Ocean Sediments Importance of Sediments Economic Value Oil

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 Silt Sand Gravel <4 μm 4 -62 μm 62 -2000 μm >2000 μm

Table 3. 1

Basic Sediment Transport (READ CC 4)

Sediment Sorting Well-sorted sediments are those of similar size class – Beach: well sorted (far from source) – Glacier: not sorted (close to source)

Sediment Angularity Sediment 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

Wind & Rain erosion www. naturalphotos. com

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

Aerial dust transport • Winter • Summer

St Helens

• http: //geohazards. cr. usgs. gov/ • http: //web. umr. edu/~rogersda

• http: //www. hihwnms. noaa. gov/graphics/

Biogenous Sediments • Composed of planktonic organism remains – Calcareous skeletons (Ca. CO 3) – Siliceous skeletons (Si. O 2) • Accumulation rate controlled by: – Primary productivity – Rate of dissolution (Importance of fecal pellets)

Figure 3. 21 a Diatoms (siliceous high latitudes) Coccololithospheres (calcareous – mid latitides)

Figure 3. 21 b 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 p. H (high C 02) Carbonate Compensation Depth (CCD)

Carbonate Compensation Depth • CCD varies with Latitude • CCD varies between Oceans • North Pacific: 1000 m • South Pacific: 2500 m • Atlantic: 4000 m

Carbonate Compensation Depth • New Deep Waters have low CO 2 conc. • Old Deep Waters have high CO 2 conc. – Animal respiration – Decomposer activities Pacific Deep Waters are older than Atlantic Deep Waters

Global Thermohaline Circulation

Carbonate Compensation Depth & Greenhouse Effect? • CO 2 atmosphere, seawater & sediments are interrelated! • Will increase in atmospheric CO 2 cause increase in dissolved seawater CO 2? • 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 - Ca. CO 3 precipitates at: • High Temperature • Low Pressure • High p. H (low CO 2) – Caused by high productivity - photosynthesis

Bahamian Bank

Carbonate Sediments

Figure 3. 23

Chicxulub crater

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