Topic started on 20-4-2003 @ 07:02 PM by dragonrider
Geologists Weary, But Elated by Chicxulub Drilling Operations
A schematic diagram of a buried complex crater with impact breccias overlying impact melt. This is a generalized diagram of how the Chicxulub impact
crater may be structured. It is buried beneath several hundred to one thousand meters of sediment, so drilling is needed to sample rocks from the
impact crater. The Chicxulub Scientific Drilling Project is designed to drill through the overlying sediments, the impact breccias, the impact melt,
and into the underlying impact-fractured rock.
The drilling crew on the Chicxulub Scientific Drilling Project near Merida, Yucatan, Mexico, has been doing "a fantastic job," last week recovering
between 35 and 40 meters of exceptional core samples each day, according to a University of Arizona scientist and co-investigator on the project.
The Chicxulub Scientific Drilling Project (CSDP) is an international project to core 1.8-kilometers into an immense crater created by the impact of an
asteroid or comet 65 million years ago. The Cretaceous-Tertiary (K/T) impact is thought to have led to one of the greatest mass extinctions in Earth
history, including dinosaur extinction.
Universidad Nacional Autonoma de Mexico (UNAM) is the lead institution on the $1.5 million, approximately 2-month project. The goal is to discover
what the impactor was and the details of the catastrophic impact that wiped out more than 75 percent of all plant and animal species on Earth.
University of Arizona's Professor Kring holding a long segment of rock core that was recovered from about 4,200 feet. This core is composed of
several layers of sedimentary rock that either represent a mammoth block of rock in the crater's impact breccias or the fractured floor beneath the
crater. It is a sample of the rocks that were hit by the asteroid or comet that produced the vast Chicxulub crater. It is composed mostly of anhydrite
(a calcium sulphate mineral) which, when vaporized in an impact event, produces sulfur-oxide gases that can alter Earth's climate. When injected into
the atmosphere by the impact event, the sulfur-oxide gases form aerosols which cooled the Earth's surface and then eventually rained out of the
atmosphere as sulfuric acid rain. This was probably one of the more severe consequences of the impact event and is likely partly responsible for the
extinction of dinosaurs and other species 65 million years ago. Photograph by Jake Bailey, NASA/UA Space Imagery Center.
"The crew is drilling 24 hours a day, 7 days a week, at a far faster pace that we ever thought possible," said UA planetary scientist David A.
Kring. "We had hoped to recover as much as 25 meters of core samples each day, but at the rate they are drilling, we will probably reach depths of
1.5 kilometers by the end of the project, despite the loss of a diamond drill head earlier in this effort."
The CSDP drilling team members are from DOSECC (Drilling, Observation, and Sampling of the Earth's Continental Crust, Inc.), and Pitsa, a drilling
contractor in Mexico.
"We are getting a 100 percent core-recovery rate," Kring added. Scientists by such drilling operations often recover only between 50 percent or 60
percent, and sometimes as little as 20 percent, of intact core samples, he said.
The drilling crew hands each core barrel pulled from the crater to onsite geologists who then remove and process the core samples.
Kring and UA undergraduate student Jake Bailey last week helped relieve their tired Mexican colleagues in onsite geology duties, working 12-hour
shifts. Kring worked a 28-hour stretch as well.
When Kring left Chicxulub last Saturday night, the team had drilled to more than 1.2 kilometers (4,200 feet).
Kring, director of the NASA/UA Space Imagery Center, has posted photographs and more details on recent operations on the Space Imagery Center website