More than 65 million years ago, a six-mile wide asteroid smashed into Mexico's Yucatán peninsula, triggering earthquakes, tsunamis and an explosion of debris that blanketed the Earth in layers of dust and sediment.
Now analysis of commercial oil drilling data—denied to the academic community until recently—offers the first detailed look at how the Chicxulub impact reshaped the Gulf of Mexico. Figuring out what happened after these types of impacts gives researchers a better idea of how they redistribute geological material around the world. It also gives scientists an idea of what to expect if another such impact were to occur now.
The Chicxulub impact, which wiped out large dinosaurs and giant marine reptiles, created a global layer of debris that is now part of the geologic record. Geologists refer to this layer as the Cretaceous–Paleogene boundary, because it marks the switch between these two geologic time periods.
“It is truly a tree ring for the Earth, because how we define time geologically is by extinction events,” says Sean Gulick of the University of Texas Institute for Geophysics in Austin. “Everywhere on Earth this layer marks exactly the time when the mass extinction happened.”
The boundary can be less than a tenth of an inch thick in areas far from the impact site. But in the Gulf of Mexico, researchers weren't able to say for sure just how much sediment and debris the impact threw around the region—until now.
The new analysis shows that the Chicxulub impact mobilized nearly 48,000 cubic miles of sediment across the gulf. It wiped out the contours of the bottom of the gulf, covering everything from the Yucatán to the Caribbean in hundreds of feet of debris.
“This deposit was literally laid down in a matter of days and weeks,” says lead author Jason Sanford, previously of the University of Texas Institute for Geophysics and now working as an exploration geologist for Chevron.
To create this new picture of the asteroid's effects in the gulf, Sanford and his colleagues used a combination of data on rocks and sediment gleaned from 408 drilling wells that penetrated up to 35,000 feet into the seafloor, as well as seismic data. Seismic vibrations sent into Earth's crust are reflected back toward the surface and can give scientists a three-dimensional view of the subsurface.
But the team's comprehensive view wouldn't have been possible without the commercial drilling data, and obtaining it was a major achievement. When David Kring, of the Lunar and Planetary Institute in Houston, discovered and named the Chicxulub impact site in 1991, he immediately started talking to oil companies about gaining access to their Gulf of Mexico data. Because the region was a valuable oil resource, the conversations went nowhere.
“For over 20 years I have been hoping that somebody would be able to get hold of that data,” says Kring, who was not involved in the study. “So I am ecstatic that this group at the University of Texas has been able to do that.”
Using these datasets, the team was able to probe up to 50,000 feet below sea level to determine the thickness, volume and nature of the boundary layer in the gulf region. As they report in a recent paper in the Journal of Geophysical Research: Solid Earth, the scientists found that the volume of material moved by the Chicxulub impact dwarfed that of the next biggest instantaneous deposit—the Nuuanu debris flow in Hawaii—by two orders of magnitude.
“It was always going to be big numbers,” Kring says. “It is not that scientists didn't think that those kinds of slump deposits existed in the past, but this paper quantifies those numbers basin wide, which is an important next step.”
Further afield, the boundary layer consists of fine grains of sediment, but closer to the impact site, the layer consists of hundreds of feet of sand, gravel, cobble and even boulders. Sanford and his colleagues showed that when the asteroid slammed into Earth, the impact set off earthquakes that shook loose rocks and boulders and whipped up tsunamis that carried in debris from as far away as what are now Texas and Florida.
“That’s why the layer can be hundreds of meters thick,” Gulick says. “It is full of everything falling down the hill, tsunami deposits and also the stuff that fell out of the sky.”
The Chicxulub impact released as much energy as a hundred terratons of TNT, beyond a billion times the power of the atomic bomb dropped on Hiroshima.
“The atomic bomb, the most powerful earthquake—these are already events that we have difficulty conceiving of,” Sanford says. “It was a constant exercise in trying to keep our minds open to what's possible in terms of the amount of sediment, the amount of energy and the speed at which things happen.”