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

[John Scanlon <riversleigh@outbackatisa.com.au>]

I can't put my hand on the reference at the moment, but I saw a very
interesting paper in the early 90's proposing that the antipodes to the K-T
impact was near the west coast of India at the time, and the convergence of
shock waves ruptured the crust and instigated the flood basalts (Deccan
Traps).  

Ah, I see there was some discussion of this on the list in '95, e.g.
http://dml.cmnh.org/1995Jan/msg00350.html 

As pointed out in that post, the time and place seem to be far enough out
that it isn't likely.
 
-----------------------------------------------
Dr John D. Scanlon
Palaeontologist, 
Riversleigh Fossil Centre, Outback at Isa
19 Marian Street / PO Box 1094
Mount Isa  QLD  4825
AUSTRALIA
Ph:   07 4749 1555
Fax: 07 4743 6296
Email: riversleigh@outbackatisa.com.au
http://tinyurl.com/f2rby


> -----Original Message-----
> From: Phillip Bigelow [mailto:bigelowp@juno.com]
> Sent: Saturday, September 02, 2006 5:33 AM
> To: dinosaur@usc.edu
> Subject: 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
> antipode?
> 
> 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.
> 
> <pb>
> --
> 
>