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Marine Sediments

Marine Sediments. Chap 5. Lithogenous / Terrigenous Sediment. Derived from land Origin from weathering/erosion Mainly quartz (SiO 2 ) – resistant to abrasion Main constituent of continental shelf sediment can also be found in deep ocean. Sediment Texture.

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Marine Sediments

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  1. Marine Sediments Chap 5

  2. Lithogenous/Terrigenous Sediment • Derived from land • Origin from weathering/erosion • Mainly quartz (SiO2) – resistant to abrasion • Main constituent of continental shelf sediment can also be found in deep ocean

  3. Sediment Texture

  4. Sediment Erosion, Transportation, Deposition

  5. Sediment Maturity

  6. Neretic Deposits • found along continetal margins and islands – mainly lithogenous • Beach deposits – mainly quartz rich sands – but what ever is available • Continental Shelf deposits – carried by rivers • Turbiditedeposites due to underwater avalanches – from turbidity currents –show graded bedding • Glacial Deposits – grinding by ice and trapped in glacial ice

  7. Pelagic Deposits • Fine grained material that accumulates on the ocean floor. • Abyssal Clay >70% clay sized particles from continent- due to lack of other particles • Contain oxidized iron making them red-brown or buff

  8. Biogenous Sediment • Derived from hard parts of once-living organisms – algae and protozoans. • Macroscopic can be seen with eyes • Microscopic too small to be seen with unaided eye • Microscopic organisms produce small shells called tests and accumulates in the deep ocean to form ooze. • video

  9. Composition • Calcium Carbonate - CaCO3 (makes mineral calcite) • Silica SiO2.

  10. Silica forms Siliceous Ooze • Silica biogenous ooze made mainly from planktonic algae called diatoms and a protozoans called radiolarians • Diatomaceous earth used in filters, abrasives, absorbents, glass. Also diatoms have a droplet of oil in them that have accumulated into petroleum deposits (ex: off California) • Silica dissolves is seawater and will only accumulate silica ooze where there is high production.

  11. Calcium Carbonate forms Calcareous Ooze • Foraminiferans are protozoans with porous CaCO3shells . • Coccolithophores are microalgae that are 10-100 times smaller than diatoms, they are called nanoplankton. They have CaCO3 plates (cocoliths) that make up their shell. These decompose to form cocolith-rich CaCO3 ooze that can later lithify to form chalk and limestone. Dover

  12. Stromatolites • Lobate structures made of layers of carbonate from cyanobacteria at particular shallow depth.

  13. Calcite Compensation Depth -CCD • CaCO3 is saturate in warm shallow waters and can form sediments. • At deeper cooler waters CaCO3 is not saturated so does not form deposits after a certain depth – CCD. • Average CCD is 4500 m • Below 5000 m, calcareous ooze not usually found unless it was made at a higher depth and then covered before it’s present depth. lysocline

  14. Hydrogenous Sediment • Derived from seawater • Chemical reaction cause minerals to precipitate out of sea water usualy when there is a temperature or pressure change

  15. Manganese nodules • 5-20 cm lumps of Mn, Fe and other metals • Found on deep ocean floor 100/m2

  16. Phosphates • Phosphate bearing compounds found on rocks and nodules on the continental shelf and banks at depths < 1000m. • Used as fertilizer and other agricultural proposes

  17. Carbonates • Aragonite and calcite are the two most important carbonate sediments • Aragonite has a different crystalline structure and is less stable and changes into calcite over time. • Biogenous in origin, aragonite crstals can form hydrogenously by precipitating directly from seawater. • Oolites are small calcite spheres that form in shallow tropical waters with high CaCO3 concentrations.

  18. Metal Sulfides • Made by black smokers at hydrothermal vents • Iron, nickel, copper, zinc silver and other metals.

  19. Evaporites minerals • In restricted circulation areas where evaporation is high – seawater becomes saturated with minerals and the minerals precipitate out. • Collectively called salts, some evaporites may taste salty because of NaCl and other do not like calcium sulfate minerals anhydrite (CaSO4) amd gypsum (and H20)

  20. Cosmogenous Sediment • Extraterrestrial origin • Spherules = microscopic, usually once molten basalt from impact events, forms tektites • Although 90% of tektites are destroyed by frictional heating with the atmosphere, 300,000 metric tons/year reach Earth • Meteor = macroscopic, impact material made of rock (chondrites) or iron and nickel (irons) settle out around impact sites.

  21. % of Pelagic Sediments • 47.7% Carbonate • 14.2% Siliceous • 38.1% Abyssal

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