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Chapter 4 Marine Sediments

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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

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