Unconformity


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Related to Unconformity: disconformity

unconformity

[¦ən·kən′fȯr·məd·ē]
(geology)
The relation between adjacent rock strata whose time of deposition was separated by a period of nondeposition or of erosion; a break in a stratigraphic sequence.

Unconformity

 

(geology), the occurrence of relatively young strata of rock on the erosion surface of older strata. There are two main types of unconformities: parallel and angular. In parallel unconformities (disconformities), strata of different ages lie parallel to one another and are separated only by an erosion surface—a stratigraphic break. In angular unconformities (disconformities), strata of different ages are not only separated by an erosion surface but dip at different angles; as a result, the ends of the old strata abut the base of the younger overlying stratum. Angular unconformities are formed when previously deposited strata have been tilted or folded and then the upper parts of the strata destroyed (by marine erosion, for example) and layers of a new stratum deposited on the erosion surface.

The study of unconformities is of great importance in elucidating the history of the movements and deformations of the earth’s crust. Analysis of unconformities also helps date magmatic activity, ore formation, and other geological processes.

References in periodicals archive ?
The existence of a pockmark directly over a sediment mound at the unconformity found at a location close to the Oak Bay Fault in Passamoquoddy Bay (Figs.
This cover tectonically undisturbed rests over an unconformity that is Bajocian in age and forms the base of the Middle Jurassic succession (Dieni et al., 1983).
The Rift or Beaufortian is marked by the Jurassic unconformity, overlain by a layer of sandstone, the Kuparuk Formation and upper Kingak shale and lower Kingak shale.
The Permian-Triassic boundary located near Haftad Gholleh is an erosional unconformity or disconformity, as in other parts of Iran, where Permian sequences contain dolomitic limestone, shale and sandstone situated below the Triassic sequence at a disconformity.
Seismic interpretation reveals a regional Early Miocene Unconformity (EMU) separating pre-Oligocene to Miocene rifted basement from overlying undeformed Upper Miocene-Pliocene bathyal sediments.
The depth to the Athabasca unconformity is very shallow, ranging from zero to 350 metres (1,148 ft).
The Paleocene sequence is separated from the underlying Upper Cretaceous sequence by a regional unconformity with local conglomerate at its base.
New research shows that the answer may lie in a second geological curiosity - a dramatic boundary, known as the Great Unconformity, between ancient igneous and metamorphic rocks and younger sediments.
The findings described here are also supported, as (1) the Cervini and Muntiacicni split is reported at the transition of Miocene-Pliocene; due to this reason Early Pliocene age is referred to these fossil sites, (2) Some isolated molar remains of Hipparion also indicate the Early Pliocene age, and (3) an unconformity is present close to the Miocene-Pliocene boundary.
The company has completed five holes in November and December 2011, with two holes encountering anomalous alteration, and another containing chloritic alteration at various intervals below the unconformity, a common feature found in host rocks containing uranium mineralisation.
The expansion is the result of two years of study by experts supplied via a Compass Foundation grant, and work by the graphic design and communications firm Unconformity.