Science Magazine has a piece about some "megaripples" found in central Louisiana. These fossilized trace fossils are thought to be from the tsunami caused by the meteor which brought about the KPg mass extinction at the end of the Cretaceous Period about 66 million years ago. A new paper in the journal Earth and Planetary Science Letters describes the discovery.
When a giant space rock struck the waters near Mexico’s Yucatán Peninsula 66 million years ago, it sent up a blanket of dust that blotted out the Sun for years, sending temperatures plummeting and killing off the dinosaurs. The impact also generated a tsunami in the Gulf of Mexico that some modelers believe sent an initial tidal wave up to 1500 meters (or nearly 1 mile) high crashing into North America, one that was followed by smaller pulses. Now, for the first time, scientists have discovered fossilized megaripples from this tsunami buried in sediments in what is now central Louisiana.
“It’s great to actually have evidence of something that has been theorized for a really long time,” says Sean Gulick, a geophysicist at the University of Texas, Austin. Gulick was not involved in the work, but he co-led a campaign in 2016 to drill down to the remains of the impact crater, called Chicxulub.
To look for ancient buried structures, researchers rely on seismic imaging techniques to “see” underground. They set off explosives or use industrial hammers to send seismic waves into the earth, and listen for reflections from the layers of sediment and rock below. Companies use the technique to search for oil and gas, and they have mountains of data—especially in areas such as the Gulf of Mexico.
More than 10 years ago, Gary Kinsland, a geophysicist at the University of Louisiana, Lafayette, obtained seismic imaging data for central Louisiana from Devon Energy. At the time of the dino-killing impact, sea levels were higher, and Kinsland thought information from this region would hold clues to what happened in the shallow seas off the coastline.