So far, the Chicxulub crater has not convinced me as the source of the global iridium anomaly that marks the K-T boundary. Other extinction events have already been linked with trap volcanism (P-T boundary, T-J boundary [see also this blog entry]) and therefore I had always favoured the Deccan traps as a major contribution to the environmental changes that lead to major extinction at the K-T boundary.
Now I might be able to have the cake and eat it. A structure known as the "Bombay High", which previously has been investigated as a reservoir of hydrocarbons, is now tentatively identified as a meteorite crater. Since the object that made this crater must have had a diameter of 40 km, comparable to the asteroid Ganymed, the crater should actually be classified as an asteroid crater. With a diameter of 500 km it would also be the largest known impact structure and much younger than impacts of comparable size.
The GSA press release says:
"It's hard to imagine such a cataclysm. But if the team is right, the Shiva impact vaporized Earth's crust at the point of collision, leaving nothing but ultra-hot mantle material to well up in its place. It is likely that the impact enhanced the nearby Deccan Traps volcanic eruptions that covered much of western India. What's more, the impact broke the Seychelles islands off of the Indian tectonic plate, and sent them drifting toward Africa.
The geological evidence is dramatic. Shiva's outer rim forms a rough, faulted ring some 500 kilometers in diameter, encircling the central peak, known as the Bombay High, which would be 3 miles tall from the ocean floor (about the height of Mount McKinley). Most of the crater lies submerged on India's continental shelf, but where it does come ashore it is marked by tall cliffs, active faults and hot springs. The impact appears to have sheared or destroyed much of the 30-mile-thick granite layer in the western coast of India.
The team hopes to go India later this year to examine rocks drill from the center of the putative crater for clues that would prove the strange basin was formed by a gigantic impact."Sankar Chatterjee, The significance of the contemporaneous Shiva impact structure and Deccan volcanism at the KT boundary, 2009 GSA Annual Meeting, Portland, OR. [Abstract]