x. chemical components of sediment
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Chemical components of sediment
X.
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Introduction
• The sediments deposited in the ocean are an archive of historical information about the Earth
• They provide information about global biogeochemical cycles
• The distribution of sediments in the ocean is determined by biological and chemical processes
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The origin of sediment
Sediments
Autochtonous (authigenic)precipitation
Hydrogenous Biogenous
AllochtonousSolid form
Lithogenous (clastic) Cosmogenous
Anthropogenic
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Grain-size of sediments
http://www.virtual-geology.info/sediments-and-strata/grainsize.html
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Grain-size distribution
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Lithogenous sediment
• From the earth`s crust as a process of weathering and volcanic activity
• Terrigenous particles are the products of weathering of continental rocks
• It enters the ocean via rivers, glaciers, and winds
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Volcanic activity
• Sediments from volcanic activity normally larger than clays
• In the ocean, the particles undergo weathering as a result of chemical attack by seawater
• Their mineralogy is primarily that of amphiboles, pyroxine , and olivine (rock-forming silicate minerals contain ions iron and magnesium in their structure)
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AmphibolesOlivine
Pyroxine
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Biogenous sediments
• Composed of detrital (nonliving) hard and soft parts formed by marine organisms
• The hard parts are fragments of structural components, including shell, endoskeletons, and exoskeletons
• The soft parts composed of organic matter, such as tissues, organic exoskeletons, and excretions (fecal pellets)
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Examples
• Calcite (CaCO3) deposited by coccolithophorids (< 60 µm) and foraminiferans (< 2 mm)
• Opaline (SiO2) deposited by diatoms (mostly < 50 µm) and radiolarians ( 20-300 µm)
• Aragonite polymorphous with calcite• Barite (BaSO4)
• Celestite (SrSO4)• Carbonate-rich fluoroapatite minerals (francolite)
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Hydrogenous sediments
• Sediments formed by the abiogenic precipitation of solutes from seawater
1. Evaporites: salt crystals that form when seawater evaporates
2. Metal sulfide deposits at mid-ocean ridges3. Manganese nodules4. Phosphorites5. Some clay minerals around mid-ocean ridges
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Evaporites
Form when seawater evaporates and is not relaced with fresh water
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Cosmogenous sediments
• Extraterrestrial material that is constantly entering earth`s atmosphere with particle diameter is less than 1 mm
• Composed primarily of fragments of comets and asteroids in the 5 to 50 µm size range
• Because of its small size, some of these particles are able to pass through earth`s atmosphere and reach the sea surface without melting
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Calcareous oozes (CaCO3)
• Is calcium carbonate mud formed from the hard parts (tests) of the bodies of free floating animals
• the primary calcareous organisms are foraminifera (microscopic animals) and coccoliths (algae)
• When the planktonic organisms die their calcareous shells fall to the ocean bottom
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Stability of CaCO3
http://www.utdallas.edu/~pujana/oceans/calcium.html
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Siliceous oozes (SiO2)• made up of the tests of floating (planktonic)
organisms that extract silica from seawater to make their hard parts
• The most abundant of these are the diatoms (plants) and the radiolarians (animals)
DiatomsRadiolarians
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Siliceous oozes