Some 66 million years after the Chicxulub asteroid impact kickstarted the Cretaceous–Paleogene (K-T) extinction, scientists are still finding stunning evidence of its destruction.
In 2021, researchers spotted “megaripples” nearly one mile below the surface, suggesting that the megatsunami created by the impact left behind geologic formations as the waves collided with the continental shelf.
Now, the authors have expanded the search and found evidence of megaripples in a 900-square-mile area throughout the Gulf of Mexico, along with their varying formations along the upper shelf and the deep sea.
Of the five mass extinctions that have impacted our planet in the past 500 million years, the Cretaceous–Paleogene (K-T) extinction event certainly delivers on dramatic flair. On a spring day some 66 million years ago, a six-mile-wide asteroid smashed down just north of what is now Mexico’s Yucatan Peninsula. This sudden impact created tsunamis stretching one mile tall and racing outward from the asteroid’s dino-killing blow. As those waves raced toward present-day Louisiana (which was largely underwater at the time), they achieved most of their gargantuan height as they reached the ramp of the continental shelf.
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In 2021, using seismic data gathered by the oil and natural gas company Devon Energy, scientists led by Gary Kinsland from the University of Louisiana at Lafayette found evidence of this geologic trauma in the form of 52-foot-tall “megaripples” located one mile underground—an area of rock associated with the end-Cretaceous period. Initially surveying a 77-mile area, Kinsland and his team determined that these subterranean ripples likely formed as the asteroid-generated megatsunamis disturbed sediment near the shore.
Now, a new study from the same team reveals that these “megaripples”—roughly spaced up to one kilometer apart—can be found both further up the shelf of what is now central Louisiana and further down in deeper waters of the Gulf of Mexico. The scientists behind this new paper found evidence of megaripples in a larger, 900-square-mile area, and explain that these formations vary depending on where the tsunami impacted sediments along the paleo-shelf. The results of the study were published in the journal Marine Geology.
“The megaripples are different on the slope, at the shelf break and further up the shelf,” Kinsland, the lead author of the new study, told Live Science. “This is important information in modeling of tsunami, in prediction of future tsunami interactions with shelves and in the understanding of the Chicxulub tsunami.”
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As the study explains, the largest of these megaripples can be seen along the paleo-shelf break—the area where the Gulf’s depth dramatically increases down the slope of the continental shelf toward the deep sea. The way that waves interact with the continental shelf is a well-known process known as the “Van Dorn effect,” which describes how waves surge over a shelf. The study also discovered that megaripples further inland were more weakly asymmetric, suggesting the waves’ behavior changed as they entered shallower waters. Conversely, megaripples in the deep sea took on varied shapes, likely as a result of interactions with faults and collapses, according to Live Science.
“From the coverage of the three areas here in Louisiana we infer that the buried northern Gulf of Mexico shelf system, from Texas to Florida, is covered with megaripples from at least the paleo-slope up to the paleo-bathymetry where Gulf storms would have eroded the megaripples after their formation,” the team said in a press statement.
While this gives scientists a better understanding of how the Chicxulub impact tsunami affected the region, it also provides a stunningly powerful example of how tsunamis interact with continental shelves. And if our worst fears are ever realized, it may help us prepare for future asteroid encounters during Earth’s never-ending journey through the universe.
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Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.