Shiva crater

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This computer graphic shows the elevation of the formation, with red peaks being the highest. Specific basins are labeled.
This computer graphic shows the elevation of the formation, with red peaks being the highest. Specific basins are labeled.

The Shiva crater is an ancient sea floor structure 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, 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.

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.[1] The debate over whether or not Shiva is a crater is ongoing, but if Shiva is in fact an impact feature, 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."[2]

Contents

[edit] Discovery

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[edit] Feature specifics

[edit] Geology and morphology

Unlike many known crater formations, the Shiva complex is teardrop shaped, 600 kilometers by 400 km[3] (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;[4] other researchers have noted that rock faults and impacts could modify the crater shape.[5] 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.[3]

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;[6][7] these types of rocks and features suggest an impact origin.[3] In addition, the K-T boundary layer in India is one meter thick.[3] 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.

[edit] Shiva and mass extinction

Main article: Cretaceous–Tertiary extinction event

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.[8] 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.[9]

While Chatterjee is confident that Shiva was one of many impacts, stating that "the K-T extinction was definitely a multiple-impact scenario,"[10] 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.[10]

[edit] References

  1. ^ Agrawal, P., Pandey, O (November 2000). "Thermal regime, hydrocarbon maturation and geodynamic events along the western margin of India since late Cretaceous". Journal of Geodynamics 30 (4): 439–459. doi:10.1016/S0264-3707(00)00002-8. Lay summary. 
  2. ^ Chatterjee, Sankar (August 1997). "Multiple Impacts at the KT Boundary and the Death of the Dinosaurs". 30th International Geological Congress 26: 31–54. 
  3. ^ a b c d Teters, Thomas J. (2005-07-28). Wiping out the Dinosaur with Five Simultaneous Impacts…. Starmon.com. Retrieved on 3008-01-23.
  4. ^ 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. 
  5. ^ Melosh, H. J (1989). Impact cratering: a geologic process.. New York: Oxford University Press. 
  6. ^ 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. 
  7. ^ 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. 
  8. ^ SpringerLink - Journal Article
  9. ^ 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 on 2008-02-12.
  10. ^ a b Mullen, Leslie (2004-11-02). Shiva: Another K-T Impact?. SpaceDaily. Retrieved on 2008-02-20. - original article at source

[edit] External links

Coordinates: 18°40′N, 70°14′E

Cretaceous–Tertiary extinction event
Proposed K-T boundary craters
Boltysh crater Chicxulub Crater
Shiva crater Silverpit crater
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