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CHAPTER 4: Marine Sediments

CHAPTER 4: Marine Sediments. S. Fig. CO-4. S. Marine sediments. 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. P. Classification of marine sediments.

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CHAPTER 4: Marine Sediments

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  1. CHAPTER 4: Marine Sediments S Fig. CO-4

  2. S Marine sediments • 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

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

  4. P Lithogenous sediments • 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)

  5. P BY PERCENT Transport Mechanism

  6. S

  7. S Lithogenous sediments Fig. 4.5

  8. P Lithogenous sediments • Most lithogenous sediments at continental margins • Coarser sediments closer to shore • Finer sediments farther from shore WHY? • Mainly mineral quartz (SiO2)

  9. P

  10. S 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

  11. S 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

  12. S Smaller particles have a larger SA/Vol. ratio, increasing the frictional drag (sinking rates) and making small particles sink more slowly than large particles

  13. S Relationship of fine-grained quartz and prevailing winds Fig. 4.6b

  14. 04_06t S

  15. S Brazos River Meets the Gulf of Mexico FLOCCULATION- THE JOINING TOGETHER OF ELECTRICALLY CHARGED CLAY PARTICLES WHICH SETTLE MORE RAPIDLY THAN INDIVIDUAL ONES

  16. S Brazos River

  17. S Distribution of sediments • Neritic(NEARSHORE - OVER CONT. SHELF) • Shallow water deposits • Close to land • Dominantly lithogenous • Typically deposited quickly • Pelagic(OPEN OCEAN - OFF CONT. SHELF) • Deeper water deposits • Finer-grained sediments • Deposited slowly

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

  19. S Pelagic lithogenous sediments • 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

  20. P Biogenous marine sediments • 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

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

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

  23. S Siliceous ooze • Seawater undersaturated with silica • Siliceous ooze commonly associated with high biologic productivity in surface ocean Fig. 4.12

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

  25. S White Cliffs of Dover

  26. P Calcium carbonate in biogenous sediments • Foraminifera (protozoans) • Use external food • Calcareous ooze

  27. Living Foraminifera S

  28. S Distribution of biogenous sediments • Most common as pelagic deposits • Factors controlling distribution • Productivity • Destruction (dissolution)

  29. P Calcareous ooze and the CCD • 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

  30. S Calcareous ooze and the CCD • Scarce calcareous ooze below 5000 m in modern ocean • Ancient calcareous oozes at greater depths if moved by sea floor spreading Fig. 4.13

  31. S Distribution of calcareous oozes in surface sediments of modern seafloor Why in these places?

  32. P Hydrogenous marine sediments • Minerals precipitate directly from seawater • Manganese nodules • Phosphates • Carbonates • Metal sulfides • Small proportion of marine sediments • Distributed in diverse environments

  33. P

  34. S Iron-Manganese nodules • Fist-sized lumps of manganese, iron, and other metals • Very slow accumulation rates Fig. 4.15a

  35. S

  36. Manganese nodules S Fig. 4.26

  37. P Cosmogenous marine sediments • Macroscopic meteor debris • Microscopic iron-nickel and silicate spherules • Tektites • Space dust • Overall, insignificant proportion of marine sediments

  38. 04_C S

  39. S Microtektites - extraterrestrial

  40. 04_D S

  41. 04_E S

  42. 04_F S

  43. P Mixtures of marine sediments • 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

  44. P Distribution of neritic and pelagic marine sediments Fig. 4.19

  45. 04_T04 P 1 m .01 m .001 m

  46. S

  47. S

  48. 04_18 P

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