CHAPTER 4: Marine Sediments

1. CHAPTER 4: Marine Sediments

2. Marine sediments • Eroded rock particles and fragments • Transported to ocean • Deposit by settling through water column • Oceanographers decipher Earth’s history through studying sediments http://serc.carleton.edu/images/microbelife/topics/proxies/.gif

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

4. Lithogenous sediments • Eroded rock fragments from land • Reflect composition of rock from which derived • Transported from land by • Water (e.g., river-transported sediment) • Wind • Ice/glacier • Gravity

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

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

7. Distribution of sediments • Neritic • Found on continental shelves and shallow water • Generally course grained • Pelagic • Found in deep ocean basins • Typically fine grained

8. Distribution of sediments • Neritic • Shallow water deposits • Close to land • Dominantly lithogenous • Typically deposited quickly http://disc.gsfc.nasa.gov/oceancolor/images/SeaWiFS_Feb28_sediments_enhanced.jpg

9. Distribution of sediments • Pelagic • Deeper water deposits • Finer-grained sediments • Deposited slowly • Sources of fine pelagic lithogenous sediments: • Volcanic ash (volcanic eruptions) • Wind-blown dust • Fine-grained material transported by deep ocean currents

10. Pelagic lithogenous sediments • Abyssal clay (red clay) • At least 70% of clay-sized grains from continents • Transported by winds and currents • Oxidized iron – gives reddish color • Abundant if other sediments absent http://www.ncptt.nps.gov/images/ac/prospection-in-depth-2006/album/Whittington/16NA241%20G5%20Closeup%20on%20red%20clay%20bleeding%20into%20lighetr%20soil.jpg

11. Biogeneous 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 http://inst.sfcc.edu/~gmead/ocbasins/CALCCORL.gif

12. Biogeneous marine sediments • Commonly either calcium carbonate (CaCO3)orsilica(SiO2 or SiO2·nH2O) • Usually planktonic (free-floating) • When the plankton die, they settle on the bottom

13. Silica in biogenic sediments • Diatoms (algae) • Photosynthetic • Where they are abundant, thick deposits accumulate when they die • Diatomaceous earth – light white rock • Radiolarians(protozoans) • heterotrophic • Produces siliceous ooze

14. Siliceous ooze • Seawater undersaturated with silica so continually dissolves back into water • Therefore, detectable “siliceous ooze” found in the sediments is commonly associated with high biologic productivity in surface ocean because once buried, they don’t dissolve easily

15. Calcium carbonate in biogeneous sediments • Coccolithophores (algae) • Photosynthetic • Coccoliths(nano-plankton) • Accumulation of dead ones results in • Rock chalk

16. Calcium carbonate in biogeneous sediments • Foraminifera (protozoans) • Heterotrophic • Calcareous ooze Fig. 4.8c http://serc.carleton.edu/images/microbelife/topics/proxies/foraminefera.jpg

17. Carbonate deposits (CO3) • Limestone • Lithified carbonate sediments • Used for cement, glass • White Cliffs of Dover, England is hardened coccolithophore ooze • CaCO3 • Stromatolites • Warm, shallow-ocean, high salinity • Cyanobacteria Fig. 4.10a

18. Hydrogenous marine sediments • Minerals precipitate directly from seawater • Manganese nodules • Phosphates • Carbonates • Metal sulfides • Small proportion of marine sediments • Distributed in diverse environments Deep sea ferromanganese nodules on the floor of the South Pacific Ocean (individual nodules are 5-10 cm diameter). http://www2.ocean.washington.edu/oc540/lec01-16/99.540.1.2.jpg

19. Hydrogenous marine sediments • Phosphates • Phosphorus-bearing apatite sedimentary rock • Occur beneath areas in surface ocean of very high biological productivity  phosphates released into interstitial water by decomposition • Economically useful: fertilizer A phosphate mine in Hardee County in central Florida. Seventy-five percent of the phosphate used in the United States comes from the region. http://www.nytimes.com/2007/08/04/us/04phosphates.html?_r=1&oref=slogin

20. Hydrogenous marine sediments Aragonite • Carbonates (CaCO3) • Aragonite and calcite • Calcite found in limestones, marbles, chalks • Used in antacids, toothpaste • Aragonite (marine shells) is less stable and reverts to calcite crystalline form over time • Used in cement, fertilizer • Oolites • Small, round calcite spheres found in shallow, tropical waters with high carbonate concentrations • Small, used in aquariums Calcite Oolitic sand http://www.advancedaquarist.com/2005/2/short_album/GreatSaltLakeSand.jpg/variant/medium http://www.outreach.canterbury.ac.nz/resources/geology/glossary/calcite.jpg

21. Hydrogenous marine sediments • Metal sulfides • Contain iron, nickel, copper, zinc, silver, and other metals • Associated with hydrothermal vents http://scienceblogs.com/deepseanews/2008/03/deep_oceans_and_deep_space.php

22. Hydrogenous marine sediments • Evaporites • Minerals that form when seawater evaporates • Restricted open ocean circulation • High evaporation rates • Halite (common table salt) and gypsum http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Gypsum_Halite/GypsumSelenite.JPG

23. Cosmogenous marine sediments • Macroscopic meteor debris • Microscopic iron-nickel and silicate spherules • Tektites • Space dust • Overall, insignificant proportion of marine sediments • Space dust http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Two_tektites.JPG/800px-Two_tektites.JPG

24. 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 sea floor http://lh5.ggpht.com/_xdSF9NzTieY/SGE4kkTxFEI/AAAAAAAACsk/FPHuZspT7SM/Zou+zou's+mud+2.JPG

25. Marine sediments often represent ocean surface conditions  preserves record of past • Temperature • Nutrient supply • Abundance of marine life • Atmospheric winds • Ocean current patterns • Volcanic eruptions • Major extinction events • Changes in climate • Movement of tectonic plates

26. Retrieving sediments • Dredge • Gravity corer • Rotary drilling • Deep Sea Drilling Program • Ocean Drilling Program • Integrated Ocean Drilling Program http://www.usgcrp.gov/usgcrp/images/ocp2007/gallery-large/thumbnails/OCP07_Fig-10.jpg

27. Resources from marine sediments • Energy resources • Petroleum • Mainly from continental shelves • Gas hydrates • Sand and gravel (including tin, gold, and so on) • Evaporative salts • Phosphorite • Manganese nodules and crusts Ultra-Deep Oil Drilling, capable of drilling in 10,000 feet of water and penetrating 30,000 feet through earth’s crust. http://joejaworski.files.wordpress.com/2007/09/oil_plat.jpg

28. Other reasons to study sediments • Contaminants in water column will sometimes settle in the sediment • Conditions that effect toxicity of sediments • Sediment type • Sediment texture (in fine sediment, there is more surface area for toxins to adhere, increasing toxicity) • Dredging and other human activity • Sediment Toxicity in Indian River Lagoon • http://www.teamorca.org/cfiles/fast.cfm

29. Misconceptions – what have we learned that make these statements false? • Carbon is only produced by trees. • The bioshpere has never caused major changes in the other spheres that make up the Earth system, such as the rocks and air. • Few products we use everyday have anything to do with taking rocks and minerals from the ground. • We will never run out of natural resources such as coal, oil, and other minerals.