The global boundary stratotype and section point (GSSP) for the base of the Santonian Stage, "Cantera de Margas", Olazagutia, northern Spain

The GSSP for the base of the Santonian Stage is defined at 94.4 m in the eastern border of the "Cantera de Margas" quarry, Olazagutia (Navarra, N. Spain: 42° 52′ 05.3" N, 2° 11′ 40" W) and marked by the first occurrence (FO) of the inoceramid bivalve Platyceramus undulatoplicatus. This first occurrence is located about 9 m below the contact between a lower marly unit and an upper more calcareous unit. The FO of the planktonic foraminifer Sigalia carpatica is the secondary marker of the GSSP and first occurs 7 m below the primary marker, but it becomes consistently present about 4.2 m above the boundary. In addition, six peaks in the carbon stable isotope curve can be recognized between the Kingsdown Event 17.2 m below and the Bedwell Event 12.35 m above the GSSP. The basal Santonian GSSP was approved by the International Subcommission on Cretaceous Stratigraphy in September 2010, by the International Commision of Stratigraphy in April 2012, and ratified by the International Union of Geological Sciences in January 2013.