Unconformity and different types in Geology

When the layers of rock that have been deposited essentially without interruption, they are called conformable. However, throughout Earth history, the deposition of sediment has been interrupted again and again. All such breaks in the rock record are called unconformities.

What is unconformity in Geology?

Unconformity represents a period of erosion and deposition. An unconformity denotes a long period throughout which deposition ceased, erosion removed previously formed rocks, and then new deposition resumed. It happens by upliftment of old strata and erosion; followed by subsidence and renewed sedimentation.

Geologists recognize three kinds of unconformities in the field:

Angular unconformity

An unconformity in which younger sediments rest upon the eroded surface of tilted or folded older rocks showing an angular relationship. The strata below the unconformable surface generally dip more steeply than those above younger strata.

Disconformity

An unconformity in which the strata above and below the eroded surface are essentially parallel, indicating a significant interruption in the orderly sequence of sedimentary rocks, generally by a considerable interval of erosion or sometimes of non-deposition. It is usually marked by irregular or uneven erosion surface of appreciable relief. Unless the erosional surface separating the older from the younger parallel beds is well defined or distinct, the disconformity frequently resembles an ordinary bedding plane.

Nonconformity

An unconformity which is developed between younger sedimentary rocks and older plutonic igneous or massive metamorphic rocks that had been exposed to erosion followed by deposition of overlying younger sediments. In this case, the erosional surface cut into metamorphic or igneous rocks and covered by sedimentary rocks. This type of unconformity closely resembles an intrusive igneous contact with sedimentary rocks.