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

[Chris Glen <s370548@student.uq.edu.au>]

OK, I have to ask what opinions are on the Shiva Crater. I think this is
what John Scanlon is referring too...

I'm a biologist not a geologist (have a grasp of the basics), so I've always
been interested to hear what those who know what they're talking about make
of this idea since I first flipped through the paper:

Chatterjee, S. and Rudara, D.K. (1996) "KT events in India: impact, rifting,
volcanism and dinosaur extinction" Proceedings of the Gondwanan Dinosaur
Symposium - Memoirs of the Queensland Museum 39(3): 489-532.

Confession - I haven't read it properly, only flipped through it (OK I
looked at the pictures, I promise to sit down and read it now).

Chatterjee summarises the idea in his book "The Rise of Birds" (p231-248),
but appears to be more info and diagrams in the paper.

The paper and idea appears to be overlooked - probably because "Memoirs of
the QM" might be a relatively obscure journal for those not in Australia.
(This issue is for the Gondwanan Dinosaur Symposium 1994 and Authors include
Chiappe, Norell, Clark, Novas, Molnar, Vickers-Rich and Wiffen among the
well known dino palaeontologists.)

Alternatively, has the idea been rejected by most researchers (which I
assume is the more likely case)? That being said, even if the overall
conclusion is not accepted could some of the geological structures correlate
with the antipode discussed in this thread? I had only a quick search for
the "Shiva Crater" in the DML archive (61 hits spread between 1996 and 2005)
and most that I saw were asking similar questions to mine here, but I didn't
see many answers offered (perhaps they're there but didn't find them), and I
haven't had time to do a search in a lit data base (eg Web of science etc.).

What I get from this thread is that the antipode of the Chicxulub impact
would have been somewhere in the middle of the Indian ocean, just as India
was passing through on its way to its appointment with asia about starting
up the Himalayas.

Now this paper actually suggests (citing Boslough in press) it's the other
way around, the main impact occurred in the Indian Ocean (or what becomes
the Indian ocean) and hit the SW edge of India as it was passing through
this ocean) - the Shiva Crater - and that Chicxulub is the antipode (The
alternative they do suggest is that they could both be impacts, which they
say is plausible if the rotation of the earth is taken into account and the
meteor was fragments travelling in convoy).

They suggest the Shiva Crater is now found in two large halves equidistant
from the mid Indian ocean rift (Carlsberg Ridge), bottom half (SW) being the
Amirente arc near the Seychelles and the top half (NE) being the Narmada
fault and Panvel Flexure. Being equidistant from the Carlsberg Ridge, they
suggest the impact shattered the crust triggered rifting and exacerbated the
volcanism of the Deccan Traps (which I understand is regarded as having
already started before the impact).

As I said I haven't actually read it properly (and its way out of my field)
but after quick scan I can't see any suggestion in this paper that the Shiva
Crater being the antipode of the Chicxulub Crater which I guess could be
possible.

Anyway, it's a fairly convincing paper to a relative novice in this field
that something was going on here in roughly the right timeframe - even if it
isn't the primary impact - what ever happened here suggests a lot of
horrific geological disturbance happened in that part of the world at KT
boundary seeing the faults, rifting and volcanism occurring at the same time
as the Chicxulub crater appeared. 

(Would also be interesting to see if more rifts could be initiated with
impacts... is this an idea suggested elsewhere - or is it an unlikely
scenario?)

[just noticed a discrepancy between the size of the crater in the figures
depicting the crater today and the reconstruction of it soon after the
impact (reproduced from the paper in Rise of Birds as figures 11.3 and 11.4,
pp236-237). In Fig 11.3 going by the scale bar the modern remnants suggest a
crater ~1350km at longest diameter (conservative estimate), 11.4
reconstructs it as ~700km, which is closer to the ~600km mentioned in the
text.]


Cheers,
Chris

PS. Shiva - creative name for the crater (Hindu god of destruction which
allows following creation... check wikipedia... which seems appropriate for
the KT Boundary) if you don't mind the incorporation of religious
terminology in scientific terms.




-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of
John Scanlon
Sent: Monday, 4 September 2006 10:59 AM
To: 'Phillip Bigelow'; dinosaur@usc.edu
Subject: RE: Chicxulub's Antipode (Re: cause of death at KT)

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>
> --
> 
>