So discovery channel had this show on what really killed the dinosaurs. They started with the normal single impact iridium conventional theory. Then they brought up new findings that suggest it was not one, but two impacts that wiped out the dinosaurs.
Apparently two scientists found 8 meters below the iridium layer tiny rocks that were melted by the first impact commonly thought to have wiped out the dinosaurs, came back to Earth and settled. Then a layer of mud which would have taken thousands of years to form. Then a layer of sand, then another layer of mud which shows colonization by worms, then sand then the sandstone and iridium and molten rocks.
It would seem to incidate the yunctan impact wiped out most species, but the 2nd impact 300,000 or so years later finished off the dinos.
This of course shows that science can change and adapt.
Just possibly about five major craters instead of one: in the Ukraine, off Maine, in the North Sea, and a real monster off India. http://www.spacedaily.com/news/deepimpact-04r.html
Several are still somewhat speculative, though. There's enough oil around of those last two that some "piggyback" research should be possible in cores that oil companies will be drilling up anyway. Give it a few years...
I think we are looking at a combination of events. The Dakar Traps in India caused some major stress to the environment not that long before the impact.
I read sometime ago that dinosaurs where already in trouble before the meteor. Some statistical studies of fossil beds showed the the diversity of the dinosaur was crashing, though actual numbers of animals remained strong