Phoenix used for Precise U-Pb Study of end-Triassic Extinction

Phoenix TIMS used for precise U-Pb DATINGMore than 200 million years ago, the end-Triassic extinction wiped out 76 percent of marine and terrestrial species.

Whilst it’s not entirely clear what caused the end-Triassic extinction, it seems that over a relatively short period of time volcanism from the Central Atlantic Magmatic Province (CAMP) erupted huge amounts of lava and gas. This sudden release of gases into the atmosphere may have created intense global warming and ocean acidification killing off thousands of plant and animal species but until now the precise timing of events has been the subject of some debate.

Now researchers at MIT, Columbia University and elsewhere have determined that the volcanism coincided precisely with the extinction, providing strong evidence that the volcanic activity did indeed trigger the end-Triassic extinction. Their results are published in the journal Science.

The team very precisely determined the age of basalts and other features along the East Coast of the United States and in Morocco.  The geology of both regions includes igneous rocks from the CAMP eruptions as well as sedimentary rocks that accumulated in a large lake. The researchers used a combination of techniques, including very high precision U-Pb dating on an Isotopx Phoenix 62 TIMS to date the rocks and to pinpoint CAMP’s beginning and duration.

From its measurements, the team reconstructed the region’s volcanic activity 201 million years ago, discovering that the eruption of magma occurred in repeated bursts over a period of 40,000 years.

“This extinction happened at a geological instant in time,” says Sam Bowring, the Robert R. Shrock Professor of Geology in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “There’s no question the extinction occurred at the same time as the first eruption.”

The paper’s co-authors are Terrence Blackburn (who led the project as part of his PhD research) and Noah McLean of MIT; Paul Olsen and Dennis Kent of Columbia; John Puffer of Rutgers University; Greg McHone, an independent researcher from New Brunswick; E. Troy Rasbury of Stony Brook University; and Mohammed Et-Touhami of the Université Mohammed Premier Oujda in Morocco.

The end-Triassic extinction is one of five major mass extinctions in the last 540 million years. For several of these events large igneous provinces arose at about the same time. But, as Bowring points out, “Just because they happen to approximately coincide doesn’t mean there’s cause and effect.” For example, while massive lava flows overlapped with the extinction that wiped out the dinosaurs, scientists have linked that extinction to an asteroid collision.

 

Highest Possible Precision

“If you really want to make the case that an eruption caused an extinction, you have to be able to show at the highest possible precision that the eruption of the basalt and the extinction occurred at exactly the same time,” Bowring says.

In the case of the end-Triassic, Bowring says researchers have dated volcanic activity to right around the time fossils disappear from the geologic record, providing evidence that CAMP may have triggered the extinction. But these estimates have a margin of error of 1 million to 2 million years. “A million years is forever when you’re trying to make that link,” Bowring says.

To determine how long the volcanic eruptions lasted, the group combined astrochronology and geochronology. The former technique links variations in sediments to changes in the tilt of the Earth (Milankovich Cycles) with the resulting climate change being preserved in the cyclicity of sediments.

Bowring says the technique is good for directly dating rocks up to 35 million years old, but beyond that, it’s unclear how reliable the technique can be. His team used astrochronology to estimate the age of the sedimentary rocks and then tested those estimates against high-precision zircon U-Pb dates from CAMP basalts provided by the Phoenix TIMS at MIT. Rocks were dated to within approximately 30,000 years in 200 million – an incredibly precise measurement in geologic terms.

Taken together, the geochronology and astrochronology techniques gave the team precise estimates for the onset of volcanism 200 million years ago, and revealed three bursts of magmatic activity over 40,000 years — an exceptionally short period of time during which massive amounts of carbon dioxide and other gas emissions may have drastically altered Earth’s climate, killing off thousands of plant and animal species.

While the team’s evidence is the strongest thus far to link volcanic activity with the end-Triassic extinction, Bowring says more work can be done. “The CAMP province extends from Nova Scotia all the way down to Brazil and West Africa,” Bowring says. “I’m dying to know whether those are exactly the same age or not. We don’t know.”

 

Full article at  Science Daily, link to the paper in Science (subscription required).

For more information on high precision U-Pb dating  available on Phoenix 62 TIMS contact Colin Fenwick.

 

 

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Category: Geology, Customer News, Applications
Published: Tuesday, March 26th, 2013 at 2:10 pm

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