IODP-ICDP Expedition 364: Drilling Chicxulub, the K-Pg impact structure.

English Abstract:

Joint IODP-ICDP drilling of the Chicxulub impact structure, Mexico is scheduled for early 2016. The current team of multi-disciplinary co-proponents team consists of some 28 researchers from 9 nations. Chicxulub is unique in the terrestrial impact record in that its formation is associated with a mass extinction event (K-Pg) and it has a (albeit buried) preserved peak ring structure. Although peak ring structures occur on the other terrestrial planets, there is no consensual agreement on either the formational mechanism or the nature of the rocks that form a topographic peak ring. A 1.2-1.5 km hole will be drilled offshore that will penetrate the crater’s peak ring; thus, providing the first ground-truth data on a peak ring. Geophysical data indicate that the peak ring at Chicxulub is characterized by relatively low velocity and density material, suggesting that the rocks are highly fractured. Numerical models of large impacts require that target rocks behave temporarily in a fluid-like manner to facilitate the dramatic modification of a large bowl-shaped transient cavity resulting from the cratering flow-field to form a broad, flat final complex craters. Competing hypotheses for weakening include so-called thermal softening and acoustic fluidization. Sampling material at Chicxulub will allow the first study of the actual rocks of a peak ring, and better constrain the weakening mechanism and large crater formation. Other science goals include: detailed lithology and porosity of the target rocks, which are fundamental input parameters to models of ejecta interaction with the atmosphere and volumes of soot, dust and climatically-active gases essential for evaluating post-impact environmental change; mineralogical and geochemical studies related to post-impact hydrothermal systems and identification of the impactor type; and a series of biological and sedimentological studies of both the impact and post-impact lithologies.