DEEP-SEA BIOGENIC SEDIMENTS

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DEEP-SEA BIOGENIC SEDIMENTS

• GEOL 3213

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MARINE SEDIMENTATION RATES THICKNESSES

• About 90 of sediments and sedimentary rocks are
  marine!

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SEDIMENTATION RATES OF DEEP-SEA DEPOSITS
high
low
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TYPES OF MODERN OCEAN FLOOR SURFACE SEDIMENTS

• Terrigenous
• Biogenic
• Authigenic
• Volcanic
• Clays

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DEEP-SEA SEDIMENT DISTRIBUTION PATTERNS
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BIOGENIC SEDIMENTS

• Mostly skeletal plankton
• Calcareous oozes
• Calcareous CaCO3
• Ooze
• fine-grained
• at least 30 skeletal
• 3 Kinds
• Foraminiferal
• Coccolith
• Pteropod
• Siliceous oozes
• Siliceous SiO2
• Kinds
• Radiolarian
• Diatom
• Songe spicules

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CALCAREOUS OOZES

• Major calcareous microfossils in deep-sea
  sediments
• Forams
• Coccoliths
• Pteropods
• Forams and coccoliths have been the most
  important contributors to deep-sea oozes since
  the beginning of the Cretaceous Period about 144
  Ma ago.
• Coccoliths
• Forams
• Pteropods may have been of less importance, but a
  contributing factor since the Late Cretaceous

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CHALK FORAMS IN A "FINE-GRAINED MATRIX"
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Chalk Cliffs of Dover, England, were once
deep-sea calcareous oozes
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MATRIX DISCOVERED TO BE COCCOLITH PLATES

• Coccolith plates

2-3 µm
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SEM Image of a Coccolithophere

• Coccoliths are 2-3 um diameter articulating
  plates that cover outer surface of algal cell
• Usually form spheres (coccolithospheres)
• Best studied with SEM

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PTEROPOD OOZES

• Less common than foraminiferal and coccolith
  oozes
• Pteropods are tiny snail-like mollusks that live
  in the plankton
• Calcareous skeletons are often conical in shape
  or coiled like a snail shell

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Plankton Influence on Mantle Recycling

• Calcareous oozes have probably changed the
  chemistry of the oceans and the biogeochemical
  cycles with the mantle since the K.

Since mid-Mesozoic, calcareous oozes on the
deep-sea floor have caused a major change in
Earth chemical cycles, e. g., new recycling into
the mantle. Calcareous are oozes scraped from
the seafloor and squeezed down into the mantle at
subduction zones formed where lithospheric plates
collide.
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Basal Sediment Ages of Pacific Ocean Basin
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DISTRIBUTIONS OF DEEP-SEA SEDIMENTS

• Thicknesses
• Thickest beneath continental shelves and
  continental rises
• Thinnest on the flanks of mid-ocean ridges
• Areas
• Calcareous oozes 48
• Siliceous oozes 14
• Pelagic clays 38
• Age
• No seafloor crust is older than about 200 Ma
• Total area of sedimentary sequences decreases as
  age increases
• Why?
• Depth
• Younger sedimentary sequences are in less deep
  ocean
• Older sedimentary sequences are in deeper oceans
• Why?

area
age
depth
age
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Deep-Sea Calcium Carbonate Accumulation

• Below the CCD, cold water holds more CO2, which
  results in more carbonic acid, which dissolves
  CaCO3 faster.

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Carbonate Compensation Depth (CCD) in the Atlantic

• Calcareous oozes occur at shallower depths (lt4
  000 m)
• Siliceous oozes occur at deeper depths (gt 4 000 m)

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Carbonate Sediments Accumulate in Shallower
Deep-Sea Areas

• At mid-ocean ridges

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Solution of Silica and Calcium Carbonate with
Depth

• Lysocline significant increase in rate of
  solution
• CCD

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DISTRIBUTIONS OF DEEP-SEA BIOGENIC OOZES

• Calcareous oozes
• Less deep areas above CCD
• Especially Atlantic Ocean
• Siliceous oozes
• Below CCD
• Diatom oozes
• No. Pacific
• Antarctic Ocean
• Radiolarian oozes
• Equatorial Pacific
• Antarctic Ocean

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COMPONENTS OF SILICEOUS OOZES

• Siliceous SiO2nH2O opalline silica
• Mostly skeletal plankton (microfossils)
• Major siliceous microfossil taxa
• Radiolaria
• Diatoms
• Siliceous sponge spicules

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RADIOLARIA

• Animal-like plankton related to Foraminifera
• Lace-like, porous spinose siliceous skeletons

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RADIOLARIA viewed with transmitted light
microscopy
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RADIOLARIAN-DIATOM SILICEOUS OOZE
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DIATOM

• Algae
• "Grass of the sea"
• Microscopic, porous, siliceous skeleton composed
  of 2 "dishes" (one inverted fitted into the
  other)

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DIATOMS

• "Centric" forms

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DIATOM

• Pennate form

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SILICEOUS BENTHIC SPONGE SPICULES

• Spicules skeletal elements with needle-like
  shapes
• Composition opalline silica, SiO2 nH2 O
• Contribute to some siliceous ( calcareous) oozes

forams
3-rayed spicule
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PHOSPHATES

• Calcium Phosphate
• Characterizzes the composition of fish bones and
  teeth
• Can be somewhat concentrated in outer continental
  shelf some deep-water sediments
• Can be chemically remobilized and precipitated
• In the sediments, especially continental margin
  sediments
• As fillings of the chambers of forams
• As replacements of fecal pellets of invertebrates
  and vertebrates.

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SKELETAL SEDIMENT CONSTITUENTSAn Ecological
Summary

• Phytoplankton (producers (photosynthesizers)
  autotrophs)
• Calcareous
• Coccolithophores (flagellates with coccolith
  plates)
• Siliceous
• Diatoms (2-dish skeletal algae)
• Zooplankton (consumers heterotrophs)
• Calcareous
• Foraminifera (Protista)
• Pteropods (snail-like mollusks)
• Siliceous
• Radiolaria (Protista)
• Siliceous benthic sponges (simple invertebrates)
• Nektic (or nektonic) higher consumer organisms
• Phosphates (Calcium phosphate)
• Fish teeth bones

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SUMMARY MODERN DEEP-SEA OOZES

• Deep-sea oozes
• fine-grained
• at least 30 microfossil skeletons
• Carbonate compensation depth (CCD)
• calcium carbonate dissolves in deeper, colder
  waters
• Sea-floor distributions
• calcareous oozes cover 48 of seafloor
• Plate tectonic influences
• recycling into the mantle since the mid- Mesozoic

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