Sediments of the Ocean

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Sediments of the Ocean

• Chapter 5

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Sediments of the Oceans

• Are particles of organic or inorganic matter that
  accumulates in a loose unconsolidated form
• Originates from
• Weathering
• Erosion
• Living organism

• Volcanic eruptions
• Chemical process
• Outer space

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Why study Sediments

• Sediments are the history book of the planet
  recording
• Movement of plates
• Ocean currents
• Ancient climates and past ocean temperatures
• Mountain building and continental collision

• Evolution of life
• Volcanic eruptions
• Meteorite and asteroid impacts
• Sediments are also the waste products of both the
  continents and oceans.

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Weathering processes

• Mechanical weathering is the physical breakdown
  of rock biological sediments
• Chemical weathering is breakdown of rock by
  chemical processes
• Igneous rock water what type of rock?
• Sedimentary

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Erosion, Transportation, and Deposition

• Water delivers the vast majority of particulate
  and dissolved material to the sea.
• Wind transports only a small fraction of the
  sediment reaching the oceans
• Glaciers In polar regions, they deliver
  considerable quantities of coarse sediment.

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Sediment Rounding Sorting

• As material is transported, it is sorted by size,
  since current velocity will set a maximum on the
  size of particle that can be transported.
• Collisions between particles, particularly the
  larger ones, and with the bottom of a stream,
  will result in rounding of the particles.

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• All 4 particles types have 4 properties
• 1. Texture
• 2. Porosity
• 3. Permeability
• 4. Composition

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1. TEXTURE

• sizes of particles (Table 5-1)
• boulders, cobbles, pebbles, granules, sand, silt,
  clay, colloids.
• Silt clay mud)
• sorting (how much of each size particle all same
  size well-sorted mix of mud, gravel, sand
  poorly sorted)

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• Larger particles require more energy to be moved
  (fig. 5.5)
• The energy is supplied by moving water or wind.
• The faster the water or wind, the larger size
  particle can be picked up.

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2. POROSITY

• the spaces between particles
• highest porosity occurs in clay

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3. PERMEABILITY

• how inter-connected the pores are
• highest permeability is in sand lowest is in
  clay

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4. COMPOSITION

• A) Minerals (naturally-occurring, inorganic
  compounds with a specific chemical composition
  and a crystalline structure
• examples halite, calcite, silicate minerals
• minerals from rocks basalt on the left contains
  black silicate minerals granite, on the right,
  contains mostly white silicate minerals with a
  few black ones scattered through.

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• minerals from living organisms, calcite from
  corals

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• B) Non-minerals a. Organic contains C (carbon)
  and H (hydrogen),
• Ex.plant matter, algal matter (oil)

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• b. Inorganic lacks the crystalline structure (
  glass) examples volcanic ash the silica (SiO2)
  of diatom shells

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Classifying Sediments
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Terrigenous or Detrital

• Detrital sediments consist of particles which
  arise from weathering on the continents chemical
  sediments precipitate from seawater.
• Most sediments are a mixture of various
  components, but often one component is dominant
• Sediment are classified according to this
  dominant component.

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Lithogenous or Terrigenous (cont.)

• Rivers and volcanic eruptions are the main source
• Igneous rocks, sands, mud of the continental shelf

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• Volcanic Ash layers
• Glacial Marine sediment delivered to the oceans
  by glaciers and carried by icebergs.

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Biogenous

• Biogenous, or biogenic, sediments are the remains
  of organisms
• most abundant, often the shells of single cell
  organisms living in the surface waters.
• Calcareous Oozes (consist of gt30 CaCO3 shells
  eventually forms chalk or limestone)

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• Foraminferal or Globigerina Oozes (protozoans).

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• Pteropod Oozes (swimming snails rare)

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• Coccolith Oozes (algae)

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• Siliceous Oozes (consist of gt30 SiO2 shells

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• Diatom Oozes (algae)

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• Radiolarian Oozes (protozoans)

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• Coral Reefs reefs grow in shallow water
  carbonate skeletons of coral and cemented debris

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Hydrogenous (Chemical)

• Precipitated from the water
• Evaporites are an important group of hydrogenous
  deposits
• Form when sea water evaporates

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• Typical evaporite, It doesn't look like table
  salt yet, because it has red clay and black
  organic matter in it

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• Manganese (Mn) nodules grow by precipitation of
  iron and manganese hydroxides from seawater (fig.
  5.12)
• Require very low sedimentation rates.
• Phosphate Nodules grow by precipitation from
  sediment

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Cosmogenic

• micrometeorites are an identifiable component in
  slowly accumulating sediments.
• Microtektites in the shape of a drop can be
  observed on cosmogenic sediments (fig. 5.7)

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Distribution of Marine Sediments

• Near-shore Deposition coarsest materials are
  deposited close to source and close to shore
• sediment on shelves tends to be coarser (larger)
  in grain size (gravel, sand, and silt), while
  sediment in the deep areas tends to be finer
  (smaller) in grain size (silt and clay)

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Turbidites

• Turbidity Currents play an important role in
  transporting sediment to deep ocean
• Turbidity Currents are density currents a
  flowing mixture of sediment and water which is
  denser than surrounding water.

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• image of a turbidity current moving down the
  continental slope off California 

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• Like rivers, they seek lowest point.
• Characteristics of Turbidite deposits graded
  bedding
• Turbidity currents occur catastrophically.
• Associated features submarine canyons, fans,
  levees

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Clays

• Abyssal Clays (Brown Clays) In general, these
  are very fine-grained products of continental
  weathering
• Gray clays often distal ends of turbidity
  currents.
• Red clays (contain hydrogenous component)
  wind-blown material is most important constituent.

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• calcareous oozes (carbonate) accumulates in
  shallower areas of the deep sea, along mid-ocean
  ridges,
• siliceous oozes accumulate in cold water areas
  (around Antarctica and off the coast of Alaska)
  and
• siliceous oozes accumulate where there is a
  source of rich nutrients (along the equator in
  the Pacific Ocean)

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• Calcite (calcareous) particles dissolve in deeper
  ocean water.
• The pteropods go first, followed by the forams,
  and, lastly, the coccoliths.
• The water depth at which all of the forams
  dissolve is called the lysocline.

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• The water depth at which the coccoliths dissolve
  is called the Calcium Compensation Depth, the CCD
  (fig. 5.9)

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• red clay fills in the rest of the area
• 'H' stands for 'hydrogenous', which is the same
  as 'authigenic'.
• These occur where sedimentation rates are very
  low (in red clay areas), and where deep ocean
  currents move swiftly (Cape of Good Hope,
  southern Africa also between Florida and the
  Bahamas)

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