Sediments and Diagenesis

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Sediments and Diagenesis
The Rock Cycle is a group of changes. It is an
ongoing process. Igneous rock can change into
sedimentary rock or into metamorphic
rock. Sedimentary rock can change into
metamorphic rock or into igneous rock.
Metamorphic rock can change into igneous or
sedimentary rock.
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Sediments and Diagenesis
Sediment Diagenesis 75 of all the rocks
exposed at the Earths land surface (only 5 of
Earths outer 10 miles - so mostly at the
surface) I. Sediment Rock fragments created by
weathering and erosion Accumulates
everywhereoceans, beaches, lakes, rivers,
deserts, swamps, caves, base of glaciers
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Sediments and Diagenesis

• Classified based on its origin.
• Detrital composed of transported solid fragments
  (detritus) of preexisting rocks
• 2. Chemical forms when previously dissolved
  minerals either precipitate from solution or are
  extracted from water by living organisms and
  converted to shells/skeletons

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Sediments and Diagenesis
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Sediments

• B. Sediment Transport and Deposition
• Detrital
• Generally move from high ground to low ground by
  the pull of gravity (assisted by water, wind, or
  glacial ice)
• Deposited when the carrying material loses its
  capacity to carry the sediment
• 2. Chemical
• Ions remain in solution until theres a change in
  the waters temperature, pressure, or chemical
  composition and then the ions precipitate

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Sediments
C. Sediment Texture Detrital sediment and
chemical sediment are classified based on
composition. 1. Grain size Grain composition -
some minerals are stronger than others. a.
Distance - smaller grains travel longer
distances. b. Energy of the transportation
medium - high energy environment moves larger
grains.
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Sediments
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Sediments
2. Grain shape a. Distance transported - over far
distances, grained become more rounded. b.
Transportation medium High energy river, wind
produce rounded grains Middle of glacier,
mudflow, debris flow preserve angular grains
not enough distance to round grains
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Sediments
C. Sediment Texture detrital sediment and
chemical sediment are classified based on
composition. 3. Sorting Related to the carrying
capacity of the transport medium Well sorted
wind Medium - well sorting waves Medium - poor
sorting streams Poorly sorted glaciers,
debris flows
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Sediments
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Sediments and Diagenesis
II. Turning sediments into rock Eventually
accumulated sediment turns into rock A.
Diagenesis All the chemical, physical, and
biological changes that take place after
sediments are deposited. Burial Alteration by
groundwater Recrystallization regrowth of less
stable minerals into more stable
ones. Lithification occurs within the upper few
kilometers of the crust at temperatures lt 200?C
(400?F)
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Sediments and Diagenesis

• II. Turning sediments into rock
• B. Lithification the process by which
  unconsolidated sediments are transformed into
  solid sedimentary rocks (part of diagensis)
• Compaction pressure (from overlying sediment)
  reduces the volume of sediment
• Compaction forces out air and water and packs
  grains together.

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Sediments and Diagenesis
II. Turning sediments into rock B.
Lithification 2. Cementation Cements grains
together - ions dissolved in water by chemical
weathering may be deposited by groundwater
circulating through the sediment. Calcium
carbonate CaCO3 Calcium ions plus CO2 and
H2O Silica SiO2 is produced by chemical
weathering of silicate igneous rocks Iron oxide
Fe2O3
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Sediments and Diagenesis
III. Types of Sedimentary rocks A. Detrital
Sedimentary rocks made of sediment that is
transported as solid particles Particle size is
the primary basis for distinguishing various
detrital sedimentary rocks. Particle size
indicates environment of deposition Water and
air currents sort by size. Stronger current
larger grain sizes
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Sediments and Diagenesis

• III. Types of Sedimentary rocks
• A. Detrital Sedimentary rocks made of sediment
  that is transported as solid particles
• 1. Shale (mudstone, siltstone)
• gt50 of all sedimentary rocks
• Silt and clay
• Small grain size settling from quiet,
  non-turbulent water
• Silt and class form in lakes, lagoons, swamps,
  deep ocean.
• Need quiet water depositional setting

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• III. Types of Sedimentary rocks
• A. Detrital Sedimentary rocks
• 2. Sandstone sand sized particles (1/16 2
  millimeters)
• 25 of all sedimentary rocks
• Windblown dunes, some rivers, and beaches
• Shape and sorting important for determining
  depositional environment.
• Sorting well sorted wind waves poorly sorted
  streams
• Shape well rounded water or wind transported
  over long distances
• Angular glacier or debris flow
• Transported over short distances

Sediments and Diagenesis
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• III. Types of Sedimentary rocks
• Detrital Sedimentary rocks
• 2. Sandstone sand sized particles (1/16 2
  millimeters) (
• 25 of all sedimentary rocks
• Windblown dunes, some rivers, and beaches
• Shape and sorting important for determining
  depositional environment.
• Sorting well sorted wind waves poorly sorted
  streams
• Shape well rounded water or wind transported
  over long distances
• Angular glacier
• Transported over short distances

Sediments and Diagenesis
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• III. Types of Sedimentary rocks
• Detrital Sedimentary rocks
• 2. Sandstone sand sized particles (1/16 2
  millimeters) (
• 25 of all sedimentary rocks
• Windblown dunes, some rivers, and beaches
• Shape and sorting important for determining
  depositional environment.
• Sorting well sorted wind waves poorly
  sorted streams
• Shape well rounded transported over long
  distances (water)
• Angular transported over short distances
  (glacier)

Sediments and Diagenesis
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Sediments and Diagenesis

• III. Types of Sedimentary rocks
• Detrital Sedimentary rocks
• 3. Conglomerate and Breccia
• Composed of gravels (pea to large boulders, gt2
  mm)
• Conglomerate composed of rounded grains of
  difference sizes.
• Formed in energetic mountain streams or coasts
  (storm deposits)
• Breccia composed of angular pieces.
• Did not travel far glaciers, landslides

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Sediments and Diagenesis

• III. Types of Sedimentary rocks
• Detrital Sedimentary rocks
• 3. Conglomerate and Breccia
• Composed of gravels (pea to large boulders, gt2
  mm)
• Conglomerate composed of rounded grains of
  difference sizes.
• Formed in energetic mountain streams or coasts
  (storm deposits)
• Breccia composed of angular pieces.
• Did not travel far glaciers, landslides, (close
  to source)