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Re: SVP press coverage

>From my recollection, Keller's position has gradually shifted over the years 
>from doubting the existence of an impact to doubting the impact had anything 
>to do with the extinctions to -- in the paper Heather cites -- suggesting that 
>Chicxulub may not have been the only impact, with a bigger impact (or a large 
>outburst of the Deccan volcanism) coming later and pushing a stressed 
>environment over the threshold for a mass extinction. I have not followed her 
>arguments in enough detail to know how she has responded to critiques about 
>possible redeposition of forams.

The truth is there is a LOT we don't know about large impact processes and 
their effects on the terrestrial environment. That includes explaining what 
killed the non-avian dinosaurs and why groups that made it through the KT 
managed to survive. Keller has done a service by pointing out weak points in 
the impact theory of extinction, but the preponderance of evidence still is in 
favor of the Chicxulub impact being the culprit. To tilt the balance in her 
favor, somebody needs to turn up another crater of the right size at the right 
time, or widely distributed dual impact debris layers separated by the right 
interval. -- Jeff Hecht


At 9:47 PM -0800 11/25/04, Heather Yager wrote:
>On Thu, 25 Nov 2004 21:01:30 -0500 (EST), John Bois <jbois@umd5.umd.edu> wrote:
>> Right.  Did she address this, I wonder?  One would think you could model
>> it.  Doesn't she argue that the manner of deposition is indicative of low
>> energy conditions?  I wonder if she has refined this argument?
>Here is the website of Keller and team's findings:
>And she does indeed argue that the manner of dep.=low energy
>environments at Chicxulub (although I have not read her older stuff so
>I don't know how it compares :)
>>From the conclusions section:
><blockquote> a) Yaxcopoil-1 contains a 50 cm thick laminated micritic
>limestone between the impact breccia and the KT boundary. This
>interval contains five thin green layers of glauconite formation with
>each interval bioturbated. This indicates deposition occurred in
>variable, but generally low energy environments interrupted by long
>pauses of little or no deposition and glauconite formation.
>b) There are no grain-size grading (except for dolomite rhombs that
>may give that impression), no cross-bedding, no flaser bedding, no
>sand grains in insoluble residues, that would indicate high energy
>deposition due to backwash and crater infill. Though such evidence is
>present in the top 15 m of the impact breccia.
>-Heather Yager