Transcript Chapter 4: Marine sediments

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
 Lithogenous (derived from land)
 Biogenous (derived from organisms)
 Hydrogenous (derived from water)
○ Also known as Authigenic
 Cosmogenous (derived from outer space)
Lithogenous sediments
Eroded rock fragments from
land
 Reflect composition of rock from
which derived
 Transported from land by
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 Water (e.g., river-transported
sediment)
 Wind
 Ice
 Gravity
Distribution of sediments
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Neritic
○ Found on continental shelves and shallow
water
○ Generally course grained
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Pelagic
○ Found in deep ocean basins
○ Typically fine grained
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-depth2006/album/Whittington/16NA241%20G5%20Closeup%20on%20red%20clay%20bleeding%
20into%20lighetr%20soil.jpg
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
Biogeneous marine sediments
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Commonly either calcium
carbonate (CaCO3) or
silica (SiO2 or SiO2·nH2O)
Usually planktonic (freefloating)
○ When the plankton die, they
settle on the bottom
Siliceous ooze
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Fig. 4.11
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
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)

Limestone
 Lithified carbonate sediments

White Cliffs of Dover, England is
hardened coccolithophore ooze
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
CaCO3
Stromatolites
 Warm, shallow-
ocean, high
salinity
 Cyanobacteria
Fig. 4.10a
Hydrogenous marine sediments

Minerals precipitate directly from
seawater
 Manganese nodules
 Phosphates
 Carbonates
 Metal sulfides
Deep sea ferromanganese nodules on the floor of the South Pacific
Ocean (individual nodules are 5-10 cm diameter).
Small proportion of marine sediments
 Distributed in diverse environments

http://www2.ocean.washington.edu/oc540/lec01-16/99.540.1.2.jpg
Cosmogenous marine sediments
Macroscopic meteor
debris
 Microscopic iron-nickel
and silicate spherules

Tektites
 Tektites
 Space dust
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Overall, insignificant
proportion of marine
sediments
http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Two_tektites.JPG/800px-Two_tektites.JPG
Space dust
Marine sediments often represent ocean
surface conditions  preserves record of
past
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Temperature
Nutrient supply
Abundance of marine life
Atmospheric winds
Ocean current patterns
Volcanic eruptions
Major extinction events
Changes in climate
Movement 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 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
Other reasons to study sediments
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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
Florida Sediments
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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
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Clay hills of north Florida
 Carried from Appalachian mountains
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Sand hills
 Ancient barrier islands and dunes
Misconceptions – What have we learned that
make these statements false?
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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
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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.