[meteorite-list] The old one two punch

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed, 07 Jan 2009 11:16:08 -0500
Message-ID: <g7l9m4plq724mink7q079pj1tbq83pd1rl_at_4ax.com>

http://www.sciencedaily.com/releases/2009/01/090107085320.htm

Catastrophic Coincidence: Second Ever Example Of Contemporaneous Meteorite
Impact And Flood Volcanism Discovered

ScienceDaily (Jan. 7, 2009) ? Scientists have discovered only the second example
of a meteorite impact that occurred at the same time as massive volcanic
activity, in research published in the Journal of the Geological Society the
week of Jan 12. The first time such a coincidence was observed, at the
Cretaceous-Tertiary boundary, was the catastrophic event thought to be
responsible for the extinction of the dinosaurs, 65 million years ago.

This new event, uncovered after the 17 km diameter Logoisk impact structure in
Belarus was precisely dated, is thought to have taken place around 30 million
years ago. The crater was dated using argon isotopes, and found to have occurred
at a similar time to a period of massive volcanism known as the Afro-Arabian
flood volcanism, which started in NW Yemen at around 30.9 Mya, and SW Yemen at
around 29.0 Mya.

The impact also coincides broadly with a period of sudden global cooling and sea
level fluctuation. The researchers, led by Sarah Sherlock at the Open
University, argue that massive volcanic eruptions and meteorite impacts are
likely to have coincided much more frequently than has previously been thought,
but because the preservation of impact craters on Earth is poor much of the
evidence for these coincidences is lost.

The relationships between meteorite impact craters, volcanism and changes in
climate is a subject of much debate among scientists. Prior to the study, only
one example of an impact coinciding with volcanism had been found: the Chicxulub
and Boltysh impacts and the Deccan Traps flood volcanism, all of which occurred
at the Cretaceous-Tertiary boundary. In 2002, the discovery of their coincidence
with a global mass extinction led to debate over the causative links between
meteorite impacts, volcanism and mass extinction events, and fuelled the search
for more impacts at stratigraphic boundaries.

Unlike the Cretaceous-Tertiary event, the combination of the Logoisk impact and
the Afro-Arabain flood volcanism does not seem to have caused an extinction
event. The researchers suggest that the reason for this may be that the
magnitude of the event was not sufficiently large in comparison. Whilst the
Chicxulub crater associated with the extinction of the dinosaurs measures 170km
in diameter and the Deccan Traps released around (2-4) x106 km3 of lava, in
comparison the Logoisk impact structure measures 17km across and the
Afro-Arabian flood volcanism is around 1.2 x106 km3 in volume.

As a result, the effects of each event were likely to have been very different.
At the Cretaceous-Tertiary boundary, it is thought that one of the deadly
effects was the release of sulphur dioxide, either as acid rain or in the
stratosphere, where it would have prevented heat from reaching the earth and
caused massive global cooling. Around 8000 billion tons of SO2 are thought to
have been released by the volcanism and meteorite impact. In comparison, the
Logoisk impact and the Afro-Arabian volcanism are thought to have contributed
only 30 billion tons of SO2.

Meteorite impact craters are extremely difficult to date, but an understanding
of their age and frequency is crucial to attempts to control the number of
future impacts, as well as understanding the links between impacts and other
catastrophic events such as large volcanic eruptions and mass extinctions.
Around 90% of the Earth?s record of meteorite impacts is lost, and the
researchers argue that coincidences between impacts and flood volcanism are far
from rare. They suggest that, for every incidence of flood volcanism, at least
one crater the size of Logoisk is likely to form, although few such coincidences
are likely to be on a scale grand enough to bring about an extinction event
comparable with that which destroyed the dinosaurs.
Received on Wed 07 Jan 2009 11:16:08 AM PST