U-Pb ages of zircons from sites in Spain and Italy provide more evidence linking the Chicxulub impact to the global K-P boundary layer

Details U-Pb ages of zircons from sites in Spain and Italy provide more evidence linking the Chicxulub impact to the global K-P boundary layer U-Pb ages of zircons from sites in Spain and Italy provide more evidence linking the Chicxulub impact to the global K-P boundary layer

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53c1527m&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P53C-1527

Physics

[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering

Scientific paper

The K-P boundary layer possesses an extra-terrestrial signature and contains highly shocked terrestrial minerals. The only plausible explanation for the K-P layer is that it was formed when a large meteorite hit the Earth, causing the ejection of both meteoritic material and shocked fragments of target rock around the globe. There is now universal agreement that the Chicxulub structure is an impact crater, and dating of the impact melt rocks within the crater place it close in age to the K-P boundary. Two significant lines of evidence indicate a genetic link between Chicxulub and the global K-P layer: 1) the size of the ejected particles in the layer decreases with palaeodistance from Chicxulub, and 2) U-Pb dating of shocked zircons from the Chicxulub impact site and in several K-P sites in North America are near-identical in age, texture and lead-loss pattern. However, even with such apparently incontrovertible evidence linking Chicxulub and the K-P boundary, a minority continue to question the link and suggest that the Chicxulub impact occurred ~300 ka before the K-P boundary. Here we present the results of U-Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS) for shock-metamorphosed zircon crystals from the K-P boundary layer at Caravaca, Spain, and Petriccio, Italy. We find that the determined ages form a mixing line between a primary source age of ~549 Ma and the approximate time of impact. This is analytically identical to ages obtained previously for similarly shocked zircon grains at Chicxulub and from K-P boundary sites in North America. Caravaca and Petriccio are the most distal K-P sites that can be directly linked to Chicxulub through the dating of individual shocked zircon grains. These results, along with the completeness of the K-P transition at several sites around the globe, including Caravaca, cannot be explained by the alternative scenario that the Chicxulub impact occurred ~300 ka prior to the K-P boundary.

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