Ocean Sediments

1
Ocean Sediments

• Origin and Distribution

2
Continental Margins and Ocean Basins

• Review from last week

• Shape of ocean floor

• Continental Margins
• Active Margins
• Passive Margins

• Ocean Basins

3
Marine Sediments

• Most ocean floor covered by marine sediments

• Sediment thickness is thinnest at mid-ocean ridge
  and thickest at continental margins

4
Types of Ocean Sediments

• Terrigenous rock-derived

• Biogenous life-derived

• Hydrogenous water-derived

• Cosmogenous cosmic-derived

5
Lithogenous Sediments

• Derived from the weathering of rocks
• continents or volcanic islands

• Transported by rivers, glaciers or wind

• Most deposited on continental margins

• Covers about 45 of ocean floor

• Composed mostly of quartz sand and clay

6
Sediment Distribution - Terrigenous
7
Terigenous Sediment - Examples
Mississippi River
Sahara Desert
Mt. Pinatubo

• Red Clays

• Sediment from rivers, dust, and volcanic ash

• Transported to deep ocean by winds and surface
  currents

• Common in deep oceans

• Accumulates 2 mm (1/8) every 1,000 years

8
Biogenous Sediment

• Biogenic ooze greater than 30 biogenous
  sediment

• Composed mostly of hard skeletal parts of
  once-living organisms

• Two main compositions of hard parts

• Calcium Carbonate (CaCO3)
• Coccolithophore (phytoplankton)
• Foraminifera (zooplankton)

2. Silica (SiO2) a) Diatoms (phytoplankton)
b) Radiolarian (zooplankton)
9
Sediment Distribution - Biogenous

• Calcareous and Siliceous Oozes

10
Biogenous Calcareous Examples
Foraminifera
Foraminifera

• Composed of CaCO3

• Widespread in relatively shallow areas

Coccolithophore
11
Biogenous Calcareous oozes

• Cover greater than 50 of ocean floor

• Distribution controlled by dissolution processes

• Calcium Carbonate Compensation Depth (CCD) the
  depth at which the rate of accumulation of
  calcareous sediments equals the rate of
  dissolution

• Pacific Ocean 500-1,500 m

CaCO3 is found

• Atlantic Ocean 4,000 m

12
Sediment Distribution Calcareous/Siliceous
13
Biogenous Siliceous Ooze Examples
Radiolarians

• Composed of SiO2

• Base of food chain

Diatoms
14
Biogenous Siliceous Ooze

• Covers 15 of ocean floor

• Distribution - areas of high productivity (zones
  of upwelling)

• Dissolve more slowly than calcareous particles

• Diatoms common at higher latitudes

• Radiolarians common at equatorial regions

15
Siliceous Oozes
16
Sediment Distribution - Hydrogenous
17
Hydrogenous Sediments

• Produced by chemical processes in seawater
• Sediment precipitates from water

• Some Examples

• Oolites occur in surface waters supersaturated
  in CaCO3

• Manganese Nodules manganese, iron deposits
  accumulate in areas of low sedimentation

• Evaporites salt precipitates form in areas of
  high evaporation

18
Hydrogenous - Examples
Sea salt
Manganese Nodules
Oolitic sand
19
Cosmogenous microtektites
Microtektites

• Sediments derived from extraterrestrial material
  (micrometeorites)

• Tektites result from collisions with
  micrometeors
• Fragments of Earths crust melt and spray outward
  from impact crater
• Crustal material re-melts as it falls back and
  forms glassy tektites

• Widespread but not abundant

20
Sediment Distribution