The Chicxulub Impact - Connection to K/T Boundary Event Based on Petrophysical and Paleomagnetic Investigations

Establishing relationships between the Chicxulub impact crater and the K/T boundary event has been one of the main reasons for Chicxulub Scientific Drilling what was carried out in framework of the International Continental Drilling Program (ICDP). Drilling-site (Hacienda Yaxcopoil) was chosen on the basis of previous work achieved by drillings of the oil exploratory program by Petróleos Mexicanos and more recently by the National University of Mexico (UNAM). The Yaxcopoil-1 borehole is 1511 m deep, and sampling started from 404 m. Drillcore runs through 3 intervals: the post-impact layer, the impact layer and the pre-impact target rock. Samples of this study were gathered in collaboration of many institutions (Helsinki University, UNAM, Vrije University of Amsterdam and Humboldt University of Berlin) and cover all these intervals. Standard petrophysical and paleomagnetic measurements (including magnetostratigraphy) were carried out in order to clarify some of the dating issues. Results show that paleomagnetic measurements of the drillcore, coupled with petrophysical data provide a good tool of isolating various units including the impact layer, the K/T boundary- and the post-impact sequences. NRM and susceptibility values of samples from pre- and post-impact layers show that most samples are very weakly magnetized, with exception of the interval from 790 m to 900 m that includes the K/T boundary layer. Also our data show that magnetostratigraphy of the impact layer is quite complex due to possible hydrothermal remagnetization process. Additionally these data reveal that the Chicxulub impact event took probably place within the magnetic chron 29R and therefore can be related to K/T boundary event.