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Re: extinction



> "We report here an unusually high concentration of iridium in some
> alkali basalts and alkaline rocks of Deccan region having an age of
> about 65Ma, similar to the age of the Cretaceous-Tertiary boundary.

I wonder how precise this age is.

> The alkali basalts of Anjar, in the western periphery of Deccan
> province, have iridium concentration as high as 178pg/g

Interesting. 178 ppt is still far below the Ir anomalies in K-T sediments,
but clearly different from 0.1 ppt! :-) Many thanks for this information.

(Gubbio: some 9 ppb, a site in eastern Montana: some 2.6 ppb. Source: a
popular book by David M. Raup which reproduces fig. 4 and 10 of L. W.
Alvarez, PNAS 80, 627 -- 642 [1983].)

> indicating the significance of alkaline magmatism in the iridium
> inventory at the Cretaceous-Tertiary boundary."

Considering the fact that there are still some 3 orders of magnitude between
this and the anomalies in the sediments, I'm not so sure about that.

> The highest iridium measurements were from the Anjar, Gujarat, India,
> locality which supposedly has a preserved K-T boundary interval.
>
> However, Hansen et al. (2001) have concluded on the basis of their
> magnetic susceptibility and carbon isotope studies, that the Anjar
> locality does not contain the K-T boundary.

Hm... great. This will surprise a few people on this list. :-)