Transcript Chapter 4: Marine sediments

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
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

 Water (e.g., river-transported
sediment)
 Wind
 Ice/glacier
 Gravity
Lithogenous sediments

Most lithogenous sediments at continental
margins
 Coarser sediments closer to shore
 Finer sediments farther from shore
 Mainly mineral quartz (SiO2)
Relationship of fine-grained quartz and
prevailing winds
Fig. 4.6b
Distribution of sediments

Neritic
○ Found on continental shelves and shallow
water
○ Generally course grained

Pelagic
○ Found in deep ocean basins
○ Typically fine grained
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
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
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


Commonly either calcium
carbonate (CaCO3) or
silica (SiO2 or SiO2·nH2O)
Usually planktonic (freefloating)
○ When the plankton die, they
settle on the bottom
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
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

Calcium carbonate in biogeneous sediments

Coccolithophores
(algae)
 Photosynthetic
 Coccoliths (nano-
plankton)
 Accumulation of
dead ones results in
 Rock chalk
Calcium carbonate in biogeneous sediments

Foraminifera
(protozoans)
 Heterotrophic
 Calcareous ooze
Fig. 4.8c
http://serc.carleton.edu/images/microbelife/topics/proxies/foraminefera.jpg
Carbonate deposits (CO3)

Limestone
 Lithified carbonate sediments
 White Cliffs of Dover,
England is hardened
coccolithophore ooze
 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
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
Hydrogenous marine sediments
 Carbonates
Aragonit
e
(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
Calcit
e
Oolitic
sand
http://www.advancedaquarist.com/2005/2/short_album/Gr
eatSaltLakeSand.jpg/variant/medium
http://www.outreach.canterbury.ac.nz/resources/geology/glossary/calcite.jpg
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.
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_Halit
e/GypsumSelenite.JPG
Cosmogenous marine sediments
Macroscopic meteor
debris
 Microscopic iron-nickel
and silicate spherules

 Tektites
 Space dust

Overall, insignificant
proportion of marine
sediments
http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Two_tektites.JPG/800px-Two_tektites.JPG
Space dust
Mixtures of marine sediments

Usually mixture of
different sediment types
 For example, biogenic oozes
can contain up to 70% nonbiogenic components

Typically one sediment
type dominates in
different areas of sea
floor
http://lh5.ggpht.com/_xdSF9NzTieY/SGE4kkTxFEI/AAAAAAAACsk/FP
HuZspT7SM/Zou+zou's+mud+2.JPG
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
http://www.usgcrp.gov/usgcrp/images/ocp2007/gallery-large/thumbnails/OCP07_Fig-10.jpg
 Deep
Sea Drilling
Program
 Ocean Drilling
Program
 Integrated Ocean
Drilling Program
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

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
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.