Shiva crater: Difference between revisions
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==Feature specifics== |
==Feature specifics== |
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===Geology and morphology=== |
===Geology and morphology=== |
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Unlike many known crater formations, the Shiva complex is teardrop shaped, 600 kilometers by 400 km<ref name="starmon morph">{{cite web|author=Teters, Thomas J.|date=2005-07-28|url=http://starmon.com/KT_craters.html|title=Wiping out the Dinosaur with Five Simultaneous Impacts…|work=Starmon.com|accessdate=3008-01-23}}</ref> (373 by 249 mi). The complex itself is also unusually rectangular. Chatterjee hypothesizes that the low angle of an impact combined with boundary fault lines and unstable rock led to this unusual formation;<ref name="chatterjee 5">{{cite journal |last=Chatterjee|first= Sankar |authorlink= Sankar Chatterjee|coauthors= |year=2002 |month= |title=Shiva Structure: A Possible K-T Boundary Impact Crater on the Western Shelf of India |journal=Special Publications, Museum Texas Tech University |volume= |issue= |pages=5-6 |id= |url= |accessdate= |quote= }}</ref> other researchers have noted that rock faults and impacts could modify the crater shape.<ref name="melosh impact">{{cite book|author=Melosh, H. J|year=1989|title= Impact cratering: a geologic process.|publisher= Oxford University Press|location=New York}}</ref> Similar to craters of its large size, the Shiva complex has concentric rings with a collapsed outer rim and a central spire- Shiva's is as high as Mount Everest.<ref name="starmon morph"/> |
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The age of the crater is inferred from the Deccan traps, which contain high amounts of [[iridium]] (an element rare on Earth but common in asteroids.) The crater also contains larger than average amounts of alkaline melt rocks, [[shocked quartz]], and iron oxide laced with iridium;<ref name="chatterjee 20">{{cite journal |last=Chatterjee|first= Sankar |authorlink= Sankar Chatterjee|coauthors= |year=2002 |month= |title=Shiva Structure: A Possible K-T Boundary Impact Crater on the Western Shelf of India |journal=Special Publications, Museum Texas Tech University |volume= |issue= |pages=20 |id= |url= |accessdate= |quote= }}</ref><ref name="bhandari, et al">{{cite journal |author=Bhandari, N., et al |authorlink= |coauthors= |year=2002 |month= |title=Global occurrence of magnetic and superparamagnetic iron phases in Cretaceous-Tertiary boundary clays. |journal=Geological Society of America Special Paper |volume= |issue=356 |pages=201-211 |id= |url= |accessdate= |quote= }}</ref> these types of rocks and features suggest an impact origin.<ref name="starmon morph"/> In addition, the K-T boundary layer in India is one meter thick.<ref name="starmon morph"/> Assuming that the clay layer is the remains of scattered deposits from an asteroid impact, the thick layer would suggest that the actual impact occurred near India. |
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===Shiva and mass extinction=== |
===Shiva and mass extinction=== |
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Revision as of 15:02, 22 February 2008
The Shiva crater is an ancient sea floor structure —thought by some researchers to be an impact crater— located beneath the Indian Ocean, west of Mumbai, India. It was named by the paleontologist Sankar Chatterjee after Shiva, the Hindu god of destruction and renewal.
According to the impact hypothesis, it formed around 65 million years ago, at about the same time as a number of other impact craters and the Cretaceous-Tertiary extinction event (K-T boundary). Although the site has shifted since its formation because of sea floor spreading, it has been suggested that when pieced together the putative crater would have been about 600 km by 400 km across and 12 km deep (and may be just part of a larger crater). It is estimated that a crater of that size would have been made by an asteroid or comet 40 km in diameter.
At the time of the K-T extinction, India was located over the Réunion hotspot of the Indian Ocean. Hot material rising from the mantle flooded portions of India with a vast amount of lava, creating a plateau known as the Deccan Traps. The eruptions started a few million years before the K-T extinction and become very abundant at about 65 million years ago. The fact that the supposed Shiva crater lies near the Deccan Traps has been claimed as support for the controversial idea that the eruptions were triggered or accelerated by an impact event. However, it is now thought that impact events ought to cause eruptions on the opposite side of the Earth to where they impacted. It has been hypothesized that either the crater or the deccan traps associated with the area are the reason for the high level of oil and natural gas reserves in the region.[1]
Discovery
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Feature specifics
Geology and morphology
Unlike many known crater formations, the Shiva complex is teardrop shaped, 600 kilometers by 400 km[2] (373 by 249 mi). The complex itself is also unusually rectangular. Chatterjee hypothesizes that the low angle of an impact combined with boundary fault lines and unstable rock led to this unusual formation;[3] other researchers have noted that rock faults and impacts could modify the crater shape.[4] Similar to craters of its large size, the Shiva complex has concentric rings with a collapsed outer rim and a central spire- Shiva's is as high as Mount Everest.[2]
The age of the crater is inferred from the Deccan traps, which contain high amounts of iridium (an element rare on Earth but common in asteroids.) The crater also contains larger than average amounts of alkaline melt rocks, shocked quartz, and iron oxide laced with iridium;[5][6] these types of rocks and features suggest an impact origin.[2] In addition, the K-T boundary layer in India is one meter thick.[2] Assuming that the clay layer is the remains of scattered deposits from an asteroid impact, the thick layer would suggest that the actual impact occurred near India.
Shiva and mass extinction
The discovery of Shiva and other features similar to impact craters like the Chicxulub site has led to the hypothesis that there were in fact multiple impacts which caused the massive extinction event at the end of the Cretaceous period.[7] Other theories have argued that since the Chicxulub impact is believed by some researchers to have occurred earlier than the extinction of the dinosaurs, Shiva's impact was enough cause the mass extinction.[8]
While Chatterjee is confident that Shiva was one of many impacts, stating that "the K-T extinction was definitely a multiple-impact scenario,"[9] other scientists remain unconvinced both that the extinction event was caused by multiple impacts, and that the Shiva feature is in fact a crater; for example, a recent article in the journal Nature suggested another supposed impact feature at Silverpit was in fact a sinkhole depression.[9]
References
- ^ http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V9X-402K864-4&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3b9de0be5aa1e39026ba23a166b27643
- ^ a b c d Teters, Thomas J. (2005-07-28). "Wiping out the Dinosaur with Five Simultaneous Impacts…". Starmon.com. Retrieved 3008-01-23.
{{cite web}}: Check date values in:|accessdate=(help) - ^ Chatterjee, Sankar (2002). "Shiva Structure: A Possible K-T Boundary Impact Crater on the Western Shelf of India". Special Publications, Museum Texas Tech University: 5–6.
{{cite journal}}: Cite has empty unknown parameters:|month=and|coauthors=(help) - ^ Melosh, H. J (1989). Impact cratering: a geologic process. New York: Oxford University Press.
- ^ Chatterjee, Sankar (2002). "Shiva Structure: A Possible K-T Boundary Impact Crater on the Western Shelf of India". Special Publications, Museum Texas Tech University: 20.
{{cite journal}}: Cite has empty unknown parameters:|month=and|coauthors=(help) - ^ Bhandari, N.; et al. (2002). "Global occurrence of magnetic and superparamagnetic iron phases in Cretaceous-Tertiary boundary clays". Geological Society of America Special Paper (356): 201–211.
{{cite journal}}: Cite has empty unknown parameters:|month=and|coauthors=(help); Explicit use of et al. in:|author=(help) - ^ http://www.springerlink.com/content/j0204x4768353r20/
- ^ Davis, John W (2006-11-15). "Texas Tech Paleontologist Finds Evidence That Meteorite Strike Near Bombay May Have Wiped Out Dinosaurs". Texas Tech University. Retrieved 2008-02-12.
- ^ a b Mullen, Leslie (2004-11-02). "Shiva: Another K-T Impact?". SpaceDaily. Retrieved 2008-02-20. - original article at source
External links
- The Shiva Crater: Implications for Deccan Volcanism, India-seychelles Rifting, Dinosaur Extinction, and Petroleum Entrapment at the Kt Boundary by Chatterjee, Sankar; Guven, Necip; Yoshinobu, Aaaron; and Donofrio, Richard; Paper No. 60-8, 2003 Seattle Annual Meeting of Geological Society of America (November 2–5, 2003).
- Deep Impact - Shiva: Another K-T Impact? by Leslie Mullen for Astrobiology Magazine (Nov. 2004).