ocean sediments. importance of sediments economic value –oil, fossil fuels –salt &...
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Ocean Sediments
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
Sediment Thickness
Topographic profiles
Law of Superposition
Younger sediments over Old sediments
YOUNG----------------------
OLD
Sediment Classification
• By Grain Size• By Origin
Sediment Classification
• Grain Size– Clay <4 μm– Silt 4-62 μm– Sand 62-2000 μm– Gravel >2000 μm
Table 3.1
Basic Sediment Transport(READ CC4)
Sediment Sorting
Well-sorted sediments are those of similar size class
– Beach: well sorted (far from source)– Glacier: not sorted (close to source)
Sediment AngularitySediment weathering during transport
induces loss in angularity
– Angular grains (close to source)– Rounded grains (far from source)
Sediment Classification
• Origin– Lithogenous or Terrigenous (~75%)– Biogenous (~20%)– Hydrogenous– Cosmogenous
Lithogenous Sediments
• Fragments of rocks broken, weathered and eroded form lithogenous sediments
Frost Wedging http://images.google.com
www.naturalphotos.com
Wind & Rain erosion
Lithogenous Sediments
• Transport of sediments by:– Rivers– Glaciers– Waves– Wind– Landslides– Humans
www.southalabama.edu http://earthobservatory.nasa.gov
Sediment Discharge by Rivers
• Ganges: 1700 million Tm/year• Amazon:900 million Tm/year• Mississippi 260 million Tm/year
(Figure 6-2)
•http://www.pbs.org/harriman/images/
•http://www.pbs.org/harriman/images/
walrus.wr.usgs.gov/elnino/coastal/ images/
http://earthobservatory.nasa.gov
•Winter
•Summer
Aerial dust
transport
St Helens
•http://geohazards.cr.usgs.gov/ •http://web.umr.edu/~rogersda
•http://www.hihwnms.nos.noaa.gov/graphics/
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)
Figure 3.21a
Diatoms (siliceous high latitudes)Coccololithospheres (calcareous – mid latitides)
Figure 3.21b
Radiolarians (siliceous – low latitudes)
Foraminifera (calcareous – all latitides)
Pteropods (calcareous – all latitudes)•http://www.mbari.org/expeditions/
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)
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)
Carbonate Compensation Depth
•CCD varies with Latitude
•CCD varies between Oceans
•North Pacific: 1000m
•South Pacific: 2500m
•Atlantic: 4000m
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
Global Thermohaline Circulation
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?
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
Bahamian Bank
Carbonate Sediments
Figure 3.23
Chicxulub crater
End