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Ancient Meteorite Impact Spawned Giant Submarine Avalanches

News Services
University of North Carolina-Chapel Hill

Contact: David Williamson or Bret Johnson, (919) 962-8596.

Release No. 281				March 30, 1998

Embargoed until 6 p.m.Tuesday, March 31, 1998

Ancient meteorite collapsed margin, spawned giant submarine avalanches

By DAVID WILLIAMSON, UNC-CH News Services

CHAPEL HILL -- After untold years of streaking across the galaxy, a giant
meteorite smacked the Earth 65 million years ago with the force of a million
atomic bombs.

The collision, which scientists believe led dinosaurs and many other species
to die off within a few years, also caused massive landslides along the edge
of the continent north of Mexico's Yucatan Peninsula, new evidence suggests.
Six miles wide, the rock and metal chunk cut a hole 120 miles across and
devastated an area from northeast Mexico to what is now the U.S. Gulf Coast.

"Until now, little has been known about the effect of the impact on the
continental margin closest to the crater, which is directly north of the
Yucatan," said Dr. Timothy Bralower, professor of geology at the University
of North Carolina at Chapel Hill. "Because it happened so long ago, you
can't even see the crater from the air or from space."

In a paper published in the April issue of the journal Geology, Bralower and
colleagues report evidence that the impact caused parts of the Yucatan
margin to slide into the deep sea. Co-authors are Drs. Charles K. Paull,
professor of geology at UNC-CH, and R. Mark Leckie of the University of
Massachusetts at Amherst.

"In cores of sediment taken from the base of the margin by the Ocean
Drilling Program, we found fragments of several types of rock and fossils of
various ages matching the strata from different levels on the margin,"
Bralower said.

Fragments were mixed with minute, round melted rock beads known as spherules
flung from the impact site, he said. Such beads are direct evidence of an
impact blast.

"The blast shattered large chunks of the edge of the margin, and they
literally slid down to the depths of the ocean," Bralower said.

Collapsing margins triggered giant submarine avalanches that moved at up to
hundreds of miles an hour and spread across the Gulf of Mexico and into the
Caribbean.

"We find the same mixture of fossils, rocks and spherules in Haiti and in
the central part of the Caribbean suggesting that the submarine avalanches
traveled great distances," Bralower said.

Geologists cannot rule out the possibility that other margins collapsed
because of the blast and that avalanches came from a number of sources, he
said. But it's clear that the impact had a huge effect on Gulf of Mexico
topography.

Among the more spectacular results of the margin collapse, which suddenly
displaced billions of gallons of water, were giant tidal waves that
inundated coastlines around the gulf.

Scientists named the event, which was like a cannon ball hitting a duck pond
-- except on a vastly larger scale -- the Chicxulub impact, after the
Yucatan crater site. Bralower and colleagues dubbed the mixture of
microfossils, rock fragments and impact-created materials they studied the
"Cretaceous-Tertiary boundary cocktail."

Core sampling to about 3,000 feet took place aboard the 470-foot JOIDES
Resolution, the world's largest scientific drill ship.

The National Science Foundation and the Texas A&M University-based Ocean
Drilling Program supported the research.

                                   - 30 -

Note: Bralower can be reached at (919) 962-0704.


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