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



Hi Dave,

I was under the impression that the KT boundary had been found within the
Deccan Traps that therefore spanned the KT.  Is this another case of
scientists disagreeing, like the impact theory that also moves around the KT
boundary depending on who's paper you are reading.

John

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf Of
David Marjanovic
Sent: 13 March 2006 22:12
To: DML
Subject: Re: The K-T boundary extinction: bolide or volcano?

>
http://www2.le.ac.uk/ebulletin/news/press-releases/2000-2009/2006/03/npartic
le-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.

----------------------------------

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."