An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of 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. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) The phenomenon of angular unconformities was discovered by James Hutton, who found examples at Jedburgh in 1787 and at Siccar Point in 1788. James Hutton MD (3 June 1726 OS (14 June 1726 NS) Edinburgh 26 March 1797 was a Scottish Geologist, Jedburgh (Referred to locally Jeddart or Jethart is a town and former Royal burgh in the Scottish Borders and historically in Roxburghshire. Siccar Point is a rocky promontory in the county of Berwickshire on the east coast of Scotland. [1]
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 deposited and 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 geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other The interval of geologic time not represented is called a hiatus. There are four types of unconformities: disconformity, nonconformity, angular unconformity and paraconformity.
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Disconformity
An unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) A paraconformity is a type of disconformity in which the separation is a simple bedding plane; i. e. , there is no obvious buried erosional surface. (AGI, 366) 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.
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. Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock
Angular Unconformity
An unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers that may be either vertical or at an angle to the overlying horizontal layers. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes The whole sequence may later be deformed and tilted by further orogenic activity. Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and
Paraconformity
An unconformity where beds above and below are parallel and no erosional surface is evident. Paraconformity can only be recognized based on the gap in the rock record when rocks of a particular age are absent from the sequence of rocks.
See also
References:
- American Geological Institute. The Great Unconformity is a geologic feature where two adjacent layers of rock were not formed one after another in the earth's development Dictionary of Geological Terms. New York: Dolphin Books, 1962.
- 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. Retrieved on 2008-03-26. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1026 - Pope John XIX crowns Conrad II as Holy Roman Emperor.
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