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Re: extinction



> > "How do you go from the million or so years of intermittent
> > Deccan eruptions to the neat global iridium anomaly?"
>
> [...]
>
> > note that several K-T sections from around the world display
> > multiple K-T transition iridium spikes:

Spikes. And not diffuse enrichments.

> Your list is not sufficiently informative.

And _quite_ short -- there are meanwhile perhaps 200 sites in the world
where a K-T Ir anomaly has been found. Does that list mean that all the rest
has only one spike?

> > The metallic iridium particles could have originated via an impact
> > event. But, who knows?

Metallic Ir particles??? I've only read of metallic platinum-group metal
particles which contain the traces of Ir.

> The two possible sources for the iridium (volcanism vs. impact) should be
> distinguishable by analysing the Platinum Group Metal ratios in the K-T
> iridium layer.  Platinum Group Metals in meteorites are chemically and
> isotopically nonfractionated.  Platinum Group metals in volcanic rocks
> are highly fractionated.  Isotopic ratios of the Platinum Group Metals
> should also help to distinguish between the two possible sources of the
> K-T iridium.  These two studies could have been conducted (or, at least,
> attempted) 25 years ago.  Have either of these two studies been
> conducted yet?

The first thing I ever read about the K-T impact hypothesis, over 10 years
ago, was about "iridium and osmium". I don't know a ref anymore (hm... it
should be in Night Comes to the Cretaceous), but the Os isotopes are
consistent with meteorites and inconsistent with volcanic material.
        If it were not so, we would still have to find a suitable volcano!
Deccan can't have been it, it fits neither in time nor in Ir content, as we
have seen.

> > Volcanic debris can float for long
> > distances via marine currents.

But certainly not uphill to the purely terrestrial Nanxiong Basin. You'd
need a second impact to create the gihugrongous tsunami necessary to wash
seawater into that basin, and I _am_ taking paleogeography into account.

> I don't know if the reason is
> because of a lack of research funds or if there is some psychological
> need on the part of researchers to *not* do the necessary research in
> order to keep the issue unresolved.  ;-)

I suspect that not everyone reads all relevant journals. It's the same in
paleontology -- Neues Jahrbuch für Geologie und Paläontologie is apparently
inaccessible in large parts of the US (note that almost all of its papers
are in English!), Ameghiniana is inaccessible here, and had I not found some
refs, I'd _never_ have got the idea that journals like Geology or Modern
Geology or Acta Geologica Sinica or Annual Review of Planetary and Earth
Sciences have articles about paleontology (the latter even about _molecular_
divergence date estimates!!!).