Louisiana's deepest caves are home to ancient "megaripples", five-story structures that were once as tall as the rest of the world. A new study has found that their unique geology suggests that they formed immediately after the asteroid strike that decimated nonavian dinosaurs.Researchers said that the megaripples, which measure 52 feet (16 meters) in height, are located under the Iatt Lake area of north central Louisiana. They date back to the end the Cretaceous period 66 millions years ago when the area was still underwater. Researchers believe that the megaripples formed after a giant space rock known as the Chicxulub Asteroid smashed into the Yucatn Peninsula. This caused the Chicxulub Impact tsunami, which caused waves to rush into shallower waters, creating the megaripple marks on its seafloor.Gary Kinsland (a researcher at the School of Geosciences at Louisiana at Lafayette), said that the occurrence of "ripples of this size" indicates something had to disturb the water column. This is yet more evidence that the Chicxulub Impact ended the Cretaceous Period.Related: In photos: How North America grew into a continentDevon Energy, an energy company, conducted a 3D seismic study of Iatt Lake. A seismic survey involves creating high-frequency sound waves (often with explosives or big thumps), and then placing detectors on the ground to capture the sound waves returning from the underground rock layers. Researchers can create maps of underground geology using data from sound waves.Kaare Egedahl was a co-researcher and was a master's student in petroleum geology at Louisiana at Lafayette. He took the Devon Energy data to create a seismic image of subterranean areas. "Kaare brought the data to me and said, 'What is this?' Kinsland stated that it is so different from anything you might expect to find in deposits made by rivers or the sea. "I saw it and thought, "OMG!Kaare Egedahl, study co-researcher, created a black-and-white seismic picture of the megaripples for his master's thesis. The seismic image covers approximately 11 by 7 miles (18 and 11 km). (Image credit to Kinsland, GL. et al. Earth and Planetary Science Letters (2021); Kaare EdahlKinsland had previously studied Chicxulub's impact crater. He said that he saw the seismic image and knew immediately the direction in which the water had to have traveled "to create them." "And I knew that Chicxulub is right in front of me if you look backwards."Kinsland was able determine the tsunami's direction due to the megaripples being asymmetrical. This indicates the direction that the water flowed 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, he said.This map shows Chicxulub's impact crater (red Arrow) and the location the newly discovered megaripples, (red Star), which were likely caused by a tsunami that occurred when the asteroid struck 66 million years back. These numbers are previously identified tsunami deposits that were left by the event. (Image credit to Kinsland GL. et al. Earth and Planetary Science Letters (2021); Original Base Map by Ron Blakey/Colorado Plateau Gesystems; Nina Zamanialavijeh).Megaripples have a wavelength of 1,968 feet (600m) from one crest to another. The megaripples' 52-foot-high amplitude makes them the "largest ripples on Earth", according to the researchers.The megaripples also lie at the Cretaceous/Paleogene geoological boundary and date to 66,000,000 years ago. They are below a layer of debris, which was thrown up by the Chicxulub impact.Similar: The history's worst tsunamisHow could the megaripples continue?Megaripples show that, after the impact of space rock on Earth 66 millions years ago, a tsunami rushed through the Gulf of Mexico. It then shoaled and broke off as it "reached an abrupt shallowing of Gulf of Mexico within what's now central Louisiana", the researchers wrote in their study. The seismic data shows the formation of the asymmetric megaripples, which were created by the water flowing north-northeast across the shelf.However, tiny ripples created by waves on sandy beaches are very short-lived. How did megaripples last for 66,000,000 years?They remained submerged after the tsunami caused the megaripples. Kinsland stated that the megaripples were so deep underwater that even after storms battered the Gulf of Mexico, they remained unaffected. He said that the megaripples were then buried in shale, an essence of sedimentary rock composed of clay, clay, and mineral fragments for a period of approximately 5 million years during the Paleocene Epoch (66 million to 56 millions years ago). He added that later, the shale was covered with even younger sediments.The July 2nd online publication of the study in Earth and Planetary Science Letters was made.Original publication on Live Science
