuslithologic contactsequence boundarysequence stratigraphystratigraphic trapstratumunconformity trap

Photograph of Siccar Point unconformity.
Photograph of Siccar Point unconformity.

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