Mike,
I have to be careful not to post things that people tell me that are not yet public. But, I already posted the AGU special session description, which is public, that Kennett and others think that the megafauna (like Mammoths) became extinct at about 13,000 years ago because of an impact in North America..this also caused the Younger Dryas climate deterioration where the ice sheets advanced again...for a while. I'll link to various abstracts as they become available at AGU...AGU's web site says Oct 16. I have not seen the abstracts...
Chris