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Chapter 4 Marine Sediments

Chapter 4 Marine Sediments. Essentials of Oceanography 7 th Edition. Ocean sediment. Various materials settle through the water column and accumulate on the ocean floor Layers represent a record of Earth history, including: Movement of tectonic plates Past changes in climate

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Chapter 4 Marine Sediments

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  1. Chapter 4Marine Sediments Essentials of Oceanography 7th Edition

  2. Ocean sediment • Various materials settle through the water column and accumulate on the ocean floor • Layers represent a record of Earth history, including: • Movement of tectonic plates • Past changes in climate • Ancient ocean circulation patterns • Cataclysmic events

  3. Collecting ocean sediment • Specially designed ships collect cores by rotary drilling • Cores allow scientists to analyze ocean sediment Figure 4B

  4. The 4 main types of sediment • Lithogenous = composed of fragments of pre-existing rock material • Biogenous = composed of hard remains of once-living organisms • Hydrogenous = formed when dissolved materials come out of solution (precipitate) • Cosmogenous = derived from outer space

  5. Origin of lithogenous sediment • Forms by: • Weathering = breakup of exposed rock • Transportation = movement of sediment • Deposition = settling and accumulation Sediment-transporting media Figure 4-4

  6. Lithogenous sediment composition • Most lithogenous sediment is composed of quartz, which is: • Abundant • Chemically stable • Durable Figure 4-5

  7. Lithogenous sediment texture • Texture includes: • Grain size • Sorting • Rounding • Maturity Figure 4-7

  8. Distribution of lithogenous sediment • Lithogenous sediment occurs as: • Neritic (nearshore) deposits • Beaches • Continental shelves • Turbidites • Glacial-rafted debris • Pelagic (deep ocean floor) deposits • Abyssal clay

  9. Origin of biogenous sediment • Organisms that produce hard parts die • Material rains down on the ocean floor and accumulates as: • Macroscopic shells, bones, teeth • Microscopic tests (shells) • If comprised of at least 30% test material, called biogenous ooze

  10. Biogenous sediment composition • Microscopic biogenous tests are composed of 2 main chemical compounds: • Silica (SiO2) including opal (SiO2 · nH2O) • Diatoms (algae) • Radiolarians (protozoan) • Calcium carbonate or calcite (CaCO3) • Coccolithophores (algae) • Foraminifers (protozoan)

  11. Examples of silica-secreting microscopic organisms Diatom Radiolarian Figure 4-8

  12. Siliceous ooze • Silica-secreting organisms accumulate to form siliceous ooze (>30% siliceous test material) Figure 4-8c

  13. Examples of calcite-secreting microscopic organisms Coccolithophores Foraminifers Figure 4-9

  14. Calcareous ooze • Calcite-secreting organisms accumulate to form calcareous ooze (>30% calcareous test material) Figure 4-9d

  15. Biogenous ooze turns to rock • When biogenous ooze hardens and lithifies, can form: • Diatomaceous earth (if composed of diatom-rich ooze) • Chalk (if composed of coccolith-rich ooze) Chalk cliffs of southern England Figure 4-10

  16. Distribution of biogenous ooze • Most biogenous ooze found as pelagic deposits • Factors affecting the distribution of biogenous ooze: • Productivity (amount of organisms in surface waters) • Destruction (dissolving at depth) • Dilution (mixing with lithogenous clays)

  17. Distribution of siliceous ooze • Silica slowly but steadily dissolves in seawater • Siliceous ooze found where it accumulates faster than it dissolves Figure 4-11

  18. Distribution of calcareous ooze • Calcite dissolves beneath the calcite compensation depth (CCD) at 4.5 km • Calcareous ooze can be found below the CCD if it is buried and transported to deep water Figure 4-12

  19. Biogenous ooze as environmental indicator

  20. Origin of hydrogenous sediment • Hydrogenous sediment forms when dissolved materials come out of solution (precipitate) • Precipitation is caused by a change in conditions including: • Changes in temperature • Changes in pressure • Addition of chemically active fluids

  21. Types of hydrogenous sediment • Manganese nodules • Phosphates • Carbonates • Metal sulfides • Evaporite salts Mining manganese nodules Figure 4-25 Evaporite salts Figure 4-15

  22. Cosmogenous sediment • Cosmogenous sediment is composed of material derived from outer space • Two main types: • Microscopic space dust • Macroscopic meteor debris • Forms an insignificant proportion of ocean sediment Microscopic cosmogenous spherule Figure 4-16

  23. Mixtures • Most ocean sediment is a mixture of sediment types • One type of sediment usually dominates, allowing it to be classified as primarily: • Lithogenous • Biogenous • Hydrogenous • Cosmogenous

  24. Worldwide distribution of neritic and pelagic sediment Figure 4-17

  25. Ocean sediments as a resource • Ocean sediments contain many important resources, including: • Petroleum • Gas hydrates • Sand and gravel • Evaporative salts • Phosphorite • Manganese nodules and crusts Offshore drilling rig Figure 4-21

  26. End of Chapter 4 Essentials of Oceanography 7th Edition

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