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 ?

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.

The Middle Jurassic Alpine Tethyan unconformity and the eastern Sardinia - Corsica Jurassic high: a sedimentary and regional analysis

The Shublik shale layer and Sadlerochit Group, layers of sandstone and shale, are interrupted by the Permian unconformity, which divides the Ellesmerian into upper and lower sequences.

Chukchi shelf stratigraphy: core study reveals pre-Cenozoic bedrock

Occurring worldwide, the Great Unconformity juxtaposes old rocks, formed billions of years ago deep within the Earth's crust, with relatively young Cambrian sedimentary rock formed from deposits left by shallow ancient seas that covered the continents just a half billion years ago.

'The Great Unconformity' may hold key to understanding Cambrian explosion

The upper contact of the Horton Bluff Formation is almost everywhere an angular unconformity with the overlying Cheverie Formation; thus the angle of tilting of the Horton Bluff Formation and the extent of erosion also contributed to thickness variations.

Uranium occurrences in the Horton Group of the Windsor area, Nova Scotia and the environmental implications for the Maritimes Basin

Figure 3 is a structural cross-section along Post Oak Creek showing the angular unconformity between the horizontal Warrensburg Sandstone and an excellent section of underlying dipping Desmoinesian Series sedimentary rocks.

Valley anticline associated with the Warrensburg Sandstone in Missouri

In the Australian case, the presence of an unconformity clearly indicates a land surface reaching above sea level.

The search for early dirt

The first-priority issue for proposed ODP drilling in the Newfoundland Basin is to ascertain the origin of the "U" unconformity and the nature of underlying crust.

Scientific ocean drilling and continental margins: understanding the fundamental transition from continent to ocean

2005), with a slight palaeorelief at the unconformity surface (Verges et al.

Stratigraphy and structure of the Punta Negra Anticline. Implications on the structural evolution of the Argentine Precordillera

The alteration zone is a 25-metre thick interval of clay minerals at and below the unconformity.

-Athabasca Uranium Inc's AU4-1 encounters alteration zone at Keefe Lake

The Cigar Lake and Jabiluka deposits are among the largest unconformity uranium deposits ever discovered.

Super junior uranium company, Bayswater Uranium, is well positioned in emerging uranium boom

The Sibley Basin is the least explored for unconformity uranium deposits in Canada, mostly due to a lack of the necessary technology.

Rampart netting prime uranium near Nipigon

Garnet porphyroblasts from upper amphibolite facies show a textural unconformity defined by inclusion-free rims, which coincides with changes in the garnet composition for both major a nd trace elements, including Cr.

Trace element zoning in calcic, pelitic garnet: garnet growth histories and Cr immobility. (Geological Association of Canada 2000 Annual Technical Meeting Newfoundland Section)