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