[meteorite-list] Meteorites from the bottom of the ocean - Part 2 of 2

[David Weir]

Here's a photo to go with the story:

http://meteoritestudies.com/KTFOSSIL.JPG

David

bernd.pauli at paulinet.de wrote:
> Sky & Telescope, March 1999, p. 22: Piece of a Killer Asteroid ?
> 
> Like finding a stray bullet at a crime scene, a researcher believes he has uncovered
> a long-sought chunk of the impactor thought to have snuffed out 70 percent of the
> species of life on Earth 65 million years ago. Scientists found the "smoking gun" in
> 1990: a 180-kilometer-wide circular structure centered beneath the town of Puerto
> Chicxulub on the coast of Mexico's Yucatán Peninsula. But no piece of the impactor
> had surfaced.
> Geochemist Frank T. Kyte (University of California, Los Angeles) has been studying
> a core sample from the bottom of the Pacific Ocean containing dark clay marking the
> boundary of the Cretaceous and Tertiary periods (the K-T boundary). As Kyte
> describes in Nature for November 19, 1998, the clay layer included a 4-millimeter-wide
> piece of lighter-colored clay. Upon splitting open the nugget, he discovered a fossil
> meteorite. More detailed examination of this sedimentary pearl revealed that it contains
> high concentrations of iron oxides, principally hematite.
> While the mineralogy of the fossil meteorite has undoubtedly changed over time, Kyte
> reports that the amounts of iron, chromium, and iridium are nevertheless close to the
> ranges seen in carbonaceous chondrites, a common meteorite type. Yet the specimen
> has one significant compositional oddity: it has 1,000 times more gold than chondritic
> meteorites commonly have, a curiosity that Kyte finds puzzling.
> Because the ocean-floor sediments at the K-T boundary accumulated over perhaps as
> much as 500,000 years, there is no way to prove that this truly is a piece of the
> K-T impactor. However, a meteoritic impact is most consistent with Kyte's analysis;
> he largely discounts the possibilities that the material is interplanetary dust or
> cometary debris. Moreover, he thinks it quite conceivable that a piece of the asteroid
> that struck the Yucatán Peninsula survived the blast and landed 9,000 kilometers away.