Editing Sandstone (section)

==Origins==
{{sediment sidebar|rock}}

Sandstones are ''[[clastic rock|clastic]]'' in origin (as opposed to either ''organic'', like [[chalk]] and [[coal]], or ''chemical'', like [[gypsum]] and [[jasper]]).<ref name="LF">"A Basic Sedimentary Rock Classification", L.S. Fichter, Department of Geology/Environmental Science, [[James Madison University]] (JMU), Harrisonburg, Virginia, October 2000, [http://csmres.jmu.edu/geollab/fichter/SedRx/sedclass.html JMU-sed-classif] {{Webarchive|url=https://web.archive.org/web/20110723075119/http://csmres.jmu.edu/geollab/fichter/SedRx/sedclass.html |date=2011-07-23 }} (accessed: March 2009): separates clastic, chemical & biochemical (organic).</ref> The silicate sand grains from which they form are the product of physical and chemical [[weathering]] of bedrock.<ref name="leeder-2011-3-28">{{cite book |last1=Leeder |first1=M. R. |title=Sedimentology and sedimentary basins : from turbulence to tectonics |date=2011 |publisher=Wiley-Blackwell |location=Chichester, West Sussex, UK |isbn=9781405177832 |pages=3–28 |edition=2nd}}</ref> Weathering and [[erosion]] are most rapid in areas of high relief, such as [[volcanic arc]]s, areas of [[continental rifting]], and [[orogenic belt]]s.<ref name="blatt-tracy-1996-241-242c258-260">{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology : igneous, sedimentary, and metamorphic. |date=1996 |publisher=W.H. Freeman |location=New York |isbn=0716724383 |pages=241–242, 258–260 |edition=2nd}}</ref>

Eroded sand is transported by rivers or by the wind from its source areas to [[depositional environment]]s where [[tectonics]] has created [[accommodation (geology)|accommodation space]] for sediments to accumulate. [[Forearc basin]]s tend to accumulate sand rich in lithic grains and [[plagioclase]]. [[Intracontinental basin]]s and [[graben]]s along continental margins are also common environments for deposition of sand.<ref name="blatt-tracy-1996-220-227">Blatt and Tracy 1996, pp. 220-227</ref>

As sediments continue to accumulate in the depositional environment, older sand is buried by younger sediments, and it undergoes [[diagenesis]].  This mostly consists of [[compaction (geology)|compaction]] and [[lithification]] of the sand.<ref name="blatt-tracy-1996-265-280">Blatt and Tracy 1996, pp. 265-280</ref><ref name="boggs-2006-147-154">Boggs 2006, pp. 147-154</ref> Early stages of diagenesis, described as ''eogenesis'', take place at shallow depths (a few tens of meters) and are characterized by [[bioturbation]] and mineralogical changes in the sands, with only slight compaction.<ref name="choquette-pray-1970">{{cite journal |last1=Choquette |first1=P.W. |last2=Pray |first2=L.C. |title=Geologic Nomenclature and Classification of Porosity in Sedimentary Carbonates |journal=AAPG Bulletin |date=1970 |volume=54 |doi=10.1306/5D25C98B-16C1-11D7-8645000102C1865D}}</ref>  The red [[hematite]] that gives [[red beds|red bed]] sandstones their color is likely formed during eogenesis.<ref>{{cite journal |last1=Walker |first1=Theodore R. |last2=Waugh |first2=Brian |last3=Grone |first3=Anthony J. |title=Diagenesis in first-cycle desert alluvium of Cenozoic age, southwestern United States and northwestern Mexico |journal=GSA Bulletin |date=1 January 1978 |volume=89 |issue=1 |pages=19–32 |doi=10.1130/0016-7606(1978)89<19:DIFDAO>2.0.CO;2|bibcode=1978GSAB...89...19W }}</ref><ref name="boggs-2006-148">Boggs 2006, p. 148</ref> Deeper burial is accompanied by ''mesogenesis'', during which most of the compaction and lithification takes place.<ref name="boggs-2006-147-154">Boggs 2006, pp. 147-154</ref>

Compaction takes place as the sand comes under increasing pressure from overlying sediments. Sediment grains move into more compact arrangements, ductile grains (such as [[mica]] grains) are deformed, and pore space is reduced. In addition to this physical compaction, chemical compaction may take place via [[pressure solution]]. Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact.<ref name="boggs-2006-147-154"/>

Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of [[Cementation (geology)|cement]] that binds the grains together. Pressure solution contributes to cementing, as the mineral dissolved from strained contact points is redeposited in the unstrained pore spaces.<ref name="boggs-2006-147-154"/>

Mechanical compaction takes place primarily at depths less than {{convert|1000|meters|feet|sp=us}}. Chemical compaction continues to depths of {{convert|2000|meters|feet|sp=us}}, and most cementation takes place at depths of {{convert|2000-5000|meters|feet|sp=us}}.<ref>{{cite journal|last1=Stone |first1=W. Naylor |last2=Siever |first2=Naylor |title=Quantifying compaction, pressure solution and quartz cementation in moderately-and deeply-buried quartzose sandstones from the Greater Green River Basin, Wyoming |year=1996 |url=http://archives.datapages.com/data/sepm_sp/SP55/Quantifying_Compaction_Pressure_Solution.htm |journal=Special Publications of SEPM|access-date=2 October 2020}}</ref>

Unroofing of buried sandstone is accompanied by ''telogenesis'', the third and final stage of diagenesis.<ref name="choquette-pray-1970"/> As erosion reduces the depth of burial, renewed exposure to [[meteoric water]] produces additional changes to the sandstone, such as dissolution of some of the cement to produce [[secondary porosity]].<ref name="boggs-2006-147-154"/>

<gallery mode="packed" heights="170px" style="float:left;">
File:MoabAlcove.JPG|[[Alcove (landform)|Alcove]] in the [[Navajo Sandstone]]
File:PetraSandStoneRock-cut tombs.jpg|[[Kokh (tomb)|Kokh-type]] tombs cut into the multicoloured sandstone of [[Petra]]
File:CoralPinkSandDunesSand.JPG|Sand grains of [[quartz]] with [[hematite]] coating providing an orange colour
File:Logan Formation Cross Bedding Scour.jpg|Cross-bedding and scour in sandstone of the [[Logan Formation]] ([[Lower Carboniferous]]) of Jackson County, [[Ohio]]
File:Lower antelope 2 md.jpg|Red sandstone interior of [[Antelope Canyon|Lower Antelope Canyon]], Arizona, worn smooth by erosion from [[flash flood]]ing over thousands of years
</gallery>
{{clear}}