Deep sea sediment refers to the loose bottom of deep sea with water depth greater than 2000 meterssediment。They are mainly distributed in ocean basins outside the continental margin.Deep-sea sedimentIt is mainly composed of marine biological remains, authigenic deposits, eolian dust, cosmic dust, volcanic ash, terrigenous clay colloid and ice raft debris.[1]It is mainly the product of biological and chemical processes, and also includes terrestrial, volcanic and cosmic materials.Turbidity current, ice borne, eolian and volcanic materials can also be the main source in some ocean floors.The authigenic mineral resources of the seabed are mainly produced in the deep sea, and the development of paleooceanography and paleoclimatology also depends on the research of deep-sea sediments.Therefore, the study of deep-sea sediments has been paid more and more attention.[2]
Chinese name
Abyssal sediment
Foreign name
pelagic deposit
Location
In the ocean basin beyond the continental margin
Type
Biogenic sediment
Features
Deep sea sediment types
Hydrodynamic conditions
Current flows slowly and the sea bottom temperature is low
Deep sea sediment refers to the loose bottom of deep sea with water depth greater than 2000 meterssediment。They are mainly distributed in ocean basins outside the continental margin.[2]Deep-sea sedimentIt is mainly the product of biological and chemical processes, and also includes terrestrial, volcanic and cosmic materials.Turbidity current, ice borne, eolian and volcanic materials can also be the main source in some ocean floors.The authigenic mineral resources of the seabed are mainly produced in the deep sea, and the development of paleooceanography and paleoclimatology also depends on the research of deep-sea sediments.Therefore, the study of deep-sea sediments has been paid more and more attention.
Classification principle
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Based on the grain size type of sediment, combined with the biological, mineral and chemical characteristics of sediment, a comprehensive analysis is made from the perspective of sediment genesis.[1]
type
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Biogenic sediment
Generally referred to as biological ooze, it refers to the sediment containing more than 30% of biological remains.[2]There are two main types:
①Calcareous ooze, which is soft mud with calcareous biological component greater than 30% (the biological component is mainly calcium carbonate), including foraminiferal soft mud（Echinococcus ooze）, chalk ooze（Coccolith ooze）And pteropod ooze.
② Siliceous ooze is the ooze with siliceous biological component greater than 30% (the biological component is mainly amorphous silica), including diatom ooze andRadiolarian ooze。
Abiogenic sediment
It mainly includes: ① brown clay, ② authigenic sediment, ③ volcanic sediment, ④ turbidite sediment, ⑤ landslide sediment, ⑥ glacial sediment, ⑦ eolian sediment.Some scholars often refer to various biological oozes and brown clays in the deep sea asPelagic sediment。[2]
form
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Deep sea sediments are mainly composed of marine biological remains, authigenic deposits, eolian dust, volcanic ash, cosmic dust, terrestrial clay colloid and ice raft debris.[3]
features
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Main types of deep-sea sediments at the bottom of modern ocean
Sponge bone schist of Qixia Formation, Anhui
Deep sea sediments are heterogeneous in nature and formed by different sedimentation.The composition of modern oceanic sediments is varied.The main sediments include terrigenous clastic sediments, siliceous sediments, calcareous sediments, deep-sea clay, deep-sea ooze, sediments related to glaciers and continental margin sediments.
Hydrodynamic conditions
The ocean current flows slowly, the sea bottom temperature is low, the physical weathering is weak, the chemical action is also very slow, and the sedimentation rate is very low.Sedimentary structure: horizontal bedding, rhythmic bedding, massive bedding.Sediment: mainly composed of deep-sea ooze and deep-sea clay.
Soft mud or deep sea soft mud
Submarine fan and its sedimentary model
Microorganism remains with content>30%, such as echinococcus ooze and radiolarian ooze (more than 50% of radiolarian remains).The average carbonate content is 65%, which can also be called calcareous ooze.Carbonate is less than 30%, which can be called siliceous ooze.Deep sea clay: less than 30% of micro biological remains are called.In deep-sea clay, brown clay is the main sediment type in deep-sea ocean, which is mainly composed of clay minerals and terrigenous stable mineral residues, as well as volcanic ash and cosmic particles.Carbonate content is less than 30%.In some areas, the chemical and biochemical precipitation of various minerals is also an important factor for the formation of deep-sea sediments, such as manganese nodulesCalciferous zeoliteCan lead to the formation of Fe, Mn, P and other minerals.In addition, submarine volcanoes, volcanic eruptions, wind and cosmic materials also provide a certain amount of material sources for the deep-sea environment.
Paleontological characteristics
Submarine fan and its sedimentary model
When turbidity stops, the deep-sea sediments contain typical pelagic plankton, such as foraminifera and radiolaria, and there are complexVestigial fossil, such as curved, spiral, grid, etc.In turbidites, there are shallow water fossils brought from other places, such as shallow benthic foraminifera, calophyta and large scale shell fossils.Submarine fan and its sedimentary model
Rock and ore characteristics
The maturity of deep-sea turbidite sandstone is low, and its mineral composition is terrigenous detritus, and most of them are unstable.In addition to quartz, there are quite a lot of rock debris, feldspar, mica and argillaceous, mostly hard sandstone or lithic sandstone and feldspathic sandstone.Sometimes it contains shallow water bioclasts.The sorting and rounding are poor, and the matrix content is generally more than 15% (matrix support structure).
The submarine fan is mainly an underwater fan shaped accumulation body formed in the deep sea at the outlet of the submarine canyon by turbidity current and partial collapse.
Main lithofacies
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Abyssal sedimentary rock
In addition to turbidite deposits, submarine fan deposits also include the following main lithofacies types (according to submarine fan sedimentary system, turbidite and Bauma sequence are only a part of them):[4]
Massive sandstone facies
It is mainly massive sandstone with a small amount of shale.There is scouring structure at the bottom of sandstone, and the progressive bedding is not obvious.Formed by liquefaction flow or particle flow.
Sedimentary model of submarine fan
Massive sandstone facies with dished and tubular structures
Its characteristics are similar to those of massive sandstone, but the difference is that disc structure and tubular structure formed by liquefaction are developed.
Gradual bedding gravelly sandstone facies
The grain size is coarser than that of turbidite A and B, and there are few shale and mudstone.Bottom boundary scouring surface and bottom mark, progressive bedding, parallel bedding.
Granular supported conglomerate facies
It can be divided into massive conglomerate, bi-directional graded conglomerate, positive graded conglomerate and graded bedded conglomerate.
Matrix supported massive conglomerate facies
The matrix containing a large amount of mud and sand between the gravels is poorly sorted and has no directional fabric, which is formed in the underwater debris flow.
Slump facies
sediment
The hybrid structure with matrix support has obvious collapse phenomenon.Fan root: the main waterway development area;It mainly consists of various coarse clastic deposits (non turbidite blocks composed of conglomerate gravity transported sediments);Massive melange conglomerate, bi-directional graded conglomerate, graded bedded conglomerate.The natural levees on both sides of the waterway are mainly low-density turbidites composed of silt and clay, which are equivalent to the C, D and E sections of the Bauma sequence.
Middle of fan: Distribution area of reticular waterways and fan front lobes.The graded bedding gravelly sandstone, massive sandstone and massive sandstone with dish structure are mainly developed in the reticulated channel;The overtopping sediments outside the waterway are mainly fine-grained low-density pelagic turbidites, equivalent to C, D and E.
Fan end: Flat, no water channel developed.Mainly turbidite.It is terminal turbidite or distal turbidite, mainly composed of C, D and E.
distribution
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Different sedimentary types of sediments have different distribution.
Calcareous ooze
It covers about 45.6% of the ocean area.Mainly distributed inAtlantic, Westthe indian oceanAnd Souththe pacific ocean。The average distribution water depth is about 3600m.Foraminiferal ooze is the most widely distributed, followed by coccolith ooze, and pteropod ooze is mainly composed ofaragoniteComposition, easy to dissolve, narrow distribution, mainly inAtlanticThe water depth in tropical areas is less than 2500~3000 meters.
Siliceous ooze。It covers about 10.9% of the ocean area.Diatomic ooze is mainly distributed in the southern and northern high latitude sea areas (Antarctic waters and the North Pacific), with an average depth of 3900 meters.Radiolarian ooze is mainly distributed in the sea area near the equator, with an average depth of 5300 meters.
Brown clay
Also called red clay or deep-sea clay, it is a clay material with less than 30% of biogenic substances.It is brown to red due to the oxidation of iron bearing minerals.It covers 30.9% of the ocean, mainly in the norththe pacific ocean、the indian oceanCentral andAtlanticDeep water.The average distribution water depth is 5400m.Due to the large distribution depth, most of the biogenic substances are dissolved, so the non biogenic components are dominant.The main components are terrigenous clay minerals, in addition to authigenic sediments (such as deep-sea sedimentary fluorite, manganese nodules, etc.), eolian sediments, volcanic debris, some undissolved biological residues, cosmic dust, etc.
Authigenic sediment
Various substances formed by chemical action in seawater.Mainly manganese nodulesmontmorilloniteandFluorsparEtc.Manganese nodules are widely distributed, but their composition varies from place to place (seeDeep-sea manganese nodule ）。Montmorillonite and fluorite are abundant in the Pacific Ocean and the Indian Ocean, but rare in the Atlantic Ocean.
Volcanic sediments
come fromvolcanoThe product of action.It is mainly distributed in the Pacific Ocean, the northeast of the Indian OceanGulf of MexicoAndmediterranean seaEtc.
Turbidite deposit
Sediments formed by turbidity flow are often sandwiched in fine-grained deep-sea sediments as terrigenous sand and silt layers.Mainly distributed inContinental slopeNear the piedmont, it is more developed in the northern Pacific Ocean and around the Indian Ocean.
Landslide sediment
Material formed by sliding or collapsing of the seabed.Mainly distributed in the oceanbasinAnd some sea areas with steep terrain.
Glacial sediment
The floating ice formed by the front end of the continental glacier falling into the sea carries debris materials from land and shallow water areas, which can reach deep sea areas far away from the continent.When the floating ice melts, the debris material sinks to the sea bottom, forming glacial sediment.Mainly distributed inantarcticAround the mainland andarcticNearby waters.
Eolian sediment
Sediment transported into the sea for wind.It is mainly distributed in the dry climate zone near 30 ° S and 30 ° N of the Pacific Ocean and the Atlantic Ocean and the northwest sea area of the Indian Ocean.Aeolian sediments are sometimes not separately classified as a type of deep-sea sediments.
In addition, cosmic dust, which is often found in deep-sea sediments, is not generally classified as a sedimentary type because of its small amount.But the study of deep-sea cosmic dust has important value.
To sum up, the distribution of deep-sea sediments is as follows: calcareous ooze and brown clay are mainly distributed in the oceans, calcareous ooze is mainly distributed in seamounts and highlands, and brown clay is found in deep-sea basins;Siliceous ooze and glacial sediments are mainly distributed in the sea area near the South and North Pole;Radiolarian ooze is mainly distributed near the equator of the Pacific Ocean;The authigenic sediments are distributed in the central and southern Pacific andthe indian oceaneast;Turbidity sediment is distributed around the ocean basin;Volcanic sediments are scattered everywhere andVolcanic zoneEnriched nearby.[3][5]
influence factor
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In addition to material sources, transport agents and sedimentation also play an important role in influencing and controlling deep-sea sedimentation.
In the deep sea area, the main agents for transporting sediment areOcean circulation, turbidity current and deep seabed laminar flow, etc.It also plays an important role in the transport of wind and ice floes in local sea areas.The circulation brings fine terrigenous suspended matter and biogenic matter to the deep sea. At the edge of the ocean with strong bottom current activity, narrow and long sedimentary bodies are often formed along the flow direction.In areas with weak bottom flow activity, sediments uniformly cover the seabed.
Due to the different biological, physical and chemical conditions in the ocean basin, the sedimentary factors of various sediments are also different.The main factors affecting calcareous sediments are: biological supply, water depth, deepwater circulation, etc.Although most calcareous organisms are dissolved in the sinking process after death, the higher the productivity, the more the absolute amount of biological residues accumulated on the seabed, so calcareous ooze is mainly distributed intropicandthe temperate zoneHigh productivity sea area.In addition,Carbonate compensation depthIt also has an important impact on the distribution of calcareous sediments.The main factors affecting siliceous sediments are: the supply of siliceous organisms, the dissolution of siliceous bones, etc.For example, there are rich diatoms in the seawater near the north and south poles, so diatom sediments are widely distributed in high latitude waters.
The sedimentation rate of deep-sea sediments is extremely slow, generally about 0.1~10 cm/1000 years.Due to the influence of terrigenous materials, from the edge of the ocean basin to the center, the sedimentation rate changes from large to small. Moreover, the sedimentation rate varies greatly for different sedimentary types, even for different parts of the ocean floor.The deposition rate of calcareous sediments is about 1~4 cm/1000 years;The sedimentation rate of siliceous sediment is about 0.1~2 cm/1000 years, and that of deep-sea clay is the lowest, less than 0.1~0.4 cm/1000 years.[2]
Development of deep-sea sedimentology
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Since the 1950s, a series of breakthroughs in deep-sea sedimentology have broken the long silence of sedimentology and promoted a series of related disciplines in the evolution of the earth system.This paper reviews the development of international deep-sea sedimentology from several aspects: from turbidity current to contourite current, from deep-sea storm to sediment trap, from sediment trap to fixed-point observation of seabed boundary layer, from time series of sedimentary process to seabed online observation system, to connecting modern sedimentary process andsequence stratigraphy "From source to sink", and the role of deep-sea sedimentary processes in the carbon cycle.As a result of this development, deep-sea sedimentology becameEarth System ScienceA key link of.Looking back at the deep-sea sedimentology over the past half century, its major progress has been closely linked to the field observation of the ocean, which has benefited from the combination with related disciplines, and has also been supported by large-scale international plans. Unfortunately, these plans are almost all in Europe and the United States.At present, China has a good opportunity to develop deep-sea sedimentology. In addition to increasing investment and equipment, it is suggested to start the implementation of large-scale deep-sea scientific research projects as soon as possible.[6]
On August 3, 2024, the Guangzhou Marine Geological Survey announced that its deep-sea element cycle and resource effect team found that deep-sea pelagic sediment rich in iron and manganese oxides is the main reservoir of zinc in the ocean, and these oxides are like tiny "zinc traps" that capture and enrich zinc from the vast sea water.[7]
