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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...

The Cretaceous/Paleogene (K/Pg) Working Group, after many years of studies, voted to define the Global Stratotype Section and Point (GSSP) for the base of the Danian Stage at the base of the boundary clay at a section near El Kef, Tunisia. The GSSP was approved by the International Commission on Stratigraphy (ICS) and ratified by the International Union of Geological Sciences (IUGS) in 1991. Nevertheless, the GSSP was not officially published, although some papers dealing with geological aspects of the K/Pg boundary at El Kef have been published and this is quite well known. In April 2006, the GSSP was revisited, a marker was put in place and protection of the site was requested. Many correlation criteria are present at the GSSP of which the most useful are the meteorite impact evidence (iridium anomaly, Ni-rich spinel, etc.) and the mass extinction of planktic micro-and nannofossils. This event coincides with the GSSP, allowing us to propose that the K/Pg boundary is marked exactly by the moment of the meteorite impact, which implies that all the sediments generated by the impact belong to the Danian. This definition solves problems of correlation in the Yucatan peninsula (Mexico) and its surroundings.

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The Oued Necham (ON) section (Kalâat Senan, central Tunisia) provides a well-exposed outcrop of a Campanian-Maastrichtian series that consists essentially of chalky limestones (i.e. the Abiod Formation) grading progressively to a marly unit (i.e. the El Haria Formation). The transitional Abiod-El Haria succession comprises a rich hemipelagic-pelagic fauna in the study area, but ammonites (e.g., Pachydiscus neubergicus, the Campanian/Maastrichtian (C/M) boundary index taxon) are scarce to absent, thus preventing the recognition of the standard zones defined for the Tethyan realm. However, the rich planktonic foraminiferal taxa of the El Haria Formation allow us to establish an accurate biostratigraphical scheme. Accordingly, this work presents a high-resolution planktonic foraminiferal biostratigraphy that is characterised by distinct bioevents associated with the reported C/M boundary (i.e. lowest occurrences (LOs) of Rugoglobigerina scotti and Contusotruncana contusa) at the Global Stratotype Section and Point (GSSP) of the Tercis-les-Bains section, south-western France. Based on these zonal markers, the rugoglobigerinids and multiserial heterohelicids are used to define a subzonal scheme spanning the standard Gansserina gansseri Zone, including the Rugoglobigerina rotundata Subzone indicative of the late Campanian and the Rugoglobigerina scotti Subzone and the Planoglobulina acervulinoides Subzone, respectively, indicative of the early Maastrichtian. The abundance of foraminiferal assemblages allowed us to carry out high-resolution quantitative analyses that document a significant climate cooling during the early Maastrichtian intermittent with short-term warming episodes. Thus, opportunist taxa (r strategists, mostly heterohelicids) thrived during the earliest Maastrichtian cooling event, whereas specialist taxa (k strategists, mostly double-keeled) that had dominated the late Campanian assemblages declined gradually without any extinction. Opportunist and specialist taxa fluctuated in opposite phases throughout the early Maastrichtian (LO of Rugoglobigerina scotti -LO of Abathomphalus mayaroensis), suggesting essentially variations in water temperature. Since surface dwellers dominated the assemblages, they imply continuous sea surface optimal conditions of nutrient supply and water connectivity induced from upwelling currents.