Impact Geology

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Impact Geology

• The Geological Implications and effects of
  extraterrestrial Impacts

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Impact Geology

• I will cover in this presentation
• What is Impact Geology
• Resultant Features of an Impact
• The K/T Boundary worldwide evidence of an Impact
  event.
• Cretaceous Extinction event.

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What is Impact Geology?

• When an Asteroid or Comet
• collides with the earth, there
• are going to be long lasting
• visual and geological effects
• which will disappear over
• relatively short periods of geologic time
  through processes of denudation.

Image Courtesy of NASA
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Image Reference Prinz, T. (no date)
Time of Impact
Moments after Impact (in order of seconds/minutes)
Crater Before Denudation
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What is Impact Geology?

• When an Asteroid or Comet
• collides with the earth, there
• are going to be long lasting
• visual and geological effects
• which will disappear over relatively short
  periods of geologic time through processes of
  denudation.
• Impact Geology is the recognition and study of
  these features.

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Resultant Features

• Direct Resultant Features
• Impact Crater
• Ejecta Rocks ejected from Crater
• Tektites Glass Spherules
• Shocked Quartz
• Indirect Resultant Features
• Preserved Wood Ash
• Sediments

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Resultant Features

• Direct Resultant Features
• Impact Crater
• Ejecta Rocks ejected from Crater
• Tektites Glass Spherules
• Shocked Quartz
• Indirect Resultant Features
• Preserved Wood Ash
• Sediments

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Impact Craters
Least Denuded
Most Denuded
1 mile
40 miles
100 miles
Meteor Crater, Arizona, U.S.A. (50 Ka)
Manicouagan Impact Crater, Canada. (200 Ma)
Chixulub Crater, Yucatán Peninsula, Mexico. (65
Ma) Crater Rim Marked by map pins

• Processes of denudation erase the feature from
  the surface.
• Depending upon the rocks in which the crater
  formed, this process can take hundreds of
  millions of years.

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Resultant Features

• Direct Resultant Features
• Impact Crater
• Ejecta Rocks ejected from Crater
• Tektites Glass Spherules
• Shocked Quartz
• Indirect Resultant Features
• Preserved Wood Ash
• Sediments

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Ejecta

• Rock Ejecta
• Tektites

Photo Credit NASA / Hubble Space Telescope
(a) (b)
Photos Courtesy of, (a) http//athene.as.arizona.
edu/lclose/teaching/a202/lect7.html (b)
www.wikipedia.org (both last accessed 23/11/07)
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Resultant Features

• Direct Resultant Features
• Impact Crater
• Ejecta Rocks ejected from Crater
• Tektites Glass Spherules
• Shocked Quartz
• Indirect Resultant Features
• Preserved Wood Ash
• Sediments

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Shocked Quartz
Pressure (Shock) Direction
Image Ref rst.gsfc.nasa.gov/Sect18/Sect18_4.html
Pressure (Shock) Direction
Lines of Pressure Deformation
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Resultant Features

• Direct Resultant Features
• Impact Crater
• Ejecta Rocks ejected from Crater
• Tektites Glass Spherules
• Shocked Quartz
• Indirect Resultant Features
• Preserved Wood Ash
• Sediments

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Indirect Evidence

• Indirect evidence for Impacts mainly focuses on
  sediments that contain
• High concentrations of Extraterrestrial Elements
  (rare on Earth, such as Iridium at K/T Boundary)
• Large amounts of wood ash
• Ocean sediments far inland

White Iridium-rich sediments as first discovered
by Walter Alvarez in Italy (K/T Boundary)
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WARNING!

• Not all Circular features visible from the air
  are Impact Craters.

Example Ardnamurchan, Scotland. This is in fact
a Ring Dyke feature.
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Further Reading

• Case Studies
• Meteor Crater, Arizona, USA
• Shoemaker, E.M. and Kieffer, S.W. (1979)
  Guidebook to the Geology of Meteor Crater,
  Arizona Arizona State University, Tempe
• Chesapeke Bay, USA
• Stanley, S.M. (2005) Earth System History 2nd
  edition, W H Freeman Co. New York. pp.465
• Chixulub Crater, Mexico
• Stanley, S.M. (2005) Earth System History 2nd
  edition, W H Freeman Co. New York. pp.433-437
• Subjects
• Shocked Quartzs and Tektites
• Stanley, S.M. (2005) Earth System History 2nd
  edition, W H Freeman Co. New York. pp.433-437
• Impact Extinction Theory
• Cowen, R. (2006) History Of Life 4th Edition,
  Blackwell Publishing, Malden (USA)/Oxford (UK)
• Further, more in-depth reading can be found at
  the National Oceanographic Library, NOC,
  Southampton

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References

• Dressler, B.O. et al. (1994) Large Meteorite
  Impacts Planetary formation Geological
  Society of America Special Paper 293.
• Silver L.T. Schultz, P.H. (1982) Geological
  Implications of Impacts of large Asteroids and
  comets on the earth Geological Society of
  America Special Paper 190

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Any Questions?