Topography

Kevin Pope, a consulting geologist now associated with the Jet Propulsion Laboratory, and two colleagues, came close to being the first to "rediscover" Chicxulub. He and Charles Duller of NASA were examining Landsat high-altitude satellite photographs, trying to determine the relationship between the ancient Mayan sites on the Yucatan Peninsula and the location of surface water deposits. They soon noticed a set of small ponds, which they later found went by the Mayan name of cenotes, that were arranged along the arc of an almost perfect circle. What could cause a set of small ponds to 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 '988, 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 '989 and early '990, 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, however, the '990 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,20 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 '70 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 '70 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.

Was this article helpful?

0 0

Post a comment