Characterization and astronomically calibrated age of the first occurrence of Turborotalia frontosa in the Gorrondatxe section, a prospective Lutetian GSSP: implications for the Eocene time scale









Aitor Payros [], Xabier Orue-Etxebarria [], Estibaliz Apellaniz [] and Fernando Caballero [], Department of Stratigraphy and Palaeontology, Faculty of Science and Technology, University of the Basque Country, PO Box 644, E-48080 Bilbao, Spain; Gilen Bernaola [], Departamento de Ingeniería Minera y Metalúrgica y Ciencias de los Materiales, Escuela Universitaria de Ingeniería Técnica de Minas y Obras Públicas, University of the Basque Country, Beurko Muinoa s/n, E-48901 Barakaldo, Spain; Jaume Dinarès-Turell [], Istituto Nazionale di Geofisica e Vulcanologia, Lab. Di Paleomagnetismo, Via di Vigna Murata, 605, I-00143 Rome, Italy; Josep Tosquella [], Department of Geodynamics and Palaeontology, Faculty of Experimental Sciences, University of Huelva, Campus del Carmen, Avenida de las Fuerzas Armadas s/n, E-21071 Huelva, Spain;


The Gorrondatxe section, a prospective Lutetian Global Stratotype Section and Point (GSSP), has recently been used as the master reference section to reassess the correlation between Eocene magnetostratigraphic and calcareous planktonic biostratigraphic scales. However, the exact calibration of some events remained ill defined, as they were thought to be missing in Gorrondatxe due to a fault. The most important missing events were the first occurrence of the planktonic foraminifera Turborotalia frontosa and the C22n/C21r chron boundary. Either might be a reliable correlation criterion for the Ypresian/Lutetian boundary, as both approach the age of the original Lutetian Stratotype. New studies allowed the identification of the former event 9 m above the Gorrondatxe fault, within magnetic polarity Chron C21r and calcareous nannofossil Zone CP12a. Distinctive test features that characterize the most primitive morphotype of T. frontosa are described. Despite the high turbidite content, recurrent pelagic limestone–marl couplets and bundles occur, whose formation was driven by precession and eccentricity astronomical cycles. The first occurrence of T. frontosa was found 27 couplets and 5.5 bundles (60 m) below the first occurrence of the calcareous nannofossil Blackites inflatus, which is dated at 48 Ma. Hence, the age of the first occurrence of T. frontosa is estimated at 48.55 Ma, confirming that it is the most suitable planktonic foraminiferal correlation criterion for the Ypresian/Lutetian boundary. These results show that the stratigraphic interval missing due to the Gorrondatxe fault cannot be greater than a few metres and reinforce the value of this section as a prospective Lutetian GSSP.