Sediments and Sedimentary Rocks

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Sediments and Sedimentary Rocks

• What are sediments?
• Sediments are loose particles of former rocks.
  Sediments may be particles in the form of mineral
  grains or boulders or they may be dissolved
  particles which will later precipitate from the
  water and form solid rock.
• What is a Sedimentary Rock? Sediments
  after they are deposited may be buried and
  undergo physical and chemical change resulting in
  a solid rock (Sedimentary Rock)

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Types of Sedimentary Rocks

• Three main types of Sedimentary rocks
• Clastic-is formed from solid particles which are
  eroded from previous rocks.
• Chemical/Biochemicalthese sediments which are
  precipitate from water either through chemical or
  biochemical processes (biological)

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Sedimentary Cycle (part of the Rock Cycle)

• Sedimentary rocks all go through the following
  cycle
• 1. weathering from previous rocks.
• 2. erosion of weathering products.
• 3. transportation from site of origin to another
  site.
• 4. deposition of the sediments.
• 5. burial of the sediments
• 6. diagenesis

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Sedimentary Rock Cycle
http//www.mtsu.edu/cdharris/GEOL100/erosion/sed-
rk-cycle.gif
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Transportation of Clastic Rock

• In general most sediments travel downhill or
  downstream.
• Mode of transportation include
• Streams, rivers
• Glaciers
• Wind
• Ocean waves/tides/currents
• The size of particle depends on the available
  force applied. Example at flood level a river
  will be able to transport larger particles than
  it would during a normal river levels. This
  results in particles being sorted by size which
  is called sorting.

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http//earth.geol.ksu.edu/liu/g100/figures/20_tran
sportation.jpg
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http//www.rjmaxwell.com/education/basic_geologica
l_classification/
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Transportation of Clastic Rock

• If the particles are being transported they bang
  into each other repeatedly resulting in the
  grains wearing down and becoming rounded. This is
  called Rounding (Dah).
• In general the farther a particle travels from it
  source the more rounded it becomes. A jagged
  particle is near the source rock, where the
  rounded, smooth particle is farther from the
  source rock.

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Sorting and Rounding
pasadena.wr.usgs.gov/office/given/geo1/lecturenote
s/SedRx_files/image010.gif
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Clastic Rock Deposition

• Sediments will be dropped by it mode of
  transportation when the energy is not sufficient
  to carry the particle farther. This is called
  deposition. A particle may be deposited numerous
  times before final deposition occurs.

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Clastic Rock Burial/Diagenesis

• As the particles are deposited and sorted they
  build up layers and become buried by later
  sediments. Layer after layer pile up on top of
  each other. Those sediments on the bottom are
  buried under increasing pressure, which compact
  the sediments and force out the water. The
  sediments are undergoing diagenesis (physical and
  chemical changes that turn sediments into
  sedimentary rocks.

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Diagenesis

• In addition to squeezing the water out, new
  minerals form in the space between the sediment
  grains which cements the grains together.
• Also some sedimentary grain may dissolve and be
  replaced by other minerals.

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http//www.rjmaxwell.com/education/basic_geologica
l_classification/
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Classification of Clastic Rocks

• There are two types of Clastic rocks
• 1.Sandstones and fine grained
• 2.Chemical/Biochemical

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Sandstones and fine grainedClastic Rocks

• Sands when buried lithifies to form Sandstone.
  Depending on the grain size, shape, and
  mineralogy they can be placed in three additional
  major categories.
• Siltstones- composed of silt size grains which
  become lithified.
• Shale- composed of silt and clay size grains
  which lithified. These tend to break on bedding
  planes. Some may contain oil but is difficult to
  separate from the rock itself.
• Mudstone- composed of lithified mud. Generally
  blocky in appearance and when freshly broken have
  a musty smell.

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Chemical/Biochemical Rocks

• Ions which were dissolved from pre-existing rocks
  go into solution and travel down stream to lakes
  and oceans. In the lakes and oceans the ion
  precipitate out either by biochemical or
  inorganic chemical processes.
• The precipitates form a solid, and go through
  biogenesis just like clastic rocks. Examples of
  this is aragonite which forms fine grain calcium
  carbonate. Halite (NaCL) is another precipitate
  that occurs in this way.

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Chemical/Biochemical Rocks

• Chemical/Biochemical Rocks can be broken down
  also into 3 major categories.
• 1. Carbonates
• 2. Evaporites
• 3. Cherts

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Carbonates

• Carbonates are formed from lithifed carbonate
  material in ocean waters through biochemical
  processes. Marine organisms extract the
  carbonate from the ocean waters and form shell
  material. Organism such as foraminifera,
  gastropods, corals, etc. make up the bulk of the
  material forming limestones, and dolomites.

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Some typical environments that carbonates can
form.
http//www.geologyrocks.co.uk/tut.php?id14
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Evaporates

• Evaporates generally form in shallow brackish
  lagoons in arid regions where the water is
  evaporated away leaving the precipitates such as
  Aragonite (carbonates), rock salt, and gypsum.
• Some large salt deposits also occur, such as the
  M zone in the Mediterranean Sea.

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http//www.geo.msu.edu/geo333/images/salt-cycle.jp
g
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Chert

• Cherts form in the deep, deep ocean environments
  where organism which secret a siliceous shell
  have deposited after death. Diatoms will
  accumulate and form a siliceous ooze which will
  then go through diagenesis, becoming chert.

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Summary

• You should know the following
• What are sediments?
• What are sedimentary rocks.
• What are the major sedimentary rocks.
• Able to label and draw the processes which make
  up the sedimentary rock cycle.
• How do sedimentary rocks (clastic and
  chemical/biochemical) form and how are they
  classified.

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SITES USED

• Thanks to Greg Anderson for use of lecture notes.
• http//pasadena.wr.usgs.gov/office/ganderson/es10/
  lectures
• ALSO http//earth.geol.ksu.edu/liu/g100/figures/2
  0_transportation.jpg
• http//www.rjmaxwell.com/education/basic_geologica
  l_classification/
• pasadena.wr.usgs.gov/office/given/geo1/lecturenote
  s/SedRx_files/image010.gif
• http//www.rjmaxwell.com/education/basic_geologica
  l_classification/
• http//www.geologyrocks.co.uk/tut.php?id14
• http//www.geo.msu.edu/geo333/images/salt-cycle.jp
  g
• http//www.mtsu.edu/cdharris/GEOL100/erosion/sed-
  rk-cycle.gif