Scientific Method / Science & Exploration

Dino-killing asteroid also triggered mind-blowing submarine landslides

Huge deposits identified in Gulf of Mexico and beyond.


Try as we might, it’s difficult to imagine what it must have been like when the asteroid that ended the reign of the dinosaurs crashed into the Earth just off the modern-day Yucatán Peninsula. Clearly, it wasn’t pleasant, given the number of species that didn’t live through it. Unfathomable shockwaves would have ripped outward from the impact site, followed by widespread fires. Ash and dust blocked out the Sun and fell as a deadly blanket. The massive influx of carbon dioxide to the atmosphere then set off intense warming. It’s the kind of stuff that requires you to take the word “awesome” back from surfers so that you can use it for describing things that would make you wet your pants.

Thanks to a recent paper in Geology, you can add another jaw-dropper to that list: huge volumes of sediment along the entire northern slope of the Gulf of Mexico became destabilized and slid down into the ocean basin. And that’s only part of the story.

The researchers had reason to expect there would be undersea landslides (more on that in a bit), so they took advantage of publicly available data from 33 deep wells drilled by the oil and gas industry in the Gulf of Mexico. They combined that information with seismic images of the region—which are a bit like sonar maps of the seafloor, except that they penetrate deep into the Earth, showing layers of sediment and rock.

In 31 of those 33 boreholes, they found a peculiar layer at the end of the Cretaceous. Fossils of organisms that lived at different times—spanning the last 20 million years of the Cretaceous— were jumbled together in the limestone. Closer to the coast, the layer was 30 to 200 feet thick, but thickened to as much as 650 feet farther offshore and downslope.

Seafloor “landslide” deposits are pretty distinctive. Since they’re dropped in one big event, the largest, heaviest particles sink out first, followed by slightly smaller ones, and so on, producing a smooth size gradient. If there were multiple events, you’d see a large-to-small sequence marking each one. In this case, even the 650-foot-thick portion shows just one such sequence, indicating it was the product of just a single slide.

That adds up to clear evidence of a large landslide that occurred at the time of the asteroid impact. The researchers found it in boreholes stretching over 600 miles along the Gulf Coast of the US, but it goes far beyond that. Similar layers of rock have already been identified on the southern side of the Gulf of Mexico, on the Bahamas side of the Yucatán Peninsula, even running the entire length of the East Coast of the United States. Together, those deposits make this the largest known landslide event by a wide margin. It seems that the Chicxulub impact shook loose sediment along well over 2,000 miles of submarine slopes. That cascade of sediment probably triggered tsunamis—although the impact would have directly spawned tsunamis of its own in the Gulf of Mexico.

Not even the most expensive and preposterous Roland Emmerich disaster flick could match the grand scale of destruction that carved its fury into the Earth’s surface and caused one of the biggest die-offs the planet has ever seen.

Geology, 2013. DOI: 10.1130/G34503.1  (About DOIs).

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