Geoscience Reference
In-Depth Information
line up along the circumference of a circle? In an attempt to answer,
Pope and Duller assembled PEMEX gravity and drill-core data and
in 1988, during a conference in Mexico at which they first presented
the cenote ring finding, showed the results to geologist Adriana
Ocampo. She came to the brilliant conclusion that the combined
gravity, core, and satellite data revealed a buried impact crater.
Between 1989 and early 1990, the three worked on a paper to be
submitted to
Science,
outlining their theory that a crater of K-T age
was buried in the Yucatan. Before they were able to send it off, how-
ever, the 1990
Science
paper by Hildebrand and Boynton appeared.
Pope and his colleagues were astounded to learn that others were
looking for a crater in the Yucatan. Pope then contacted Hildebrand,
who sent preprints of a paper in which he named the structure
Chicxulub. Pope, Ocampo, and Duller eventually saw their work
published,
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but by then priority for the rediscovery had gone to
Hildebrand. Of course, the original discoverers were Penfield and
Camargo.
As far as we know, the only process that can produce a circular
ring with a diameter of 170 km is impact; no volcanic caldera is both
so large and so perfectly circular. Pope, Ocampo, and colleagues
interpret the cenote ring as having forming by postimpact collapse
of the Yucatan limestones at the boundary between the fractured
and unfractured zones that mark one of the impact rings, an effect
commonly seen on other planets. If they are correct, the cenote ring
is an inner circle, not the outer perimeter, and Chicxulub is much
larger than 170 km. Later work on the morphology, topography, and
soil types at the surface has led them to conclude that the crater is
about 260 km in diameter.
ROCK TYPES
In 1992, the indefatigable Officer and Drake weighed in.
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Along
with the late Arthur Meyerhoff, an American geologist who had
been a consultant to PEMEX in the 1960s when the Chicxulub
structure was drilled, they published an article in
GSA Today,
whose
title, "Cretaceous-Tertiary Events and the Caribbean Caper," sug-
gested that, far from having capitulated and accepted Chicxulub as
the K-T impact crater, the authors intended instead to treat the
notion as risible. Meyerhoff had been one of the most bitter oppo-
nents of plate tectonics and had made fossil identifications that, if
correct, falsified the claim that Chicxulub was the K-T impact
crater. He had a great deal at stake.
PEMEX's drilling of the Chicxulub structure in the 1960s and
1970s uncovered what their specialists at the time interpreted as a
