Re: astroblemes and extinctions

[Stan Friesen <swf@tdat.ElSegundoCA.NCR.COM>]

 >
 > I assume you refer to another Rampino hypothesis concerning
 antipodal
 > volcanism.

Yep, and based on the best data available - it is total garbage.
Flood basalts like the Deccan's are produced by the initial
surfacing of a new hot spot.  (*All* flood basalt deposits
known can be paired with a hot spot).

At present there is no known way an impact could generate an
antipodal hot spot.  And even if it were possible, the time
sequence would be wrong - hot spots are *deep* structures
(penetrating at least the asthenospere), and any hot spot
produced by an impact would take *many* millions of years to
reach the surface.

 > I don't know what to make of the K/T impact-Deccan traps
 > correlation or the P/T impact-Siberian traps correlation

The Deccan traps *pre*date the impact.

The impact occured during the 29R magnetostratigraphic interval.
The Deccan volcanism started in the preceding normal interval.

 > note that the Deccan traps span the K/T interval, the lava poured
 out
 > some before, some during and some after the Iridium spike. It might
 be
 >erroneous to insist on volcanic activity as solely caused by the
 impact,
 > or conversely that the impact had no effect on the volcanism.

But, given the neraly perfect correlation of flood basalt volcanism
and major (and minor) extinctions, it seems that flood basalts are
more likely a major player in extinctions than impacts.

[I believe that the P-T iridium spike has been shown to have the
signature expected of volcanogenic rather than extra-terrestrial
origin].

Also - if *any* extinction was gradual, it was the P-T extinction,
which appears to have extended over several million years.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.