what is a nonconformity? earth science

Nonconformities are unconformities that separate igneous or metamorphic rocks from overlying sedimentary rocks. They usually indicate that a long period of erosion occurred prior to deposition of the sediments (several km of erosion necessary).

"Unconformities Unconformities are gaps in the geologic record that may indicate episodes of crustal deformation, erosion, and sea level variations. They are a feature of stratified rocks, and are therefore usually found in sediments (but may also occur in stratified volcanics).

They are surfaces between two rock bodies that constitute a substantial break (hiatus) in the geologic record (sometimes people say inaccurately that ""time"" is missing). Unconformities represent times when deposition stopped, an interval of erosion removed some of the previously deposited rock, and finally deposition was resumed.

Commonly three types of unconformities are distinguished by geologists: ANGULAR UNCONFORMITIESDISCONFORMITIESNONCONFORMITIESAngular Unconformities are those where an older package of sediments has been tilted, truncated by erosion, and than a younger package of sediments was deposited on this erosion surface.

The sequence of events is summarized in the pictures at left. First: subsidence and sediment deposition occurs; Second: rocks are uplifted and tilted (deformation); Third: erosion removes the uplifted mountain range; Fourth: subsidence occurs, the sea covers the land surface, and new sediments deposition occurs on top the previous land surface.

Then the cycle may repeat. For geologists, one of the most famous angular unconformity is the Grand Unconformity in the Grand Canyon of Arizona. Here tilted sedimentary rocks of Precambrian age (lower half of photo) are overlain by younger sedimentary rocks of Phanerozoic age (Cambrian and younger, upper half of photo). The two packages of strata are clearly separated by an angular unconformity that is best seen just left of the center of the photo.

Disconformities are also an erosion surface between two packages of sediment, but the lower package of sediments was not tilted prior to deposition of the upper sediment package. The sequence of events is as follows: First: subsidence and sediment deposition ; Second: uplift and erosion ; Third: renewed subsidence and deposition .

Because the beds below and above the disconformity are parallel, disconformities are more difficult to recognize in the sedimentary record. In the diagram at left, the disconformity is indicated by an irregular black line between the 3rd and 4th rock unit from the bottom. This picture shows a disconformity in Capitol Reef National Park, Utah. The Chinle Formation (Triassic), the slope forming unit in the central portion of the picture, has a very sharp contact (black line) with the overlying Wingate Sandstone (uppermost Triassic, forms steep cliff). This contact is considered a disconformity.

1. Lack of conformity; nonconformity.2. Geology A surface between successive strata representing a missing interval in thegeologic record of time, and produced either by an interruption in deposition or by the erosion of depositionally continuous strata followed by renewed deposition.

unconformity

unconformity Also found in: Thesaurus, Legal, Encyclopedia, Wikipedia. Related to unconformity: disconformityun·con·for·mi·ty (ŭn′kən-fôr′mĭ-tē)n. pl. un·con·for·mi·ties

American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.unconformity ( ˌʌnkənˈfɔːmɪtɪ) n, pl -ties1. lack of conformity2. (Geological Science) the contact surface between younger and older rocks representing a discontinuity in the geological record.

Most commonly it represents an erosional surface Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © Harper Collins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014un•con•form•i•ty (ˌʌn kənˈfɔr mɪ ti)n., pl. -ties.1. lack of conformity; incongruity; inconsistency.2. Geol. a discontinuity in a stratigraphic sequence. [1590–1600]Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.unconformity A level where sedimentary rocks cover an older rock surface partly removed by erosion.

Thelevel marks a time gap. Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited Want to thank TFD for its existence? Tell a friend about us, add a link to this page, or visit the webmaster's page for free fun content . Link to this page: Facebook Twitter

es Lack of conformity; nonconformity. Geology A surface between successive strata representing a missing interval in the geologic record of time, and produced either by an interruption in deposition or by the erosion of depositionally continuous strata followed by renewed deposition.

unconformity

"LINK / CITE ADD TO FLASH CARDSunconformityun·con·for·mi·tynounpl. -·tiesa lack of conformity; inconsistency; incongruity Geol.a break in the continuity of rock strata in contact, separating younger from older rocks and usually resulting from erosion of the surface of the older bed before the younger bed was laid downthe surface of contact between such strata Webster's New World College Dictionary, Fifth Edition Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company.

All rights reserved. Link/Citeunconformitynounpl. un·con·for·mi·ti

THE AMERICAN HERITAGE® DICTIONARY OF THE ENGLISH LANGUAGE, FIFTH EDITION by the Editors of the American Heritage Dictionaries.

Copyright © 2016, 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved. Link/Citeunconformity Noun ( plural unconformities) (nonstandard) a lack of conformity (geology) a gap in time in rock strata, where erosion occurs while deposition slows or stops Originun- +""Ž conformity English Wiktionary.

Available under CC-BY-SA license. Link/Cite Link/Cite "

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.

Unconformity

"File: Hutton Unconformity , Jedburgh.jpg An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record.

The significance of angular unconformity (see below) was shown by James Hutton, who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in 1788. [1] [2]The rocks above an unconformity are younger than the rocks beneath (unless the sequence has been overturned).

An unconformity represents time during which no sediments were preserved in a region. The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area.

The interval of geologic time not represented is called a hiatus . Contents [ show]Types of unconformities Edit Disconformity Edit File: Disconformity.jpg A disconformity is an unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition. [3] Disconformities are marked by features of subaerial erosion. This type of erosion can leave channels and paleosols in the rock record. [4] A paraconformity is a type of disconformity in which the separation is a simple bedding plane with no obvious buried erosional surface. [5]

Nonconformity Edit File: Nonconformity.jpg 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 by metamorphism, the plane of juncture is a nonconformity.

[6]Angular unconformity Edit File: Angular unconformity.jpg 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 paleotectonic evolution of the Briançonnais realm (Swiss and French Prealps) during the Jurassic (Septfontaine, 1984, 1995).

File: Briançonnais modèles 7F.jpg File: Discordances successives Jurassique Préalpes.jpg Paraconformity Edit File: Paraconformity.jpg A paraconformity is a type of unconformity in which strata are parallel; there is little apparent erosion and the unconformity surface resembles a simple bedding plane. It is also called nondepositional unconformity or pseudoconformity. Buttress unconformity Edit A buttress unconformity is when younger bedding is deposited against older strata thus influencing its bedding structure.

Template: Clear Gallery Edit Taum Sauk precambrian-cambrian unconformity.jpg There is a billion-year gap in the geologic record where this 500-million-year-old dolomite nonconformably overlies 1.5-billion-year-old rhyolite. Angular unconformity mcr1. JPGThe ""Taconic Unconformity"" near Catskill, NY. This angular unconformity separates the Austin Glen Formation ( Ordovician) from the overlying Rondout Formation ( Silurian) and Manlius Formation ( Devonian)Eemian Erosion Surface GI.

JPGEemian disconformity in a fossil coral reef on Great Inagua, The Bahamas. Foreground shows corals truncated by erosion; behind the geologist is a post-erosion coral pillar which grew on the disconformity after sea level rose again.

Siccar Point red capstone closeup.jpg Hutton's angular unconformity at Siccar Point where 345 million year old Devonian Old Red Sandstone overlies 425 million year old Silurian greywacke. [7]Edwards Disconformity.jpg Disconformity with the Lower Cretaceous Edwards Formation overlying a Lower Permianlimestone; hiatus is about 165 million years; Texas.

Fountain fm unconf redrocks.jpg Nonconformity between the Pennsylvanian Fountain Formation (left) and Precambrian Gneiss (right) at Red Rocks Park, near Golden, Colorado Borden-Sharon unconformity.jpg Disconformity (at the hammer) between underlying Mississippian Borden Formation and overlying Pennsylvanian Sharon Conglomerate, on US Rt. 35, near Jackson, Ohio Angular unconformity Shawangunk Martinsburg Otisville NY.jpg Angular unconformity of Shawangunk Formation overlying Martinsburg Formation at railroad cut near Otisville, NYAdd a photo to this gallery See also Edit Hutton's Unconformity References Edit Template: Commons category↑ Hutton's Unconformity↑ Keith Montgomery (2003).

""Siccar Point and Teaching the History of Geology"" (pdf). University of Wisconsin. http://nagt.org/files/nagt/jge/abstracts/Montgomery_v51n5.pdf. Retrieved 2008-03-26.↑ Monroe J. S., Wicander R. & Hazlett R. W. (2007). Physical geology: exploring the Earth.

Cengage Learning. pp. 267. ISBN 9780495011484 ISBN 9780495011484. http://books.google.co.uk/books?id=i Xfh Fno QBQ0C&pg=PA267&dq=disconformity+definition+geology&hl=en&sa=X&ei=ye Fw Uf Sq NKr K0QXLm YDg CA&ved=0CDw Q6AEw Ajg K#v=onepage&q=disconformity%20definition%20geology&f=false.↑ Disconformity at EPGeology↑ American Geological Institute. Dictionary of Geological Terms. New York: Dolphin Books, 1962.↑ Stokes, W. Lee (1982). Essentials of Earth History 4th Edition.

Prentice Hall,Inc.. p. 65. ISBN 0-13-285890-8 ISBN 0-13-285890-8.↑ Cliff Ford (2 September, 2003). ""Siccar Point"". Field Excursion Preview. University of Edinburgh School of Geo Sciences. http://www.geos.ed.ac.uk/undergraduate/field/siccarpoint/.

Retrieved 2008-10-20. U. S. Bureau of Mines Dictionary of Mining, Mineral, and Related Terms published on CD-ROM in 1996. Keith Montgomery (2003). ""Siccar Point and Teaching the History of Geology"" (pdf). University of Wisconsin. http://nagt.org/files/nagt/jge/abstracts/Montgomery_v51n5.pdf. Retrieved 2008-03-26.• Septfontaine M. (1984): Le Dogger des Préalpes médianes suisses et françaises - stratigraphie, évolution paléogéographique et paléotectonique.- Mém. Soc. Helv. Sci. Nat., vol. 97, 121 p. (Birkhäuser éd. )• Septfontaine M. (1995): Large scale progressive unconformities in Jurassic strata of the Prealps South of lake Geneva: interpretation as synsedimentary inversion structures. Paleotectonic implications.- Eclogae geol. Helv., 88/3, 553-576. Categories: Stratigraphy Add category "