The End of the Cretaceous Was in Late Spring or Early Summer

(h/t, John) Amazing the detail from 66 million years ago!:

In the new research, scientists turned to the Tanis fossil site in western North Dakota, a part of the vast Hell Creek Formation, a geological layer that spans several states and is dated to have been laid down at the time of the impact. Some 10 – 13 minutes after the impact in Mexico, immense seismic waves passed the Tanis site, causing flooding that most likely came from the nearby Western Interior Seaway, a huge but shallow sea that ran north/south across western North America at the time. This in turn created what’s called a seiche, a huge standing wave in water that can generate waves a hundred meters high. This is similar, for a much smaller and mundane scale, to when you scooch back and forth in a bathtub in time with the waves generated, amplifying the crests enough that you can splash water out of the tub.

Now picture the tub being a lake, and the waves reaching 20 stories high. 

This happened quite suddenly at Tanis, and the geography of the area makes it possible to actually get extremely fine time resolution of the events. It’s also replete with fossils, including fish, insects, plants, and more. Here’s where this gets cool: By examining these fossils, it’s possible to figure out the time of year of the impact.