Re: Deccan traps

["Norton, Patrick" <Patrick.Norton@state.me.us>]

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.