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Ocean Sediments

Ocean Sediments. Marine Science 2012. Sediment size, color, texture…. Sediments : particles of organic or inorganic matter than accumulate on the ocean floor. Size Classification. Most marine sediments are small: sands, silts, clays

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Ocean Sediments

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  1. Ocean Sediments Marine Science 2012

  2. Sediment size, color, texture… • Sediments: particles of organic or inorganic matter than accumulate on the ocean floor

  3. Size Classification • Most marine sediments are small: sands, silts, clays • The smaller the particle, the longer it can remain suspended • Larger particles require more energy to erode • However, clay requires more energy to erode than sand • Clay is more cohesive than sand

  4. Source Classification • Terrigenous/Lithogenous • Originate on land from erosion & volcanoes • Majority of sediment volume • Made of granite, quartz • Biogenous • Of biological origin • CaCO3 & Si from shells/skeletons of marine organisms

  5. Source Classification • Hydrogenous • Chemical reactions within seawater • Rxn cause minerals to precipitate • Particles settle to bottom • Most of these are called manganese nodules • composed of layers of metals such as manganese (Mn), iron (Fe), nickel (Ni), cobalt (Co) and copper (Cu) • Cosmogenous • Extraterrestrial origin (cosmic dust) • Most comes all at once • Ex: asteroid that caused the KT mass extinction

  6. Continental-Shelf Sediments • Continental shelf- close to the coast line • Mix of lithogenous & biogenous • Tides, waves, & currents influence sedimentation • Larger particles settle in high wave zone • Smaller particles settle further away from coast due to less wave impact • Sedimentation rate is more rapid than deep ocean rate • Rivers transport sedimentation to estuaries

  7. Deep Ocean Basin Sediments • High in Biogenous material • Less lithogenous sediment (due to far away from land) • Oozes • Deep ocean sediment that consist of 30% or more biogenous sediment • Lack of lithogenous sediment available • Composed primarily of plankton • Siliceous & Calcareous shells of plankton • Location: Dominate away from continental slope • Accumulate slowly

  8. Why aren’t Calcarous oozes everywhere? • What happens when you add Carbon Dioxide to water? • Carbonic Acid • Dissolves the calcium carbonate • About 3,000 m below sea level • Cold water holds more CO2 • CO2 levels are higher Carbonate Compensation Depth • Tend to see more silicon oozes below the CCD level (shells dissolves slower)

  9. Studying Sediments • Clamshell sampler - Scoops up top layer of material • Deep water cameras & Core samples • Usefulness of cores? • Evidence for tectonics • Evolutionary history • Climate history

  10. The Ocean Drilling Program • Prepare cores on boats • Arrive in 30 foot sections • ½ to archives • ½ to labs • Tests run • Density, molecular composition • Age of sediments using isotopes • Past temperatures • Pollen grains analyzed

  11. Sediments as Historical Records • Stratigraphy • The analysis of layered sediments • Paleoceanography • Study of the ocean’s past • Use cores to track ice ages, past life, ocean circulation, etc.

  12. Economic Importance of Marine Sediments • Oil & natural gas • 1/3 petroleum & ¼ natural gas come from continental shelf • Dissolved minerals from hot vents • Salts for mining • Building materials • Sand & gravel • Construction industry • Mn nodules (future)

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