Added blam just the one time. A couple of links, no biggie:
Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1994902
http://www.pnas.org/cgi/reprint/0706977104v1.pdf
Chicxulub and the Cretaceous Tertiary Boundary
http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Chicx_title.html
Thanks. Bookmarked to read during the next blizzard.