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Re: extinction

Response to Phil Bigelow's Sun, 11 Jan 2004 12:34:18 post.

Hi Phil, your first two questions are fundamental to the Deccan Traps and K-T iridium distribution problem, and ones that I have long meditated on. David Marjanovic also addressed the topic.

Before responding, I've contacted one of NASA's foremost experts on experimental biomass burns to get the latest information on how widely particulates from single events are globally distributed. He provided some information, and will send me more details. After I receive the information, I'll discuss your first two questions at the same time.

Re the Columbia River flood basalts, I've studied the literature, but have never done anything with it. I'm far more interested in linkages between older episodes of flood basalt volcanism and mass extinctions such as the K-T and P-Tr, etc.

Dewey McLean


"Dewey M. McLean" <dmclean@vt.edu> writes:

 But, this does not alter the fact that some Deccan Traps lavas
 contain high amounts of iridium.

 Dewey McLean

Hi Dewey,
Three questions:

- What percentage (by volume) of the total Deccan floods do these alkali
basalts comprise?  Surely, the *volume* is important here, not the fact
that there is an iridium anomaly in some of the flows.

- What mechanism pumped the dense iridium-bearing component high into the
stratosphere?  Modern basaltic volcanism does not put ash into the lower
troposphere, let alone the stratosphere.  If the Deccan flows were
typical flood basalt flows (and the evidence suggests that they were),
then the eruptions were quiet and very fluid.  Not explosive.  So how do
you get the iridium dust from India to Montana without invoking some form
of special pleading?

- Have you studied the Columbia River Basalt Group flood basalts (CRBs),
and have you looked for similar iridium anomalies in the correlative
Miocene sedimentary units of the Pacific Northwest?  It would seem that
the CRBs would offer you an excellent "test bed" (pardon the pun) for
flood-basalt-induced extinction.  How many extinctions (local or global)
correlate with the eruptions of the CRBs?