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Re: Deccan traps
I've just finished reading Sankar Chatterjee's book "The Rise of Birds"
(John Hopkins University Press, 1997) in which he briefly discusses,
among other things, the Shiva Crater---a large impact structure located
on the west coast of India immediately proximate to the Deccan traps. He
describes the Shiva Crater as located precisely on the KT boundary and
approximately 450 x 600 km in size at the time it was formed. He states
that it was created by a low angle impact of an object ~40 km in
diameter. Although Chatterjee accepts that Deccan volcanism was occurring
intermittently for about 1 Ma before the impact event, he does suggest
that the enormous Deccan lava output at the KT boundary itself may have
been "enhanced" by the Shiva impact. The Shiva Crater appears to be a
complicated geologic puzzle today, since subsequent Deccan lava flows
have buried much of it and two halves of the crater are now separated by
about 2800 km due to spreading of the Carlsberg Ridge.
The Shiva Crater has been mentioned briefly on the list a couple times,
but this is the first account I have read that had any detail. If this
crater is real, it would mean that the KT boundary may represent a
substantially more devasting impact event than previously thought.
Chatterjee even predicts a third impact site in the Pacific along the
line of a "great circle" drawn around the globe that connects the
Chicxulub and Shiva craters. More craters along that line could suggest
an event not unlike the multiple poundings Jupiter took several years ago
from the 21 fragments of the comet Shoemaker-Levy 9.
I thought that others more familiar than I with the KT boundary or Deccan
trap literature may have more to add about the Shiva Crater. How real is
it? Is it at the KT boundary? There doesn't seem to be much published on
it. The references about the Shiva Crater in Chatterjee's book were to
only three articles; each of which list him as the pricipal author
(Chatterjee, S. 1992. New Concepts in Global Tectonics, 33-62. Texas
University Press; ___, 1996, The Last Dinosaurs in India, The Dinosaur
Society Report 12-17; and Chatterjee and D.K. Kudra. 1996. KT events in
India: impacts, rifting, volcanism and dinosaur extinctions, in
Proceedings of the Gondwanan Dinosaur Symposium 39:489-532). I only
turned up two other articles in a quick search: Subramanian, K.S. The
Shiva Crater, Journal of the geological society of India Nov. 01, 1997 v.
50, No. 5; and Rampino and Haggerty, The "Shiva Hypothesis": Impacts,
Mass Extinctions and the Galaxy, in Earth, Moon and the Planets, 1996,
Vol. 72, No. 1/3.