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Re: Volcanoes (comments on pterosaur extinction)
Title: Re: Volcanoes (comments on pterosaur
1. Geophysicists have already shown it unlikely that a bolide -
no matter how big - can perturb the mantle and cause outpourings of
lava at the antipode. Mantle dynamics are just way too slow. If it
WERE possible, the lag time would probably be enormous - thousands of
2. Based on magnetostratigraphy, the Deccan are thought to have
been erupted in about 600,000 yrs. (Coincidntally the same duration as
both CAMP just after the TJB, and the Siberian Traps, ~ Permo-Triassic
boundary). ALso, the magstrat and chemostrat (i.e. Iridium) show the
KTB to be in the middle of the Deccan.
3. So, what chance of the Iridium hanging around in the
atmosphere for say 300,000 yrs (assuming the KTB to be in the middle
of the Deccan) after the initiation of eruptions; which in turn, if
caused by the bolide, would be several thousand years after impact?
Any dust that COULD hang around that long would have been severely
diluted and then the Ir anomaly probably would not be
detectable....i.e. not an anomaly at all!
Some bedtime reading if you are REALLY interested :-)
Olsen, P.E., D.V. Kent, B.
Cornet, W.K. Witte and R.W. Schlische. 1996. High-resolution
stratigraphy of the Newark Rift Basin (Early Mesozoic, eastern North
America). Geological Society of America Bulletin
Renne, P.R. and A.R. Basu.
1991. Rapid eruption of the Siberian Traps flood basalts at the
Permo-Triassic boundary. Science 253:176-179.
Renne, P.R., Z. Zhang, M.A.
Richards, M.T. Black and A.R. Basu. 1995. Synchrony and causal
relations between Permian-Triassic boundary crises and Siberian flood
volcanism. Science 269:1413-1416.
Bhandari, N., P.N. Shukla,
Z.G. Ghevariya and S.M. Sundaram. 1995. Impact did not trigger Deccan
volcanism: Evidence from Anjar K/T boundary intertrappean sediments.
Geophysial Research Letters 22:433-436.
Marzoli, A., P.R. Renne, E.M.
Piccirillo, M. Ernsesto, G. Bellieni and A. De Min. 1999. Extensive
200-million-year-old continental flood basalts of the Central Atlantic
Magmatic Province. Science 284:616-618.
Olsen, P.E., R.W. Schlische
and M.S. Fedosh. 1996. 580 Ky duration of the Early Jurassic flood
basalt event in eastern North America estimated using Milankovitch
cyclostratigraphy; pp. 11-22 in M. Morales (eds.), The
Continental Jurassic. Museum of Northern Arizona Bulletin
Gallet, Y., R. Weeks, D.
Vandamme and V. Courtillot. 1989. Duration of Deccan trap volcanism: A
statistical approach. Earth and Planetary Science Letters
Courtillot, V., C. Jaupart, I.
Manighetti, P. Tapponnier and J. Besse. 1999. On causal links between
flood basalts and continental breakup. Earth and Planetary Science
Ken Kinman wrote back:
Since I'm not a
geologist, I don't know if this will make sense, but what about the
1. Bolide crashes into the Earth.
2. Deccan traps triggered to erupt.
3. Iridium (etc.) rains down on top of
initial lava beds
during the following
weeks and months
4. Iridium layer is then covered by
eruptions, and thus
Is such a scenario possible (and if so,
very probable)? I suppose someone has proposed such
a scenario, but I'm not sure what the arguments might be against
From: "Emma C. Rainforth"
except, the iridium layer and all other impact-related features
in the MIDDLE of the Deccan.....i.e. the Deccan traps were already
erupting before the bolide hit.
BTW, the Triassic-Jurassic mass extinction PREdates the central
Atlantic magmatic province (which is bigger than Deccan). So
volcanism can NOT have caused this
Ken Kinman wrote:
I don't know much
about geology, but it seems likely to me that
the bollide collision probably set off a lot of the volcanic
activity, and that this just added insult to injury and
was of secondary importance
Emma C. Rainforth
Geosciences Rm. 206E
Lamont-Doherty Earth Observatory
ph. (845) 365-8621
fax (801) 838-4126