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{{Short description|Accumulated material on seafloor}}
{{Use British English|date=August 2021}}
{{Use dmy dates|date=August 2021}}
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{{Sediment sidebar|marine}}
 
'''Marine sediment''', or '''ocean sediment''', or '''seafloor sediment''', are deposits of insoluble particles that have accumulated on the [[seafloor]]. These particles either have their origins in [[soil]] and [[Rock (geology)|rock]]s and have been [[Sediment transport|transported]] from the land to the sea, mainly by rivers but also by dust carried by wind and by the flow of glaciers into the sea., Additionalor depositsthey comeare [[Biogenic substance|biogenic]] deposits from marine organisms andor from chemical precipitation in seawater, as well as from underwater volcanoes and meteorite debris.
 
Except within a few kilometres of a [[mid-ocean ridge]], where the volcanic rock is still relatively young, most parts of the seafloor are covered in [[sediment]]. This material comes from several different sources and is highly variable in composition. Seafloor sediment can range in thickness from a few millimetres to several tens of kilometres. Near the surface seafloor sediment remains unconsolidated, but at depths of hundreds to thousands of metres the sediment becomes [[lithified]] (turned to rock).
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The distributions of some of these materials around the seas are shown in the diagram at the [[#Top|start of this article ↑]]. Terrigenous sediments predominate near the continents and within inland seas and large lakes. These sediments tend to be relatively coarse, typically containing sand and silt, but in some cases even pebbles and cobbles. Clay settles slowly in nearshore environments, but much of the clay is dispersed far from its source areas by ocean currents. Clay minerals are predominant over wide areas in the deepest parts of the ocean, and most of this clay is terrestrial in origin. Siliceous oozes (derived from radiolaria and diatoms) are common in the south polar region, along the equator in the Pacific, south of the Aleutian Islands, and within large parts of the Indian Ocean. Carbonate oozes are widely distributed in all of the oceans within equatorial and mid-latitude regions. In fact, clay settles everywhere in the oceans, but in areas where silica- and carbonate-producing organisms are prolific, they produce enough silica or carbonate sediment to dominate over clay.<ref name=Earle2019 />
 
Carbonate sediments are derived from a wide range of near-surface pelagic organisms that make their shells out of carbonate. These tiny shells, and the even tinier fragments that form when they break into pieces, settle slowly through the water column, but they don’tdon't necessarily make it to the bottom. While calcite is insoluble in surface water, its solubility increases with depth (and pressure) and at around 4,000 m, the carbonate fragments dissolve. This depth, which varies with latitude and water temperature, is known as the [[carbonate compensation depth]]. As a result, carbonate oozes are absent from the deepest parts of the ocean (deeper than 4,000 m), but they are common in shallower areas such as the mid-Atlantic ridge, the East Pacific Rise (west of South America), along the trend of the Hawaiian/Emperor Seamounts (in the northern Pacific), and on the tops of many isolated seamounts.<ref name=Earle2019 />
 
==Texture==
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Wind: [[Windborne transport|Windborne (aeolian) transport]] can take small particles of sand and dust and move them thousands of kilometres from the source. These small particles can fall into the ocean when the wind dies down, or can serve as the nuclei around which raindrops or snowflakes form. Aeolian transport is particularly important near desert areas.<ref name=Webb2019 />
 
<gallery mode=packed heights=160>
[[File:Packrafting at Spencer Glacier. Chugach National Forest, Alaska.jpg|thumb|right| The face of blue glacial ice melting into the sea]]
[[File:Yukon Delta.jpg|thumb|180px|left| River discharge in the Yukon Delta, Alaska. The pale color demonstrates the large amounts of sediment released into the ocean via the rivers.]]
[[File:Sudan dust storm - NASA.jpg|thumb|center| A plume of wind-borne particles from Sudan (left) blow over the Red Sea]]
 
</gallery>
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[[Glacier]]s and [[ice rafting]]: As glaciers grind their way over land, they pick up lots of soil and rock particles, including very large boulders, that get carried by the ice. When the glacier meets the ocean and begins to break apart or melt, these particles get deposited. Most of the deposition will happen close to where the glacier meets the water, but a small amount of material is also transported longer distances by rafting, where larger pieces of ice drift far from the glacier before releasing their sediment.<ref name=Webb2019 />
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The primary sources of microscopic biogenous sediments are unicellular algaes and protozoans (single-celled amoeba-like creatures) that secrete tests of either [[calcium carbonate]] (CaCO<sub>3</sub>) or [[silica]] (SiO<sub>2</sub>). Silica tests come from two main groups, the [[diatom]]s (algae) and the [[radiolarian]]s ([[protozoan]]s).<ref name=Webb2019 />
 
Diatoms are particularly important members of the phytoplankton, thefunctioning as small, drifting algal photosynthesizers. A diatom consists of a single algal cell surrounded by an elaborate silica shell that it secretes for itself. Diatoms come in a range of shapes, from elongated, pennate forms, to round, or centric shapes that often have two halves, like a Petri dish. In areas where diatoms are abundant, the underlying sediment is rich in silica diatom tests, and is called [[diatomaceous earth]].<ref name=Webb2019 />
 
Radiolarians are planktonic protozoans (making them part of the zooplankton), that like diatoms, secrete a silica test. The test surrounds the cell and can include an array of small openings through which the radiolarian can extend an amoeba-like "arm" or pseudopod. Radiolarian tests often display a number of rays protruding from their shells which aid in buoyancy. Oozes that are dominated by diatom or radiolarian tests are called [[siliceous ooze]]s.<ref name=Webb2019 />
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Foraminiferans (also referred to as ''forams'') are protozoans whose tests are often chambered, similar to the shells of snails. As the organism grows, is secretes new, larger chambers in which to reside. Most foraminiferans are benthic, living on or in the sediment, but there are some planktonic species living higher in the water column. When coccolithophores and foraminiferans die, they form [[calcareous ooze]]s.<ref name=Webb2019 />
 
Older calcareous sediment layers contain the remains of another type of organism, the [[discoaster]]s; single-celled algae related to the coccolithophores that also produced calcium carbonate tests. Discoaster tests were star-shaped, and reached sizes of 5-40&nbsp;µmμm across. Discoasters went extinct approximately 2 million years ago, but their tests remain in deep, tropical sediments that predate their extinction.<ref name=Webb2019 />
 
Because of their small size, these tests sink very slowly; a single microscopic test may take about 10–50 years to sink to the bottom! Given that slow descent, a current of only 1&nbsp;cm/sec could carry the test as much as 15,000&nbsp;km away from its point of origin before it reaches the bottom. Despite this, the sediments in a particular location are well-matched to the types of organisms and degree of productivity that occurs in the water overhead. This means the sediment particles must be sinking to the bottom at a much faster rate, so they accumulate below their point of origin before the currents can disperse them. Most of the tests do not sink as individual particles; about 99% of them are first consumed by some other organism, and are then aggregated and expelled as large [[fecal pellet]]s, which sink much more quickly and reach the ocean floor in only 10–15 days. This does not give the particles as much time to disperse, and the sediment below will reflect the production occurring near the surface. The increased rate of sinking through this mechanism has been called the "fecal express".<ref name=Webb2019 />
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Seawater contains many different dissolved substances. Occasionally chemical reactions occur that cause these substances to precipitate out as solid particles, which then accumulate as hydrogenous sediment. These reactions are usually triggered by a change in conditions, such as a change in temperature, pressure, or pH, which reduces the amount of a substance that can remain in a dissolved state. There is not a lot of hydrogenous sediment in the ocean compared to lithogenous or biogenous sediments, but there are some interesting forms.<ref name=Webb2019 />
 
In [[hydrothermal vent]]s seawater percolates into the seafloor where it becomes superheated by magma before being expelled by the vent. This superheated water contains many dissolved substances, and when it encounters the cold seawater after leaving the vent, these particles precipitate out, mostly as metal sulfides. These particles make up the "smoke" that flows from a vent, and may eventually settle on the bottom as hydrogenous sediment.<ref name=Webb2019 /> Hydrothermal vents are distributed along the Earth's plate boundaries, although they may also be found at intra-plate locations such as hotspot volcanoes. Currently there are about 500 known active submarine hydrothermal vent fields, about half visually observed at the seafloor and the other half suspected from water column indicators and/or seafloor deposits.<ref>{{cite journal |last1=Beaulieu |first1=Stace E. |last2=Baker |first2=Edward T. |last3=German |first3=Christopher R. |last4=Maffei |first4=Andrew |title=An authoritative global database for active submarine hydrothermal vent fields |journal=Geochemistry, Geophysics, Geosystems |date=November 2013 |volume=14 |issue=11 |pages=4892–4905 |doi=10.1002/2013GC004998 |bibcode=2013GGG....14.4892B |doi-access=free |hdl=1912/6496 |hdl-access=free }}</ref>
 
[[Manganese nodule]]s are rounded lumps of [[manganese]] and other metals that form on the seafloor, generally ranging between 3–10&nbsp;cm in diameter, although they may sometimes reach up to 30&nbsp;cm. The nodules form in a manner similar to pearls; there is a central object around which concentric layers are slowly deposited, causing the nodule to grow over time. The composition of the nodules can vary somewhat depending on their location and the conditions of their formation, but they are usually dominated by manganese- and iron oxides. They may also contain smaller amounts of other metals such as copper, nickel and cobalt. The precipitation of manganese nodules is one of the slowest geological processes known; they grow on the order of a few millimetres per million years. For that reason, they only form in areas where there are low rates of lithogenous or biogenous sediment accumulation, because any other sediment deposition would quickly cover the nodules and prevent further nodule growth. Therefore, manganese nodules are usually limited to areas in the central ocean, far from significant lithogenous or biogenous inputs, where they can sometimes accumulate in large numbers on the seafloor (Figure 12.4.2 right). Because the nodules contain a number of commercially valuable metals, there has been significant interest in mining the nodules over the last several decades, although most of the efforts have thus far remained at the exploratory stage. A number of factors have prevented large-scale extraction of nodules, including the high costs of [[deep sea mining]] operations, political issues over mining rights, and environmental concerns surrounding the extraction of these non-renewable resources.<ref name=Webb2019 />
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<gallery mode="packed" heights=160px"200px" style="float:left;">
File:Diatomaceous Earth BrightField.jpg|[[Diatomaceous earth]] is a soft, [[siliceous]], [[sedimentary rock]] made up of microfossils in the form of the [[frustule]]s (shells) of single cell [[diatoms]]<br /><small>(click 3X to fully magnify)</small>
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| image2 = Radiolarian - Podocyrtis ampla (29391267424).jpg
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| caption2 = {{center|[[Radiolarian]]}}
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| under 0.1&nbsp;mm{{hsp}}<ref name=Moheimani2012>{{citation |journal=[[Algal Research]] |volume=1 |issue=2 |year=2012 |pages=120–133 |title=Bioremediation and other potential applications of coccolithophorid algae: A review. . Bioremediation and other potential applications of coccolithophorid algae: A review |first1=N.R. |last1=Moheimani |first2=J.P. |last2=Webb |first3= M.A. |last3=Borowitzka |doi=10.1016/j.algal.2012.06.002}}</ref>
| [[File:CSIRO ScienceImage 7202 SEM Coccolithophorid.jpg|100px]]
| Coccolithophores are the largest global source of biogenic calcium carbonate, and significantly contribute to the global [[carbon cycle]].<ref>{{cite journal | last1 = Taylor | first1 = A.R. | last2 = Chrachri | first2 = A. | last3 = Wheeler | first3 = G. | last4 = Goddard | first4 = H. | last5 = Brownlee | first5 = C. | year = 2011 | title = A voltage-gated H+ channel underlying pH homeostasis in calcifying coccolithophores | journal = PLOS Biology | volume = 9 | issue = 6| page = e1001085 | doi = 10.1371/journal.pbio.1001085 | pmid = 21713028 | pmc = 3119654 | doi-access = free }}</ref> They are the main constituent of chalk deposits such as the [[white cliffs of Dover]].
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<gallery mode="packed" heights="160px" style="float:left;">
File:Nanoplankton-fossil-sediment hg.jpg| {{center| Calcareous microfossils from marine sediment consisting mainly of star-shaped [[discoaster]] with a sprinkling of coccoliths}}
File:PSM V44 D483 Globigerina ooze.jpg|Illustration of a ''[[Globigerina]]'' ooze
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{{further|sedimentary rock}}
 
<gallery mode="packed" heights="160px" style="float:left;">
File:Coober Pedy Opal Doublet.jpg| Opal can contain protist microfossils of diatoms, radiolarians, silicoflagellates and ebridians <ref name=Haq1998>Haq B.U. and Boersma A. (Eds.) (1998) [https://books.google.co.nzcom/books?id=0XezCm7IwpUC&printsec=frontcover&dqq=%22Introduction+to+Marine+Micropaleontology%22&hl=en&sa=X&ved=0ahUKEwjf9oD5psznAhXEYysKHbDXA2UQ6AEIKTAA#v=onepage&q=%22Introduction%20to%20Marine%20Micropaleontology%22&f=false ''Introduction to Marine Micropaleontology''] Elsevier. {{ISBN|9780080534961}}</ref>
File:MarmoCipollino FustoBasMassenzioRoma.jpg| Marble can contain protist microfossils of foraminiferans, coccolithophores, [[calcareous nannoplankton]] and algae, [[ostracode]]s, [[pteropod]]s, calpionellids and [[bryozoa]]<ref name=Haq1998 />
File:Carbonate-Silicate Cycle (Carbon Cycle focus).jpg|[[Carbonate-silicate cycle]]
</gallery>
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==Distribution==
<gallery mode="packed" style="float:right" heights="210px">
File:Continentalmargin.jpg
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<gallery mode="packed" style="float:right" heights="237px">
File:Mid-ocean ridge cut away view.png
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{{multiple image
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| width1 = 166
| caption1 = {{center| Southern-ocean sediment}}
| image2 = Mid-ocean ridge topography.gif
| width2 = 270
| caption2 = {{center| Magma rising from a chamber below the mid-ocean ridge forms new [[ocean crust]] that spreads away from the ridge}}
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[[File:2008 age of oceans plates.jpg|thumb|upright=2| {{center|Age of the ocean crust{{hsp}}<ref name="Müller 2008">{{cite journal |title = Age, spreading rates, and spreading asymmetry of the world's ocean crust|year = 2008|doi = 10.1029/2007GC001743|last1 = Müller|first1 = R. Dietmar|last2 = Sdrolias|first2 = Maria|last3 = Gaina|first3 = Carmen|last4 = Roest|first4 = Walter R.|journal = Geochemistry, Geophysics, Geosystems|volume = 9|issue = 4|pages = n/a|bibcode = 2008GGG.....9.4006M| s2cid=15960331 |url = https://archimer.ifremer.fr/doc/2008/publication-3900.pdf}}</ref>}} In this diagram the youngest parts of the ocean crust are coloured red. These young parts are found either side of the [[mid-ocean ridge]]. New crust emerges and spreads out from this ridge, which traverses central parts of the ocean.]]
[[File:Marine sediment thickness (cropped).jpg|thumb|upright=2| {{center|Thickness of marine sediments}} The sediments sit on top of the ocean crust, and are thick (green and yellow) along the continental shelves and down the continental slopes. They are at their thinnest (dark blue) near and along the mid-ocean ridge.]]
 
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Bioturbators are [[ecosystem engineer]]s because they alter resource availability to other species through the physical changes they make to their environments.<ref name=":30" /> This type of ecosystem change affects the evolution of cohabitating species and the environment,<ref name=":30" /> which is evident in [[trace fossil]]s left in marine and terrestrial sediments. Other bioturbation effects include altering the texture of sediments ([[diagenesis]]), [[bioirrigation]], and displacement of microorganisms and non-living particles. Bioturbation is sometimes confused with the process of [[bioirrigation]], however these processes differ in what they are mixing; bioirrigation refers to the mixing of water and solutes in sediments and is an effect of bioturbation<ref name=":18" />
 
[[Walrus]]es and [[salmon]] are examples of large bioturbators.<ref name=":12">Humphreys, G. S., and Mitchell, P. B., 1983, A preliminary assessment of the role of bioturbation and rainwash on sandstone hillslopes in the Sydney Basin, in Australian and New Zealand Geomorphology Group, p. 66-80.</ref><ref name=":21">{{Cite journal|last=Pillay|first=D|date=2010-06-23|title=Expanding the envelope: linking invertebrate bioturbators with micro-evolutionary change|journal=Marine Ecology Progress Series|language=en|volume=409|pages=301–303|doi=10.3354/meps08628|issn=0171-8630|bibcode=2010MEPS..409..301P|doi-access=free}}</ref><ref>{{Cite journal|last1=Ray|first1=G. Carleton|last2=McCormick-Ray|first2=Jerry|last3=Berg|first3=Peter|last4=Epstein|first4=Howard E.|title=Pacific walrus: Benthic bioturbator of Beringia|journal=Journal of Experimental Marine Biology and Ecology|volume=330|issue=1|pages=403–419|doi=10.1016/j.jembe.2005.12.043|year=2006}}</ref> Although the activities of these large macrofaunal bioturbators are more conspicuous, the dominant bioturbators are small invertebrates, such as [[polychaete]]s, [[Thalassinidea|ghost shrimp]] and mud shrimp.<ref name=":18" /><ref name=":23">{{Cite journal|last1=Braeckman|first1=U|last2=Provoost|first2=P|last3=Gribsholt|first3=B|last4=Gansbeke|first4=D Van|last5=Middelburg|first5=JJ|last6=Soetaert|first6=K|last7=Vincx|first7=M|last8=Vanaverbeke|first8=J|date=2010-01-28|title=Role of macrofauna functional traits and density in biogeochemical fluxes and bioturbation|journal=Marine Ecology Progress Series|language=en|volume=399|pages=173–186|doi=10.3354/meps08336|issn=0171-8630|bibcode=2010MEPS..399..173B|doi-access=free|hdl=20.500.11755/e43f4d57-cf7f-494d-a724-a4b2aab2a772|hdl-access=free}}</ref> The activities of these small invertebrates, which include burrowing and ingestion and defecation of sediment grains, contribute to mixing and the alteration of sediment structure.
 
===Bioirrigation===
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==Pelagic sediments==
<gallery mode="packed" heights="300px" style="float:right" caption="Pelagic and hemipelagic processes">
File:Ocean hemipelagic and pelagic processes.webp| Sediment supply from terrigenous and biological sources<br />as well as its dispersion and settling through the water column{{hsp}}<ref name=Stow2020 />
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Based upon the composition of the ooze, there are three main types of pelagic sediments: [[siliceous ooze]]s, [[Calcareous#Marine sediments|calcareous oozes]], and [[Pelagic red clay|red clays]].<ref name="Rothwell2005a">Rothwell, R.G., (2005) ''Deep Ocean Pelagic Oozes'', Vol. 5. of Selley, Richard C., L. Robin McCocks, and Ian R. Plimer, Encyclopedia of Geology, Oxford: Elsevier Limited. {{ISBN|0-12-636380-3}}</ref><ref name="HüNekeOther2011">HüNeke, H., and T. Mulder (2011) ''Deep-Sea Sediments''. Developments in Sedimentology, vol. 63. Elsiever, New York. 849 pp. {{ISBN|978-0-444-53000-4}}</ref>
 
An extensive body of work on deep-water processes and sediments has been built over the past 150 years since the voyage of HMS Challenger (1872–1876), during which the first systematic study of seafloor sediments was made.<ref>Murray, J. and Renard, A.F. (1891) [https://books.google.com/books?id=rPlCAQAAIAAJ&printsec=frontcover#v=onepage&q&f=false ''Report on deep-sea deposits based on the specimens collected during the voyage of HMS Challenger in the years 1872 to 1876'']. ''HM Stationery Office''.</ref><ref>Murray, J., Hjort, J., Gran, H.H. and Helland-Hansen, B. (1912) [https://books.google.com/books?id=MczPAAAAMAAJ&printsec=frontcover#v=onepage&q&f=false ''The depths of the ocean: a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic''], Volume 37, Macmillan.</ref> For many decades since that pioneering expedition, and through the first half of the twentieth century, the deep sea was considered entirely pelagic in nature.<ref name=Stow2020>{{cite journal | last1=Stow | first1=Dorrik | last2=Smillie | first2=Zeinab | title=Distinguishing between Deep-Water Sediment Facies: Turbidites, Contourites and Hemipelagites | journal=Geosciences | publisher=MDPI AG | volume=10 | issue=2 | date=13 February 2020 | issn=2076-3263 | doi=10.3390/geosciences10020068 | page=68| doi-access=free }} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>
 
The composition of pelagic sediments is controlled by three main factors. The first factor is the distance from major landmasses, which affects their dilution by terrigenous, or land-derived, sediment. The second factor is water depth, which affects the preservation of both siliceous and calcareous biogenic particles as they settle to the ocean bottom. The final factor is ocean fertility, which controls the amount of [[Biogenic substance|biogenic]] particles produced in surface waters.<ref name="Rothwell2005a"/><ref name="HüNekeOther2011"/>
▲{{clear-}}
 
===Turbidites===
<gallery mode="packed" heights="165px" style="float:right">
File:NOAA Turbidity Current Diagram.jpg| Continental margins can experience slope failures triggered by earthquakes or other geological disturbances. These can result in [[turbidity current]]s as turbid water dense with suspended sediment rushes down the slope. Chaotic motion within the sediment flow can sustain the turbidity current, and once it reaches the deep [[abyssal plain]] it can flow for hundreds of kilometres.<ref>[https://oceanservice.noaa.gov/facts/turbidity.html What is a turbidity current?] NOAA. Last updated: 26 February 2021. {{PD-notice}}</ref>
</gallery>
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[[Turbidite]]s are the [[Deposition (geology)|geologic deposits]] of a [[turbidity current]], which is a type of amalgamation of fluidal and [[sediment gravity flow]] responsible for distributing vast amounts of [[clastic]] [[sediment]] into the [[deep ocean]]. Turbidites are deposited in the deep ocean troughs below the continental shelf, or similar structures in deep lakes, by underwater avalanches which slide down the steep slopes of the continental shelf edge. When the material comes to rest in the ocean trough, it is the sand and other coarse material which settles first followed by mud and eventually the very fine particulate matter. This sequence of deposition creates the [[Bouma sequence]]s that characterize these rocks.
 
Turbidites were first recognised in the 1950s{{hsp}}<ref>{{cite journal | last1=Kuenen | first1=Ph. H. | last2=Migliorini | first2=C. I. | title=Turbidity Currents as a Cause of Graded Bedding | journal=The Journal of Geology | publisher=University of Chicago Press | volume=58 | issue=2 | year=1950 | issn=0022-1376 | doi=10.1086/625710 | pages=91–127| bibcode=1950JG.....58...91K | s2cid=129300638 }}</ref> and the first [[facies]] model was developed by Bouma in 1962.<ref>Bouma, A.H. (1962) [https://books.google.com/books?id=FJM1AAAAMAAJ&q=%22Sedimentology+of+some+flysch+deposits%22&dq=%22Sedimentology+of+some+flysch+deposits%22&hl=en&newbks=1&newbks_redir=0&sa=X&redir_esc=y ''Sedimentology of some flysch deposits. Agraphic approach to facies interpretation'']. Elsevier Publishing Company.</ref> Since that time, turbidites have been one of the better known and most intensively studied deep-water sediment facies. They are now very well known from sediment cores recovered from modern deep-water systems, subsurface (hydrocarbon) boreholes and ancient outcrops now exposed on land. Each new study of a particular turbidite system reveals specific deposit characteristics and facies for that system. The most commonly observed facies have been variously synthesised into a range of facies schemes.<ref>{{cite book | last=Pickering | first=K. T. | title=Deep-marine systems : processes, deposits, environments, tectonics and sedimentation | url=https://books.google.com/books?id=-ZIvCgAAQBAJ| publisher=John Wiley & Sons Inc | publication-place=Chichester, West Sussex Hoboken, NJ | year=2015 | isbn=978-1-118-86549-1 | oclc=908192785}}</ref><ref>{{cite book | last=Hüneke | first=Heiko | title=Deep-sea sediments | url=https://books.google.com/books?id=Ci9ImF4xVhQC | publisher=Elsevier | publication-place=Amsterdam Boston | year=2011 | isbn=978-0-08-093187-6 | oclc=706803062 | language=lt}}</ref><ref name=Stow2020 />
 
===Contourites===
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<gallery mode="packed" heights="220px" style="float:right" caption="Ocean bottom (contour) current">
File:Ocean bottom (contour) current.webp| Identifying the current core, eddies and strands within a deep-water mass{{hsp}}<ref>{{cite journal | last1=Stow | first1=Dorrik | last2=Smillie | first2=Zeinab | title=Distinguishing between Deep-Water Sediment Facies: Turbidites, Contourites and Hemipelagites | journal=Geosciences | publisher=MDPI AG | volume=10 | issue=2 | date=13 February 2020 | issn=2076-3263 | doi=10.3390/geosciences10020068 | page=68| doi-access=free }}</ref><ref name=Stow2020 />
</gallery>
 
A [[contourite]] is a sedimentary deposit commonly formed on [[Continental shelf#Topography|continental rise]] to lower slope settings, although they may occur anywhere that is below storm [[wave base]]. Countourites are produced by [[thermohaline circulation|thermohaline]]-induced [[Ocean current|deepwater bottom currents]] and may be influenced by wind or [[Tide|tidal]] forces.<ref name="Hollister1993">{{cite journal |first1=C.D. |last1=Hollister|title=The concept of deep-sea contourites |journal=[[Sedimentary Geology (journal)|Sedimentary Geology]] |year=1993 |volume=82 |issue=1–4|pages=5–11 |bibcode=1993SedG...82....5H |doi=10.1016/0037-0738(93)90109-I }}</ref><ref name="Rebesco">[https://books.google.com/books?id=D7JLNLvWeMsC&pg=PT432&lpg=PT432&dq=contourites+definition&sourcepg=bl&hl=en&oi=book_result&ct=result&resnum=7PT432 Rebesco, M. & Camerlenghi, A. 2008. Contourites, Elsevier Science, 688pp.] {{ISBN|978-0-444-52998-5}}</ref> The geomorphology of contourite deposits is mainly influenced by the deepwater bottom-current velocity, sediment supply, and seafloor topography.<ref name="Faugeresetal1993">{{cite journal |first1=J.-C. |last1=Faugères |first2=M.L. |last2=Mézerais |first3=D.A.V |last3=Stow |title=Contourite drift types and their distribution in the North and South Atlantic Ocean basins |journal=Sedimentary Geology |year=1993 |volume=8 |issue=1–4 |pages=189–203 |doi=10.1016/0037-0738(93)90121-k|bibcode = 1993SedG...82..189F }}</ref>
 
Contourites were first identified in the early 1960s by [[Bruce Heezen]] and co-workers at [[Woods Hole Oceanographic Institute]]. Their now seminal paper{{hsp}}<ref>{{cite journal | last1=Heezen | first1=Bruce C. | last2=Hollister | first2=Charles D. | last3=Ruddiman | first3=William F. | title=Shaping of the Continental Rise by Deep Geostrophic Contour Currents | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=152 | issue=3721 | date=22 April 1966 | issn=0036-8075 | doi=10.1126/science.152.3721.502 | pages=502–508| pmid=17815077 | bibcode=1966Sci...152..502H | s2cid=29313948 }}</ref> demonstrated the very significant effects of contour-following bottom currents in shaping sedimentation on the deep continental rise off eastern North America. The deposits of these semi-permanent alongslope currents soon became known as contourites, and the demarcation of slope-parallel, elongate and mounded sediment bodies made up largely of contourites became known as contourite drifts.<ref>Hollister, C.D. and Heezen, B.C. (1972) [ "Geologic effects of ocean bottom currents: Western North Atlantic"]. In: Gordon, A.L., ''Studies in Physical Oceanography'', Gordon and Breach Science Publishers. {{ISBN|9780677151700}}.</ref><ref>{{cite book | last1=McCave | first1=I. N. | last2=Tucholke | first2=Brian E. | title=The Western North Atlantic Region | chapter=Deep current-controlled sedimentation in the western North Atlantic | year=1986 | pages=451–468 | publisher=Geology of North America | publication-place=North America | doi=10.1130/dnag-gna-m.451| isbn=0813752027 }}</ref><ref name=Stow2020 />
 
===Hemipelagic===
[[Hemipelagic sediment]]s, or ''hemipelagite'', are a type of marine sediments that consists of clay and silt-sized grains that are [[terrigenous]] and some [[biogenic]] material derived from the landmass nearest the deposits or from organisms living in the water.<ref name="Ochoa et al 2013">{{cite journal |doi=10.1306/04221312086 |title=Recognition criteria for distinguishing between hemipelagic and pelagic mudrocks in the characterization of deep-water reservoir heterogeneity |journal=AAPG Bulletin |volume=97 |issue=10 |pages=1785–803 |year=2013 |last1=Ochoa |first1=Jesús |last2=Wolak |first2=Jeannette |last3=Gardner |first3=Michael H |bibcode=2013BAAPG..97.1785O }}</ref><ref name="Stow 1994">{{cite book |last1=Stow |first1=D.A.V. |year=1994 |chapter=Deep sea processes of sediment transport and deposition |editor1-last=Pye |editor1-first=K. |title=Sediment Transport and Depositional Processes |location=London |publisher=Blackwell |pages=257–91 }}</ref> Hemipelagic sediments are deposited on [[continental shelves]] and [[continental rise]]s, and differ from [[pelagic sediment]] compositionally. Pelagic sediment is composed of primarily biogenic material from organisms living in the water column or on the seafloor and contains little to no terrigenous material.<ref name="Ochoa et al 2013"/> Terrigenous material includes minerals from the [[lithosphere]] like [[feldspar]] or [[quartz]]. [[Volcanism]] on land, wind blown sediments as well as particulates discharged from rivers can contribute to Hemipelagic deposits.<ref name="Aksu et al 1995">{{cite journal |doi=10.1016/0025-3227(95)80003-T |title=Origin of late glacial—Holocene hemipelagic sediments in the Aegean Sea: Clay mineralogy and carbonate cementation |journal=Marine Geology |volume=123 |pages=33–59 |year=1995 |last1=Aksu |first1=A.E |last2=Yaşar |first2=D |last3=Mudie |first3=P.J |issue=1–2 |bibcode=1995MGeol.123...33A }}</ref> These deposits can be used to qualify climatic changes and identify changes in sediment provenances.<ref name="Trentesaux et al 2001">{{cite journal |doi=10.1306/2DC4096E-0E47-11D7-8643000102C1865D |title=Carbonate Grain-Size Distribution in Hemipelagic Sediments from a Laser Particle Sizer |journal=Journal of Sedimentary Research |volume=71 |issue=5 |pages=858 |year=2001 |last1=Trentesaux |first1=A |last2=Recourt |first2=P |last3=Bout-Roumazeilles |first3=V |last4=Tribovillard |first4=N |bibcode=2001JSedR..71..858T |url=https://hal.archives-ouvertes.fr/hal-03303385/document |hdl=20.500.12210/62326 |hdl-access=free }}</ref><ref name="Weedon 1986">{{cite journal |doi=10.1016/0012-821X(86)90083-X |title=Hemipelagic shelf sedimentation and climatic cycles: The basal Jurassic (Blue Lias) of South Britain |journal=Earth and Planetary Science Letters |volume=76 |issue=3–4 |pages=321–35 |year=1986 |last1=Weedon |first1=G.P |bibcode=1986E&PSL..76..321W }}</ref>
 
----
<gallery mode="packed" heights="170px style=float:left" caption="Diagrams of pelagic sediment types">
File:Ocean medium-grained turbidite family.webp| '''Medium-grained turbidite family'''<br />The ideal Bouma facies model showing the complete sequence of divisions A–E,<ref>Bouma, Arnold H. (1962) [https://books.google.com/books?id=FJM1AAAAMAAJ&q=%22Sedimentology+of+Some+Flysch+Deposits:+A+Graphic+Approach+to+Facies+Interpretation%22&dq=%22Sedimentology+of+Some+Flysch+Deposits:+A+Graphic+Approach+to+Facies+Interpretation%22&hl=en&newbks=1&newbks_redir=0&sa=X&redir_esc=y ''Sedimentology of Some Flysch Deposits: A Graphic Approach to Facies Interpretation''] Elsevier Publishing Company.</ref> while F is a typical partial sequence found in nature.{{hsp}}<ref name=Stow2020 />
File:Ocean sandy contourite family.webp| '''Sandy contourite family'''<br />for muddy sands, fine-to-medium sands<br />and medium-to-coarse sands{{hsp}}<ref>{{cite journal | last1=Brackenridge | first1=Rachel E. | last2=Stow | first2=Dorrik A. V. | last3=Hernández-Molina | first3=Francisco J. | last4=Jones | first4=Claudia | last5=Mena | first5=Anxo | last6=Alejo | first6=Irene | last7=Ducassou | first7=Emmanuelle | last8=Llave | first8=Estefanía | last9=Ercilla | first9=Gemma | last10=Nombela | first10=Miguel Angel | last11=Perez-Arlucea | first11=Marta | last12=Frances | first12=Gillermo | editor-last=Marzo | editor-first=Mariano | title=Textural characteristics and facies of sand-rich contourite depositional systems | journal=Sedimentology | publisher=Wiley | volume=65 | issue=7 | date=12 April 2018 | issn=0037-0746 | doi=10.1111/sed.12463 | pages=2223–2252| hdl=10261/172929 | s2cid=134489105 }}</ref><ref name=Stow2020 />
File:Ocean hemipelagite facies models.webp| '''Hemipelagite facies models'''<br />Standard model showing simple cyclicity between clay-rich and biogenic-rich parts. Variations depend on component inputs.<ref name=Stow2020 />
</gallery>
▲{{clear}}
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==Ecology==
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Marine [[microbenthos]] are microorganisms that live in the [[benthic zone]] of the ocean – that live near or on the seafloor, or within or on surface seafloor sediments. The word ''benthos'' comes from Greek, meaning "depth of the sea". Microbenthos are found everywhere on or about the seafloor of continental shelves, as well as in deeper waters, with greater diversity in or on seafloor sediments. In shallow waters, [[seagrass meadow]]s, [[coral reef]]s and [[kelp forest]]s provide particularly rich habitats. In [[photic zone]]s benthic diatoms dominate as photosynthetic organisms. In [[intertidal zone]]s changing [[tide]]s strongly control opportunities for microbenthos.
 
<gallery mode="packed" heights="180px" style="float:left;">
File:Elphidium-incertum hg.jpg|''[[Elphidium]]'' a widespread abundant genus of benthic forams
File:FMIB 50025 Textilaria.jpeg|''[[Heterohelix]]'', an extinct genus of benthic forams
</gallery>
 
<gallery mode="packed" heights="150px" style="float:right;" caption="Marine microanimals">
File:Gastrotrich.jpg|[[Dark field microscopy|Darkfield photo]] of a [[gastrotrich]], 0.06-3.0 mm long, a worm-like animal living between sediment particles
File:Pliciloricus enigmatus.jpg|Armoured ''[[Pliciloricus enigmaticus]]'', about 0.2 mm long, live in spaces between marine gravel
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{{clear}}
 
[[Diatom]]s form a (disputed) phylum containing about 100,000 recognised species of mainly unicellular algae. Diatoms generate about 20 percentper cent of the oxygen produced on the planet each year,<ref name="livescience.com">[https://www.livescience.com/46250-teasing-apart-the-diatom-genome.html The Air You're Breathing? A Diatom Made That]</ref> take in over 6.7 billion metric tons of [[silicon]] each year from the waters in which they live,<ref>{{cite journal | last1 = Treguer | first1 = P. | last2 = Nelson | first2 = D. M. | last3 = Van Bennekom | first3 = A. J. | last4 = Demaster | first4 = D. J. | last5 = Leynaert | first5 = A. | last6 = Queguiner | first6 = B. | year = 1995 | title = The Silica Balance in the World Ocean: A Reestimate | journal = Science | volume = 268 | issue = 5209| pages = 375–9 | pmid = 17746543 | doi = 10.1126/science.268.5209.375 | bibcode = 1995Sci...268..375T | s2cid = 5672525 }}</ref> and contribute nearly half of the organic material found in the oceans.
 
[[File:Benthic Diatom.jpg|thumb| {{center|Benthic diatom}}]]
 
<gallery mode="packed" heights="145px" style="float:left;">
File:Diatoms (248 05) Various diatoms.jpg|[[Diatom]]s are one of the most common types of phytoplankton
File:Diatom Helipelta metil.jpg|Their protective shells (frustles) are made of silicon
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{{multiple image
| align = right
| caption_align = center
| direction = horizontal
| header = Coccolithophores
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| width1 = 107
| alt1 =
| caption1 = {{center|...have plates called [[coccolith]]s}}
| image2 = Discoaster surculus 01.jpg
| width2 = 133
| alt2 =
| caption2 = {{center|...extinct fossil}}
}}
 
<gallery mode="packed" heights="130px" style="float:left;">
File:Coccolithus pelagicus.jpg
File:JRYSEM-247-05-azurapl.jpg|{{center|[[Syracosphaera azureaplaneta|Coccolithophores]] named after the BBC documentary series<br />''[[The Blue Planet]]''}}
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[[Radiolarian]]s are unicellular predatory [[#Marine protists|protists]] encased in elaborate globular shells usually made of silica and pierced with holes. Their name comes from the Latin for "radius". They catch prey by extending parts of their body through the holes. As with the silica frustules of diatoms, radiolarian shells can sink to the ocean floor when radiolarians die and become preserved as part of the [[ocean sediment]]. These remains, as [[#Marine microfossils|microfossils]], provide valuable information about past oceanic conditions.<ref name=Wassilieff2006b>Wassilieff, Maggy (2006) [http://www.TeAra.govt.nz/en/photograph/5138/radiolarian-fossils "Plankton - Animal plankton"], ''Te Ara - the Encyclopedia of New Zealand''. Accessed: 2 November 2019.</ref>
 
<gallery mode="packed" heights="150px" style="float:left;">
File:Mikrofoto.de-Radiolarien 6.jpg|Like diatoms, radiolarians come in many shapes
File:Theocotylissa ficus Ehrenberg - Radiolarian (34638920262).jpg|Also like diatoms, radiolarian shells are usually made of silicate
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{{multiple image
| align = right
| caption_align = center
| direction = horizontal
| header = Foraminiferans
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| width1 = 136
| alt1 =
| caption1 = {{center|...can have more than one nucleus}}
| image2 = G bulloides Brady 1884.jpg
| width2 = 104
| alt2 =
| caption2 = {{center|...and defensive spines}}
}}
 
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The sudden [[Cretaceous–Paleogene extinction event|extinction event]] which killed the dinosaurs 66 million years ago also rendered extinct three-quarters of all other animal and plant species. However, deep-sea benthic forams flourished in the aftermath. In 2020 it was reported that researchers have examined the chemical composition of thousands of samples of these benthic forams and used their findings to build the most detailed climate record of Earth ever.<ref>[https://www.livescience.com/oldest-climate-record-ever-cenozoic-era.html Earth barreling toward 'Hothouse' state not seen in 50 million years, epic new climate record shows] ''LiveScience'', 10 September 2020.</ref><ref name=Westerhold2020>Westerhold, T., Marwan, N., Drury, A.J., Liebrand, D., Agnini, C., Anagnostou, E., Barnet, J.S., Bohaty, S.M., Vleeschouwer, D., Florindo, F. and Frederichs, T. (2020) [https://www.science.org/doi/10.1126/science.aba6853 "An astronomically dated record of Earth’s climate and its predictability over the last 66 Million Years"]. ''Science'', '''369'''(6509): 1383–1387. {{doi|10.1126/science.aba6853}}.</ref>
 
Some [[endolith]]s have extremely long lives. In 2013 researchers reported evidence of endoliths in the ocean floor, perhaps millions of years old, with a generation time of 10,000 years.<ref>Bob Yirka [http://phys.org/news/2013-08-soil-beneath-ocean-harbor-bacteria.html 29 Aug 2013]</ref> These are slowly metabolizing and not in a dormant state. Some [[Actinomycetota]] found in [[Siberia]] are estimated to be half a million years old.<ref>[http://www.guardian.co.uk/theobserver/2010/may/02/rachel-sussman-oldest-plants Sussman: Oldest Plants], [[The Guardian]], 2 May 2010</ref><ref>{{Cite web |url=https://www.itsokaytobesmart.com/post/91481365622/siberian-actinobacteria-oldest-living-thing |title=ArchivedIt's copyOkay to be Smart • the oldest living thing in the world: These |access-date=2018-07-13 |archive-url=https://web.archive.org/web/20180713074804/https://www.itsokaytobesmart.com/post/91481365622/siberian-actinobacteria-oldest-living-thing |archive-date=2018-07-13 |url-status=dead }}</ref><ref>{{Cite journal|title=Ancient bacteria show evidence of DNA repair|first1=Eske |last1=Willerslev|first2=Duane |last2=Froese|first3=David |last3=Gilichinsky|first4=Regin |last4=Rønn|first5=Michael|last5=Bunce|first6=Maria T.|last6=Zuber |first7=M. Thomas P.|last7=Gilbert |first8=Tina |last8=Brand |first9=Kasper |last9=Munch |first10=Rasmus|last10=Nielsen |first11=Mikhail|last11=Mastepanov|first12=Torben R. |last12=Christensen |first13=Martin B.|last13=Hebsgaard |first14=Sarah Stewart|last14=Johnson |date=4 September 2007|journal=Proceedings of the National Academy of Sciences|volume=104|issue=36|pages=14401–14405|doi=10.1073/pnas.0706787104 |pmid=17728401|pmc=1958816 |bibcode=2007PNAS..10414401J|doi-access=free }}</ref>
 
{{clear}}
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{{further|Geological history of Earth}}
 
To begin with, the Earth was molten due to extreme [[volcanism]] and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid [[crust (geology)|crust]] and water began accumulating in the atmosphere. The [[Moon]] formed soon afterwards, possibly as a result of the impact of a planetoid with the Earth. [[Outgassing]] and volcanic activity produced the primordial atmosphere. Condensing [[water vapor]], augmented by ice delivered from [[comet]]s, [[Origin of water on Earth|produced the oceans]].<ref name="SCI-20200828">{{cite journal |author=Piani, Laurette |title=Earth's water may have been inherited from material similar to enstatite chondrite meteorites |url=https://www.science.org/doi/10.1126/science.aba1948 |date=28 August 2020 |journal=[[Science (journal)|Science]] |volume=369 |issue=6507 |pages=1110–1113 |doi=10.1126/science.aba1948 |pmid=32855337 |bibcode=2020Sci...369.1110P |s2cid=221342529 |access-date=28 August 2020 }}</ref><ref name="SCI-20200827wu">{{cite news |author=Washington University in SaintSt. Louis |author-link=Washington University in SaintSt. Louis |date=27 August 2020 |title=Meteorite study suggests Earth may have been wet since it formed - Enstatite chondrite meteorites, once considered 'dry,' contain enough water to fill the oceans -- and then some |work=EurekAlert! |url=https://www.eurekalert.org/pub_releases/2020-08/wuis-mss082620.php |date=27 August 2020 |work=[[EurekAlert!]] |access-date=28 August 2020 }}</ref><ref name="SCI-20200827aa">{{cite news |author=[[American Association for the Advancement of Science]] |title=Unexpected abundance of hydrogen in meteorites reveals the origin of Earth's water |url=https://www.eurekalert.org/pub_releases/2020-08/aaft-uao082420.php |date=27 August 2020 |work=[[EurekAlert!]] |access-date=28 August 2020 }}</ref>
 
By the start of the [[Archean]], about four billion years ago, rocks were often heavily metamorphized deep-water sediments, such as [[graywacke]]s, [[mudstone]]s, volcanic sediments and [[banded iron formation]]s. [[Greenstone belt]]s are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. High-grade rocks were derived from volcanic [[island arc]]s, while low-grade metamorphic rocks represented deep-sea sediments eroded from the neighboring island rocks and deposited in a [[forearc|forearc basin]].<ref>{{harvnb|Stanley|1999|pp=302&ndash;303}}</ref> The earliest-known supercontinent [[Rodinia]] assembled about one billion years ago, and began to break apart after about 250 million years during the latter part of the [[Proterozoic]].
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** [[Interplanetary dust cloud|Interplanetary dust]]
* [[Deep biosphere]]
* [[Great Calcite Belt]]
* [[Marine clay]]
* [[Microbially induced sedimentary structure]]
* [[Oolitic aragonite sand]]
* [[Organic-rich sedimentary rocks]]
* [[{{section link|Paleolimnology#|Paleoclimate proxies]]}}
* [[Redox gradient]]
* [[Seafloor depth versus age]]
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