Shiva Impact

The dinosaurs' true demise?

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Location of Shiva Impact
Location of Shiva Impact

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Dec. 5, 2011 — What is being called the Shiva Impact, might have created the Shiva Basin off the coast of India — perhaps the largest, multi-ringed impact crater on the face of the earth. A new study suggests this impact — and not the better known one that occurred at about the same time at the northern end of what is today Mexico's Yucatan Peninsula — was responsible for killing off the dinosaurs (KT extinction).

Sankar Chatterjee of Texas Tech University and a team of researchers took a close look at the massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and gas resources. Some complex craters are among the most productive hydrocarbon sites on the planet. Chatterjee will present his research at this month's Annual Meeting of the Geological Society of America in Portland, Oregon.

"If we are right, this is the largest crater known on our planet," Chatterjee said. "A bolide of this size, perhaps 40 kilometers (25 miles) in diameter creates its own tectonics."

By contrast, the object that struck the Yucatan Peninsula, and is commonly thought to have killed the dinosaurs was between 8 and 10 kilometers (5 and 6.2 miles) wide.

It's hard to imagine such a cataclysm. But if the team is right, the Shiva impact vaporized Earth's crust at the point of collision, leaving nothing but ultra-hot mantle material to well up in its place. It is likely that the impact enhanced the nearby Deccan Traps volcanic eruptions, suggests Chatterjee, that covered much of western India. What's more, he says, the impact might have broken the Seychelles islands off of the Indian tectonic plate, and sent them drifting toward Africa.

The geological evidence is dramatic. Shiva's outer rim forms a rough, faulted ring some 500 kilometers (310 miles) in diameter, encircling the central peak, known as the Bombay High, which rises 3 miles above the ocean floor (about the height of Mount McKinley). Much of the crater lies submerged beneath India's continental shelf, but where it does come ashore it is marked by tall cliffs, active faults and hot springs. The impact appears to have sheared or destroyed much of the 30-mile-thick granite layer in the western coast of India.

The team plans to go India later this year to examine rocks drilled from the center of the putative crater for proof that the strange basin was formed by a gigantic impact.

"Rocks from the bottom of the crater will tell us the telltale sign of the impact event from shattered and melted target rocks. And we want to see if there are breccias, shocked quartz, and an iridium anomaly," Chatterjee said. Asteroids are rich in iridium, and such anomalies are thought of as the fingerprint of an impact.

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Adapted from materials obtained from the AAAS