Cubic Zirconiums and dinosaurs - geochronology marches on!

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Reilly

Mountain climber
The Other Monrovia- CA
Topic Author's Original Post - Mar 22, 2013 - 09:16am PT
Big news from the Rockhound Dept!



Volcano-induced die-off paved way for dinosaurs, study suggests

New findings support the theory that a massive volcanic event tore apart Pangea and dramatically changed Earth's climate, ushering in the biggest biological shift in the planet's history.


By Geoffrey Mohan, Los Angeles Times
March 21, 2013, 5:14 p.m.


More than 200 million years ago, toothy crocodile-like creatures stalked a hot, dry mega-continent while squid-like mollusks with spiral shells drifted in the surrounding ocean. Then, in what passes for an instant in geologic time, they vanished making way for the age of the dinosaurs.

How some 50% of terrestrial vertebrates and an even larger share of marine life died off in the late Triassic period has become more clear from new research published online Thursday in the journal Science.

The work lends greater validity to the theory that a massive volcanic event tore apart that continent and blanketed Earth's atmosphere, turning the ocean acidic and snuffing out animals that could not adapt. That geologic event, which created the Atlantic Ocean, ushered in the biggest biological shift in the planet's history.

"It set the stage for the dinosaurs to take over, biologically," said Paul Olsen, a geologist at Columbia University's Lamont-Doherty Earth Observatory, who did much of the field work on which the study is based.

Pushed by the nascent Atlantic, the ruptured pieces of Pangea drifted off and further split, carrying the evidence of ecological collapse to such distant locales as Morocco, Nova Scotia and New Jersey.

Matching the fossil record in sedimentary rock with the dense basalt formed by the volcanic eruptions proved difficult, even with sophisticated tools of the 21st century. It was difficult to say whether the eruptions happened before the mass extinction.

Olsen and others, however, hacked rare zircon crystals from the basalt formations and measured traces of lead and uranium for radiometric dating tests. The results narrowed the margin of error in dating the lava to a mere 15,000 to 22,000 years stunning precision for geochronology.

The crystals were not easy to find, or to process, although Olsen mined one from a rocky outcrop at a New Jersey highway exit near his home.

Zirconium is a stubborn element that did not readily mix with the magma but formed large crystals of zirconium silicate best known as the mineral zircon that incorporated uranium in their lattices. Over time, that uranium decayed to lead. Measuring the ratio of uranium to lead enabled the scientists to date the rock with great precision.

"People have long suspected that flood basalts had caused the extinction event, but the problem was there was an uncertainty of 1 [million] to 3 million years," said geologist Terrence Blackburn of the Carnegie Institution in Washington, the study's lead author.

The more refined ages put "a sharper tip on that pencil," said Paul Renne, a geochronologist at UC Berkeley who has done similar research but wasn't involved in the new study. "It says all this stuff is true and here's when it happened."

The mass extinction occurred 201.56 million years ago, around the age of one of the basalt rock formations dated by the team, according to the researchers.

There were several pulses that spewed millions of cubic miles of lava, each separated by tens of thousands of years, Blackburn said. The first of them was probably big enough to cause the extinction, and subsequent ones occurred as life began to recover and dinosaurs exploited the territory left empty by the mass die-off.

For now, the data "strongly imply a causal relationship" between the eruption that broke up Pangea and the extinction that occurred around the same time, the researchers concluded. How the die-off happened "remains unclear," they wrote, though they offer support for a massive climatic shift brought on by volcanoes.

Renne praised the researchers for their "very clever" use of zircon. But he noted that focusing on these relatively obscure pockets could introduce some bias. "If you're only looking at these lavas, you may not be sampling a representative suite," he said.

If there is a lesson for modern climate change, it is mixed. Doubling the amount of carbon in the atmosphere in 20,000 years or less which scientists say occurred in the late Triassic would be catastrophic to life on Earth, Olsen said. Industrialization is probably adding carbon to the atmosphere at a far more rapid pace.

"You're basically turning the ocean into soda pop," he said. "That's the problem we're facing now turning the ocean acidic. Here we are, doing it in less time."

It may be too early to draw a parallel with modern times, however. Carbon in the atmosphere was far higher to begin with during the Triassic, Olsen noted.

"It would be a mistake to assume we're headed into a mass extinction," he said.

geoffrey.mohan@latimes.com


Copyright 2013, Los Angeles Times

Birth of the dinosaur era
cliffhanger

Trad climber
California
Mar 22, 2013 - 01:23pm PT
Interesting research. Thanks
Reilly

Mountain climber
The Other Monrovia- CA
Topic Author's Reply - Mar 22, 2013 - 08:04pm PT
I thought there were a bunch of geologists here?
nature

climber
Boulder, CO
Mar 22, 2013 - 08:16pm PT
raises hand (other hand has beer proving my entry in the geologist club).


wow... that kind of resolution on geochronology is crazy...
rottingjohnny

Sport climber
mammoth lakes ca
Mar 22, 2013 - 08:17pm PT
Geology...? Where are the crotch shots Lindsay Lohan getting out of her Limo...?
Dingus McGee

Social climber
Laramie
Mar 24, 2013 - 06:24am PT
It may be too early to draw a parallel with modern times, however. Carbon in the atmosphere was far higher to begin with during the Triassic, Olsen noted.

It is the rate of change of co2 now stupid that exceeds any in the past!
Jaybro

Social climber
Wolf City, Wyoming
Mar 24, 2013 - 06:48am PT
True, Dingus, but fascinating nonethe less. Refining the dates and causes of Any of the big extinctions is a big deal in the paleo world. It will be interesting, in half a billion years or so to see what conclusions they come up with when picking over our own bones.
Dr. F.

Big Wall climber
SoCal
Mar 24, 2013 - 09:00am PT
Cubic Zirconiums are completely differernt than the naturally occuring mineral zircon

Cubic Zirconiums are a man made gem
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Mar 24, 2013 - 11:35am PT
Interesting stuff...thanks for posting

Here's the abstract

Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province

Terrence J. Blackburn1,Paul E. Olsen, Samuel A. Bowring,Noah M. McLean1, Dennis V. Kent,John Puffer,Greg McHone,E. Troy Rasbury,Mohammed Et-Touhami

The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here, we present new zircon U-Pb geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over ~600,000 years, indicating expansive volcanism even as the biologic recovery was under way.

FYI, this 2011 Earth & Planetary Science Letters paper...
http://www.ldeo.columbia.edu/~polsen/nbcp/schaller+12.pdf

suggests that although the short-term impact of the mid-Atlantic volcanism which occurred over ~ 0.5 MY period was an increase in atmospheric CO2, the long-term (1-2 MY) impact was a net decrease to below pre-eruptive levels due to increased rates of global silicate weathering.

Presumably the CO2 became sequestered in large equatorial carbonate deposits. Later these deposits would be subducted and some of the CO2 extruded back into the atmosphere...and so it goes.



hillrat

Trad climber
reno, nv
Mar 24, 2013 - 03:15pm PT
One day, long long ago, a smaller planetoid thing hit the recently formed earth, sending it into a spin and spinning off what we now call the moon, leaving a high spot named Pangea. Billions of years passed, with humans being less than a blip on the radar. Then a comet came along and...
blip.
Gone, like last new years resolutions.
locker

Social climber
Some Rehab in Bolivia
Mar 24, 2013 - 03:19pm PT

Knowing will not change the fact that...














































"Yer GONNA die!!!"...



But it IS, interesting...

;-)

Jaybro

Social climber
Wolf City, Wyoming
Mar 24, 2013 - 05:38pm PT
But how, do they encrust the tweezers?
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Mar 24, 2013 - 07:36pm PT
RP3

Big Wall climber
El Portal/Chapel Hill
Mar 24, 2013 - 07:48pm PT
t_t: Is that a CL image? Beautiful stuff...
hillrat

Trad climber
reno, nv
Mar 24, 2013 - 07:57pm PT
http://www.mindat.org/min-4421.html

Actually, it's pretty amazing what we can do these days, in all the sciences.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Mar 24, 2013 - 07:58pm PT
t_t: Is that a CL image?
yup

Cathodoluminescence (CL) image of the mineral zircon (ZrSiO4) showing internal concentric-growth zonation and a complex history.

http://eps.wustl.edu/photos/732


here are some CL images of Zircons in one of my favorite rock types Eclogite
RP3

Big Wall climber
El Portal/Chapel Hill
Mar 25, 2013 - 08:14am PT
Poor eclogite Zircons...they sure look beat up!
BASE104

Social climber
An Oil Field
Mar 25, 2013 - 08:57am PT
Zircons are really easy to find in granitic rocks, but they are very rare in basaltic rocks such as "lava."

You have to churn your way through a lot of basalt just to find a few zircons. It is a lot of work. Zircon U-Pb dating is incredibly accurate now. It is amazing how they can be used to date and reassemble different terrains.

I'm pretty sure that that event is the one that caused a large CO2 driven hothouse event. There was a time of widespread ocean acidification which created a global anoxic event.

What that means is carbon raining to the seafloor was preserved rather than gobbled up. This formed the organic rich source rocks which created the oil in the middle east, which I believe is late Jurassic.

It is very interesting because there is an actual case of global climate change that was induced by CO2 released naturally by a huge volcanic event.

The same thing happened in the Devonian. Almost all of the shale gas reservoirs are from an Anoxic Event in the late Devonian. From the Marcellus to the Barnett and all in between.
moosedrool

Trad climber
lost, far away from Poland
Mar 25, 2013 - 09:14am PT
Isn't the Earth 6,000 years old, or something?
BASE104

Social climber
An Oil Field
Mar 25, 2013 - 09:17am PT
There are several ways to find out if this was a climate event. One, look at the fossil assemblage around the world. Second is to use proxy fossils such as Gingko leaves and measure Stomata density, which is directly affected by CO2 concentrations.

We know that there was a mid Cenozoic hothouse period. You find ferns near the north pole. We also know that there was massive ocean acidification which was recently correlated globally instead of a local confined event.

I read a paper a while back that estimated the CO2 concentrations of that event, which I think was later than the Atlantic event, and it looked like concentrations were about 4 times the pre industrial revolution concentration. We have already doubled that CO2 concentration and if we double it again, we will have crossed the line into a climate event which will take millions of years to reverse.

I doubt if it will cause humans to go extinct, but plenty of real estate will change in appearance.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Mar 25, 2013 - 11:23am PT
I believe you are referring to the PETM (Paleocene-Eocene Thermal Maximum)



which may have been in part caused by destabilization of oceanic methane clathrates.

mechrist

Gym climber
South of Heaven
Mar 25, 2013 - 11:31am PT
This formed the organic rich source rocks which created the oil in the middle east, which I believe is late Jurassic.

It is very interesting because there is an actual case of global climate change that was induced by CO2 released naturally by a huge volcanic event.

and we are releasing that stored carbon again... but over a period of hundreds of years, rather than tens of thousands.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Mar 25, 2013 - 06:06pm PT
yup...the rate of increase in atmospheric CO2 during the last 100 years appears to be unprecedented in earth history
RP3

Big Wall climber
El Portal/Chapel Hill
Mar 26, 2013 - 06:59am PT
Here are some CL images of zircons from the Fish Canyon Tuff from SW Colorado (Schmitz and Bowring 2001). Tuff, of course, being my second favorite rock after granite.

It amazes me how many geoscientific applications there are for zircons. The field would be hurting if they didn't exist!

Credit: RP3
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