The Mandelbear's Musings

It's impossible not to use surperlatives describing the paper published today in Proceedings of the National Academy of Sciences. It's nothing less than the smoking gun that links the Chicxulub asteroid impact with the extinction of the dinosaurs at the end of the Cretaceous.

The article describes a set of deposits that were laid down in the Hell Creek formation in North Dakota, apparently during the first hour after the impact.

The fallout from the impact deposited a thin layer of sediments called the Cretaceous–Paleogene (formerly Tertiary) boundary, rich in micro-tektites (blobs of melted rock) and iridium (scarce on Earth, abundant in meteorites). The tektites would have started coming down in North Dakota, about 5,000 miles from the Yucatán Peninsula, ten to fifteen minutes after the impact. The metallic dust from the vaporized asteroid would have settled out somewhat later. The seismic shock waves would have reached North Dakota at about the same time.

When an earthquake hits a body of water, such as a lake or river, it makes the water slosh back and forth, a phenomenon called a seiche. (Seiches emptied swimming pools all over Southern California during the 1994 Northridge earthquake.) When it hit North Dakota, water and mud sloshed out of a river bed (along with whatever fish were in it, mostly sturgeon and paddlefish), knocked down whatever trees and dinosaurs were in its way, and left a wave-by-wave record of the event.

According to the article in The New Yorker that came out Friday, the debris included sturgeons that died with their mouths gaping and full of tektites, a dinosaur feather, the hip-bone of a ceratopsid, and much, much, more. Some time shortly thereafter, a small mammal burrowed into the mud, dug right through the boundary, and died there.

There's a reason why Robert dePalma, who discovered the site, named it Tanis. He told the New Yorker that "It’s like finding the Holy Grail clutched in the bony fingers of Jimmy Hoffa, sitting on top of the Lost Ark." It's really too improbable for fiction.

Resources

  @ A seismically induced onshore surge deposit at the KPg boundary, North Dakota and 
    Supplementary Information for A SEISMICALLY INDUCED ONSHORE SURGE DEPOSIT AT THE KPG
    BOUNDARY, NORTH DAKOTA  - the actual paper at PNAS, via National Geographic:
  @ Fossils may capture the day the dinosaurs died. Here's what you should know.
  @ Hell Creek Formation - Wikipedia footnotes point to the New Yorker article, plus
  @ Fossil Site Reveals Day That Meteor Hit Earth and, Maybe, Wiped Out Dinosaurs|NYT
  @ 66 million-year-old deathbed linked to dinosaur-killing meteor | Berkeley
    News
  @ The Day the Dinosaurs Died | The New Yorker

... and a tip of the fedora to Minoanmiss for pointing me at the New Yorker article.