The evening after the discovery of shocked quartz and impact melt was was described by Kring at the 1991 Lunar and Planetary Science Conference, a group of scientists met at the LPI to form the International Chicxulub Consortium, which was organized to access existing exploration data in a coordinated manner and to develop a proposal to drill into the crater. A specially designed drilling program was essential, as the previous petroleum exploration only recovered a fragmentary rock record.
Pemex Exploration Boreholes
The existing petroleum exploration boreholes into the buried structure were Chicxulub-1, Sacapuc-1, and Yucatán-6. The discovery samples of polymict breccia and impact melt came from the Yucatán-6 borehole, located near the peak ring of the crater. By re-interpreting the drilling logs based on those samples, the Yucatán-6 borehole appears to have penetrated ~250 meters of polymict breccia and ~380 meter of melt rock before bottoming in anhydrite at a depth of 1631 meters. Another important impact melt sample from the central melt sheet came from the Chicxulub-1 borehole. The locations of those boreholes were designed to explore a semi-circular gravity anomaly on the northern margin of the Yucatán Peninsula. Other boreholes in that petroleum exploration program (e.g., Ticul-1, Yucatán-1, and Yucatán-2) penetrated the peninsula outside the crater and beyond the limits of the gravity anomalies.
Chicxulub Gravity Map and Boreholes
The subsurface structure of the Chicxulub crater can be seen in a gravity map of the northwestern margin of the Yucatán Peninsula. A black circle outlines the ~180 kilometer diameter crater. The original petroleum exploration borehole locations (C1, S1, and Y6) are shown where intermittent core was recovered. That core was sufficient, however, to prove the crater had an impact origin. A scientific borehole was drilled near the Haciende Yaxcopoil (Yax-1) in 2001-2002 and produced continuous rock core for study. A borehole is being drilled at sea (Chicx-03A)
Illustration Credit: David A. Kring
Chicxulub Gravity and Borehole Map
The Chicxulub crater is buried beneath Tertiary sediments. Geologists and geophysicists use several techniques to study it. One of those techniques is to measure subtle changes in gravity above the structure. Those gravity contrasts can be caused by less-dense rock created by impact-generated shattering of the rock or more-dense rock created by melting of the Earth’s crust, forming a thick pool of impact melt that eventually solidified into a dense mass of igneous rock. Those features create a semi-circular anomaly in the gravity of the northern Yucatán Peninsula. This anomaly was recognized decades before the structure was identified as an impact crater. Based on three petroleum exploration boreholes (S1, C1, and Y6) drilled into the structure, it was initially interpreted to be a buried volcanic complex. A reexamination of those core rocks by Kring, Hildebrand, and Boynton showed that those rocks were actually impact lithologies. A decade later, the International Continental Drilling Program (ICDP) drilled another borehole (Yax-1) into the structure, producing the first continues core sequence through the impact melt-bearing rocks in the crater.
Illustration Credit: Lukas Zurcher and David A. Kring
Chicxulub Surface Geology Map
Geologic map of the surface above the Chicxulub impact crater and the immediate vicinity, Yucatán, Mexico. The surface of the Yucatán is covered with Tertiary-Paleocene (Tpa), Tertiary-Eocene (Te), Tertiary-Oligocene (To), Tertiary-Miocene (Tm), Neogene (N), and Quaternary (Q) post-impact lithologies, all of which are highlighted in color. Target lithologies and impact lithologies have been sampled by exploration boreholes, whose locations are shown: Chicxulub-1 (C1), Sacapuc-1 (S1), Yucatán-6 (Y6), Yaxcopoil-1 (Yax1), Ticul-1 (T1), UNAM-5 (U5), UNAM-7 (U7), Yucatán-2 (Y2), Yucatán-5a (Y5a), Yucatán-1 (Y1), and Yucatán-4 (Y4). Two faults are represented by blue lines. The map was originally published by D. A. Kring, 2005, Hypervelocity collisions into continental crust composed of sediments and an underlying crystalline basement: comparing the Ries (~24 km) and Chicxulub (~180 km) impact craters, Chemie der Erde 65, 1-46.
Illustration Credit: David A. Kring
ICDP Chicxulub Scientific Drilling Program
The International Continental Drilling Program (ICDP) agreed to drill into the crater to recover a continuous core of the impactites. The Chicxulub Scientific Drilling Project (CSDP) occurred in 2001-2002, producing the Yaxcopoil-1 borehole adjacent to Hacienda Yaxcopoil south of the city of Merida. The Principal Investigators of the CSDP were Jaime Urrutia Fucugauchi, Dante Jaime Morán-Zenteno, Virgil (Buck) Sharpton, Richard Buffler, Dieter Stöffler, and Jan Smit, who were supported by a large, international science team.
Chicxulub Scientific Drilling Project
In 2001-2002, the International Continental Drilling Program (ICDP) drilled into the Chicxulub crater. The project was called the Chicxulub Scientific Drilling Project (CSDP). The drilling site is called Yaxcopoil-1, because it is located near the Yaxcopoil hacienda in the Yucatán, Mexico. This view was taken on a cool clear morning. Often conditions are hot and steamy or wet with rain.
Photographic Credit: David A. Kring
Chicxulub Polymict Breccia in the Yaxcopoil-1 Borehole
Impact-melt bearing polymict breccia from the Yaxcopoil-1 core in the Chicxulub impact crater. The breccia is dominated by green fragments of partially altered impact melt that were fragmented while being ejected from the crater. The volume of melt in the Chicxulub breccias is much larger than that seen at other, smaller craters. The melt fragments were mixed with surviving clasts of target material, including a mafic clast from deep in the Earth’s crust. These materials were excavated from depths up to 13 kilometers and deposited at the surface. This sample, like all other impactites in the Chicxulub crater, was eventually buried by Tertiary sediments. It was recovered from a depth of 836 meters in the Yaxcopoil-1 core. The field of view is approximately 2 millimeters wide. This sample was described by Kring, Hörz, Zurcher, and Urrutia Fucugauchi (2004, Impact lithologies and their emplacement in the Chicxulub impact crater: Initial results from the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico, Meteoritics and Planetary Science 39, 879-897). This picture was also used on the cover of February 2005 issue of Chemie der Erde, which included a review article by Kring (2005, Hypervelocity collisions into continental crust composed of sediments and an underlying crystalline basement: comparing the Ries (~24 km) and Chicxulub (~180 km) impact craters, Chemie der Erde 65, 1-46).
Photographic Credit: David A. Kring
Chicxulub Impact Melt Rock in the Yaxcopoil-1 Borehole
At the base of the impactite sequence recovered from the Yaxcopoil-1 core in the Chicxulub impact crater is a green impact melt rock. The Chicxulub impact event melted the Earth’s crust down to a depth of ~27 kilometers. That melt entrained a few surviving clasts of target material (e.g., the dark clasts seen here) while it was being transported and deposited. This material was produced within the 100 kilometer diameter transient crater, but was ejected or flowed into the topographic trough between the crater’s peak ring and final crater rim. This sample, like all other impactites in the Chicxulub crater, was eventually buried by Tertiary sediments. This sample was recovered from a depth of 864 meters. The field of view is approximately 2.5 millimeters wide. This sample was described by Kring, Hörz, Zurcher, and Urrutia Fucugauchi (2004, Impact lithologies and their emplacement in the Chicxulub impact crater: Initial results from the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico, Meteoritics and Planetary Science 39, 879-897).
Photographic Credit: David A. Kring
For additional images of CSDP drilling operations and the rock core it recovered, visit the LPI’s Classroom Illustration library.
Compared with polymict breccias found at smaller craters, the Chicxulub breccias are incredibly rich in melt fragments. That finding confirmed models indicating the volume of impact melt increases faster than the diameter of the crater increases. Thus, the proportion of melt relative to rock in a large crater is larger than that in smaller crater.
The Yaxcopoil-1 core was also extremely important because it illuminated the hydrothermal activity that the Chicxulub impact event produced. The hot rock generated by the impact event heated groundwater in the crust of the Earth and caused it to circulate. The system vented hydrothermally as both steam and hot water onto the floor of the crater. Because those hot fluids circulated through the impactite sequence, the impact mineralogy was altered, producing a series of secondary mineral assemblages. Model calculations suggest the hydrothermal system may have persisted for more than a million years. That result prompts a question: Did that hydrothermal system affect the recovery of life within the Chicxulub crater?
Geologists also used the Chicxulub hydrothermal system as a proxy for the consequences of older impact events. During the early evolution of Earth, impact bombardment was severe. The entire surface of the Earth was resurfaced by impact events. Some of the impact craters were thousands of kilometers in diameter, dwarfing the Chicxulub crater. Those impacts would have made conditions at the surface of the Earth hostile for any life. On the other hand, the impact-generated subsurface hydrothermal systems would have been possible refuges for life. That prompted David Kring to propose the impact-origin of life hypothesis.
Early Earth Impact Crater Lakes and Hydrothermal Systems
For more information about impact cratering on the early Earth, please visit LPI’s Impact Cratering on Hadean Earth.
IODP-ICDP Chicxulub Impact Crater Expedition 364
An initiative to drill into another location within the Chicxulub crater was recently approved. The International Ocean Discovery Program (IODP), in collaboration with ICDP, is launching Expedition 364, the Chicxulub Impact Crater project. This project is a Mission Specific Platform Expedition, meaning it is being drilled from a platform specially selected for the project, rather than IODP’s JOIDES Resolution or Chikyu ships. The selected drilling site is in an area with ecologically-sensitive reefs and a shallow 17 to 18 meter water depth, demanding the specialized equipment. Sixty days are planned for drilling, coring, and downhole measurements in April and May, 2016. The drilling goal is to reach a depth of 1200 to 1500 m and recover ~500 m, possibly more, of peak ring rocks. The borehole site was selected to drill into the crater's peak ring. It is an ideal site to test models of peak-ring formation. It is also a good site to further test models of impact-generated hydrothermal activity and its potential effect on life.
Chicxulub Drilling Site 2016
A borehole is being drilled into the peak ring of the Chicxulub crater in 2016. International Ocean Discovery Program (IODP) in collaboration with the International Continental Drilling Program (ICDP) is drilling ~30 kilometers northwest of Progreso and the north shore of the Yucatán Peninsula of Mexico. That borehole, labeled Chicx-03A on a gravity map (inset), is targeting the peak ring in that quadrant of the crater. Expedition 364 Chicxulub Impact Crater project is a Mission Specific Platform Expedition, meaning it is being drilled from a platform specially selected for the project, rather than IODP’s JOIDES Resolution or Chikyu ships. The selected drilling site is in an area with ecologically-sensitive reefs and a shallow 17 to 18 meter water depth, demanding the specialized equipment. Sixty days are planned for drilling, coring, and downhole measurements in April and May, 2016. The drilling goal is to reach a depth of 1200 to 1500 m and recover ~500 m, possibly more, of peak ring rocks. The background image is a detail from a map produced by Reto Stockli, NASA Earth Observatory, as part of the Blue Marble project. The gravity map was produced by Lukas Zurcher and David A. Kring (2004) and updated with the Expedition 364 borehole location (Chicx-03A).
Illustration Credit: David A. Kring
The scientific goals of the project include an assessment of peak-ring lithologies, how they may have been deformed and, thus, flowed during the cratering event, to test models of peak ring formation. Those models are guided, in part, by observations of similar structures, such as the exquisitely exposed Schrödinger basin on the Moon, but need to be evaluated with core samples from Chicxulub. The drilling project will also measure the hydrothermal-alteration in the peak ring and physical properties, such as permeability, needed to further test models of impact-generated hydrothermal systems; to evaluate the habitability of the peak ring; and investigate the recovery of life in a sterile zone. The nature and composition of any impact breccias and melt rocks, including any dikes in the peak ring, will be analyzed. An assessment of target lithologies will also be made to fine-tune estimates of the impact’s climatic effects. Finally, studies of the core and correlative downhole measurements will provide a calibration point for crater-wide geophysical imaging of the subsurface, greatly enhancing future 3D application of those geophysical techniques to the entire impact basin.
This section of our educational website will be updated with Expedition 364 results as they become available.
Chicxulub and Schrödinger Peak-Ring Craters
The most dramatic impact event during the past half-billion years is the Chicxulub impact (inset, bottom center) that extinguished dinosaurs (inset, lower left) and most life on Earth at the K-T boundary 65 million years ago. The ~180 km diameter Chicxulub crater (left background) is the best-preserved example of a peak-ring basin on Earth, but it is buried beneath Tertiary sediments. To help understand the formation of that type of impact basin, geologists also study analogue structures, such as the magnificently exposed Schrödinger basin on the lunar farside (right background) that formed ~3.8 billion years ago (inset, lower right). Illustration credits: Background art, left, by William K. Hartmann (©1991) and used with permission. Background illustration, right, was produced by NASA GSFC’s Scientific Visualization Studio. Insets (left to right) were produced by LPI, William K. Hartmann (©1983), and Daniel D. Durda (©2011). This educational illustration was released as part of the LPI’s Never Stop Exploring series.
Photographic Credit: LPI/CLSE
Testing Models of Chicxulub Peak-Ring Formation
One of the objectives of the IODP-ICDP Chicxulub Impact Crater Expedition 364 is to test models of peak-ring formation. In one model, the peak ring forms when a central uplift rises from the center of the crater and then, too weak to withstand gravity, collapses, with rock flowing outward to form a circular peak ring. The process severely deforms target rocks (left) into a final peak ring structure (right) that emplaces crystalline basement rocks (e.g., mica schists, gneisses, amphibolites) over sedimentary rocks (e.g., limestone, anhydrite, red beds, and quartzite). The left side of the diagram is adapted from Kring (2005, Chemie der Erde 65, 1-46) and the right side of the diagram is adapted from Collins et al. (2008, Earth and Planetary Science Letters 270, 221-230).
Illustration Credit: LPI/David A. Kring
This website was produced by the LPI for academic use in a classroom.
Any other use of the information and images requires permission of David A. Kring and the LPI.
This web site is an updated version of information originally created for the University of Arizona Space Imagery Center's Impact Cratering Series.