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© 2011 Pearson Education, Inc. CHAPTER 4 Marine Sediments
© 2011 Pearson Education, Inc. Chapter Overview Marine sediments contain a record of Earth history. Marine sediments provide a variety of important resources. Marine sediments have a variety of origins.
© 2011 Pearson Education, Inc. Marine Sediments Eroded rock particles and fragments –Transported to ocean Deposit by settling through water column Oceanographers decipher Earth history through studying sediments.
© 2011 Pearson Education, Inc. Paleoceanography and Marine Sediments Paleoceanography – study of how ocean, atmosphere, and land interactions have produced changes in ocean chemistry, circulation, biology, and climate –Marine sediments provide clues to past changes.
© 2011 Pearson Education, Inc. Marine Sediment Classification Classified by origin Lithogenous – derived from land Biogenous – derived from organisms Hydrogenous or Authigenic – derived from water Cosmogenous – derived from outer space
© 2011 Pearson Education, Inc. Marine Sediments
© 2011 Pearson Education, Inc. Lithogenous Sediments Eroded rock fragments from land Also called terrigenous Reflect composition of rock from which derived Produced by weathering –Breaking of rocks into smaller pieces
© 2011 Pearson Education, Inc. Lithogenous Sediments Small particles eroded and transported Carried to ocean –Streams –Wind –Glaciers –Gravity Greatest quantity around continental margins
© 2011 Pearson Education, Inc. Lighogenous Sediment Transport
© 2011 Pearson Education, Inc. Lithogenous Sediments Reflect composition of rock from which derived Coarser sediments closer to shore Finer sediments farther from shore Mainly mineral quartz (SiO 2 )
© 2011 Pearson Education, Inc. Lithogenous Quartz and Wind Transport
© 2011 Pearson Education, Inc. Grain Size Proportional to energy of transportation and deposition
© 2011 Pearson Education, Inc. Sediment Texture Grain size sorting –Indication of selectivity of transportation and deposition processes Textural maturity –Increasing maturity if Clay content decreases Sorting increases Non-quartz minerals decrease Grains are more rounded (abraded)
© 2011 Pearson Education, Inc. Sediment Distribution Neritic –Shallow-water deposits –Close to land –Dominantly lithogenous –Typically deposited quickly Pelagic –Deeper-water deposits –Finer-grained sediments –Deposited slowly
© 2011 Pearson Education, Inc. Neritic Lithogenous Sediments Beach deposits –Mainly wave-deposited quartz-rich sands Continental shelf deposits –Relict sediments Turbidite deposits –Graded bedding Glacial deposits –High latitude continental shelf –Currently forming by ice rafting
© 2011 Pearson Education, Inc. Pelagic Deposits Fine-grained material Accumulates slowly on deep ocean floor Pelagic lithogenous sediment from –Volcanic ash (volcanic eruptions) –Wind-blown dust –Fine-grained material transported by deep ocean currents
© 2011 Pearson Education, Inc. Pelagic Deposits Abyssal Clay –At least 70% clay sized particles from continents –Red from oxidized iron (Fe) –Abundant if other sediments absent
© 2011 Pearson Education, Inc. Biogenous Sediment Hard remains of once-living organisms Two major types: –Macroscopic Visible to naked eye Shells, bones, teeth –Microscopic Tiny shells or tests Biogenic ooze Mainly algae and protozoans
© 2011 Pearson Education, Inc. Biogenous Sediment Composition Two most common chemical compounds: –Calcium carbonate (CaCO 3 ) – Silica (SiO 2 or SiO 2 ·nH 2 O)
© 2011 Pearson Education, Inc. Silica in Biogenous Sediments Diatoms –Photosynthetic algae –Diatomaceous earth Radiolarians –Protozoans –Use external food
© 2011 Pearson Education, Inc. Silica in Biogenous Sediments Tests from diatoms and radiolarians generate siliceous ooze. Siliceous ooze lithifies into diatomaceous earth.
© 2011 Pearson Education, Inc. Calcium Carbonate in Biogenic Sediments Coccolithophores –Also called nannoplankton –Photosynthetic algae –Coccoliths – individual plates from dead organism –Rock chalk Lithified coccolith- rich ooze
© 2011 Pearson Education, Inc. Calcium Carbonate in Biogenic Sediments Foraminifera –Protozoans –Use external food –Calcareous ooze
© 2011 Pearson Education, Inc. Distribution of Biogenous Sediments Depends on three processes: –Productivity –Destruction –Dilution
© 2011 Pearson Education, Inc. Neritic Deposits Dominated by lithogenous sediment, may contain biogenous sediment Carbonate Deposits –Carbonate minerals containing CO 3 –Marine carbonates primarily limestone – CaCO 3 –Most limestones contain fossil shells Suggests biogenous origin –Ancient marine carbonates constitute 25% of all sedimentary rocks on Earth.
© 2011 Pearson Education, Inc. Carbonate Deposits Stromatolites –Fine layers of carbonate –Warm, shallow-ocean, high salinity –Cyanobacteria
© 2011 Pearson Education, Inc. Calcareous Ooze and the CCD CCD – Calcite compensation depth –Depth where CaCO 3 readily dissolves –Rate of supply = rate at which the shells dissolve Warm, shallow ocean saturated with calcium carbonate Cool, deep ocean undersaturated with calcium carbonate –Lysocline – depth at which a significant amount of CaCO 3 begins to dissolve rapidly
© 2011 Pearson Education, Inc. Calcareous Ooze and the CCD
© 2011 Pearson Education, Inc. Calcareous Ooze and the CCD Scarce calcareous ooze below 5000 meters (16,400 feet) in modern ocean Ancient calcareous oozes at greater depths if moved by sea floor spreading
© 2011 Pearson Education, Inc. Sea Floor Spreading and Sediment Accumulation
© 2011 Pearson Education, Inc. Distribution of Modern Calcium Carbonate Sediments
© 2011 Pearson Education, Inc. Hydrogenous Marine Sediments Minerals precipitate directly from seawater –Manganese nodules –Phosphates –Carbonates –Metal sulfides Small proportion of marine sediments Distributed in diverse environments
© 2011 Pearson Education, Inc. Manganese Nodules Fist-sized lumps of manganese, iron, and other metals Very slow accumulation rates Many commercial uses Unsure why they are not buried by seafloor sediments
© 2011 Pearson Education, Inc. Phosphates and Carbonates Phosphates –Phosphorus-bearing –Occur beneath areas in surface ocean of very high biological productivity –Economically useful as fertilizer Carbonates –Aragonite and calcite –Oolites
© 2011 Pearson Education, Inc. Metal Sulfides Metal sulfides –Contain: Iron Nickel Copper Zinc Silver Other metals –Associated with hydrothermal vents
© 2011 Pearson Education, Inc. Evaporites –Minerals that form when seawater evaporates –Restricted open ocean circulation –High evaporation rates –Halite (common table salt) and gypsum
© 2011 Pearson Education, Inc. Cosmogenous Marine Sediments Macroscopic meteor debris Microscopic iron- nickel and silicate spherules (small globular masses) –Tektites –Space dust Overall, insignificant proportion of marine sediments
© 2011 Pearson Education, Inc. Marine Sediment Mixtures Usually mixture of different sediment types Typically one sediment type dominates in different areas of the sea floor.
© 2011 Pearson Education, Inc. Pelagic and Neritic Sediment Distribution Neritic sediments cover about ¼ of the sea floor. Pelagic sediments cover about ¾ of the sea floor.
© 2011 Pearson Education, Inc. Pelagic and Neritic Sediment Distribution Distribution controlled by –Proximity to sources of lithogenous sediments –Productivity of microscopic marine organisms –Depth of water –Sea floor features
© 2011 Pearson Education, Inc. Pelagic Sediment Types
© 2011 Pearson Education, Inc. Sea Floor Sediments Represent Surface Ocean Conditions Microscopic tests sink slowly from surface ocean to sea floor (10-50 years) Tests could be moved horizontally Most biogenous tests clump together in fecal pellets –Fecal pellets large enough to sink quickly (10-15 days)
© 2011 Pearson Education, Inc. Worldwide Marine Sediment Thickness
© 2011 Pearson Education, Inc. Resources from Marine Sediments Energy resources –Petroleum Mainly from continental shelves –Gas hydrates Sand and gravel (including tin, gold, and so on) Evaporative salts Phosphorite Manganese nodules and crusts
© 2011 Pearson Education, Inc. Mining Sea Salt
© 2011 Pearson Education, Inc. Distribution of Manganese Nodules
© 2011 Pearson Education, Inc. End of CHAPTER 4 Marine Sediments
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