Shiva crater

, the Hindu god of destruction and renewal.

Its age is estimated to 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, the formation is approximately 600 kilometers long by 400 km wide. It is estimated that a crater of that size would have been made by an asteroid or comet approximately 40 km in diameter. The Shiva complex adds weight to the theory that the K-T extinction was caused by a massive asteroid fragmenting and hitting the Earth in several locations, known as the "Multiple impact theory."cite journal |author=Chatterjee, Sankar|authorlink=Sankar Chatterjee |coauthors= |year=1997 |month=August |title=Multiple Impacts at the KT Boundary and the Death of the Dinosaurs|journal= 30th International Geological Congress|volume= 26|issue= |pages=31–54 |id= |url=http://books.google.com/books?hl=en&lr=&id=3IORF1Ei3LIC&oi=fnd&pg=PA31&dq=Chatterjee+and+Rudra+1996+Shiva&ots=ngYDm9C0s_&sig=pv_rRhdm0ZaWQ32GCjDhgN4SnuA#PPA31,M1|accessdate= 2008-02-22 |quote= ]

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. 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. [cite journal |author=Agrawal, P., Pandey, O |coauthors= |year=2000 |month=November |title= Thermal regime, hydrocarbon maturation and geodynamic events along the western margin of India since late Cretaceous|journal= Journal of Geodynamics|volume= 30|issue=4 |pages=439–459 |id= |laysummary= 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|accessdate= |quote= |doi= 10.1016/S0264-3707(00)00002-8 ]

Feature specifics

Geology and morphology

Unlike many known crater formations, the Shiva complex is teardrop shaped, 600 kilometers by 400 kmcite 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] (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;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= ] other researchers have noted that rock faults and impacts could modify the crater shape.cite book|author=Melosh, H. J|year=1989|title= Impact cratering: a geologic process.|publisher= Oxford University Press|location=New York] 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.

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;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= ] 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= ] these types of rocks and features suggest an impact origin. In addition, the K-T boundary layer in India is one meter thick. 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.

hiva 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. [ [http://www.springerlink.com/content/j0204x4768353r20/ SpringerLink - Journal Article ] ] 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 to cause the mass extinction.cite web|author=Davis, John W|date=2006-11-15|url=http://www.depts.ttu.edu/communications/news/stories/06-11-dinosaur.php|title=Texas Tech Paleontologist Finds Evidence That Meteorite Strike Near Bombay May Have Wiped Out Dinosaurs|work=Texas Tech University|accessdate=2008-02-12] [Dinosaur theory now extinct?; Asteroid didn't destroy species, researchers find Mexican crater older than first believed; [ONT Edition] Toronto Star. Toronto, Ont.: Mar 2, 2004. pg. A.02]

While Chatterjee is confident that Shiva was one of many impacts, stating that "the K-T extinction was definitely a multiple-impact scenario,"cite web|author=Mullen, Leslie|date=2004-11-02|url=http://www.spacedaily.com/news/deepimpact-04r.html|title=Shiva: Another K-T Impact?|work=SpaceDaily|accessdate=2008-02-20 - original article at [http://www.astrobio.net/news/article1281.html source] ] 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.

References

External links

* [http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_58126.htm 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).
* [http://www.spacedaily.com/news/deepimpact-04r.html Deep Impact - Shiva: Another K-T Impact?] by Leslie Mullen for Astrobiology Magazine (Nov. 2004).