Transcript Chapter 5: Marine Sediments

Chapter 5: Marine Sediments
Fig. 5-23
Marine sediments
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Eroded rock particles and fragments
Transported to ocean
Deposit by settling through water
column
Oceanographers decipher Earth history
through studying sediments
Marine Sediments
Fig. CO-4
Sediments reveal Earth history
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Sediments lithified
Mineral composition
Sedimentary texture
Past climate
 Plate motions
 Age of seafloor
 Fossil evolution and extinction
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Sediments classified by origin
Lithogenous
 Biogenous
 Hydrogenous
 Cosmogenous
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Lithogenous sediments
Rock fragments from land
 Transported to oceans by
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Rivers
 Wind
 Ice
 Gravity flows (e.g. turbidity
currents)
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Lithogenous sediments
Fig. 4.5
Rivers transport much sediment
Fig. 5-5
Lithogenous sediments
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Most accumulate near continental
margins
Wind-blown dust in deep ocean
makes abyssal clay (red clay)
Mostly quartz (SiO2)
Chemically stable
 Abrasion resistant
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Relationship of fine-grained
quartz and prevailing winds
Fig. 4.6b
Sediment Texture
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Grain size indicates energy of
transportation and deposition
Fig. 5-8
Sediment texture
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Grain size sorting
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Indication of selectivity of transportation
and deposition processes
Textural maturity
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Increasing maturity if
 Clay content decreases
 Sorting increases
 Non-quartz minerals decrease
 Grains are more rounded (abraded)
Textural maturity
Fig. 5-9
Distribution of sediments
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Neritic
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Shallow water deposits
Close to land
Dominantly lithogenous
Typically deposited quickly
Pelagic
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Deeper water deposits
Finer-grained sediments
Deposited slowly
Neritic lithogenous sediments
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Beach deposits
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Mainly wave-deposited quartz-rich sands
Continental shelf deposits
Turbidite deposits
Glacial deposits
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High latitude continental shelf
Pelagic lithogenous sediments
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Sources of fine material:
Volcanic ash (volcanic eruptions)
 Wind-blown dust
 Fine-grained material transported by
deep ocean currents
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Abyssal clay (red clay)
Oxidized iron
 Abundant if other sediments absent
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Biogenous sediments
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Hard parts of once-living organisms
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Shells, teeth, bones
Fig. 5-10
Biogenous marine sediments
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Commonly either calcium carbonate
(CaCO3) or silica (SiO2 or SiO2·nH2O
- opal)
Usually planktonic (free-floating)
Biogenous sediments
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Calcareous ooze (CaCO3)
Microscopic protozoans, foraminifera
 Microscopic algae, coccolithophores
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Siliceous ooze (SiO2)
Microscopic protozoans, Radiolaria
 Microscopic algae, diatoms
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Calcium carbonate in biogenous
sediments
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Coccolithopho
res (algae)
 Photosynth
etic
 Coccoliths
(nanoplankton)
 Rock chalk
Fig. 4.8a
Calcium carbonate in biogenous
sediments
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Foraminifera
(protozoans)
Use
external
food
 Calcareous
ooze
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Fig. 4.8c
Carbonate deposits
Limestone (lithified carbonate
sediments)
 Stromatolites
Warm, shallowocean, high
salinity
 Cyanobacteria
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Fig. 4.10a
Calcareous ooze and the CCD
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Warm, shallow ocean saturated with
calcium carbonate
Cool, deep ocean undersaturated with
calcium carbonate
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Calcite compensation depth CCD--depth
where CaCO3 readily dissolves
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Rate of supply = rate at which the shells dissolve
Calcareous ooze and the CCD
Fig. 4.13
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Scarce calcareous ooze below 5000 m in
modern ocean
Ancient calcareous oozes at greater
depths if moved by sea floor spreading
Distribution of calcareous oozes in
surface sediments of modern sea floor
Fig. 4.14
Silica in biogenic sediments
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Diatoms (algae)
Fig. 4.7a
Photosynthetic
 Diatomaceous
earth
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Radiolarians
(protozoans)
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Use external food
Siliceous ooze
Fig. 4.7b
Siliceous ooze
Fig. 4.11
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Seawater undersaturated with silica
Siliceous ooze commonly associated with high biologic
productivity in surface ocean
Biogenous marine sediments
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Neritic biogenic seds
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Modern carbonates shallow,
warm ocean
Coral reefs
 Ooid shoals
 Beach sands
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Stromatolites hypersaline
Biogenous marine sediments
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Pelagic biogenic seds
Siliceous ooze beneath areas of
surface ocean upwelling (high
biologic productivity)
 Calcareous ooze on seafloor less
than about 4500 m
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CaCO3 dissolves in cold seawater
Distribution of biogenic seds
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Ooze is 30% or more biogenic
material (by weight)
Biologic productivity
Dissolution as shells settle through
ocean
Dilution by non-biogenic material
Shells and silt-clay fall through
seawater column to seafloor
Hydrogenous marine
sediments
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Minerals precipitate directly from
seawater
Manganese nodules
 Evaporites
 Inorganic Carbonates
 Metal sulfides
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Small proportion of marine sediments
Distributed in diverse environments
Fig. 4.15a
Manganese nodules
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Very low rate of
accumulation
Larger nodules grow
larger faster
Origin is unknown
Cosmogenous sediments
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Extraterrestrial fragments
Glassy tektites
 Fe-Ni micrometeorites
 Found in deep ocean where other
sediments accumulate very
slowly
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Meteorite impact
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K-T meteorite
crater off Yucatan
peninsula
Tektites and
spherules found
in marine seds
Shocked quartz in
marine seds
Fig. 5D
Mixtures of marine sediments
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Usually mixture of different sediment
types
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For example, biogenic oozes can contain
up to 70% non-biogenic components
Typically one sediment type
dominates in different areas of the
sea floor
Distribution of neritic and pelagic marine
sediments
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Neritic sediments cover about ¼ of sea
floor
Pelagic sediments cover about ¾
Distribution controlled by
 Proximity to sources of lithogenous
sediments
 Productivity of microscopic marine
organisms
 Depth of water
 Sea floor features
Distribution of neritic and pelagic marine sediments
Fig. 4.19
Marine sediments often represent
ocean surface conditions
Temperature
 Nutrient supply
 Abundance of marine life
 Atmospheric winds
 Ocean current patterns
 Volcanic eruptions
 Major extinction events
 Changes in climate
 Movement of tectonic plates
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Retrieving sediments
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Deep Sea Drilling
Program
Ocean Drilling
Program
Integrated Ocean
Drilling Program
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Dredge
Gravity corer
Rotary drilling
Studies reveal support for plate
tectonics and global climate change.
Resources from marine
sediments
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Energy resources
 Petroleum
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Gas hydrates
Sand and gravel (including tin, gold, and
so on)
Evaporative salts
Phosphorite
Manganese nodules and crusts
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Mainly from continental shelves
Manganese
nodules
Fig. 4.27
End of Chapter 5: Marine Sediments
Fig. 5E