Deccan volcanic eruption behind mass extinction of dinos

November 14th, 2007 - 8:08 am ICT by admin  
“It’s the first time we can directly link the main phase of the Deccan Traps to the mass extinction,” said Princeton University palaeontologist Gerta Keller.

The main phase of the Deccan eruptions spewed 80 percent of the lava, which spread out for hundreds of miles.

It is believed to have released ten times more climate altering gases into the atmosphere than the nearly concurrent Chicxulub meteor impact, according to volcanologist Vincent Courtillot from the Physique du Globe de Paris.

Keller said the crucial link between the eruption and the mass extinction came in the form of microscopic marine fossils that are known to have evolved immediately after the mysterious mass extinction event.

She said the same telltale fossilized planktonic foraminifera were found at Rajahmundry near the Bay of Bengal, about 1000 kilometres from the centre of the Deccan Traps near Mumbai.

At Rajahmundry, two lava “traps” exist, each containing four layers of lava. Between these traps are about nine metres of marine sediments.

Keller said the sediments just above the lower trap, which was the mammoth main phase, contained the incriminating microfossils.

Previous research had first narrowed the Deccan eruption timing to within 800,000 years of the extinction event.

Scientists had used paleomagnetic signatures of Earth’s changing magnetic field frozen in minerals that crystallized from the cooling lava to arrive at their conclusion.

Then radiometric dating of argon and potassium isotopes in minerals narrowed the age to within 300,000 years of the 65-million-year-old Cretaceous-Tertiary (a.k.a. Cretaceous-Paleogene) boundary, sometimes called the K-T boundary.

Keller said the microfossils gave a far more specific date, as they demonstrated directly that the biggest phase of the eruption ended right when the aftermath of the mass extinction event began.

She said that sort of clear-cut timing has been a lot tougher to pin down with Chicxulub-related sediments, which predate the mass extinction.

“Our results are consistent and mutually supportive with a number of new studies, including Chenet, Courtillot and others (in press) and Jay and Widdowson (in press), that reveal a very short time for the main Deccan eruptions at or near the K-T boundary and the massive carbon dioxide and sulphur dioxide output of each major eruption that dwarfs the output of Chicxulub,” said Keller.

“Our K-T age control combined with these results strongly points to Deccan volcanism as the likely leading contender in the K-T mass extinction,” she said.

She further said the Deccan Traps could also provide answer to the mystery as to why did it take close to 300,000 years for marine species to recover from the extinction event.

“The solution is in the upper, later Deccan Traps eruptions. It’s been an enigma. The very last one was Early Danian, 280,000 years after the mass extinction, which coincides with the delayed recovery,” said Keller.

Keller and her colleagues are now planning to explore the onset of the main phase of Deccan volcanism, that is, the rocks directly beneath the main phase lavas at Rajahmundry.

Keller and her collaborator Thierry Adatte from the University of Neuchatel, Switzerland, presented their findings on Tuesday, October 30 at the annual meeting of the Geological Society of America in Denver. (ANI)

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