Sedimentary rock 44412 225867057 2008-07-15T19:44:05Z Wavelength 271168 /* See also */ adding 1 internal link: *[[Dunham classification]] {{Nofootnotes|article|date=February 2008}} [[Image:Limestoneshale7342.jpg|thumb|Two types of sedimentary rock: limey [[shale]] overlain by [[limestone]]. [[Cumberland Plateau]], [[Tennessee]]]] '''Sedimentary rock''' is one of the three main [[Rock (geology)|rock]] types (the others being [[igneous rock|igneous]] and [[metamorphic rock]]). Rock formed from [[sediments]] covers 75-80% of the Earth's land area, and includes common types such as [[chalk]], [[limestone]], [[dolomite]], [[sandstone]], [[conglomerate (geology)|conglomerate]] and [[shale]].<ref>"Sediment and Sedimentary Rocks." <span class="plainlinks">[http://www.eeescience.utoledo.edu/Faculty/Phillips/Syllabus-MP/Physical%20Geology/SEDIMENTARY%20ROCKS%20Chapter%207%202007.htm Sedimentary Rocks.]</span> Retrieved on [[July 29]] [[2007]].</ref> Sedimentary rocks are classified by the source of their sediments, and are produced by one or more of: *[[clastic rock]] formed from fragments broken off from parent rock, by ** [[weathering]] in situ or ** [[erosion]] by water, ice or wind, followed by [[Transportation (sediment)|transportation]] of sediments, often in [[Suspension (chemistry)|suspension]], to the place of [[Deposition (sediment)|deposition]]; * [[Biogenic substance|biogenic]] activity; or * [[precipitation (chemistry)|precipitation]] from [[solution]]. The sediments are then [[Compaction (geology)|compacted]] and converted to rock by the process of [[lithification]]. ==Formation== [[Image:Sedimentary-rock.jpg|thumb|Sedimentary-rock formation, [[Karnataka]], [[India]]]] '''Sedimentary''' [[rock (geology)|rock]]s are formed because of the [[overburden pressure]] as particles of [[sediment]] are [[settling|deposited]] out of air, ice, wind, gravity, or water flows carrying the particles in [[Suspension (chemistry)|suspension]]. As sediment deposition builds up, the overburden (or 'lithostatic') pressure squeezes the sediment into layered solids in a process known as [[lithification]] ('rock formation') and the original [[connate fluids]] are expelled. The term [[diagenesis]] is used to describe all the chemical, physical, and biological changes, including [[cementation]], undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface weathering. Sedimentary rocks are laid down in layers called beds or strata. That new rock layers are above older rock layers is stated in the [[Law of superposition|principle of superposition]].There are usually some gaps in the sequence called [[unconformity|unconformities]]. These represent periods in which no new sediments were being laid down, or when earlier sedimentary layers were raised above sea level and eroded away. Sedimentary rocks contain important information about the [[history of Earth]]. They contain [[fossil]]s, the preserved remains of ancient [[plant]]s and [[animal]]s. Coal is considered a type of sedimentary rock. The composition of sediments provides us with clues as to the original rock. Differences between successive layers indicate changes to the environment which have occurred over time. Sedimentary rocks can contain fossils because, unlike most igneous and metamorphic rocks, they form at temperatures and pressures that do not destroy fossil remains. The sedimentary rock cover of the continents of the Earth's [[Crust (geology)|crust]] is extensive, but the total contribution of sedimentary rocks is estimated to be only 5% of the total. As such, the sedimentary sequences we see represent only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. == Classification== Sedimentary rocks are classified into three groups. These groups are clastic, chemical precipitate and biochemical or biogenic. ===Clastic=== {{main|Clastic rock}} Clastic sedimentary rocks are composed of discrete fragments or clasts of materials derived from other rocks. They are composed largely of [[quartz]] with other common minerals including [[feldspar]], [[amphibole]]s, [[clay minerals]], and sometimes more exotic [[igneous]] and [[metamorphic rock|metamorphic]] minerals. Clastic sedimentary rocks, such as breccia or sandstone, were formed from rocks that have been broken down into fragments by weathering, which then have been transported and deposited elsewhere. Clastic sedimentary rocks may be regarded as falling along a scale of [[Particle size|grain size]], with [[shale]] being the finest with particles less than 0.002&nbsp;mm, [[siltstone]] being a little bigger with particles between 0.002 to 0.063&nbsp;mm, and [[sandstone]] being coarser still with grains 0.063 to 2&nbsp;mm, and [[conglomerate (geology)|conglomerate]]s and [[breccia]]s being more coarse with grains 2 to 263&nbsp;mm. Breccia has sharper particles, while conglomerate is categorized by its rounded particles. Particles bigger than 263&nbsp;mm are termed ''blocks'' (angular) or ''boulders'' (rounded). ''[[Lutite]]'', ''[[Arenite]]'' and ''[[Rudite]]'' are general terms for sedimentary rock with clay/silt-, sand- or conglomerate/breccia-sized particles. The classification of clastic sedimentary rocks is complex because there are many variables involved. Particle size (both the average size and range of sizes of the particles), composition of the particles, the cement, and the matrix (the name given to the smaller particles present in the spaces between larger grains) must all be taken into consideration. Shales, which consist mostly of clay minerals, are generally further classified on the basis of composition and bedding. Coarser clastic sedimentary rocks are classified according to their particle size and composition. Orthoquartzite is a very pure quartz sandstone; [[arkose]] is a sandstone with quartz and abundant feldspar; [[greywacke]] is a sandstone with quartz, clay, feldspar, and metamorphic rock fragments present, which was formed from the sediments carried by turbidity currents. {{nowrap|All rocks disintegrate when exposed to mechanical and chemical [[weathering]] at the Earth's surface.}} [[Image:Lower antelope 3 md.jpg|thumb|[[Antelope Canyon|Lower Antelope Canyon]] was carved out of the surrounding [[sandstone]] by both mechanical weathering and chemical weathering. Wind, sand, and water from [[flash flood]]ing are the primary weathering agents.]] '''Mechanical weathering''' is the breakdown of rock into particles without producing changes in the chemical composition of the minerals in the rock. Ice is the most important agent of mechanical weathering. Water percolates into cracks and fissures within the rock, freezes, and expands. The force exerted by the expansion is sufficient to widen cracks and break off pieces of rock. Heating and cooling of the rock, and the resulting expansion and contraction, also aids the process. Mechanical weathering contributes further to the breakdown of rock by increasing the surface area exposed to chemical agents. '''Chemical weathering''' is the breakdown of rock by chemical reaction. In this process the minerals within the rock are changed into particles that can be easily carried away. Air and water are both involved in many complex chemical reactions. The minerals in igneous rocks may be unstable under normal atmospheric conditions, those formed at higher temperatures being more readily attacked than those which formed at lower temperatures. Igneous rocks are commonly attacked by water, particularly acid or alkaline solutions, and all of the common igneous rock forming minerals (with the exception of quartz which is very resistant) are changed in this way into clay minerals and chemicals in solution. Rock particles in the form of clay, silt, sand, and gravel, are transported by the agents of erosion (usually water, and less frequently by ice and wind) to new locations and redeposited in layers, generally at a lower elevation. These agents reduce the size of the particles, sort them by size, and then deposit them in new locations. The sediments dropped by streams and rivers form alluvial fans, flood plains, deltas, and on the bottom of lakes and the sea floor. The wind may move large amounts of sand and other smaller particles. Glaciers transport and deposit great quantities of usually unsorted rock material as [[till]]. These deposited particles eventually become compacted and cemented together, forming clastic sedimentary rocks. Such rocks contain inert minerals which are resistant to mechanical and chemical breakdown such as quartz, [[zircon]], [[rutile]], and [[magnetite]]. Quartz is one of the most mechanically and chemically resistant minerals. ===Organic=== [[Image:OilShaleEstonia.JPG|thumb|Outcrop of [[Ordovician]] oil shale ([[kukersite]]), northern Estonia.]] Organic sedimentary rocks contain materials generated by living organisms, and include carbonate minerals created by organisms, such as [[coral]]s, [[mollusk]]s, and [[foraminifera]], which cover the [[ocean floor]] with layers of [[calcite]] which can later form [[limestone]]. Other examples include [[stromatolite]]s, the [[flint]] nodules found in [[chalk]] (which is itself a biochemical sedimentary rock, a form of limestone), and coal and [[oil shale]] (derived from the remains of tropical plants and subjected to pressure). ===Chemical=== Chemical sedimentary rocks form when mineral solutions, such as [[sea water]], evaporate. Examples include the [[evaporite]] minerals [[halite]] (rock salt) and [[gypsum]]. ==Economic and scientific relevance== Sedimentary rocks are economically important in that they can easily be used as construction material because they are soft and easy to cut. For example, the White House in Washington DC is made of sandstone. In addition, sedimentary rocks often form [[porosity|porous]] and [[Permeability (fluid)|permeable]] reservoirs in [[sedimentary basin]]s in which [[petroleum]] and other [[hydrocarbons]] can be found (see [[Bituminous rocks]]). It is believed that the relatively low levels of [[carbon dioxide]] in the [[Earth]]'s [[Earth's atmosphere|atmosphere]], in comparison to that of [[Venus (planet)|Venus]], is because of large amounts of carbon being trapped in limestone and [[dolomite]] sedimentary layers. The flux of carbon from eroded sediments to marine deposits is part of the [[carbon cycle]]. The shape of the particles in sedimentary rocks has an important effect on the ability of [[micro-organisms]] to colonize them. This interaction is studied in the science of [[geomicrobiology]]. One measure of the shape of these particles is the roundness factor, also known as the Krumbein number after the geologist [[William C. Krumbein|W. C. Krumbein]]. ==See also== {{commons|Sedimentary rock}} *[[Back-stripping]] *[[Deposition (sediment)]] *[[Dunham classification]] *[[List of minerals]] *[[List of rock types]] *[[Transportation (sediment)]] ==Footnotes== {{reflist}} ==References== *Blatt, Harvey and Robert James Tracy, 1994, ''Petrology: Igneous, Sedimentary and Metamorphic'', Freeman, 2nd Ed. ISBN 0-7167-2438-3 *Folk, R.L., 1965, [http://www.lib.utexas.edu/geo/folkready/folkprefrev.html ''Petrology of sedimentary rocks'' PDF version]. Austin: Hemphill’s Bookstore. 2nd ed. 1981, ISBN 0-914696-14-9 *[http://csmres.jmu.edu/geollab/fichter/SedRx/sedclass.html Basic Sedimentary Rock Classification] [[Category:Petrology]] [[Category:Sedimentary rocks| ]] {{Link FA|sk}} [[ar:صخر رسوبي]] [[be:Асадкавыя горныя пароды]] [[bg:Седиментна скала]] [[bs:Sedimentne stijene]] [[ca:Roca sedimentària]] [[cs:Sedimentární hornina]] [[de:Sedimente und Sedimentgesteine]] [[et:Settekivim]] [[el:Ιζηματογενές πέτρωμα]] [[es:Roca sedimentaria]] [[eo:Sedimentaj petroj]] [[eu:Arroka sedimentario]] [[fr:Roche sédimentaire]] [[gl:Rocha sedimentaria]] [[ko:퇴적암]] [[hr:Sedimentne stijene]] [[id:Batuan sedimen]] [[is:Setberg]] [[it:Roccia sedimentaria]] [[he:סלע משקע]] [[hu:Üledékes kőzetek]] [[ms:Batuan enapan]] [[mn:Тунамал чулуулаг]] [[nl:Sedimentair gesteente]] [[ja:堆積岩]] [[no:Sedimentær bergart]] [[nn:Sedimentær bergart]] [[nds:Sedimentit]] [[pl:Skały osadowe]] [[pt:Rocha sedimentar]] [[ro:Roci sedimentare]] [[ru:Осадочные горные породы]] [[simple:Sedimentary rock]] [[sk:Usadená hornina]] [[sl:Sedimentne kamnine]] [[sr:Седиментне стене]] [[sh:Sedimentne stene]] [[fi:Sedimenttikivilaji]] [[sv:Sedimentär bergart]] [[ta:படிவுப் பாறை]] [[th:หินตะกอน]] [[vi:Đá trầm tích]] [[tr:Tortul kayaçlar]] [[uk:Осадова гірська порода]] [[zh:沉积岩]]