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The Deccan Traps



As I understand it (my understanding seems often to be wrong, but
that doesn't stpo me trying to argue), the K-T lies in the middle
of maganetic  chron 29R (the 29th period of reversed magnetic
field, counting back from the  present).  The Deccan vulcanism
started latish in the previous chron 30 and ended about the 
start of   chron 29.  The average length of a chron is about
1.2 million years, but both 29R and 30 were shorter than averge.
Without cosulting any references (they are all at work, and I am 
at home), I recall about 0.75 years for the duration of 30
and 0.6  for 29R.  That makes a little over a million years for
the maximum extent of the Deccan vulcanism, even i ncluding  most
of chron 30 and all of chron 29R.   TRhe largest part of the
vulcanism occurred late in chron 29R, after the K-T, though it
certainly started well before.  In other words, the Deccan
extrusion of lava started from a pre-existing hot spot well
before the K-T (but NOT 5,000,000 years before - that would put
it in chron 32), bu t was exacerbated  at the K-T.  I still think
the K-T impact broke open the mantle at  an antipodeal point which
was already weak at a hot spot.  Both the Sandia model and my own
show heavy stresses at the antopodeal point from a major i mpact.
        Of course the Deccan vulcanism contributed to local
extinction of animals, j ust as th e Laki eruption in the late
eighteenth century in Iceland killed off much of that islands
livestock, but it is not sufficient for golabal mass extinctions,
or even for extinctions of single species, merely for mass deaths.
I am not disputing its role, but only as a subsidiary cause, making
things worse after the i mpact.  The very existence of dinosaur
fossil remains in the interstadial layers between the basal
Deccan lava flows indicates that periodic vulcanism on this scale
did not produce mass extinctions, or there would have been none
to come back to colonize the land after the fi rst ph ase of the
eruption died down.
        The total energy released in the e ruption of the Deccan
Traps is of the same order of magnitude as the amount released
at Ch icxolub.  The difference is that the energy from Deccan
was spread over a million years, while that from the impact was
released in a matter of seconds (if we i nclude the atmospheric 
passage) or less than a second (if we count o nly the time of
the impact itself).  R
The RATE of release o f the energy matters greatly for extinction
on a global scale;  the to tal energy release  is not all that 
important.  Certzinly it h as some significance in the events, but not as much 
as the rate.  
David

--
>From: David Brez Carlisle
bk090@Freenet Carleton.CA