Marine sediments Eroded rock particles and fragments Transported to ocean Deposit by settling...
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Transcript of Marine sediments Eroded rock particles and fragments Transported to ocean Deposit by settling...
Marine sediments Eroded rock particles and
fragments Transported to ocean Deposit by settling
through water column Oceanographers decipher
Earth history through studying sediments
http://serc.carleton.edu/images/microbelife/topics/proxies/.gif
Classification of marine sediments Classified by origin
LithogenousLithogenous (derived from land)BiogenousBiogenous (derived from organisms)HydrogenousHydrogenous (derived from water)
○ Also known as AuthigenicCosmogenousCosmogenous (derived from outer space)
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 Gravity
Distribution of sediments
Neritic○ Found on continental shelves and
shallow water○ Generally course grained
Pelagic○ Found in deep ocean basins○ Typically fine grained
Pelagic lithogenous sediments
Abyssal clay (red clay)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
Biogeneous marine sediments Hard remains of once-living Hard remains of once-living
organismsorganismsShells, bones, teethMacroscopic (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
Biogeneous marine sediments
Commonly either calcium carbonate calcium carbonate (CaCO3) or silicasilica (SiO2 or SiO2·nH2O)
Usually planktonicplanktonic (free-floating)
○ When the plankton die, they settle on the bottom
Siliceous ooze Seawater undersaturated with silica so continually
dissolves back into water Therefore, detectable “siliceous ooze” commonly
associated with high biologic productivity in surface ocean because once buried, they don’t dissolve easily
Fig. 4.11
Calcareous Ooze
• Destruction of calcium carbonate varies with depth
• At warmer surface, seawater is saturated with calcium carbonate so calcite doesn’t dissolve
• However, as decomposed material sinks further, it reaches cold ocean water
• Colder water holds more dissolved CO2
• CO2 forms carbonic acid and causes calcareous material to dissolve
• High pressure also helps with this• This is where the CCD is reached (Calcite
Compensation Depth) – below this little calcium carbonate survives
Carbonate deposits (CO3)
StromatolitesStromatolitesWarm, shallow-
ocean, high salinity
CyanobacteriaFig. 4.10a
Limestone Limestone Lithified carbonate sediments White Cliffs of Dover, England is
hardened coccolithophore ooze CaCO3
Hydrogenous marine sediments Minerals precipitate directly from
seawaterManganese nodulesManganese nodulesPhosphatesPhosphatesCarbonatesCarbonatesMetal sulfidesMetal sulfides
Small proportion of marine sediments Distributed in diverse environments
http://www2.ocean.washington.edu/oc540/lec01-16/99.540.1.2.jpg
Deep sea ferromanganese nodules on the floor of the South Pacific Ocean (individual nodules are 5-10 cm diameter).
Cosmogenous marine sediments
Macroscopic meteor debris
Microscopic iron-nickel and silicate spherulesTektitesSpace dust
Overall, insignificant proportion of marine sediments
http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Two_tektites.JPG/800px-Two_tektites.JPG
Tektites
Space dust
Marine sediments often represent ocean surface conditions preserves record of past
TemperatureNutrient supplyAbundance of marine lifeAtmospheric windsOcean current patternsVolcanic eruptionsMajor extinction eventsChanges in climateMovement of tectonic plates
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
Resources from marine sediments
Energy resourcesPetroleum
○ Mainly from continental shelves
Gas hydrates
Sand and gravel (including tin, gold, and so on)
Evaporative salts Phosphorite Manganese nodules and crusts
http://joejaworski.files.wordpress.com/2007/09/oil_plat.jpg
Ultra-Deep Oil Drilling, capable of drilling in 10,000 feet of water and penetrating 30,000 feet through earth’s crust.
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 Lagoonhttp://www.teamorca.org/cfiles/fast.cfm
Florida Sediments
3 characteristics distinguish Florida from regions to the north
○ Marine sediments, limestone and calcium magnesium carbonate, lie in thick layers at or below surface
○ Whole southeastern US coastal plain is deeply layered with clay, silt, sand, and gravel
○ Layer of organic soil lies on or is mixed into surface sediments
- Can be very thick under wetlands
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.
Ocean Literacy Principles 1g. - The ocean is connected to major lakes, watersheds and waterways because all major
watersheds on Earth drain to the ocean. Rivers and streams transport nutrients, salts, sediments and pollutants from watersheds to estuaries and to the ocean.
1h. - Although the ocean is large, it is finite and resources are limited.