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Chicxulub's Antipode (Re: cause of death at KT)

On Fri, 01 Sep 2006 22:09:18 +0200 David Marjanovic
<david.marjanovic@gmx.at> writes:
> > The antipodes would probably be worse. There is a strong 
> concentration
> > of re-entering debris there, and it will all be moving at orbital 
> speeds, 
> > so
> > anything living there is likely to be fried.

> What would have been at the antipodes? 

AFAIK, the best guess is open sea.

Modern coordinates of Chicxulub:  21.33 degrees N; 89.5 degrees W

Modern anitpode of Chicxulub:   21.33 degrees S; 90.5 degrees E (which is
presently occupied by a lot of sea water)  But was a land mass there 65
mya?  I made a quick perusal of the DML archives, and it appears that the
our current knowlege of latest Maastrichtian plate movements and relative
plate positions place no major land mass at the antipode.

Regarding what type of effects one might have witnessed at the antipode:

- Tsunamic effects would have been minor, because North and South America
would have blocked the waveform from the paleo Pacific and Tethys Oceans.
 Europe and Africa would have blocked the waveform from entering from the
opposite direction.

- What about reentering ejecta?  It was probably no worse than elsewhere
on the globe.  Keep in mind that just because some material went
suborbital or fully orbital doesn't *require* that the material must fall
at the antipode.  It could fall just about anywhere on Earth, which is
dictated by the ejecta's altitude (ejecta in low Earth orbit will reenter
sooner; higher orbits may take hundreds of years to degrade to reentry).

- Seismicity:  Now *those* effects would have been interesting (that is,
if the antipode was part of a land mass.....which it apparently wasn't).
In addition to the P-Wave arrival, which would have been brutal (imagine
the earth beneath your feet throwing you up in the air about a third of a
meter), there would have been some righteously bitchin' S-Waves which
would be coming toward you from every azimuth.
So if you were standing on land, you would first have been thrown up in
the air by the P-wave, and then shortly thereafter, you would have been
thrown in every lateral direction radomly, probably quite violently, by
the S-waves.  [What DO converging S-waves do to bedrock?  I'll bet that
is an understudied topic in geophysics and structural geology!]

Has anyone thought of the following:

Let's assume for the sake of argument that the Chicxulub antipode was
occupied by sea floor rather than by dry land. Is this part of the sea
floor still preserved?  If it is, and if the site can be located, would
it would be worthwhile to drill into into it and see what types of
faulting patterns characterize a mega-converging seismic event at an

I'm thinking of the structural geology seen at the antipode of the
Caloris [impact] Basin on Mercury and the structural geology seen at the
antipode of the Stickney Crater on Phobos.  Not to mention the antipodal
structures on Mimas.