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Re: Chicxulub crater



jamolnar wrote (5/1/97; 8:14p):

>I've been reading up on the critiques of the asteroid impact 
>hypothesis for the sole cause of the K-T extinction.

I guess I'm responsible for some of the support heard here for a K-T 
impact, in part from a look at some of the data first-hand, and 
discussing it individually with Alvarez, Rampino, and Pope.  However, I, 
for one, have never suggested it was the "sole cause," and hope that 
nobody else does.

>I've come across a 1994 reference which refers to a 1960s well 
>drilling into the Chicxulub {spelling?} crater that is interpreted as 
>showing it can't be an impact crater of any kind.  Also, examination 
>of 2 Deep Sea Drilling Project cores from sites that are the closest
>to this crater confirm non-impact signatures. 

I believe any drilling data from near-by can also be interpreted as 
consistent with an impact.  To a physical stratigrapher such as myself, 
some of the arguments in Officer's book are obviously open to other 
interpretations.  I don't know about the geochemical arguments.

>The crater is also shown to be the wrong time, with late
>Cretaceous sediments overlying the actual depression.

Of course, any such crater would have to be filled with something.  
Material from the presumed crater margin slumped or washed into it would 
include material of pre-impact age.  There are apparently some huge 
blocks of pre-impact strata within the crater.  That's why the cores 
appear to include undisturbed pre-impact sediment within the crater, and 
why the microfossils used to date those strata are not corroded.

If this were a criminal trial, I think a reasonable doubt as to an impact 
could be established by any competent attorney.  A reasonable doubt could 
probably be established for just about any scientific question.  Such 
questions therefore can only be decided on the preponderance of evidence, 
and, as you note, since more evidence is always coming in, the decision 
must remain tentative.  Personally. I find the data from recent Atlantic 
margin ODP cores to be compelling, even though I have not seen it 
first-hand.  I am always most impressed by opinions expressed by those 
who have personal familiarity with the data, rather than merely with 
literature. 

>I'm trying to pursue this in a scientifically rigorous, skeptical 
>manner, so that I can present a balanced view of the topic "what 
>killed the dinosaurs?" for the summer volunteers at our museum.
>Thanks!

Way to go!  Thank you!


*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu