Disconformity A
disconformity is an unconformity between parallel
layers of
sedimentary rocks which represents a period of erosion or non-deposition. Disconformities are marked by features of
subaerial erosion. This type of erosion can leave channels and
paleosols in the rock record.
Nonconformity A nonconformity exists between sedimentary rocks and
metamorphic or
igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock. Namely, if the rock below the break is igneous or has lost its bedding due to metamorphism, then the plane of juncture is a nonconformity.
Angular unconformity An angular unconformity is an unconformity where horizontally parallel
strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. The whole sequence may later be deformed and tilted by further
orogenic activity. A typical case history is presented by the Briançonnais realm (Swiss and French Prealps) during the Jurassic. Angular unconformities can occur in
ash fall layers of
pyroclastic rock deposited by volcanoes during
explosive eruptions. In these cases, the hiatus in deposition represented by the unconformity may be geologically very short – hours, days or weeks.
Paraconformity A paraconformity is a type of unconformity in which the sedimentary layers above and below the unconformity are parallel, but there is no obvious erosional break between them. A break in sedimentation is indicated, for example, by fossil evidence. It is also called nondepositional unconformity or pseudoconformity. Short paraconformities are called
diastems.
Buttress unconformity A buttress unconformity, also known as onlap unconformity, occurs when younger bedding is deposited against older strata thus influencing its bedding structure.
Blended unconformity A blended unconformity is a type of disconformity or nonconformity with no distinct separation plane or contact, sometimes consisting of soils,
paleosols, or beds of pebbles derived from the underlying rock. ==Gallery==