Ocean Sediments. Importance of Sediments Economic Value –Oil, fossil fuels –Salt & Phosphorus...
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Transcript of Ocean Sediments. Importance of Sediments Economic Value –Oil, fossil fuels –Salt & Phosphorus...
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Ocean Sediments
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Importance of Sediments• Economic Value
– Oil, fossil fuels– Salt & Phosphorus deposits
• Determine shape & structure of Ocean bottom
• Strongly affect distribution of Benthic Organisms
• Chronological record of Earth’s history– Tectonic history– Climate history– Evolutionary history
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Sediment Thickness
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Topographic profiles
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Law of Superposition
Younger sediments over Old sediments
YOUNG----------------------
OLD
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Sediment Classification
• By Grain Size• By Origin
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Sediment Classification
• Grain Size– Clay <4 μm– Silt 4-62 μm– Sand 62-2000 μm– Gravel >2000 μm
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Table 3.1
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Basic Sediment Transport(READ CC4)
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Sediment Sorting
Well-sorted sediments are those of similar size class
– Beach: well sorted (far from source)– Glacier: not sorted (close to source)
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Sediment AngularitySediment weathering during transport
induces loss in angularity
– Angular grains (close to source)– Rounded grains (far from source)
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Sediment Classification
• Origin– Lithogenous or Terrigenous (~75%)– Biogenous (~20%)– Hydrogenous– Cosmogenous
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Lithogenous Sediments
• Fragments of rocks broken, weathered and eroded form lithogenous sediments
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www.naturalphotos.com
Wind & Rain erosion
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Lithogenous Sediments
• Transport of sediments by:– Rivers– Glaciers– Waves– Wind– Landslides– Humans
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www.southalabama.edu http://earthobservatory.nasa.gov
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Sediment Discharge by Rivers
• Ganges: 1700 million Tm/year• Amazon:900 million Tm/year• Mississippi 260 million Tm/year
(Figure 6-2)
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•http://www.pbs.org/harriman/images/
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•http://www.pbs.org/harriman/images/
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walrus.wr.usgs.gov/elnino/coastal/ images/
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http://earthobservatory.nasa.gov
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•Winter
•Summer
Aerial dust
transport
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St Helens
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•http://geohazards.cr.usgs.gov/ •http://web.umr.edu/~rogersda
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•http://www.hihwnms.nos.noaa.gov/graphics/
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Biogenous Sediments
• Composed of planktonic organism remains– Calcareous skeletons (CaCO3)
– Siliceous skeletons (SiO2)
• Accumulation rate controlled by:– Primary productivity– Rate of dissolution
(Importance of fecal pellets)
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Figure 3.21a
Diatoms (siliceous high latitudes)Coccololithospheres (calcareous – mid latitides)
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Figure 3.21b
Radiolarians (siliceous – low latitudes)
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Foraminifera (calcareous – all latitides)
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Pteropods (calcareous – all latitudes)•http://www.mbari.org/expeditions/
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Dissolution Biogenous Particles
• Silica– Ocean is UNDERSATURATED with silica– Dissolution highest in surface waters
• Low Pressure• High Temperature
Accumulation in sediments occurs in:- Areas of very high productivity
- Poles and upwelling zones (diatoms)- Tropics (Radiolarians)
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Dissolution Biogenous Particles
• Carbonates• Foraminifera (Calcite) – less soluble• Pteropods (Aragonite) – More soluble
– Dissolution is highest in Deep Waters • High pressure • Low temperatures
• Low pH (high C02)
Carbonate Compensation Depth (CCD)
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Carbonate Compensation Depth
•CCD varies with Latitude
•CCD varies between Oceans
•North Pacific: 1000m
•South Pacific: 2500m
•Atlantic: 4000m
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Carbonate Compensation Depth
• New Deep Waters have low CO2
conc.
• Old Deep Waters have high CO2 conc.– Animal respiration– Decomposer activities
Pacific Deep Waters are older than Atlantic Deep Waters
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Global Thermohaline Circulation
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Carbonate Compensation Depth
& Greenhouse Effect?
• CO2 atmosphere, seawater & sediments are interrelated!
• Will increase in atmospheric CO2 cause increase in dissolved seawater CO2?
• Consequences of a shallow CCD? • Release into atmosphere of dissolved carbonate
sediments?
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Hydrogenous Sediments
• Lower concentrations than Lithogenous and Biogenous sediments
• Ocean water usually is UNDERSATURATED, but..– Hydrothermal Vent Minerals (metal rich sedim.)
– Manganese Nodules (areas of low sedimentation)
– Carbonate banks - CaCO3 precipitates at:
•High Temperature•Low Pressure
•High pH (low CO2)– Caused by high productivity - photosynthesis
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Bahamian Bank
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Carbonate Sediments
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Figure 3.23
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Chicxulub crater
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End
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