Pakistan EarthquakePakistan Earthquake – – 7.6 M7.6 MagnitudeagnitudeOctober 8, 2005 (8:50 p.m. local time)

Ocean SedimentsOcean Sediments

Origin and DistributionOrigin and Distribution

Marine SedimentsMarine Sediments

• Most ocean floor covered by marine sedimentsMost ocean floor covered by marine sediments• Sediment thickness is thinnest at mid-ocean ridge and Sediment thickness is thinnest at mid-ocean ridge and

thickest at continental marginsthickest at continental margins

Types of Ocean Sediments

• Terrigenous – “rock-derived”Terrigenous – “rock-derived”

• Biogenous – “life-derived”Biogenous – “life-derived”

• Cosmogenous – “cosmic-derived”Cosmogenous – “cosmic-derived”

• Hydrogenous – “water-derived”Hydrogenous – “water-derived”

Sediment Distribution - Sediment Distribution - LithogenousLithogenous

LithogenousLithogenous SedimentsSediments

• Composed mostly of quartz sand and clayComposed mostly of quartz sand and clay

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

• Most deposited on continental marginsMost deposited on continental margins• Transported by rivers, glaciers or windTransported by rivers, glaciers or wind

• Covers about 45% of ocean floorCovers about 45% of ocean floor

Lithogenous Sediment - Lithogenous Sediment - ExamplesExamples

• Red ClaysRed Clays– Terrigenous from rivers, dust, and Terrigenous from rivers, dust, and

volcanic ashvolcanic ash

– Transported to deep ocean by winds Transported to deep ocean by winds and surface currentsand surface currents

– Common in deep oceansCommon in deep oceans

– Accumulates 2 mm (1/8”) every 1,000 yearsAccumulates 2 mm (1/8”) every 1,000 years

Mt. Pinatubo Mississippi River Sahara Desert

Sediment Distribution - Sediment Distribution - BiogenousBiogenous

• Calcareous and Siliceous OozesCalcareous and Siliceous Oozes

Biogenous SedimentBiogenous Sediment

• Biogenic ooze – greater than 30% biogenous sedimentBiogenic ooze – greater than 30% biogenous sediment

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

• Two main compositions of hard parts:Two main compositions of hard parts:

1.1. Calcium Carbonate (CaCOCalcium Carbonate (CaCO33))a)a)Coccolithophore (phytoplankton)Coccolithophore (phytoplankton)b)b)Foraminifera (zooplankton)Foraminifera (zooplankton)

2. Silica (SiO2. Silica (SiO22) ) a) Diatoms (phytoplankton)a) Diatoms (phytoplankton) b) Radiolarian (zooplankton)b) Radiolarian (zooplankton)

Biogenous – Calcareous ExamplesBiogenous – Calcareous Examples

• Composed of CaCOComposed of CaCO33

• Widespread in Widespread in relatively shallow relatively shallow areasareas Coccolithophore

Foraminifera

Foraminifera

Biogenous – Biogenous – Siliceous ExamplesSiliceous Examples

Diatoms

Radiolarians

• Composed of SiOComposed of SiO22

• Base of food chainBase of food chain

Sediment DistributionSediment Distribution – – Calcareous/SiliceousCalcareous/Siliceous

Biogenous – Biogenous – Calcareous oozesCalcareous oozes• Cover greater than 50% of ocean floorCover greater than 50% of ocean floor

• Distribution controlled by dissolution processesDistribution controlled by dissolution processes

• Cold bottom waters undersaturated with respect to CaCOCold bottom waters undersaturated with respect to CaCO33

– slightly acidic ( COslightly acidic ( CO22))– readily dissolves CaCOreadily dissolves CaCO33

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

• Pacific Ocean – 500-1,500 mPacific Ocean – 500-1,500 m • Atlantic Ocean – 4,000 mAtlantic Ocean – 4,000 m

CaCOCaCO33 is found is found

Biogenous – Siliceous OozeBiogenous – Siliceous Ooze

• Covers 15% of ocean floorCovers 15% of ocean floor

• Diatoms common at higher latitudesDiatoms common at higher latitudes• Radiolarians common at equatorial regionsRadiolarians common at equatorial regions

• Distribution - areas of high productivity (zones of upwelling)Distribution - areas of high productivity (zones of upwelling)• Dissolve more slowly than calcareous particlesDissolve more slowly than calcareous particles

Siliceous OozesSiliceous Oozes

Sediment Distribution - Sediment Distribution - HydrogenousHydrogenous

Hydrogenous SedimentsHydrogenous Sediments

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

• OolitesOolites – occur in surface waters supersaturated in CaCO – occur in surface waters supersaturated in CaCO33

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

• EvaporitesEvaporites – “salt precipitates” form in areas of high – “salt precipitates” form in areas of high evaporationevaporation

• Some Examples:Some Examples:

Hydrogenous - ExamplesHydrogenous - Examples

Manganese Nodules

Sea salt

Oolitic sand

Cosmogenous – microtektitesCosmogenous – microtektites

• Tektites – result from collisions with micrometeorsTektites – result from collisions with micrometeors– Fragments of Earth’s crust melt and spray outward from impact craterFragments of Earth’s crust melt and spray outward from impact crater– Crustal material re-melts as it falls back and forms glassy tektitesCrustal material re-melts as it falls back and forms glassy tektites

• Sediments derived from extraterrestrial material Sediments derived from extraterrestrial material (micrometeorites)(micrometeorites)

Microtektites

• Widespread but not abundantWidespread but not abundant