Illustration of a large asteroid colliding with Earth some 65 million years ago on the Yucatan ... [+]
Some 66 million years ago, a large asteroid about 10 kilometers (6.2 miles) in diameter struck the Earth in what is the modern day Gulf of Mexico. The impact formed the Chicxulub crater, which is around 200 kilometers (125 miles) wide, along the coast of the Yucatan Peninsula. The impact would have thrown trillions of tons of dust into the atmosphere, cooling the Earths climate significantly and leading to the Cretaceous–Paleogene extinction, a global extinction event responsible for eliminating approximately 80 percent of all species of animals, including dinosaurs.
According to computer models published in 2019, the impact also generated a tsunami with waves up to 1.5 kilometers (or nearly 1 mile) high.
In the same year, researchers reported the discovery of a site in North Dakota, 3,000 kilometers (1,800 miles) north of Chicxulub, with coarse-grained sediments and fossil remains of marine animals interpreted as debris swept inland from the tsunami.
Now, for the first time, scientists have discovered direct evidence for this tsunami some 1,000 kilometers (620 miles) north of the impact site. Seismic images of underground layers in Louisiana show fossilized sedimentary structures associated with water currents as experienced during a tsunami.
Seismic imagery is widely used in oil and gas exploration. Gary Kinsland, a geophysicist at the University of Louisiana, Lafayette, and his team analyzed seismic imaging data for central Louisiana provided by Devon Energy, a company exploring the areas surrounding the Gulf of Mexico.
At a depth of 1,500 meters (4,900 feet) underground, in marine rocks dating back 66 million years, the researchers discovered a field of 16 meters (52 feet) tall and 600 meters (about 2,000 feet) long "megaripples." Too large to be formed by marine currents, the orientation of the ripples matches the direction of waves coming from the Chicxulub impact site.
Seismic images of underground layers in Louisiana revealed megaripples associated with a tsunami.
The researches argue that the megaripples are the results of a series of impact-induced tsunami washing up an ancient seashore. The thick sand-layers deposited by the uprush and backwash currents of the tsunami waves formed symmetrical ripples on the seafloor. These megaripples are preserved in the sediments as a result of having formed below the erosion base of storm waves, and being buried later by deep water shales.
The study was published in the journal Earth & Planetary Science Letters.
