The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, "Tertiary", Cenozoic): Auxiliary sections and correlation

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: Al'n 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 meteorite impact evidence (Ir anomaly, Ni-rich spinel, etc.) and the mass extinction of planktic micro- and nannofossils. Furthermore, it was proposed 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 Paleogene. While in distal areas to the impact site the K/Pg boundary coincides with a millimetre-thick rusty layer, in proximal areas the K/Pg boundary correlates to the base of a metre-thick Clastic Unit, including a thick calcareous breccia in the sections closer to the impact crater.