International audienc

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(40)Ar/(39)Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from (40)Ar/(39)Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The (40)Ar/(39)Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

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Tunisia, Zumaya in Spain, Brazos in USA and Stevns Klint in Denmark), the chairwoman of the K/Pg Boundary Working Group submitted a written proposal to the International Commission on Stratigraphy (ICS). The GSSP of the K/Pg boundary was defined at the base of the boundary clay at the section near El Kef, Tunisia. This proposal was approved by the ICS in 1990 and was ratified by the International Union of Geological Sciences in 1991. Nevertheless, its publication in a prestigious stratigraphical journal of wide distribution, which is the final step in the definition of the GSSP, was not made until the chairman of the International Subcommission on Paleogene Stratigraphy (ISPS), in collaboration with several colleagues, including the chairwoman of the K/Pg Boundary Working Group, reviewed the studies since the original proposal and revised the main criteria defining the K/Pg boundary (Molina et al. 2006). However, this official publication of the GSSP did not include any auxiliary sections in which the event could be studied in other facies and different paleobiogeographic contexts, allowing a global correlation. Furthermore, deterioration of the outcrops at the El Kef section (Remane and Adatte, 2002), which makes necessary to trench and difficult to find the GSSP, requires assigning auxiliary sections where the K/Pg boundary is better exposed. The aim of this paper is to describe the most suitable sections, which are considered auxiliary sections of the K/Pg boundary, to establish the correlation between areas distal and proximal to the Chicxulub meteorite impact site and to solve problems of erroneous placement of the K/Pg boundary. Auxiliary sections According to Remane et al. (1996), the auxiliary sections proposed here are subordinate to the GSSP and fulfill most of the requirements to characterize a GSSP. The auxiliary sections described below are located in three different regions across the world (Fig.1): around El Kef (Tunisia), where the GSSP was defined (Aïn Settara and Ellès), in southwestern Europe where other suitable sections were proposed (Bidart, Caravaca, Zumaya) and around the Gulf of Mexico, close to the meteorite impact crater (Bochil and El Mulato). The Global Stratotype Section and Point (GSSP) for the Cretaceous/Paleogene (K/Pg) boundary was defined at the base of the boundary clay at a section near El Kef, Tunisia, but the outcrop became quite deteriorated. In order to better characterize the boundary and to solve problems of correlation, several auxiliary sections are designed and described in detail including: Aïn Settara and Ellès in Tunisia, Caravaca and Zumaya in Spain, Bidart in France and El Mulato and Bochil in Mexico. These sections are the most continuous, expanded and representative of marine sedimentation in areas proximal and distal to the Chicxulub meteorite impact site. In addition, these sections are classical, very well known, physically accessible, have been exhaustively studied and allow a very detailed global correlation. The correlation criteria used were the meteorit...