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Re: All kinds of odd observations



 From: bk090@freenet.carleton.ca (David Brez Carlisle)
 > IRIDIUM
 > 
 > Terry also queries the relevance of iridium.  This is now 
 > recorded from over a hundred sites in the K-T boundary rocks from
 > all continents and from deep-sea cores.  Even though Alvarez et
 > al. only had th ree sites for their original paper they guessed
 > right that it would turn out to be world-wide.

True.  However the interesting thing is that at *some* sites there
appear to be several iridium spike, rather than just one.  (This
is variable from site to site, but still notworthy).

 > BITING BY SAUROPODS
 > 
 > Peter Buchholz has doubted that a bite by a sauropod could be
 > much of a deterent.  Paul Willis has pointed to the bite of a
 > wombat.  

The error in this analogy is that a wombat, like most mammals,
does a fair bit of chewing.  Sauropods used their teeth mainly for
collection of leaves - their mouths were not built for chewing.
Thus they lacked the "grinding" teeth of a wombat (or a human
- a human bite is *quite* nasty).

Now the herbivorous dino *I* would hate to be bitten by is Triceratops,
since its jaw closing muscles were *enormous*
 
 > Th e nearest any   dino fossil has been found to the
 > K-T boundary is 2 meters.

This is no longer true.  Isolated dino bones have been found within
a few inches of the boundary.  (And teeth have been found up to
and *past* the boundary - but these may be reworked).
 > 
 > CRETACEOUS SEDIMENTS INSIDE CHICXOLUB CRATER
 > 
 > Any crater        more than about 4 miles across is a complex
 > crater.   The Barringer Crater in Arizona is perhaps as large
 > as any simple crater we can expect to see.  An i mpact causing
 > a crater larger than this will produce a complex c rater with
 > a central uprising and slumped walls.  Chicoxolub (I never can
 > spell that) has two main rings, the more marked one 180 km.
 > across and a fainter one,  300 km.  Alan Hildebrand (Geol.
 > Survey of CAnada) does not believe th at the 300 km ring is of
 > any great significance and p uts the primary diameter at about
 > 182 km.  In any case there are slumped rocks throughout, where 
 > the walls have collapsed.  Since these were late Creteceous,
 > then of course all blocks (many of which remain intact in such
 > slumps - see Richard Grieve's papers--one good general account
 > is in Scientific American about 1988) were cretaceous in age.
 > Any drilling i nto th ese blocks would show a late Cretaceous
 > age, espceially in the outer ring.

Hmm, I need to check the note to see if the cores were central
or peripheral, and what the position of the sediment was relative
to the melt layer. (Could a slump block, or its equivalent,
get *under* the melt layer??)

I certainly agree that a large, intact slump block could be explanation.
 > 
 > The only true criterion for the age of the crater is the
 > radiometric age of the MELT at the bo ttom of the crater.
 > Two teams have now dated this - the Berkeley group and the
 > Geol. Survey of Canada team.  Both agree that the melt
 > dates to between 64 and 65 Ma.  Both have also found late
 > Cretaceous dates from the breccia that overlies the melt.

As I said - my preference right now is that the Chicxulub crater
*is* the boundary impact, I am just unwilling to call the case
closed until it is verified that the sediments found *were* a
slump block.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.