Ocean Sediments
Origin and Distribution
Continental Margins and Ocean Basins
• Review from last week
• Shape of ocean floor
• Continental Margins
– Active Margins
– Passive Margins
• Ocean Basins
Marine Sediments
• Most ocean floor covered by marine sediments
• Sediment thickness is thinnest at mid-ocean ridge and thickest
at continental margins
Types of Ocean Sediments
• Terrigenous – “rock-derived”
• Biogenous – “life-derived”
• Hydrogenous – “water-derived”
• Cosmogenous – “cosmic-derived”
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
Sediment Distribution -
Terrigenous
Terigenous Sediment Mt. Pinatubo
Mississippi River
Examples
Sahara Desert
• 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
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:
1. Calcium Carbonate (CaCO3)
a)Coccolithophore (phytoplankton)
b)Foraminifera (zooplankton)
2. Silica (SiO2)
a) Diatoms (phytoplankton)
b) Radiolarian (zooplankton)
Sediment Distribution -
• Calcareous and Siliceous Oozes
Biogenous
Biogenous – Calcareous Examples
Foraminifera
Foraminifera
• Composed of CaCO3
• Widespread in relatively
shallow areas
Coccolithophore
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
• Cold bottom waters undersaturated with respect to CaCO3
– slightly acidic ( CO2)
– readily dissolves CaCO3
• Pacific Ocean – 500-1,500 m
CaCO3 is found
• Atlantic Ocean – 4,000 m
Sediment Distribution –
Calcareous/Siliceous
Biogenous –
Siliceous Ooze Examples
Radiolarians
Diatoms
• Composed of SiO2
• Base of food chain
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
Siliceous Oozes
Sediment Distribution -
Hydrogenous
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
Hydrogenous - Examples
Sea salt
Manganese Nodules
Oolitic sand
Cosmogenous – microtektites
Microtektites
• Sediments derived from extraterrestrial material (micrometeorites)
• Tektites – result from collisions with micrometeors
– Fragments of Earth’s crust melt and spray outward from impact crater
– Crustal material re-melts as it falls back and forms glassy tektites
• Widespread but not abundant
Sediment Distribution