P/Tr impact?

[Doug Erwin <MNHPB028@xxxxxxxxxxx>]

Just a breif note until I have a moment to draft a longer reply, but
I would like to re-emphasize (before things get out  of control here)
that there is simply no EVIDENCE in favor of P/Tr impact from any of
the good boundary sections.  The Chinese claims for iridium, summarized
by Xu Dao-Yi and repeated since, were never able to be replicated by
western labs, and indeed are discounted by most of my Chinese colleagues
working on teh P/Tr boundary.  The Meishan boundary ash has long been
known to be one of a series of ash beds in the section that show
overwhelming geochemical evidence of resulting from local pyroclastic
activity near south China.  Although iridium was recorded from ABOVE
the P/Tr boundary at the GK-1 core in austria, Holser noted that the
total geochemistry was NOT consistent with an impact.  Finally, the
spherules in China are viewed by most as resulting from the widespread
volcanism in  this area.
  Of course Retallack, Ward and others (to say nothing of Rampino)
still seem enamored of impacts.  At this point there remains no evidence
favoring impact and the onus is on those who favor the hypothesis to
provide some evidence in favor of the hypothesis.
Doug Erwin