Fossilized "megaripples" record huge tsunami from ancient asteroid impact
Around 66 million years ago, a gigantic asteroid smashed into the Earth and brought the 160-million-year reign of the dinosaurs to an end. Now, researchers have discovered direct evidence of this world-changing cataclysm in the form of fossilized “megaripples” from the tsunamis that followed in the immediate aftermath.
As fast as our current climate seems to be changing, it’s a leisurely stroll compared to the end of the Cretaceous period. An asteroid (or comet fragment) measuring at least 10 km (6.2 miles) wide slammed into what is now the Yucatan Peninsula in Mexico, and while that would have delivered a swift demise to anything unlucky enough to be too close to ground zero, the effects quickly spread worldwide.
The impact would have set off tsunamis, earthquakes, volcanic eruptions and widespread wildfires. The oceans would have become dangerously acidic, and huge amounts of rock and soot would have been thrown into the atmosphere, blocking the Sun for as long as 18 months. In all, as much as three quarters of life on Earth was wiped out, including the dinosaurs and about 93 percent of mammals.
And now, researchers have discovered physical evidence of one these disastrous consequences – tsunamis. It’s hard to spot a smoking gun after tens of millions of years, but buried 1.5 km (0.9 miles) underground, scientists at the University of Louisiana at Lafayette found fossilized megaripples from the giant waves imprinted in the rock. The ripples appear to be spaced an average of 600 m (1,968 ft) apart and stand 16 m (52.5 ft) tall on average. The team says that their orientation appears to line up exactly with the impact crater.
The breakthrough came from seismic imaging data beneath Louisiana in the southern United States, collected by Devon Energy while hunting for petroleum resources. This region lies directly across the Gulf of Mexico from the site of the Chicxulub impact, and at the time of the cataclysm it was under about 60 m (197 ft) of water, thanks to higher sea levels.
This depth likely helped preserve them for so long. The team says that after the waves had passed and the water settled, storms and other natural disturbances wouldn’t have had the power to reach that far down, allowing the seabed to hold onto its rippled pattern until it fossilized.
The new discovery adds more physical clues about the events that followed in the hours and days after the Chicxulub impact. Other recent studies found mass graves of fish thrown from the water by tsunamis and buried in mud 3,000 km (1,864 miles) away, rains of glass beads from vaporized rock, and material that was quickly deposited into the crater as water rushed back in.
The new research was published in the journal Earth and Planetary Science Letters.