22–25 Oct. GSA 2017 Annual Meeting & Exposition OCTOBER 2017 | VOL. 27, NO. 10 NO. 27, | VOL. 2017 OCTOBER A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICA® Chicxulub and the Exploration of Large Peak-Ring Impact Craters through Scientific Drilling OCTOBER 2017 | VOLUME 27, NUMBER 10 SCIENCE 4 Chicxulub and the Exploration of Large Peak-Ring Impact Craters through Scientific Drilling GSA TODAY (ISSN 1052-5173 USPS 0456-530) prints news David A. Kring, Philippe Claeys, Sean P.S. and information for more than 26,000 GSA member readers Gulick, Joanna V. Morgan and Gareth S. Collins and subscribing libraries, with 11 monthly issues (March/ April is a combined issue). GSA TODAY is published by The Cover: The Chicxulub peak ring in 83-mm-diameter core is ® Geological Society of America Inc. (GSA) with offices at composed of granitic rocks crosscut with cataclastic and hydro- 3300 Penrose Place, Boulder, Colorado, USA, and a mail- ing address of P.O. Box 9140, Boulder, CO 80301-9140, USA. thermal veins and has also been shock-metamorphosed as illus- GSA provides this and other forums for the presentation trated with planar deformation features with ~5 micron spacing of diverse opinions and positions by scientists worldwide, in quartz (inset, with field of view 245 microns wide). See regardless of race, citizenship, gender, sexual orientation, related article, p. 4–8. religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. © 2017 The Geological Society of America Inc. All rights reserved. Copyright not claimed on content prepared wholly by U.S. government employees within the scope of GSA News their employment. 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Erratum In the In Memoriam section of the July 2017 issue of GSA Today (p. 45), Bennie W. Troxel was incorrectly listed as Bernie Troxel. GSA regrets this error. Cover inset image: Mount Rainier, Seattle, WA, USA. 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 Chicxulub crater is the only well- The buried structure was confirmed by ring rock types and determine how they preserved peak-ring crater on Earth and seismic surveys conducted in 1996 and were deformed during the crater-forming linked, famously, to the K-T or K-Pg mass 2005 to be a large ~180–200-km–diameter event. That information is needed to effec- 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 The discovery of the Chicxulub impact The expedition was also designed to crater in the International Ocean structure initially prompted two scientific measure any hydrothermal alteration in Discovery Program and International drilling campaigns. In the mid-1990s, a the peak ring and physical properties of the Continental Scientific Drilling Program series of shallow onshore wells up to 700 m rocks, such as porosity and permeability, (IODP-ICDP) Expedition 364. The deep were drilled by the Universidad to calibrate geophysical data, test models Chicxulub impact event, the environmen- Nacional Autónoma de México (UNAM; of impact-generated hydrothermal sys- tal calamity it produced, and the paleobio- Urrutia-Fucugauchi et al., 1996) to sample tems, evaluate the habitability of the peak logical consequences are among the most near-surface impact breccias in the ejecta ring, and investigate the recovery of life in captivating topics being discussed in the blanket surrounding the crater. In 2002, a sterilized portion of Earth’s surface. The geologic community. Here we focus atten- the International Continental Scientific recovered rocks also make it possible to tion on the geological processes that Drilling Program (ICDP) also sponsored a evaluate shock deformation of Earth’s shaped the ~200-km-wide impact crater deep drilling project, producing a 1511 m crust, including the vaporization of rocks responsible for that discussion and the borehole between the peak ring and the that may have contributed to climate-alter- expedition’s first year results. crater rim. Continuous core beneath 404 m ing effects of the impact. A large number of geological, environmental, and biologi- INTRODUCTION included Tertiary marine sediments, poly- 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 The Chicxulub crater is the best-pre- Expedition 364. the source of those anomalies, Petróleos served peak-ring impact basin on Earth, so Mexicanos (PEMEX) drilled three explo- it is an essential target for additional study. EXPOSED PEAK-RING CRATERS ration wells (all dry) into the structure. The only other known similarly sized sur- The Schrödinger basin near the south Petrologic analyses of polymict breccias viving impact structures, Sudbury and pole on the lunar far side is the youngest and melt rock in recovered core samples Vredefort, are tectonically deformed and and best preserved peak-ring crater on the revealed shock-metamorphic and shock- eroded. Recently, the International Ocean Moon (Fig. 2A). The ~320-km-diameter melted features diagnostic of impact Discovery Program (IODP) and ICDP crater contains an ~150-km-diameter peak cratering (Kring et al., 1991; Kring and drilled an offshore borehole into the crater ring that rises up to 2.5 km above the cra- Boynton, 1992; Swisher et al., 1992, (Fig. 1), recovering core from a depth of ter floor (Shoemaker et al., 1994).