Planktonic foraminiferal bioevents in the Coniacian/Santonian boundary interval at Olazagutia, Navarra province, Spain

The interval studied comprises a 45-m-thick section of uppermost Coniacian and lower Santonian strata. More than 30 planktonic foraminiferal species were recorded. The following sequence of bioevents is recorded from bottom to top: (1) FO of Sigalia carpatica; (2) FO of Costellagerina pilula; (3) FO of typical “pill-box-like” morphotypes of Globotruncana linneiana. The planktonic foraminifera allow the subdivision of the section studied into two heterohelicid zones: Pseudotextularia nuttalli and Sigalia carpatica, and the correlation of the zonal boundary with the inoceramid scheme. The Coniacian/Santonian boundary, as defined by the first occurrence of Platyceramus undulatoplicatus (Roemer), falls in the lower part of the Sigalia carpatica Zone. FOs of Costellagerina pilula and typical “pill-box-like” morphotypes of Globotruncana linneiana are a good proxy for the stage boundary.