Re: [Geology2] New findings rock long-held assumptions about ancient mass extinction

Dear Lin,

I don't think Dr. John Geissman found what he thinks he found. He believes that he found evidence that the terrestrial Permian extinction occurred approximately 253.3 MYA, while the marine Permian extinction occurred 251.9 MYA.

He believes that the ash layer that he found in the Karoo Basin in South Africa relates to the terrestrial Permian Extinction, for which he concedes that there is a "dearth of datable volcanic deposits below and above plant and animal fossils in rocks surrounding the boundary where the Permian period ends and the Triassic begins."

The volcanic ash layer that he found dates to approx. 253.5 MYA. The only major volcanism that we know of that might be capable of creating such a huge extinction as the Permian extinction began 252.28 MYA plus or minus 11,000 years. This was the eruption of the Siberian traps, which was so huge that it made the Deccan traps (65 MYA) look small by comparison. These dates were developed by Seth Burgess of MIT and were reported by Becky Oskin of Live Science, 12/12/2013.

Becky also states: "Burgess's new age for Meishan's Bed 25 (a thin rock layer that is the global reference point for the onset of extinction) is 251.941 million years ago, plus or minus 37,000 years."

These dates fit well with Geissman's date for the marine Permian extinction, which he pegs at 251.9 MYA.

The Karoo Basin in South Africa is located about as far away from the Siberian traps as you can get. It is also in the southern hemisphere. It wouldn't be surprising that any ash layer from the Siberian traps eruptions might be fairly small and hard (or even impossible) to find in that location.

It might be more likely that the ash layer that Geissman discovered was from a local or regional volcanic event that had severe local or regional extinction effects. It is also possible that the rate of sediment deposition was not constant and that the 60 meters of depth represented 1.5 million years and not 200,000 to 300,000 years, and thus, the extinction could match up with the Siberian traps eruptions.

One would think that, if the Deccan traps were the proximate cause of the End-Cretaceous extinction 65 MYA, then the Permian Extinction would show evidence of even grander volcanism. The Siberian traps would satisfy this assumption.

If it was not the Siberian traps, then where is the evidence for other episodes of grand volcanism? I know of no major volcanism that dates to circa 253.5 MYA.

I would want to see some confirming data from another location before I would consider switching horses on this one.

Regards,

Ben Fishler
--------------------------------------------
On Thu, 11/5/15, Lin Kerns linkerns@gmail.com [geology2] <geology2@yahoogroups.com> wrote:

Subject: [Geology2] New findings rock long-held assumptions about ancient mass extinction
To: "Geology2" <geology2@yahoogroups.com>
Date: Thursday, November 5, 2015, 1:23 PM






























New
findings rock long-held assumptions about ancient mass
extinction
Date:November 2,
2015Source:University of Texas at
DallasSummary:A
geologist team describes new findings that challenge
the currently accepted model of the 'Great Dying,'
a catastrophic
extinction event that occurred more than 250 million years
ago.


Dr. John Geissman, professor and
head of the
Department of Geosciences at UT Dallas, examines a
fossilized volcanic
ash deposit in the Karoo Basin South Africa. He is part of
an
international research team studying geological evidence
related to the
largest mass extinction on Earth 250 million years
ago.
Credit: Photo courtesy Robert
Gastaldo, Colby College





New
evidence gathered from the Karoo Basin in
South Africa sheds light on a catastrophic extinction event
that
occurred more than 250 million years ago and wiped out more
than 90
percent of life in Earth's oceans and about 70 percent
of animal species
on land.

In research to be presented Nov. 4 at the annual meeting
of the
Geological Society of America and published in the October
issue of the
journal Geology, a University of Texas at Dallas
geologist and
his colleagues describe new findings that challenge the
currently
accepted model of the "Great Dying" and how it
affected land animals.
That event occurred at the end of the Permian geologic
period.
The new evidence derives from a key volcanic ash deposit
that the
team discovered in rock layers, or strata, that were
reported to
chronicle the mass extinction. By dating the volcanic
ash-bearing
deposit, researchers concluded that two phases of this
extinction -- one
on land, the other in the oceans -- occurred at least 1
million years
apart, as opposed to roughly at the same time, as the
geoscience
community has assumed for decades.
Based on previous dating of shelly fossils and ash beds
in marine
strata, the die-off among marine species has been
well-determined and is
generally agreed upon by scientists to have occurred about
251.9
million years ago.
However, the timing of the extinction on land has been
more
challenging to date definitively. This is due, in part, to a
dearth of
datable volcanic deposits below and above plant and animal
fossils in
rocks surrounding the boundary where the Permian period ends
and the
Triassic begins, said Dr. John Geissman, professor and head
of the
Department of Geosciences and one of the authors of the
study.
"There has been some concern in the scientific
community about
whether the extinction among vertebrates on land was
actually coincident
with that in the marine realm in terms of their
timing," Geissman said.
"Nonetheless, many researchers have just tacitly
assumed that the land
event occurred roughly concurrently with the marine
extinction."
Geissman is part of an international research team led by
Dr. Robert Gastaldo, lead author of the Geology
study and the Whipple-Coddington Professor of Geology at
Colby College
in Maine. Gastaldo and his colleagues have spent more than a
decade
conducting intensive study of exposed rocks in the Karoo
Basin in
southern South Africa. These regions preserve fossils that
chronicle
what has long been interpreted as the disappearance of key
reptile and
amphibian species at the end of the Permian period and the
reemergence
of completely different species in the Triassic period. The
rock layers
straddle the space in between where scientists infer the
global
extinction occurred.
Geissman joined Gastaldo's Karoo Basin team about
four years ago. As
an expert in paleomagnetism, he uses magnetic polarity
stratigraphy to
help determine the age of ancient rock layers. The process
involves
examining variations in Earth's magnetic field polarity
over time that
are preserved in the layers. Two years ago, during a hike
with a
colleague through an arroyo in the Old Lootsberg Pass area
in the Karoo
Basin, Geissman noticed a feature in the rocks that looked
familiar.
"Typically in this area, if there is a gulley,
everything exposed
will be preserved, which is ideal," Geissman said.
"As we were walking
up this arroyo I saw something that I knew I'd seen
before in the
Western U.S. where I teach a field geology class for UT
Dallas students,
but I hadn't seen it here before.
"I knew exactly what it was -- it was a fossilized
volcanic ash bed."
The find was significant for two reasons. One, zircon
crystals found
in ash beds can be dated geologically by examining the decay
rate of
uranium isotopes contained in the zircon. And secondly,
according to the
researchers, this ash bed was the first datable evidence
found in close
proximity to the position in the layers of rock where the
extinction of
land species was thought to have taken place.
The petrified ash bed lies about 60 meters below the
inferred
extinction event, which means it resulted from a volcanic
eruption that
occurred earlier than the extinction. In the world of
geology,
stratigraphic thickness equates to time -- over the eons,
layers of
sediments are laid down at a rate of so many meters per
thousand years,
and in this region of the globe, the sedimentation rates
translate those
60 meters into, roughly, between 200,000 and 300,000 years,
Geissman
said.
The team dated the volcanic ash bed at about 253.5
million years old,
so moving forward in time 200,000 years -- or 60 meters --
would
indicate the terrestrial phase of the extinction took place
about 253.3
million years ago, according to the study.
"This study places the terrestrial vertebrate
turnover about 1.5
million years earlier than the accepted estimated age of the
marine end
Permian-extinction," Geissman said. "Even if we
conservatively say they
were a million years apart, that still challenges long-held
assumptions
about the largest extinction event in Earth's
history."
Geissman's examination of the distribution of
magnetic polarity in
rock samples from the Karoo Basin backed up the team's
conclusions. In
January, Geissman will join his colleagues again for further
research in
the region.
"It's been a lot of fun working with a great
group of stimulating
colleagues willing to challenge things," Geissman said.
"It was very
gratifying to walk out along an arroyo, see something that I
had seen in
much younger rocks in the Western U.S., and just know that
the dating
should work, and indeed it did.
"Part of the satisfaction in this type of research
is the serendipity
in terms of finding things. It's all about tromping
over as much real
estate as you can."







Story
Source:
The above post is reprinted from materials
provided by University of Texas
at Dallas. Note: Materials may be edited
for content and length.


Journal
Reference:
Robert A. Gastaldo, Sandra L.
Kamo, Johann Neveling, John W. Geissman, Marion Bamford,
Cindy V. Looy. Is
the vertebrate-defined Permian-Triassic boundary in the
Karoo Basin,
South Africa, the terrestrial expression of the end-Permian
marine
event? Geology, 2015; 43 (10): 939 DOI: 10.1130/G37040.1



University
of Texas at Dallas. "New findings rock long-held
assumptions about
ancient mass extinction." ScienceDaily. ScienceDaily, 2
November 2015.
<www.sciencedaily.com/releases/2015/11/151102164056.htm>.
--

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------------------------------------
Posted by: Ben Fishler <benfishler@yahoo.com>
------------------------------------


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