"Some sort of catastrophe must have annihilated untold millions of fish."
In a book by (I think) the younger Alvarez, he describes visiting a 65mya site in Denmark (?) where there were also signs of of many dead fish. His impression was that something very catastrophic and nasty had happened there. He commented on the fact that this layer smelled bad, and I think there was also iridium found. I wish I could find the darn book in one of my piles.
:')