The Chicxulub crater is the only well-preserved peak-ring crater on Earth and linked to the Cretaceous-Tertiary mass extinction, an event 65 million years ago that wiped out the dinosaurs as well as nearly 50% of all the world’s species. For the first time, geologists have drilled into the peak ring of this crater in the International Ocean Discovery Program and International Continental Scientific Drilling Program (IODP-ICDP) Expedition 364.
This painting depicts an asteroid slamming into tropical, shallow seas of the sulfur-rich Yucatan Peninsula in what is today southeast Mexico. The aftermath of this immense asteroid collision, which occurred approximately 65 million years ago, is believed to have caused the extinction of the dinosaurs and many other species on Earth. Shown in this painting are pterodactyls, flying reptiles with wingspans of up to 50 feet, gliding above low tropical clouds. Image credit: Donald E. Davis / NASA.
The Cretaceous-Tertiary mass extinction occurred at the same time that a 10-km-diameter asteroid, dubbed Chicxulub, hit our planet in what is now the Yucatán Peninsula. The collision would have triggered earthquakes, tsunamis, and even volcanic eruptions.
The impact, its catastrophic effects, and its aftermath have engrossed researchers and the public alike since it was first discovered.
In spring 2016, an international team of geologists on the IODP-ICDP Expedition 364 drilled into the Chicxulub crater off the coast of Mexico.
The researchers 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,” they explained.
IODP-ICDP Expedition 364 drilled into the subsurface Chicxulub peak ring at borehole M0077A (red dot), which was about 30 km northwest of Progreso and the north shore of the Yucatán Peninsula. The blue circle represents the approximate diameter of the 180-200-km subsurface impact structure. The gravity signature of the structure and locations of other drilling sites are shown in the inset. The only two sites with continuous core are the ICDP Yaxcopoil-1 (Yax-1) and IODP-ICDP M0077A boreholes. Other boreholes are Yucatán-1 (Y1), Yucatán-2 (Y2), Yucatán-6 (Y6), Chicxulub-1 (C1), Sacapuc-1 (S1), and Ticul-1 (T1). Image credit: Kring et al, doi: 10.1130/GSATG352A.1.
The IODP-ICDP borehole data indicate that the peak-ring morphology of the Chicxulub crater was produced by the dynamic collapse of an uplifted central peak.
Drilling also confirmed that the peak ring at Chicxulub consists of granite, brought up from mid-crustal depths.
“The Chicxulub impact generated an environmental calamity that extinguished life. It also induced a vast sub-surface hydrothermal system that altered a portion of the Maya Block and serves as a proxy for much larger and more frequently generated hydrothermal systems during the Hadean, when bombardment rates were high,” the scientists said.
They estimated the amount of sulfur and carbon dioxide shot into the atmosphere, including a second phase of gas release when ejecta was re-vaporized.
“Release of gas from the Chicxulub impact is connected to cooling of over 20 degrees Celsius, with sub-freezing temperatures for three years,” the researchers said.
They also found that soon after the impact the crater became an oasis for the recovery of life and allowed expansion into momentarily vacant niches that, when filled, defined the modern world.
“We followed the recovery of life at ground zero, focusing on an 80-cm transitional layer and the limestone just above,” they said.
“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.”
The findings were published in the October 2017 issue of the journal GSA Today and presented yesterday at the GSA Annual Meeting in Seattle, Washington.
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David A. Kring et al. 2017. Chicxulub and the Exploration of Large Peak-Ring Impact Craters through Scientific Drilling. GSA Today 27 (10): 4-8; doi: 10.1130/GSATG352A.1
