Re: The K-T boundary extinction: bolide or volcano?

[David Marjanovic <david.marjanovic@gmx.at>]

> http://www2.le.ac.uk/ebulletin/news/press-releases/2000-2009/2006/03/nparticle-cjk-whw-tkd

I can't say anything about the Siberian Traps. They are humongous beyond 
imagination, and their precise stratigraphic relationship to the P-Tr 
boundary and any part of the mass extinction is still not known.

But what is said about the Deccan Traps, frankly, is just a rehash of the 
old "argument" that I thought had at long last died out: "if something is 1) 
popular and 2) spectacular, that proves it must be false". _Yes_, the 
biggest eruption phase of the Deccan Traps _did_ have an effect on the 
climate (the global average temperature rose by at most the difference 
between glacial and interglacial), and then the episode _ended_ and the 
climate _cooled to pre-eruption levels_ _100,000 years before_ the K-Pg 
boundary.

That was in Science, well over two years ago. In my personal experience 
Science articles are easier to miss than those of Nature, but... I mean... 
it's not the Special Papers of the Occasional Publications of the Town Hall 
Museum of Superbled-sur-Loire.

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G. Ravizza & B. Peucker-Ehrenbrink: Chemostratigraphic Evidence of Deccan 
Volcanism in the Marine Osmium Isotope Record, Science 302, 1392 -- 1395 (21 
November 2003)

Abstract:
"Continental flood basalt (CFB) volcanism is hypothesized to have played a 
causative role in global climate change and mass extinctions. Uncertainties 
associated with radiometric dating preclude a clear chronological assessment 
of the environmental consequences of CFB volcanism. Our results document a 
25% decline in the marine 187Os/188Os record that predates the 
Cretaceous-Tertiary boundary (KTB) and coincides with late Maastrichtian 
warming. We argue that this decline provides a chemostratigraphic marker of 
Deccan volcanism and thus constitutes compelling evidence that the main 
environmental consequence of Deccan volcanism was a transient global warming 
event of 3° to 5°C that is fully resolved from the KTB mass extinction."