Ocean Sediments Origin and Distribution

Continental Margins and Ocean Basins Review from last week Shape of ocean floorShape of ocean floor Continental MarginsContinental Margins – Active Margins – Passive Margins Ocean BasinsOcean Basins

Marine Sediments Most ocean floor covered by marine sediments Most ocean floor covered by marine sediments Sediment thickness is thinnest at mid-ocean ridge and thickest at continental marginsSediment thickness is thinnest at mid-ocean ridge and thickest 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”

LithogenousSediments Lithogenous Sediments Composed mostly of quartz sand and clayComposed mostly of quartz sand and clay Derived from the weathering of rocksDerived from the weathering of rocks – continents or volcanic 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 floor Covers about 45% of ocean floor

Sediment Distribution - Terrigenous

Terigenous Sediment - Examples Red Clays 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 Mt. Pinatubo Mississippi River Sahara Desert

Biogenous Sediment Biogenic ooze – greater than 30% biogenous sedimentBiogenic ooze – greater than 30% biogenous sediment Composed mostly of hard skeletal parts of once-living organismsComposed mostly of hard skeletal parts of once-living organisms Two main compositions of hard parts: Two main compositions of hard parts: 1. Calcium Carbonate (CaCO 3 ) a)Coccolithophore (phytoplankton) b)Foraminifera (zooplankton) 2. Silica (SiO 2 ) a) Diatoms (phytoplankton) a) Diatoms (phytoplankton) b) Radiolarian (zooplankton) b) Radiolarian (zooplankton)

Sediment Distribution - Biogenous Calcareous and Siliceous Oozes Calcareous and Siliceous Oozes

Biogenous – Calcareous Examples Composed of CaCO 3Composed of CaCO 3 Widespread in relatively shallow areasWidespread in relatively shallow areas Coccolithophore Foraminifera

Biogenous – Calcareous oozes Cover greater than 50% of ocean floorCover greater than 50% of ocean floor Distribution controlled by dissolution processes Distribution controlled by dissolution processes Cold bottom waters undersaturated with respect to CaCO 3 Cold bottom waters undersaturated with respect to CaCO 3 – slightly acidic ( CO 2 ) – readily dissolves CaCO 3 Calcium Carbonate Compensation Depth (CCD) – the depth at which the rate of accumulation of calcareous sediments equals the rate of dissolutionCalcium 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 Pacific Ocean – 500-1,500 m Atlantic Ocean – 4,000 m Atlantic Ocean – 4,000 m CaCO 3 is found

Sediment Distribution – Calcareous/Siliceous

Biogenous – Siliceous Ooze Examples Diatoms Radiolarians Composed of SiO 2 Composed of SiO 2 Base of food chain Base of food chain

Biogenous – Siliceous Ooze Covers 15% of ocean floor Covers 15% of ocean floor Diatoms common at higher latitudes Radiolarians common at equatorial regions Radiolarians 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 particles Dissolve more slowly than calcareous particles

Siliceous Oozes

Sediment Distribution - Hydrogenous

Hydrogenous Sediments Produced by chemical processes in seawaterProduced by chemical processes in seawater Sediment precipitates from waterSediment precipitates from water Oolites – occur in surface waters supersaturated in CaCO 3 Oolites – occur in surface waters supersaturated in CaCO 3 Manganese Nodules – manganese, iron deposits accumulate in areas of low sedimentationManganese Nodules – manganese, iron deposits accumulate in areas of low sedimentation Evaporites – “salt precipitates” form in areas of high evaporationEvaporites – “salt precipitates” form in areas of high evaporation Some Examples: Some Examples:

Hydrogenous - Examples Manganese Nodules Sea salt Oolitic sand

Cosmogenous – microtektites Tektites – result from collisions with micrometeorsTektites – 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 Sediments derived from extraterrestrial material (micrometeorites)Sediments derived from extraterrestrial material (micrometeorites) Microtektites Widespread but not abundant Widespread but not abundant

Sediment Distribution