Meteor hit between closely spaced Deccan Trap eruptions (K-T extinction)

[Dora Smith <villandra@austin.rr.com>]

This press release, I guess, was posted to some list I don't think I knew I
was on.    It presents clear evidence that the meteor fell BETWEEN
closely-spaced eruptions of the Deccan Traps.    Also presents evidence that
the Deccan Traps erupted over time in a fairly small quantity of time.

9 August 2005
GSA Release No. 05-27

Contact:  Ann Cairns, acairns@geosociety.org
Director-Communications and Marketing
(303) 357-1056, fax 303-357-1074

--

India's Smoking Gun: Dino-Killing Eruptions
New discoveries about the timing and speed of gigantic, 6500-foot (2-km)
thick lava flows that poured out of the ground 65 million years ago could
shift
the blame for killing the dinos.
The Deccan Traps of India are one of Earth's largest lava flows ever, with
the potential of having wreaked havoc with the climate of the Earth - if
they
erupted and released climate-changing gases quickly enough. French and
Indian
geologists have now identified a 600-meter (2000-foot) thick portion of the
lava
that may have piled up in as little as 30,000 years - fast enough to have
possibly caused a deadly global climate shift.
"Our working hypothesis is that the majority of the total volume of lava
might have been erupted in only a few major events spread over only a small
fraction of millennia," said Anne-Lise Chenet of the Laboratoire de
Paleomagnetisme, Institut de Physique du Globe de Paris (IPGP).
To test that hypothesis, the researchers have combined already known ages of
the traps gathered from radiometric dating with magnetic fields frozen in
the
rocks. Volcanic rocks record information about the Earth's magnetic field
with
magnetic minerals that align with Earth's field like millions of tiny
compasses
before the lava cools. When the lava solidifies, the compasses are locked in
place.
Lava layers that erupted within two or three centuries of each other will
record similar magnetic fields, explains Chenet. Longer than that and the
natural changes in Earth's magnetic field start to show up. The team also
incorporated information about the lava's chemistry, the way it flowed and
piled
up and the red weathered soils between lava layers to estimate the timing
and
number of major volcanic pulses.
All that information points to the 600 meters (2000 feet) of lava pouring
out
in as little as 30,000 years. This is enough to have possibly released a
climate-altering amount of sulfur gases, says Chenet. An estimate of just
how
much gas is still being worked out.
Chenet is scheduled to present the latest results of the team's work on
Wednesday, 10 August, at Earth System Processes 2, a
meeting co-convened by the Geological Society of America and Geological
Association of Canada this week in Calgary, Alberta, Canada.
Chenet and her colleagues' new work on the Deccan Traps is just the latest
in
a series of discoveries which appear to weaken the case implicating the
Chicxulub impact as the primary player in the Cretaceous-Tertiary (K-T) mass
extinction.
"As originally proposed by Vincent Courtillot in 1986, the volcanism might
be
a key player in mass extinctions," said Chenet. "Research in India has shown
the
remnants of the impact - iridium in sediments - sandwiched between lava
flows,
implying that volcanism started before the impact."
In fact, most mass extinctions over the past 300 million years have
coincided
with large volcanic events, said Chenet. The general rule is that massive
volcanism like the Deccan Traps correlates with all major mass extinctions
in
Earth's history, she said.
"In only one case is there evidence for both volcanism and impact," she
said.
And that is the K-T mass extinction that ended the reign of the dinosaurs.
"Our
view is that impact added to the stress already generated by an ongoing
massive
eruption, enhancing significantly the extent of the extinction, which would
however have taken place even if the impact had not occurred."
Wiped out in the K-T mass extinction were 80-90% of marine species and about
85% of land species. All land animals larger than 25 kg (55 lbs) were
obliterated.
The Deccan Traps are a huge pile of basaltic lava extending over more than
500,000 square kilometers. Its original volume likely exceeded 2 to 3
million
cubic kilometers, says Chenet. The entire volcanic episode that created the
traps took place over about one million years. The source of the massive
lava
flows is thought to have been the surfacing of a plume of hot material from
deep
in the Earth's mantle.
Magnetostratigraphy of the Upper Formations of the Deccan Traps: An
Attempt to Constrain the Timing of the Eruptive
Sequence
Wednesday, 10 August, 11:20 a.m. MDT
Lakeview
Endrooms, Calgary Westin Hotel
Abstract may be viewed at
http://gsa.confex.com/gsa/2005ESP/finalprogram/abstract_88502.htm
IMAGES AVAILABLE
PLEASE CREDIT: Courtesy of Anne-Lise
Chenet/IPGP



Yours,
Dora Smith
Austin, Texas
villandra@austin.rr.com