Moment of impact: A journey into the Chicxulub Crater

Boulder, CO, USA: When the Chicxulub asteroid slammed into Earth about 66 million years ago, it obliterated 80 percent of Earth's species, blasted out a crater 200 kilometers across, and signaled an abrupt end to the Cretaceous Period. The impact, its catastrophic effects, and its aftermath have engrossed scientists and the public alike since it was first discovered.

In spring 2016, the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling (ICDP) drilled into the Chicxulub crater off the coast of Mexico. The expedition targeted Chicxulub crater's peak ring and overlying rock sequences. Peak rings, as seen on the moon, form when rocks rebound into a peak inside the crater. The peak then collapses, leaving a center ring of rock within the larger crater. The expedition is helping answer important questions about the Chicxulub impact event and peak-ring crater formation on planetary bodies.

Highlights of IODP-ICDP Expedition 364 are featured in the October 2017 issue of GSA Today, and on Tuesday, 24 October, an entire keynote session at the GSA Annual Meeting will be devoted to the expedition. In the session, geologists will take us back to the first moments and years following the impact.

Each talk features findings from the 800-plus meters of core samples retrieved by the expedition. Topics include how the impact affected terrestrial and atmospheric chemistry, timing of events, and the Cretaceous-Paleogene mass extinction and subsequent recovery of life. Some highlights:

* David Kring explores the hydrothermal system triggered by the impact, including metasomatism (lithologic chemistry altered by hot fluids), and how the system could have incubated new life as it cooled over thousands of years post-impact. (8:25 a.m.).

* Joanna Morgan will share results of modeling to determine more accurately the amount of sulfur and CO2 shot into the atmosphere, including a second phase of gas release when ejecta was re-vaporized. Release of gas from the impact is connected to cooling of over 20 degrees C, with sub-freezing temperatures for three years (8:45 a.m.).

* In large impacts, rocks from deep in the crust are brought upward into the crater. Drilling confirmed that the peak ring at Chicxulub consists of granite, brought up from mid-crustal depths. Sean Gulick takes us back to the first day of the Cenozoic, with a look at the granite and the overlying sequence of melt glass, breccia, and deposits from a seiche (an oscillation wave within a semi-enclosed or enclosed body of water) or tsunami. (9:45 a.m.).

* Finally, Christopher Lowery follows the recovery of life at ground zero, focusing on an 80-centimeter transitional layer and the limestone just above. These units record the devastation of the impact, trace fossils from surviving species, and fossils within the limestone revealing that within 30,000 years of impact, life inside the crater was back in full swing. (11:45 a.m.).

Session No. 192 IODP-ICDP Expedition 364 to the Chicxulub Impact Crater

Tuesday, 24 October: 8:00 AM-12:00 PM

Ballroom 6A (Washington State Convention Center)

Session Link: https://gsa.confex.com/gsa/2017AM/webprogram/Session43180.html

The Geological Society of America, founded in 1888, is a scientific society with more than 25,000 members from academia, government, and industry in more than 100 countries. Through its meetings, publications, and programs, GSA enhances the professional growth of its members and promotes the geosciences in the service of humankind. Headquartered in Boulder, Colorado, GSA encourages cooperative research among earth, life, planetary, and social scientists, fosters public dialogue on geoscience issues, and supports all levels of earth science education.

Provided by Geological Society of America