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Ancient “mega-palaces” as tall as five-story buildings lurk deep beneath Louisiana, and their unique geology indicates that they formed immediately after the asteroid strike that killed the nonavian dinosaurs, according to a new study.
The 52-foot-tall (16-meter) megapples are found about 5,000 feet (1,500 m) below the Lake Iatt region in north-central Louisiana, and date from the late 1800s. Cretaceous period 66 million years ago, when this part of the state was underwater, the researchers said. The size and orientation of the mega-ipples suggest that they formed after the giant space rock, known as the asteroid Chicxulub, crashed into the Yucatán Peninsula, causing the Chicxulub Tsunami, whose waves then rushed into shallower water and created the mega-ipple marks on the seabed, the researchers said.
The appearance of “ripples of this size means that something very large must have disturbed the water column,” Gary Kinsland, principal investigator of the study, professor at the School of Geosciences at the study, told Live Science. ‘University of Louisiana at Lafayette. “This is just further proof that the impact of Chicxulub ended the Cretaceous Period.”
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The project began when energy company Devon Energy carried out a 3D seismic survey of Lake Iatt. A seismic survey involves creating strong sound waves (often made with “explosives or loud thumps,” Kinsland said) and placing surface detectors around the area that can capture the returning sound waves, which are reflected when they strike various underground rock layers. The data from these sound waves allow researchers to map the underground geology.
Study co-researcher Kaare Egedahl, then a master’s student in petroleum geology at the University of Louisiana at Lafayette, took data from Devon Energy and created a seismic image of the underground area. “Kaare brought it to me and he said, ‘What is it? “Because it’s so different from anything you’d expect to see in deposits deposited by the sea or by rivers,” Kinsland said. “I looked at it and thought ‘OMG’ to myself.”
Kinsland had previously studied the Chicxulub impact crater. When he looked at the seismic image, “I immediately saw the ripples, and I immediately knew in which direction the water should have moved. [to create them]”, he said.” And I knew if you go back you will run straight to Chicxulub. “
Kinsland was able to determine the direction of the tsunami because the mega-ipples are asymmetrical, which shows the direction in which the water flowed when they were created. In this case, the long asymmetric side of the mega-ipples has a south-southeast slant, which refers to the Chicxulub impact crater, he said.
Mega-ipples have an average wavelength (peak to peak) of 1,968 feet (600 m). That, combined with their 52-foot-high amplitude, makes them “the largest documented ripples on Earth,” the researchers wrote in the study.
Additionally, these mega-ipples sit atop the Cretaceous / Paleogene geological boundary dating back to 66 million years ago, and lie beneath a layer of debris that was lifted from the Chicxulub impact. , wrote the researchers in the study.
Related: Waves of destruction: the greatest tsunamis in history
How did the mega-ipples persist?
Mega-ipples indicate that after space rock hit Earth 66 million years ago, a tsunami rushed across the Gulf of Mexico, then formed and shattered offshore as it “reached the shallow depth of the Gulf of Mexico in what is now central Louisiana,” the researchers wrote in the study. “The resulting water pulses flowing north-northeast over the plateau area produced the asymmetric mega-ipples that are imaged in the seismic data.”
But the small ripples left by the waves on a sandy beach are short-lived. So how did mega-ipples persist for 66 million years?
After the tsunami created the mega-ipples, they remained underwater. They were deep enough underwater that when storms swept through the Gulf of Mexico, the mega-ipples remained intact, Kinsland said. Then the mega-ipples were buried by shale – essentially a sedimentary rock made up of mud mixed with clay and mineral fragments – over a period of about 5 million years, during the Paleocene era ( 66 to 56 million years ago), he said. . Later, this shale was covered with even younger sediment, he added.
The study was published online July 2 in the journal Letters of Earth and Planetary Sciences.
Originally posted on Live Science.
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