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Chicxulub and the Exploration of Large Peak-
Ring Impact Craters through Scientific Drilling

David A. Kring, Lunar and Planetary Institute, Houston, Texas 77058, USA; Philippe Claeys, Analytical, Environmental and
Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, Brussels 1050, Belgium; Sean P.S. Gulick, Institute for Geophysics and Dept.
of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78758, USA; Joanna V. Morgan
and Gareth S. Collins, Dept. of Earth Science and Engineering, Imperial College London SW7 2AZ, UK; and the IODP-ICDP
Expedition 364 Science Party.

ABSTRACT proving the structure had an impact origin. to assess the depth of origin of the peak-
The buried structure was confirmed by ring rock types and determine how they
The Chicxulub crater is the only well- seismic surveys conducted in 1996 and were deformed during the crater-forming
preserved peak-ring crater on Earth and 2005 to be a large ~180–200-km–diameter event. That information is needed to effec-
linked, famously, to the K-T or K-Pg mass impact crater with an intact peak ring tively test how peak-ring craters form on
extinction event. For the first time, geolo- (Morgan et al., 1997; Gulick et al., 2008). planetary bodies.
gists have drilled into the peak ring of that
crater in the International Ocean The discovery of the Chicxulub impact The expedition was also designed to
Discovery Program and International structure initially prompted two scientific measure any hydrothermal alteration in
Continental Scientific Drilling Program drilling campaigns. In the mid-1990s, a the peak ring and physical properties of the
(IODP-ICDP) Expedition 364. The series of shallow onshore wells up to 700 m rocks, such as porosity and permeability,
Chicxulub impact event, the environmen- deep were drilled by the Universidad to calibrate geophysical data, test models
tal calamity it produced, and the paleobio- Nacional Autónoma de México (UNAM; of impact-generated hydrothermal sys-
logical consequences are among the most Urrutia-Fucugauchi et al., 1996) to sample tems, evaluate the habitability of the peak
captivating topics being discussed in the near-surface impact breccias in the ejecta ring, and investigate the recovery of life in
geologic community. Here we focus atten- blanket surrounding the crater. In 2002, a sterilized portion of Earth’s surface. The
tion on the geological processes that the International Continental Scientific recovered rocks also make it possible to
shaped the ~200-km-wide impact crater Drilling Program (ICDP) also sponsored a evaluate shock deformation of Earth’s
responsible for that discussion and the deep drilling project, producing a 1511 m crust, including the vaporization of rocks
expedition’s first year results. borehole between the peak ring and the that may have contributed to climate-alter-
crater rim. Continuous core beneath 404 m ing effects of the impact. A large number
INTRODUCTION included Tertiary marine sediments, poly- of geological, environmental, and biologi-
mict impact breccias, an impact melt unit, cal results will emerge from the expedi-
The Chicxulub crater (Hildebrand et al., and one or more blocks of Cretaceous sedi- tion. Here, we focus on the planetary geo-
1991) on the Yucatán Peninsula of Mexico mentary target rocks. We refer readers to science findings: how the peak-ring crater
was produced by a terminal Cretaceous two special issues of Meteoritics & formed and what peak-ring and multi-ring
impact that has been linked to regional and Planetary Science (Jull, 2004a, 2004b) for craters can reveal about deep planetary
global K-T or K-Pg boundary deposits (see the major results of that ICDP project, but crusts. As the borehole pierced only a sin-
reviews by Smit, 1999; Kring, 2000, 2007; note that the project left unresolved, gle location within the crater, we begin by
Schulte et al., 2010). The subsurface struc- among other things, the geologic processes looking at a fully exposed peak-ring crater
ture was initially detected with geophysi- that produced the peak-ring morphology of on the Moon, which provides a picture of a
cal techniques (Cornejo Toledo and the crater. similar structure to that targeted by
Hernandez Osuna, 1950). While exploring Expedition 364.
the source of those anomalies, Petróleos The Chicxulub crater is the best-pre-
Mexicanos (PEMEX) drilled three explo- served peak-ring impact basin on Earth, so EXPOSED PEAK-RING CRATERS
ration wells (all dry) into the structure. it is an essential target for additional study.
Petrologic analyses of polymict breccias The only other known similarly sized sur- The Schrödinger basin near the south
and melt rock in recovered core samples viving impact structures, Sudbury and pole on the lunar far side is the youngest
revealed shock-metamorphic and shock- Vredefort, are tectonically deformed and and best preserved peak-ring crater on the
melted features diagnostic of impact eroded. Recently, the International Ocean Moon (Fig. 2A). The ~320-km-diameter
cratering (Kring et al., 1991; Kring and Discovery Program (IODP) and ICDP crater contains an ~150-km-diameter peak
Boynton, 1992; Swisher et al., 1992, drilled an offshore borehole into the crater ring that rises up to 2.5 km above the cra-
Sharpton et al., 1992; Claeys et al., 2003), (Fig. 1), recovering core from a depth of ter floor (Shoemaker et al., 1994). The
505.7–1334.7 m below the sea floor (mbsf), peak ring is topographically complex, with

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