International Ocean Discovery Program Expedition 364 Scientific Prospectus

The Chicxulub impact crater in Mexico is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic “peak ring.” Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 y of intense debate, we are still striving to answer the question as to why this impact was so catastrophic. International Ocean Discovery Program (IODP) Expedition 364 proposes to core through the peak ring of the Chicxulub impact crater to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of postimpact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Of additional interest is the transition through a rare midlatitude record of the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of impact breccias, melt rocks, and peak-ring rocks; the sedimentology and stratigraphy of the Cenozoic sequence; and any observations from the core that would help us constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical property measurements on the core and wireline logs will be used to calibrate geophysical models, including seismic reflection data. Proposed drilling directly contributes to the IODP science plan initiatives (1) Deep Biosphere and the Subseafloor Ocean and (2) Environmental Change, Processes and Effects, in particular the environmental and biological perturbations caused by the Chicxulub impact. Expedition 364 will be implemented as a mission-specific platform expedition to obtain subseabed samples and downhole logging measurements from the peak ring of the Chicxulub impact crater. The expedition aims to core a single borehole as deep as 1500 meters below seafloor (mbsf) to recover rock cores from above and into the Chicxulub impact crater preserved under the Yucatán continental shelf. Schedule for Expedition 364 Expedition 364 is based on International Ocean Discovery Program (IODP) drilling Proposal 548-Full3 and Addendum 548-Add4. Following ranking by the IODP Science Advisory Structure, the expedition was scheduled by the European Consortium for Ocean Research Drilling (ECORD) Facility Board as a mission-specific platform (MSP) expedition to be implemented by the ECORD Science Operator (ESO). At the time of publication of this Scientific Prospectus, the expedition is scheduled for April–May 2016 with a total of 60 days available for the drilling, coring, and downhole measurements described in this prospectus and on the ESO Expedition 364 webpage. The Onshore Science Party (OSP) is provisionally scheduled to start September 2016 and last for approximately 3 weeks (dependent on core recovery). The following links should be used in conjunction with this Scientific Prospectus: 3 • Proposal 548-Full3 can be found at https://www.iodp.org/doc_download/2292-548-full3cover, and Addendum 548-Add4 can be found at http://www.eso.ecord.org/docs/364/548-Add4_Morgan.pdf. • The Expedition 364 webpage will be periodically updated with expedition-specific information on the platform, facilities, coring strategy, measurements plan, scheduling, and port call (http://www.eso.ecord.org/expeditions/364/364.php). • General details about the offshore facilities provided by ESO are provided on the ESO-specific webpages on the MARUM website (http://www.marum.de/en/Offshore_core_curation_and_measurements.html). • General details about the onshore facilities provided by ESO are provided on the ESO-specific webpages on the MARUM website (http://www.marum.de/Onshore_Science_Party_OSP.html). • Supporting site survey data for Expedition 364 are archived in the IODP Site Survey Data Bank (http://ssdb.iodp.org/SSDBquery/SSDBquery.php; choose P584 in the Proposal number selection box). Please note that not all site survey data associated with this expedition are publicly available.