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Re: Deccan produced global warming that was over before the K-T boundary

> For Upper Cretaceous ages, a 500,000-year discrepency between the U-Pb
> and K-Ar methods is not unusual.


> Gradstein et al. (1995) give 65.00+/- 0.04 for the K-T boundary.
> [...]
> Is Gradstein et al.'s K-T date still authoritative?

I don't know. I was asking primarily because the U-Pb age of zircons in...
the crater or in ejecta, I forgot, is 64.98 +- 0.05 Ma.

> The boundary occurs in the upper portion of geomagnetic chron C29r

Of course.

> (approximately at C29r.7).

Is this how to write subchrons? Once (in secondary literature) I read about
a study which said the boundary occurred in a small normal subchron that
lasted only some 50,000 years (IIRC) and used it to show that there's no big
discontinuity in the Hell Creek Fm around the boundary.

> OTOH, the most accurate estimate for the age of the melt rock at the
> bottom of the Chixculub crater is 65.07 +/- 0.1 ma (K-Ar method).

This is relatively strange. :-)

> I believe that the melt rock in the crater
> also has a reversed geomagnetic polarity.

As expected. :-)