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 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 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

Wind & Rain erosion

Lithogenous Sediments Transport of sediments by: –Rivers –Glaciers –Waves –Wind –Landslides –Humans

Sediment Discharge by Rivers Ganges:1700 million Tm/year Amazon:900 million Tm/year Mississippi260 million Tm/year (Figure 6-2)

walrus.wr.usgs.gov/elnino/coastal/ images/

Winter Summer Aerial dust transport

St Helens

Biogenous Sediments Composed of planktonic organism remains –Calcareous skeletons (CaCO 3 ) –Siliceous skeletons (SiO 2 ) 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)

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 C0 2 ) 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 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 - CaCO 3 precipitates at: High Temperature Low Pressure High pH (low CO 2 ) –Caused by high productivity - photosynthesis

Bahamian Bank

Carbonate Sediments

Figure 3.23

Chicxulub crater

End