Manson impact structure

Coordinates: 42°35′N 94°33′W / 42.583°N 94.550°W / 42.583; -94.550
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Main article:
Iowa geology
Manson impact structure
Manson impact location shown in red on bedrock map of Iowa
Impact crater/structure
ConfidenceConfirmed
Diameter35 km (22 mi)
Age73.8 ± 0.3 Ma
Late Cretaceous
ExposedNo
DrilledYes
Bolide typeChondrite
Location
Coordinates42°35′N 94°33′W / 42.583°N 94.550°W / 42.583; -94.550
CountryUnited States
StateIowa
MunicipalityManson
Manson impact structure is located in the United States
Manson impact structure
Location of the impact structure in Iowa, United States
Manson impact structure is located in Iowa
Manson impact structure
Manson impact structure (Iowa)

The Manson impact structure is an impact structure near the site of Manson, Iowa where an asteroid or comet nucleus struck the Earth during the Cretaceous Period, approximately 74 Ma.[1] It was one of the largest known impact events to have happened in North America.[2] Previously it was thought to have led to the extinction of the dinosaurs until isotopic ages proved that it was too old.[3]

Description

Extent of the Manson impact structure[4]

No surface evidence exists due to comparatively recent coverage by

volcanic steam explosion). Further investigation was undertaken by Robert S. Dietz who proposed an impact origin in 1959 and by Nicholas Short in 1966 who produced evidence of shocked quartz grains which confirmed the impact origin
of the structure.

In 1991 and 1992 the U.S. Geological Survey along with others including the Iowa Geological Survey conducted detailed research in part to test the possible connection of the Manson impact structure with the Cretaceous–Paleogene extinction event. The 40
Ar/39
Ar isotope ratio dating of the core from the impact structure gave an age of about 74 Ma, or about 10 Ma older than the K–T boundary.[6]

The impactor is considered to have been a

sedimentary formations of Paleozoic age, Devonian through Cretaceous. Limestone layers that give the rest of Iowa hard water were instantaneously vaporized down to the basement rocks, giving Manson the anomalous soft water that it has today.[8]

References

  1. ^ "Manson". Earth Impact Database. Planetary and Space Science Centre University of New Brunswick Fredericton. Retrieved 2017-10-09.
  2. ^ "The Manson impact was the biggest thing that has ever occurred on the mainland United States. Of any type. Ever," Bill Bryson, A Short History of Nearly Everything 2003:238.
  3. ^ Pfeiffer, Eric. "Ancient meteorite standing between one Iowa town and its water supply". Yahoo! News. Retrieved 17 February 2012.
  4. ^ Hartung, J. B., Kunk, M.J. and Anderson, R.R., Geology, geophysics, and geochronology of the Manson impact structure. Global Catastrophes in Earth History, Geological Society of America, Special Paper 247, pp. 207-221. 1990.
  5. ^ Koeberl and Anderson 1996.
  6. S2CID 42594905
    .
  7. ^ Bryson 2002:237.
  8. ^ Bryson 2002:237.

Bibliography

  • Christian Koeberl and Raymond R. Anderson, eds; 1996, The Manson Impact Structure, Iowa: Anatomy of an Impact Crater, Geological Society of America Special Paper 302,
    ISBN 0-8137-2302-7

Further reading

External links

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