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Chapter 4 Marine Sediments Essentials of Oceanography 7 th Edition.

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Presentation on theme: "Chapter 4 Marine Sediments Essentials of Oceanography 7 th Edition."— Presentation transcript:

1 Chapter 4 Marine Sediments Essentials of Oceanography 7 th 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 1.Lithogenous = composed of fragments of pre-existing rock material 2.Biogenous = composed of hard remains of once-living organisms 3.Hydrogenous = formed when dissolved materials come out of solution (precipitate) 4.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 Figure 4-4 Sediment-transporting media

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: 1. Silica (SiO 2 ) including opal (SiO 2 · nH 2 O) Diatoms (algae) Radiolarians (protozoan) 2. Calcium carbonate or calcite (CaCO 3 ) Coccolithophores (algae) Foraminifers (protozoan)

11 Examples of silica-secreting microscopic organisms Figure 4-8 DiatomRadiolarian

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 Figure 4-9 CoccolithophoresForaminifers

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) Figure 4-10 Chalk cliffs of southern England

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 oozeCalcareous ooze Surface water temperature CoolWarm 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 Figure 4-25 Mining manganese nodules Evaporite salts Figure 4-15

22 Cosmogenous sediment Cosmogenous sediment is composed of material derived from outer space Two main types: 1. Microscopic space dust 2. Macroscopic meteor debris Forms an insignificant proportion of ocean sediment Figure 4-16 Microscopic cosmogenous spherule

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 Figure 4-21 Offshore drilling rig

26 End of Chapter 4 Essentials of Oceanography 7 th Edition


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