Megaripples from dinosaur-killing asteroid are under Louisiana
Ancient ‘megaripples’ as tall as five-storey buildings are hiding deep under Louisiana, and their unique geology indicates that they formed in the immediate aftermath of the asteroid strike that killed the non-avian dinosaurs.
The 16-metre megaripples are about 1,500 metres under the Lake Iatt area and date to the end of the Cretaceous period 66 million years ago, when that part of the state was underwater. The megaripples’ size and orientation suggest that they formed after the giant space rock, known as the Chicxulub impactor, slammed into the Yucatán Peninsula. This led to the Chicxulub impact tsunami, whose waves then rushed into shallower waters, creating the megaripple marks on the seafloor. The occurrence of “ripples of that size means something very big had to disturb the water column,” said Gary Kinsland, a professor in the School of Geosciences at the University of Louisiana at Lafayette. “This is just further evidence that the Chicxulub impact ended the Cretaceous period.”
The project began when the energy corporation Devon Energy took a 3D seismic survey of Lake Iatt. A seismic survey entails creating loud sound waves and placing surface detectors around the area that can capture the returning sound waves, which are reflected when they hit various underground rock layers. Data from these sound waves allows researchers to make maps of the underground geology. Researchers took the Devon Energy data and created a seismic image of the subterranean area. When Kinsland looked at the seismic image, “I immediately saw the ripples, and I knew the direction the water would have had to have been travelling [to create them],” he said. “I knew that if you go backwards from that, you run right into Chicxulub.”
Kinsland was able to determine the tsunami’s direction because the megaripples are asymmetrical, which shows the direction the water was flowing when they were made. In this case, the long asymmetrical side of the megaripples have a south-southeast-facing slope, which points back to the Chicxulub impact crater.
The megaripples have an average wavelength (from one crest to the next) of 600 metres. That, combined with their almost 16-metre-high amplitude, makes them “the largest ripples documented on Earth,” the researchers wrote. Moreover, these megaripples are at the top of the Cretaceous-paleogene geological boundary dating to 66 million years ago, and lie beneath a layer of debris that was kicked up in the aftermath of the Chicxulub impact.