Giant impact near India -- not Mexico -- may have doomed dinosaurs
October 15, 2009
This diagram shows a three-dimensional reconstruction of the submerged Shiva crater (~500 km diameter) at the Mumbai Offshore Basin, western shelf of India from different cross-sectional and geophysical data. The overlying 4.3-mile-thick Cenozoic strata and water column were removed to show the morphology of the crater. Credit: Sankar Chatterjee, Texas Tech University
A mysterious basin off the coast of India could be the largest, multi-ringed impact crater the world has ever seen. And if a new study is right, it may have been responsible for killing the dinosaurs off 65 million years ago.
Sankar Chatterjee of Texas Tech University and a team of researchers took a close look at the massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and gas resources. Some complex craters are among the most productive hydrocarbon sites on the planet. Chatterjee will present his research at this month's Annual Meeting of the Geological Society of America in Portland, Oregon.
"If we are right, this is the largest crater known on our planet," Chatterjee said. "A bolide of this size, perhaps 40 kilometers (25 miles) in diameter creates its own tectonics."
By contrast, the object that struck the Yucatan Peninsula, and is commonly thought to have killed the dinosaurs was between 8 and 10 kilometers (5 and 6.2 miles) wide.
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.
"Rocks from the bottom of the crater will tell us the telltale sign of the impact event from shattered and melted target rocks. And we want to see if there are breccias, shocked quartz, and an iridium anomaly," Chatterjee said. Asteroids are rich in iridium, and such anomalies are thought of as the fingerprint of an impact.
More information: View research abstract, at http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_160197.htm
Source: Geological Society of America
Oct 17, 2006 |
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You might try a search for "rock oil" regarding petrogenetic hydrocarbons.
Another item not mentioned in this article is the co-incedence of gold, silver, and rare-earth elements associated with these impact basins. Could be quite a boon for India.
Whether the Yucatan and the Deccan impacts were related or not and whether they both contributed to the KT boundary deposit is not my concern. But the relationship of these events to the extinction of the dinosaurs is of interest to me. Had either of these two events or both in combination been responsible for the extinction of the dinosaurs one would expect that some of the larger dinosaur bones would have been in contact with the KT boundary or even more probable some of the larger specimens would have had their bones protruding through the KT boundary.
Even if it took 5 or 10 years for the iridium to settle out of the atmosphere and form the KT boundary it would take a vastly greater time for these giant bones to be covered by dust or other sediments and in the meantime rains would have washed much of any atmospheric deposition off those exposed bones.
Yet to the best of my knowledge every dinosaur relic has been found below the KT boundary.
to end later
It has to be possible that dinosaurs had become extinct long before the major impacts that created the KT boundary.
This could quite easily have occurred with the arrival of flowering plants. If these proliferated at a very rapid rate and quickly supplanted the natural diet plants of the herbivores, too quickly for them to adapt to the change then they would have died out. The demise of the herbivores would have very quickly lead to the demise of the carnivores.
Should small numbers have made the transition to flowering plants they would have been too few to survive the dietary needs of the carnivores with the extinction of the bulk of the herbivores.
Because of the close proximity in time between the two events the idea of a mass extinction being caused by such an impact appears to have too much appeal for anyone to look beyond such an event as THE cause. The mass extinction of other life forms may well have been caused by such impacts and their aftermath.
As for your surprise at no fossils specifically straddling the K-T layer...that's expecting a little much, isn't it? I mean, think about it. If you take a population of animals during a mass extinction, and during a "normal" period in Earth's history, after a hundred years they're both (almost) all going to be dead. The deaths are nastier and no descendants are left during a mass extinction, but other than that the total number of deaths are the same, and there's no real reason to expect a spike in fossils--and to have one right on the boundary would be a colossal stroke of luck.
Scene: Ancient Galactic Future Membership Council reviews its efforts to eradicate Earth's dinosaurs because they are viewed as a dead end that will never evolve into the kind of members the council wants. Unfortunately, the asteroid bullet - "straight through the planet" for special effects impact on the big screen - was only partially successful. To remedy, Council authorizes Deccan fumigation. Plot follows heroic efforts of crew to light and get away.
It took me a moment to recognize your brilliant wordplay, but thank you very much.