1. Chapter 4 Marine 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
Siliceous ooze
Calcareous ooze
Surface water temperature
Cool
Warm
Main locations found
Sea floor beneath cool surface water in high latitudes; upwelling areas
Sea floor beneath warm surface water in low latitudes; not too deep (CCD)

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. Microscopic cosmogenous spherule
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. Essentials of Oceanography 7th Edition
End of Chapter 4
Essentials of Oceanography
7th Edition