[meteorite-list] K-T Impactor

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:32 2004
Message-ID: <3D050FC2.7A3DE533_at_lehrer1.rz.uni-karlsruhe.de>

Hello Tracy, David, and List,

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.


BOND P. (1999) Fossilized remnant of dinosaur killer found (Astronomy
Now, 1999, Jan, p. 9):

The fossilized remnant of an asteroid that may have caused the global
extinction of dinosaurs has been found by Frank Kyte, a geochemist
from University of California at Los Angeles. In a recent issue of the
journal Nature, Kyte described how he found the fossil meteorite while
studying the boundary layer between Cretaceous and Tertiary sediments.
It was hidden in mud and buried on the bed of the Pacific Ocean.
Although the 2.5 mm long granule no longer contains all of its original
minerals, it has retained its original shape and texture. According to
Kyte, it is probably a fragment of the asteroid which collided with the
Earth near Mexico's Yucatan peninsula 65 million years ago. His findings
suggest that the meteorite’s composition resembles a metal- and
sulphide-rich carbonaceous chondrite asteroid, as opposed to the porous
materials that would more likely be found in a comet. Detailed analysis
also identified high levels of iridium, an element found in relative
abundance in asteroid meteorites. This indicates that the dinosaur
killer was more likely to have been an asteroid than a comet. - Peter
Bond

Some references:

KYTE F.T. et al. (2001) K-T boundary impact debris
from DSDP site 577 (MAPS 36-9, 2001, A109).

KYTE F.T. (1996) Should we expect to find more pieces
of the K/T bolide? (abs. Meteoritics 31, 1996, A076).


Best regs,

Bernd
Received on Mon 10 Jun 2002 04:44:50 PM PDT