About 66 million years ago, a massive asteroid crashed into Earth near the site of the small town of Chicxulub in what is now Mexico. This impact coincides with the boundary between the Cretaceous and Paleogene periods and is the probable trigger for the last mass extinction in Earth’s history. The magnitude of the impact released energy equivalent to 1023 joules, enough to generate gigantic earthquakes, mega-tsunamis, and form a crater of 180-200 km (112-124 miles) in diameter in the Yucatan Peninsula. New research suggests that the Chicxulub impact also triggered a mega-earthquake so massive that it shook the planet for weeks to months after the collision.
Artwork depicting one dinosaur’s experience of the Chicxulub impact. Image credit: Hermann Bermúdez.
In 2014, Montclair State University researcher Hermann Bermúdez and colleagues found the so-called spherule deposits on Colombia’s Gorgonilla Island.
The deposits were filled with small glass beads (as large as 1.1 mm) and shards known as ‘tektites’ and ‘microtektites’ that were ejected into the atmosphere during an asteroid impact.
These glass beads formed when the heat and pressure of the impact melted and scattered the crust of the Earth, ejecting small, melted blobs up into the atmosphere, to then fall back to the surface as glass under the influence of gravity.
The rocks exposed on the coast of Gorgonilla Island tell a story from the bottom of the ocean — roughly 2 km (1.2 miles) down.
There, about 3,000 km (1,864 miles) southwest from the site of the impact, sand, mud, and small ocean creatures were accumulating on the ocean floor when the asteroid hit.
Layers of mud and sandstone as far as 10-15 m (33-49 feet) below the sea floor experienced soft-sediment deformation that is preserved in the outcrops today, which the authors attribute to the shaking from the impact.
Faults and deformation due to shaking continue up through the spherule-rich layer that was deposited post-impact, indicating that the shaking must have continued for the weeks and months it took for these finer-grained deposits to reach the ocean floor.
Just above those spherule deposits, preserved fern spores signal the first recovery of plant-life after the impact.
“The section I discovered on Gorgonilla Island is a fantastic place to study the Cretaceous-Paleogene boundary, because it is one of the best-preserved and it was located deep in the ocean, so it was not affected by tsunamis,” Bermúdez said.
Evidence of deformation from the mega-earthquake is also preserved in Mexico and the United States.
At the El Papalote exposure in Mexico, the researchers observed evidence of liquefaction — when strong shaking causes water-saturated sediments to flow like a liquid.
In Mississippi, Alabama, and Texas, they documented faults and cracks likely associated with the mega-quake
They also documented tsunami deposits at several outcrops, left by an enormous wave that was part of the cascading catastrophes resulting from the asteroid collision.
“Our data help explain the geologic evidence that records the end of the Cretaceous and the beginning of the Cenozoic and characterizes one of the biggest earthquakes experienced by our planet during the Phanerozoic,” they said.
The scientists will report their findings this month at the GSA Connects meeting in Denver, Colorado, the United States.
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Hermann Bermudez et al. 2022. The Chicxulub Mega-Earthquake: Evidence from Colombia, Mexico, and the United States. Geological Society of America Abstracts with Programs 54 (5); doi: 10.1130/abs/2022AM-377578
Source link: https://www.sci.news/paleontology/chicxulub-mega-earthquake-11269.html
