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> New information on this topic can be found in a paper by Zhao et al.
> titled "A possible causal relationship between extinction of
> dinosaurs and K/T iridium enrichment in the Nanxiong Basin, South
> China: evidence from dinosaur eggshells" (Palaeogeography,
> Palaeoclimatology, Palaeoecology, 2002, v. 178, pp. 1-17).
Thank you very much, this journal happens to be accessible. :-)
> The authors indicate [...] Because multiple iridium spikes were
> distributed over a temporally long Cretaceous-Tertiary duration, they
> indicate also that the source of the iridium was likely the Deccan
> Traps volcanism, and not an asteroid impact.
There are two big problems with this, IMHO.
Firstly, those multiple iridium spikes aren't found elsewhere, so I
suspect... hm... no, repeated leaching and redeposition by water should be
quite difficult with Ir... hm. :-]
Secondly, the Ir cannot _possibly_ have come from the Deccan traps, for 3
- The Deccan basalts contain 0.1 ppt (zero point one parts per trillion)
iridium -- this is one of the lowest values ever measured. Ref:
James Lawrence Powell: Night Comes to the Cretaceous. Dinosaur extinction
and the transformation of modern geology, W. H. Freeman 1998
- The main phase of Deccan volcanism ended some 100,000 years before the K-T
G. Ravizza & B. Peucker-Ehrenbrink: Chemostratigraphic evidence of Deccan
Volcanism from the Marine Osmium Isotope Record, Science 302, 1392 -- 1395
(21 November 2003). (This paper happens to confirm your idea that the Deccan
volcanism produced a greenhouse.)
- The volcanism at Deccan was effusive -- flood basalts -- and not
explosive, and therefore cannot have blasted heavy stuff like Ir high up
into the atmosphere (so that it could have fallen down all over the globe).