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Re: Deccan Traps and Fried Dinos



At 10:51 PM 2/23/98 -0800, Phillip Bigelow wrote:
>
>On Sun, 22 Feb 1998 15:54:23 -0800 Stanley Friesen <sarima@ix.netcom.com>
>>So, it is not merely the fact of volcanic eruptions, it is the 
>>existence of a *temporally* *rare*, unusually voluminous type
>>of eruptions across the boundary.
>
>True, but keep in mind that these flood basalt regions didn't
>erupt all at once. In fact, there was a vastly greater intervening
>time during which these fissures weren't erupting at all.
>The Deccan Traps are composed of many individual flows which
>are often separated by sedimentary layers containing...uhh...
>...dinosaurs.

This is not necessarily a fatal problem, as some think it is.  If, as I
believe, it is ongoing stress over long periods of time that *gradually*
eliminate susceptible species, then this is exactly what is expected.

For instance, look at the patter of extinctions in the Pliestocene.  The
final disappearance of several major groups occurred in the *Late*
Pliestocene, after several rounds of glaciation.  Indeed some formerly
major groups are still hanging on, with a small handful of species.  Now,
it is true that the last straw for some of these groups was probably human
hunting, but ecologically, that is simply one more stressor. The pattern we
see is entirely compatible with a multifactorial mass extinction, in which
humans and glaciation cycles were/are the two principle factors.  (I do not
by any means consider the Pliestocene over, and, in the absence of
anthropogenic global warming, the glaciations most certainly are NOT over -
so neither are the extinctions - we are, in short, in the *middle* of a
mass extinction right now).
>
>In the Columbia Plateau, similar sedimentary interbeds are found,
>and these thin units contain a rather rich assemblage of mammals 
>and
>plants.  As far as I am aware, no large numbers of extinctions in the
>Pacific Northwest of North America have been specifically
>tied to the eruptions of the Columbia Flood Basalts.
>
This is a more significant point.  It might be interesting to cross check
this with other contributing factors.  Perhaps it was all alone at the
time, and thus not sufficient to cause extinctions.

The Deccan's are associated with:
        - a major asteroid impact.
        - a possible episode of profound oceanic anoxia
          (which our global warming might just trigger)
        - rapid, extensive regressions, such as not seen since the 
          Permian, and not surpassed until the present. (oops, one
          more factor to contribute to the current round of 
          extinctions).

A very good possibility is that ALL of these things individually
contributed to the extinctions.

>So, if one had a time machine, and travelled to India during the
>middle of "Deccan Time", your chances of landing there during the
>middle of one of the many eruption events is practically zero.

It is probably not the direct effects of the eruptions that mattered.  It
was the secondary effects, combined with the effects of the other stressors
occurring at the same time.

>But you would have an excellent chance of seeing a titanosaur
>walking around on the fern-covered lava plains.
>
Yep.
>
>Since the Deccan Traps span the K/T Boundary, and since the
>Cretaceous half of the Traps contain abundant remains of
>dinosaurs, it would seem to me that the Indian dinos were not
>significantly effected by the eruptions.

This does not follow.  It only means they were not *immediately* killed by
the eruptions.  I maintain these things take time.

A very good reference on the multifactorial model of mass extinctions is:
        J. David Archibald, 1996. _Dinosaur Extinction and the End of an Era: 
What
the Fossils Say_.Critical Moments in Paleobiology and Earth History Series.
 Columbia University Press.

The title of chapter X is "A Cacophony of Causes", and the first section
therein is called "Three Strikes and You're Out".  That about sums up my
basic point of view.

--------------
May the peace of God be with you.         sarima@ix.netcom.com
                                          sfriesen@netlock.com