[meteorite-list] Question About Iturralde Structure, Bolivia

From: rochette <rochette_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:30 2004
Message-ID: <v04003a14ba7fd8708269_at_[193.49.98.39]>

Abstract to be presented by Wasilewski et al. at the IUGG Meeting Sapporo
Japan (July 2003):

ITURRALDE: A POSSIBLE IMPACT STRUCTURE AT THE EDGE OF THE AMAZON IN
NORTHERN BOLIVIA
The Iturralde structure is possibly the Earth's most recent "big" impact
event recording a collision with a meteor or comet that might have occurred
between 11,000 and 30,000 years ago. The most convincing evidence for the
existence of a crater comes from the Shuttle Radar Topography Mission
(SRTM) image of the structure. The feature appears as a quasi-circular
closed depression about 20 meters in depth resembling a cookie cutter
cutting heavily vegetated soft sediments and pampas at the edge of the
Bolivian Amazon. A barometric traverse from inside the crater to outside
the rim supports the 20 meter depth contrast suggested by the SRTM data. A
magnetic survey across the crater was able to define a symmetry along an
east-west axis with the center being lower than the rim. Base station
records were able to identify the Equatorial Electrojet (EEJ) geomagnetic
diurnal signal attributed to a narrow electric current sheet flowing
eastward along the magnetic dip equator. The soil magnetic susceptibility
remains low and featureless until about 1 meter depth where lateritic
nodules identifiable with the downward migration of iron are found. As yet
there are no identifiable evidences of shocked quartz in the quartz sand
collected in soil pits inside the crater, along river cuts, and at the
"rim". The expedition did not yield the "smoking gun" required for
verification. There does exist oil exploration geophysical survey data (
gravity, magnetics) which include the Iturralde structure in the survey
areas and there are seismic lines near the structure. We hope to be able to
obtain this information perhaps by presentation time. The vegetation inside
the crater appears different from that outside the crater but this may
simply reflect the inundated nature of the depressed structure which may be
underwater for a good portion of the rainy season. A return to the
structure to drill for evidence of shocked material may be the only way to
prove that the structure is a crater.

(sounds rather unconclusive....)


Pierre
Received on Mon 24 Feb 2003 09:15:45 AM PST