CHAPTER 4: Marine Sediments

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CHAPTER 4 Marine Sediments
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Fig. CO-4
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Marine sediments
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• Eroded rock particles and fragments
• Transported to or produced in the ocean
• Deposit by settling through water column
• Oceanographers decipher Earth history through
  studying sediments

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Classification of marine sediments
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• Classified by origin
• Lithogenous (derived from land)
• Biogenous (derived from organisms)
• Hydrogenous (derived from water)
• Cosmogenous (derived from outer space)

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Lithogenous sediments
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• Eroded rock fragments from land (origin)
• Transported from land by
• Water (e.g., river transported sediment)
• Wind (e.g., windblown dust)
• Ice (e.g., ice-rafted rocks)
• Gravity (e.g., turbidity currents)

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BY PERCENT
Transport Mechanism
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Lithogenous sediments
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Fig. 4.5
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Lithogenous sediments
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• Most lithogenous sediments at continental margins
• Coarser sediments closer to shore
• Finer sediments farther from shore WHY?
• Mainly mineral quartz (SiO2)

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distance rate x time d rt t d/r 4km/
2.5cm/sec 4,000m/ 2.5cm/sec 4,000m(100cm.m)/
2.5cm/sec 400,000cm / 2.5cm/sec 160,000sec/
24hr/day x 3600sec/hr 160,000sec/
86,400sec/day 1.85 days
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Clay sinks 10,000 times slower than sank, so 1.8
days x 10,000 (or 104) 18,000 days 18,000 days
49.3 years 365 days/year
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Smaller particles have a larger SA/Vol.
ratio, increasing the frictional drag (sinking
rates) and making small particles sink more
slowly than large particles
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Relationship of fine-grained quartz and
prevailing winds
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Fig. 4.6b
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Brazos River Meets the Gulf of Mexico
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• FLOCCULATION - THE JOINING TOGETHER OF
  ELECTRICALLY CHARGED CLAY PARTICLES WHICH SETTLE
  MORE RAPIDLY THAN INDIVIDUAL ONES

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Brazos River
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04_06t
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Distribution of sediments
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• Neritic
• Shallow water deposits
• Close to land
• Dominantly lithogenous
• Typically deposited quickly
• Pelagic
• Deeper water deposits
• Finer-grained sediments
• Deposited slowly
• UNDERSTANDING THE PROCESSES WOULD ALLOW YOU TO
  GENERATE THIS TABLE YOURSELVES

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Neritic lithogenous sediments
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• Beach deposits
• Mainly wave-deposited quartz-rich sands
• Continental shelf deposits
• Relict sediments
• Turbidite deposits
• Glacial deposits
• High latitude continental shelf

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Pelagic lithogenous sediments
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• Sources of fine material
• Volcanic ash (volcanic eruptions)
• Wind-blown dust
• Fine grained material transported by deep ocean
  currents
• Abyssal clay (red clay)
• Oxidized iron
• Abundant if other sediments absent

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Biogenous marine sediments
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• Hard remains of once-living organisms
• Shells, bones, teeth
• Macroscopic (large remains)
• Microscopic (small remains)
• Tiny shells or tests settle through water column
• Biogenic ooze (30 or more tests)
• Mainly algae and protozoans

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Biogenous marine sediments
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• Commonly either calcium carbonate (CaCO3) or
  silica (SiO2 or SiO2.nH2O)
• Usually planktonic (free-floating)

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Silica in biogenic sediments
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• Diatoms (algae)
• Photosynthetic
• Diatomaceous earth

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Siliceous ooze
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• Seawater undersaturated with silica
• Siliceous ooze commonly associated with high
  biologic productivity in surface ocean

Fig. 4.12
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Calcium carbonate in biogenous sediments
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• Coccolithophores (algae)
• Photo-synthetic
• Coccoliths (nanno-plankton)

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White Cliffs of Dover
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Calcium carbonate in biogenous sediments
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• Foraminifera (protozoans)
• Use external food
• Calcareous ooze

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Living Foraminifera
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Distribution of biogenous sediments
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• Most common as pelagic deposits
• Factors controlling distribution
• Productivity
• Destruction (dissolution)

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Calcareous ooze and the CCD
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• Warm, shallow ocean saturated with calcium
  carbonate
• Cool, deep ocean undersaturated with calcium
  carbonate
• Lysocline--depth at which CaCO3 begins to
  dissolve rapidly
• Calcite compensation depth CCD--depth where CaCO3
  readily dissolves

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Calcareous ooze and the CCD
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Fig. 4.13

• Scarce calcareous ooze below 5000 m in modern
  ocean
• Ancient calcareous oozes at greater depths if
  moved by sea floor spreading

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Distribution of calcareous oozes in surface
sediments of modern seafloor
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Why in these places?
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Hydrogenous marine sediments
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• Minerals precipitate directly from seawater
• Manganese nodules
• Phosphates
• Carbonates
• Metal sulfides
• Small proportion of marine sediments
• Distributed in diverse environments

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Iron-Manganese nodules
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• Fist-sized lumps of manganese, iron, and other
  metals
• Very slow accumulation rates

Fig. 4.15a
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Manganese nodules
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Fig. 4.26
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Cosmogenous marine sediments
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• Macroscopic meteor debris
• Microscopic iron-nickel and silicate spherules
• Tektites
• Space dust
• Overall, insignificant proportion of marine
  sediments

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04_C
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Microtektites - extraterrestrial
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04_D
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04_E
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04_F
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Mixtures of marine sediments
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• Usually mixture of different sediment types
• For example, biogenic oozes can contain up to 70
  non-biogenic components
• Typically one sediment type dominates in
  different areas of the sea floor

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Distribution of neritic and pelagic marine
sediments
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Fig. 4.19
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04_T04
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1 m
.01 m
.001 m
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04_18
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