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Re: Volcanoes (comments on pterosaur extinction)

Title: Re: Volcanoes (comments on pterosaur extinction)
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 years!
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 108:40-77.
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 60.
Gallet, Y., R. Weeks, D. Vandamme and V. Courtillot. 1989. Duration of Deccan trap volcanism: A statistical approach. Earth and Planetary Science Letters 93:273-282.
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 Letters 166:177-195.

Ken Kinman wrote back:
     Since I'm not a geologist, I don't know if this will make sense, but what about the following scenario:
     1.  Bolide crashes into the Earth.
     2.  Deccan traps triggered to erupt.
     3.  Iridium (etc.) rains down on top of these
         initial lava beds during the following
         weeks and months (years??).
     4.  Iridium layer is then covered by subsequent
         eruptions, and thus sandwiched between
         layers of lava.
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 it.
From: "Emma C. Rainforth" <emmar@ldeo.columbia.edu>

except, the iridium layer and all other impact-related features occur
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 the
volcanism can NOT have caused this extinction event.

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 vulcanism
was of secondary importance overall.
Emma C. Rainforth
Geosciences Rm. 206E
Lamont-Doherty Earth Observatory
Rt. 9W
NY 10964-8000
ph. (845) 365-8621                 
fax (801) 838-4126