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Re: Chicxulub: Not an impact structure?



First of all, I must say that I believe that the Chicxulub impact theory is the
best explanation. Such a large impact would naturally produce volcanic
side-effects
at the center, so such features would not prove or disprove either theory.

But there is a small detail that I wonder how came to be, because it seems
to be wrong.

At 17:08 28.02.98 -0800, Steve Excell wrote:
>Potassium feldspar grains shocked and melted to glass spheres and
distributed spatially in greater population closest to the crater site.
Dated 64.98 million years +/- 50,000 years ago.
                                                         ^^
>Yellow glassy tektites in bedrock formation on Haiti, other Carribean
islands and Gulf Coast that are classic crater ejecta.  The richness in Ca-S
match the Ca-S rich target rocks near Chixulub.  Absolute age of tektites:
65.03 +/- 0.1 Ma.
                                        ^^
Gee, this is really impressing! Just 0.02/0.03 off the 65 Ma K/T boundary!
This must
be the conclusive evidence!
Or is it? Of course NOT. I have seen the K/T boudary set to 66 Ma in some
credible sources. Britannica Online have the K/T boudary for the moment at
66.4 Ma. So those values cited are 1.400.000 years off!
It almost would seem that the researchers (childishly?) have believed that
the K/T 
boundary was forever fixed at 65.00 Ma B.P., and therefore have 'adjusted'?
their
readings to fall nicely into the right interval. Of course it don't. The values
change quite much with time as better methods of absolute age determination
comes
into use. The time of the boundary is fixed (and NOT _determined_ by anyone)
to what 
happened in the geologic record, e.g. the irridium layer. Thereafter an
absolute age 
determination is done, which is very much dependent on the quality of the
method.
The values would never fall exactly at an xx.00 value (at least only by
sheer luck),
but it would indeed if some scientific committee decided to place it there.
Unfortunately
that is not how it works in geology.

It seems to me that these values almost disprove the impact theory, if not
sommeone
can explain why they are so far off the present established value of the K/T
boundary. 

Regards,
Bjørn