Editing Sedimentology

{{Short description|Study of natural sediments and their formation processes}}
'''Sedimentology''' encompasses the study of modern [[sediment]]s such as [[sand]],<ref>Raymond Siever, ''Sand'', Scientific American Library, New York (1988), {{ISBN|0-7167-5021-X}}.</ref> [[silt]], and [[clay]],<ref>Georges Millot, translated [from the French] by W.R. Farrand, Helene Paquet, ''Geology Of Clays - Weathering, Sedimentology, Geochemistry'' Springer Verlag, Berlin (1970), {{ISBN|0-412-10050-9}}.</ref> and the processes that result in their formation ([[erosion]] and [[weathering]]), [[Transportation (sediment)|transport]], [[Deposition (geology)|deposition]] and [[diagenesis]].<ref>Gary Nichols, ''Sedimentology & Stratigraphy'', Wiley-Blackwell, Malden, MA (1999), {{ISBN|0-632-03578-1}}.</ref> Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of [[sedimentary rocks]] and [[sedimentary structures]].<ref>Donald R. Prothero and Fred Schwab, '' Sedimentary Geology: An Introduction to Sedimentary Rocks and Stratigraphy'', W. H. Freeman (1996), {{ISBN|0-7167-2726-9}}.</ref>

Sedimentary rocks cover up to 75% of the [[Earth]]'s surface, record much of the [[History of Earth|Earth's history]], and harbor the [[fossil record]]. Sedimentology is closely linked to [[stratigraphy]], the study of the physical and temporal relationships between rock layers or [[stratum|strata]].

The [[Uniformitarianism|premise]] that the processes affecting the earth today are the same as in the past is the basis for determining how sedimentary features in the rock record were formed. By comparing similar features today to features in the rock record—for example, by comparing modern [[sand dune]]s to dunes preserved in ancient [[Aeolian processes|aeolian]] sandstones—geologists reconstruct past environments.

==Sedimentary rock types==
[[Image:Triassic Utah.JPG|thumb|right|Middle [[Triassic]] marginal marine sequence of siltstones and sandstones, southwestern [[Utah]].]]
There are four primary types of [[sedimentary rocks]]: clastics, carbonates, evaporites, and chemical.
* [[Clastic rocks]] are composed of particles derived from the [[weathering]] and [[erosion]] of precursor rocks and consist primarily of fragmental material. Clastic rocks are classified according to their predominant [[Particle size|grain size]] and their composition.  In the past, the term "Clastic Sedimentary Rocks" were used to describe silica-rich clastic sedimentary rocks, however there have been cases of clastic carbonate rocks. The more appropriate term is [[siliciclastic]] sedimentary rocks.
** Organic sedimentary rocks are important deposits formed from the accumulation of biological detritus, and form [[coal]] and [[oil shale]] deposits, and are typically found within [[Depression (geology)|basins]] of clastic sedimentary rocks
* [[Carbonate rocks|Carbonates]] are composed of various [[carbonate minerals]] (most often [[calcium carbonate]] (CaCO<sub>3</sub>)) precipitated by a variety of organic and inorganic processes. 
* [[Evaporite]]s are formed through the evaporation of water at the Earth's surface and most commonly include [[halite]] or [[gypsum]].<ref>Edward J. Tarbuck, Frederick K. Lutgens, Cameron J. Tsujita, ''Earth, An Introduction to Physical Geology'', National Library of Canada Cataloguing in Publication, 2005, {{ISBN|0-13-121724-0}}</ref>
* Chemical sedimentary rocks, including some carbonates, are deposited by precipitation of minerals from aqueous solution. These include [[jaspilite]] and [[chert]].

==Importance of sedimentary rocks==
[[File:UraniumMineUtah.JPG|thumb|[[Charles Steen#Mi Vida|Mi Vida uranium mine]] in [[redox]] mudstones near [[Moab, Utah]]]]
Sedimentary rocks provide a multitude of products which modern and ancient society has come to utilise.
* [[Art]]: [[marble]], although a [[metamorphic rock|metamorphosed]] [[limestone]], is an example of the use of sedimentary rocks in the pursuit of aesthetics and art
* Architectural uses: stone derived from sedimentary rocks is used for [[dimension stone]] and in [[architecture]], notably [[slate]] (metamorphosed [[shale]]) for [[Roofing material|roofing]], [[sandstone]] for load-bearing [[buttress]]es
* [[Ceramic]]s and industrial materials: [[clay]] for [[pottery]] and [[ceramic]]s including [[brick]]s; [[cement]] and [[lime (mineral)|lime]] derived from [[limestone]].
* [[Economic geology]]: sedimentary rocks host large deposits of [[Sedimentary exhalative deposits|SEDEX]] ore deposits of [[lead]]-[[zinc]]-[[silver]], large deposits of [[copper]], deposits of [[gold]], [[tungsten]], [[Uranium]], and many other precious minerals, [[gemstones]] and industrial minerals including [[heavy mineral sands ore deposits]]
* Energy: [[petroleum geology]] relies on the capacity of sedimentary rocks to generate deposits of [[petroleum]] [[oil]]s. [[Coal]] and [[oil shale]] are found in sedimentary rocks. A large proportion of the world's [[uranium]] energy resources are hosted within sedimentary successions.
* [[Groundwater]]: sedimentary rocks contain a large proportion of the Earth's groundwater [[aquifer]]s. Our understanding of the extent of these aquifers and how much water can be withdrawn from them depends critically on our knowledge of the rocks that hold them (the reservoir).

== Basic principles ==
[[Image:HeavyMineralsBeachSand.jpg|thumb|right|Heavy minerals (dark) deposited in a [[quartz]] beach [[sand]] ([[Chennai]], India).]]
The aim of sedimentology, studying sediments, is to derive information on the depositional conditions which acted to deposit the rock unit, and the relation of the individual rock units in a basin into a coherent understanding of the evolution of the sedimentary sequences and basins, and thus, the Earth's geological history as a whole.{{cn|date=March 2024}}

The scientific basis of this is the principle of uniformitarianism, which states that the sediments within ancient sedimentary rocks were deposited in the same way as sediments which are being deposited at the Earth's surface today.<ref>{{cite journal |last1=Kravitz |first1=Gadi |title=The Geohistorical Time Arrow: From Steno's Stratigraphic Principles to Boltzmann's Past Hypothesis |journal=Journal of Geoscience Education |date=November 2014 |volume=62 |issue=4 |pages=691-700 |url=https://files.eric.ed.gov/fulltext/EJ1164156.pdf |access-date=18 February 2025}}</ref>

Sedimentological conditions are recorded within the sediments as they are laid down; the form of the sediments at present reflects the events of the past and all events which affect the sediments, from the source of the sedimentary material to the stresses enacted upon them after [[diagenesis]] are available for study.{{cn|date=March 2024}}

The [[Law of superposition|principle of superposition]] is critical to the interpretation of sedimentary sequences, and in older metamorphic terrains or fold and thrust belts where sediments are often intensely [[fold (geology)|folded]] or deformed, recognising [[Younging direction|younging]] indicators or [[graded bedding]] is critical to interpretation of the sedimentary section and often the deformation and metamorphic structure of the region.{{cn|date=March 2024}}

Folding in sediments is analysed with the [[principle of original horizontality]], which states that sediments are deposited at their angle of repose which, for most types of sediment, is essentially horizontal. Thus, when the younging direction is known, the rocks can be "unfolded" and interpreted according to the contained sedimentary information.

The [[principle of lateral continuity]] states that layers of sediment initially extend laterally in all directions unless obstructed by a physical object or topography.

The [[principle of cross-cutting relationships]] states that whatever cuts across or intrudes into the layers of strata is younger than the layers of strata.

== Methodology ==
[[Image:MudcracksCentripetal.JPG|thumb|Centripetal desiccation cracks (with a [[dinosaur]] footprint in the center) in the Lower [[Jurassic]] Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm, southwestern Utah.]]
The methods employed by sedimentologists to gather data and evidence on the nature and depositional conditions of sedimentary rocks include;
* Measuring and describing the outcrop and distribution of the rock unit;
** Describing the [[rock formation]], a formal process of documenting thickness, lithology, outcrop, distribution, contact relationships to other formations
** Mapping the distribution of the rock unit, or units
* Descriptions of rock core (drilled and extracted from wells during [[hydrocarbon exploration]])
* [[Sequence stratigraphy]]
** Describes the progression of rock units within a basin
* Describing the [[lithology]] of the rock;
** [[Petrology]] and [[petrography]]; particularly measurement of [[rock microstructure|texture]], [[Particle size|grain size]], grain shape (sphericity, rounding, etc.), sorting and composition of the sediment
* Analysing the [[geochemistry]] of the rock
** [[Isotope geochemistry]], including use of [[radiometric dating]], to determine the age of the rock, and its affinity to source regions

== Recent developments ==

The longstanding understanding of how some [[mudstone]]s form has been challenged by geologists at [[Indiana University (Bloomington)]] and the [[Massachusetts Institute of Technology]]. The research, which appears in the December 14, 2007, edition of ''[[Science (journal)|Science]]'', counters the prevailing view of geologists that mud only settles when water is slow-moving or still, instead showing that "muds will accumulate even when currents move swiftly." The research shows that some mudstones may have formed in fast-moving waters: "Mudstones can be deposited under more energetic conditions than widely assumed, requiring a reappraisal of many geologic records."<ref>Juergen Schieber, John Southard, and Kevin Thaisen, [http://www.sciencemag.org/cgi/content/full/318/5857/1760 "Accretion of Mudstone Beds from Migrating Floccule Ripples,"] ''Science'', 14 December 2007: 1760-1763.<br />See also [http://www.physorg.com/news116777974.html "As waters clear, scientists seek to end a muddy debate,"] at ''[[PhysOrg.com]]'' (accessed 27 December 2007).</ref>

Macquaker and Bohacs, in reviewing the research of Schieber et al., state that "these results call for critical reappraisal of all mudstones previously interpreted as having been continuously deposited under still waters. Such rocks are widely used to infer past climates, ocean conditions, and orbital variations."<ref>Joe H. S. Macquaker and Kevin M. Bohacs, [http://www.sciencemag.org/cgi/content/full/318/5857/1734 "Geology: On the Accumulation of Mud,"] ''Science'', 14 December 2007: 1734-1735.</ref>

Considerable recent research into [[mudstone]]s has been driven by the recent effort to commercially produce hydrocarbons from them as [[Unconventional (oil & gas) reservoir|unconventional]] reservoirs, in both the [[shale gas]] and [[tight oil]] (or Light Tight Oil) plays.<ref>Robert G. Loucks, Robert M. Reed, Stephen C. Ruppel, and Daniel M. Jarvie [http://www.wwgeochem.com/resources/Loucks+et+al+nanopore+paper.pdf "Morphology, Genesis, and Distribution of Nanometer-Scale Pores in Siliceous Mudstones of the Mississippian Barnett Shale"], Journal of Sedimentary Research, 2009, v. 79, 848-861.</ref>

Recent research by an Australian sedimentologist, [[Adriana Dutkiewicz|Dutkiewicz]], has described how geocirculation is related to global temperatures and climate change. The research described carbon and water circulation, and impacts of heat on current and future capacity of carbon capture by the ocean.  <ref>{{Cite web |date=2022-03-25 |title=Global warming speeds up currents in the ocean's abyss |url=https://samacharcentral.com/global-warming-speeds-up-currents-in-the-oceans-abyss/ |access-date=2022-04-16 |website=Samachar Central |language=en-US}}{{dead link|date=February 2025|bot=medic}}{{cbignore|bot=medic}}</ref>

== See also ==

* {{annotated link|Clastic rocks}}
* {{annotated link|Coal}}
* {{annotated link|Geology}}
* {{annotated link|Mineralogy of Mars}}
* {{annotated link|Oil shale}}
* {{annotated link|Ore genesis}}
* {{annotated link|Rock formation}}
* {{annotated link|Sequence stratigraphy}}
* {{annotated link|Vegetation-induced sedimentary structures}}

==References==
{{Reflist}}

==External links==
* {{Commons category-inline}}
{{Geology}}
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[[Category:Sedimentology| ]]
[[Category:Earth sciences]]
[[Category:Physical geography]]
[[Category:Sedimentary rocks]]