City-Sized Asteroid That Killed Dinosaurs Shook Planet For "Weeks To Months"

66 million years ago, a 10-kilometre asteroid hit Earth, triggering the extinction of the dinosaurs. New evidence suggests that the Chicxulub impact also triggered an earthquake so massive that it shook the planet for weeks to months after the collision.

The amount of energy released in this 'mega-earthquake' is estimated at 1023 joules, which is about 50,000 times more energy than was released in the magnitude 9.1 Sumatra earthquake in 2004.

Hermann Bermudez will present evidence of this "mega-earthquake" at the upcoming GSA Connects meeting in Denver this Sunday, 9 October.

Earlier this year, with support from a GSA Graduate Student Research Grant, Bermudez visited outcrops of the infamous Cretaceous-Paleogene (K-Pg) mass extinction event boundary in Texas, Alabama, and Mississippi to collect data, supplementing his previous work in Colombia and Mexico documenting evidence of the catastrophic impact.

In 2014, while doing fieldwork on Colombia's Gorgonilla Island, Bermudez found spherule deposits -- layers of sediment 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 down. There, about 3,000-km 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 meters below the sea floor experienced soft-sediment deformation that is preserved in the outcrops today, which Bermudez attributes 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.

Bermudez explains, "The section I discovered on Gorgonilla Island is a fantastic place to study the K-Pg boundary, because it is one of the best-preserved and it was located deep in the ocean, so it was not affected by tsunamis."

Evidence of deformation from the mega-earthquake is also preserved in Mexico and the United States. At the El Papalote exposure in Mexico, Bermudez observed evidence of liquefaction -- when strong shaking causes water-saturated sediments to flow like a liquid.

In Mississippi, Alabama, and Texas, Bermudez documented faults and cracks likely associated with the mega-quake. He also documents tsunami deposits at several outcrops, left by an enormous wave that was part of the cascading catastrophes resulting from the asteroid collision.

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