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Re: multiple bolide impacts

>From: Pterodon@aol.com
 > The Deccan Traps flows date from 66 mya. The crater below Mason (?) Iowa
 > (long since filled in by glacial debris) is also dated to 66 mya. Of course,
 > the Chixulub crater is dated to 65 mya. ...
 >    Could then the K-T boundary be, in reality, a phenomenon that was some one
 > or two million years in the making or perhaps 10 to hundreds of thousands of
 > years in the making?

The shorter period is more likely than the longer.
Except for the drop in *diversity* (but NOT in abundance),
there was little change across the Maastrichtian.  And
even the drop in diversity occured so long before the
extinction that it is not clear it is related (we are talking
some 4 million years earlier - at the Early to Late Maastrichtian

Personally, I think this just "set the stage".  That is, due to
the low diversity, enhanced extinction rates for other causes
more easily wiped out entire groups.

 >  Granted the Deccan Traps can be attributed to the
 > pulling away of the Seychelles from India 66 million years ago, but could
 > that rift have been triggered by a bolide impact?

Almost certainly not.
Continental drift is driven by deep mantle convection current.
Teeny surface pops like a meteorite impact could not really
effect such things very much.

Also, the Deccan volcanism was probably *not* due to the seperation.
Rather, the Deccan's were produced by the first massive eruption
of the Seychelles Hot Spot.  As India drifted north, it passed
beyond the hot spot, leaving it out in the ocean, where it probably
*formed* the Seychelles.

There is substantial evidence (not yet wholly convincing) that
hot spots come from even deeper - from the core-mantle boundary.
This means the origin of the plume must actually be many many
millions of years prior to its surface eruption.  (And even if
they do not come from quite that deep, they are still from
the deeper mantle).

 >    The Deccan Traps volcanic episode (one of many in the geologic record)
 > lasted perhaps 100,000 years and may very well have stressed marine and
 > terrestrial environments to the point that researchers see declines in
 > families in the fossil record in the latest Mastrichian. The declines would
 > have leveled off once the volcanism finally subsided, but there was too
 > little time for family or species rebound before the Chixulub event.

Actually, the impact appears to have occured more or less at the
*peak* of the Deccan volcanism.

I, too, believe that the combination is what proved so deadly.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.