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MOHIT KUMAR
Wacke ( Graywacke)
Wacke (Graywacke)
• Physically hard.
• Dark grey in colour,
• Enigmatic (ambiguous) rocks.
• Texturally, an immature
sandstone.
• Composed of sand mixed
with mud.                            Wikipedia
• Graywackes are associated with graded bedding.
Wacke (Graywacke)
• It has a dark colour, indicating its deposition in
  the low-oxygen environment of the deep sea.
• Contains more than 15% clay.
• Coarse-grained sandstone that consists of
  poorly sorted angular to subangular grains of
  quartz and feldspar.
• Clasts of monocrystalline quartz are often the
  most abundant framework component (25%
  to 50%), although the proportion fluctuates.
Wacke (Graywacke)
• Grains of chert, mudrock, limestone, polycrystalline
  quartz, and volcanic rocks are also quite common.
• Clasts of detrital muscovite, biotite, and chert occur
  in accessory amounts.
• SiO2 content of wackes ranges from 50% to 70%,
  reflecting the moderate amount of quartz and
  feldspar.




                      http://weiminhan.files.wordpress.com/2010/03/2010-03-17_161215.jpg?w=390&h=229
http://weiminhan.files.wordpress.com/2010/03/2010-03-17_161215.jpg?w=390&h=229
Wacke (Graywacke)
• Grain size distribution is bimodal with a
  primary peak for framework grains and a
  secondary peak for matrix.
• Many wackes were deposited by waning
  turbidity currents.
• They routinely display graded bedding, sole
  markings, and the systenatic upward changes
  in sedimetary structures and grain size
  characteristic of turbidities.
http://earthsci.org/mineral/rockmin/sed/silsed2.gif
Wacke (Graywacke)
• Deep water abyssal and bathyal body fossils,
  pelagic fauna and flora, and retransported
  shallow-waterorganic remains are all found
  within wacke sandstone sequences.
• Some wackes were deposited within submarine
  fan complexes, but there are also example of
  more distal deposits settled out of more diffuse
  density flows that spread out and dispersed
  across broad, flat abyssal plain surfaces.
Wacke (Graywacke)
• Wackes are the dominant sandstone of the
  Archean.
• It contains quartz, Like other sandstones, but
  it also has more delicate minerals and small
  fragments of rock (lihtics).
• Its grain are not well rounded. But this hand
  specimen is in fact a graywacke which refers
  to a specific origin as well as a wacke
  composition and texture.
Wacke (Graywacke)
• The origin of greywacke was a
  problem. Gravel, sand and
  mud should not be laid down
  together,     because       river
  outflow drops heavier grains
  first.
• Now       geologists       think
  greywacke is formed by
  submarine avalanches or
  strong turbidity currents.

                                      Wikipedia
Formation of Greywacke
             sandstone
• Sandstone is a type of sedimentary rock which is
  made from particles (sediment) that have been
  glued together. In this case, the sand is mixed
  with mud and clay and squeezed so that all the
  water disappears and the particles are pushed
  close together.
• In summary, the formation of greywacke rock is a
  result of the rock cycle processes of erosion,
  transport of eroded material by rivers, deposition
  onto the sea floor and then pushing up by plate
  tectonic movement.
Where is graywacke sandstone deposited?
• Graywacke sandstone is a sedimentary rock that is made
  up mostly of sand-size grains that were rapidly deposited
  very near the source rock from which they were
  weathered.
• Graywacke is deposited in deep ocean water near volcanic
  mountain ranges, where underwater landslides and density
  currents called turbidites quickly transport sediment short
  distances into a subduction zone or ocean trench.
• This type of sandstone contains fewer grains made of
  quartz and more made of feldspars, volcanic rock
  fragments, as well as silt and clay than most sandstone.
• It is therefore also known as “dirty sandstone.”
• The volcanic rock fragments give graywacke a greenish-
  gray color.
What makes the beds in graywacke?
• Graywacke sandstone deposits display flat-lying beds,
  each composed of sedimentary particles of different
  sizes.
• The sandstone beds can be from inches to many feet
  thick and are often separated by thin, dark shale beds.
• Each sandstone bed was formed during a single
  turbidite or submarine landslide event and was
  deposited over a short period of time from hours to
  days.
• The thin shale beds formed between turbidite events,
  when mud particles slowly settled to the sea floor, and
  may represent thousands of years.
What makes the beds in graywacke?
• Turbidites display graded bedding, that is, the
  grain size decreases upwards in the bed.
• During a turbidite event, the larger and
  heavier grains settle out first.
• As the energy in the landslide event
  decreases, finer and finer particl es settle out
  to the sea floor.
Are there fossils in graywacke?
• Graywacke sandstone occasionally contains fossil
  mollusks which sometime scan be used to tell when
  the rock was deposited.
• Sandstone deposits of the Franciscan Complex
  contain clams and ammonites from the Jurassic and
  Cretaceous periods.
• These provide ages for when the Franciscan oceanic
  rocks got close enough to North America for
  continental graywacke sediments to be deposited
  onto them.
Are there fossils in graywacke?
• The shale layers between the graywacke beds may
  contain microfossils that also can be used to date the
  rocks and to determine the depth of water in which
  they were deposited. Sometimes trace fossils areal
  so visible in graywacke.
• Trace fossils are the marks and tracks of animal s
  that burrowed, fed, crawled and lived in the
  sediments. Trace fossils can provide information on
  how deep the water was and how much oxygen was
  present when the sediments were deposited.
Graywacke sandstone exposed at Baker Beach in the Presidio displays
small holes, called tafoni weathering, typical of this type of rock.
Wacke (Graywacke)
• As a rule greywackes are not fossiliferous, but organic
  remains may be common in thefiner beds associated with
  them.
• Their component particles are usually not very roundedor
  polished, and the rocks have often been considerably
  indurated by recrystallization,such as the introduction of
  interstitial silica.
• In some districts the greywackes are cleaved, but they
  show phenomena of this kind much less perfectly than the
  slates.
• Some varieties include feldspathic greywacke, which is rich
  in feldspar, and lithic greywacke, which is rich in tiny rock
  fragments.
THANK YOU

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Wacke ( graywacke)

  • 3. Wacke (Graywacke) • Physically hard. • Dark grey in colour, • Enigmatic (ambiguous) rocks. • Texturally, an immature sandstone. • Composed of sand mixed with mud. Wikipedia • Graywackes are associated with graded bedding.
  • 4. Wacke (Graywacke) • It has a dark colour, indicating its deposition in the low-oxygen environment of the deep sea. • Contains more than 15% clay. • Coarse-grained sandstone that consists of poorly sorted angular to subangular grains of quartz and feldspar. • Clasts of monocrystalline quartz are often the most abundant framework component (25% to 50%), although the proportion fluctuates.
  • 5. Wacke (Graywacke) • Grains of chert, mudrock, limestone, polycrystalline quartz, and volcanic rocks are also quite common. • Clasts of detrital muscovite, biotite, and chert occur in accessory amounts. • SiO2 content of wackes ranges from 50% to 70%, reflecting the moderate amount of quartz and feldspar. http://weiminhan.files.wordpress.com/2010/03/2010-03-17_161215.jpg?w=390&h=229
  • 7. Wacke (Graywacke) • Grain size distribution is bimodal with a primary peak for framework grains and a secondary peak for matrix. • Many wackes were deposited by waning turbidity currents. • They routinely display graded bedding, sole markings, and the systenatic upward changes in sedimetary structures and grain size characteristic of turbidities.
  • 9. Wacke (Graywacke) • Deep water abyssal and bathyal body fossils, pelagic fauna and flora, and retransported shallow-waterorganic remains are all found within wacke sandstone sequences. • Some wackes were deposited within submarine fan complexes, but there are also example of more distal deposits settled out of more diffuse density flows that spread out and dispersed across broad, flat abyssal plain surfaces.
  • 10. Wacke (Graywacke) • Wackes are the dominant sandstone of the Archean. • It contains quartz, Like other sandstones, but it also has more delicate minerals and small fragments of rock (lihtics). • Its grain are not well rounded. But this hand specimen is in fact a graywacke which refers to a specific origin as well as a wacke composition and texture.
  • 11. Wacke (Graywacke) • The origin of greywacke was a problem. Gravel, sand and mud should not be laid down together, because river outflow drops heavier grains first. • Now geologists think greywacke is formed by submarine avalanches or strong turbidity currents. Wikipedia
  • 12. Formation of Greywacke sandstone • Sandstone is a type of sedimentary rock which is made from particles (sediment) that have been glued together. In this case, the sand is mixed with mud and clay and squeezed so that all the water disappears and the particles are pushed close together. • In summary, the formation of greywacke rock is a result of the rock cycle processes of erosion, transport of eroded material by rivers, deposition onto the sea floor and then pushing up by plate tectonic movement.
  • 13. Where is graywacke sandstone deposited? • Graywacke sandstone is a sedimentary rock that is made up mostly of sand-size grains that were rapidly deposited very near the source rock from which they were weathered. • Graywacke is deposited in deep ocean water near volcanic mountain ranges, where underwater landslides and density currents called turbidites quickly transport sediment short distances into a subduction zone or ocean trench. • This type of sandstone contains fewer grains made of quartz and more made of feldspars, volcanic rock fragments, as well as silt and clay than most sandstone. • It is therefore also known as “dirty sandstone.” • The volcanic rock fragments give graywacke a greenish- gray color.
  • 14. What makes the beds in graywacke? • Graywacke sandstone deposits display flat-lying beds, each composed of sedimentary particles of different sizes. • The sandstone beds can be from inches to many feet thick and are often separated by thin, dark shale beds. • Each sandstone bed was formed during a single turbidite or submarine landslide event and was deposited over a short period of time from hours to days. • The thin shale beds formed between turbidite events, when mud particles slowly settled to the sea floor, and may represent thousands of years.
  • 15. What makes the beds in graywacke? • Turbidites display graded bedding, that is, the grain size decreases upwards in the bed. • During a turbidite event, the larger and heavier grains settle out first. • As the energy in the landslide event decreases, finer and finer particl es settle out to the sea floor.
  • 16. Are there fossils in graywacke? • Graywacke sandstone occasionally contains fossil mollusks which sometime scan be used to tell when the rock was deposited. • Sandstone deposits of the Franciscan Complex contain clams and ammonites from the Jurassic and Cretaceous periods. • These provide ages for when the Franciscan oceanic rocks got close enough to North America for continental graywacke sediments to be deposited onto them.
  • 17. Are there fossils in graywacke? • The shale layers between the graywacke beds may contain microfossils that also can be used to date the rocks and to determine the depth of water in which they were deposited. Sometimes trace fossils areal so visible in graywacke. • Trace fossils are the marks and tracks of animal s that burrowed, fed, crawled and lived in the sediments. Trace fossils can provide information on how deep the water was and how much oxygen was present when the sediments were deposited.
  • 18. Graywacke sandstone exposed at Baker Beach in the Presidio displays small holes, called tafoni weathering, typical of this type of rock.
  • 19. Wacke (Graywacke) • As a rule greywackes are not fossiliferous, but organic remains may be common in thefiner beds associated with them. • Their component particles are usually not very roundedor polished, and the rocks have often been considerably indurated by recrystallization,such as the introduction of interstitial silica. • In some districts the greywackes are cleaved, but they show phenomena of this kind much less perfectly than the slates. • Some varieties include feldspathic greywacke, which is rich in feldspar, and lithic greywacke, which is rich in tiny rock fragments.