Lutetian
To be awarded a Stratotype is a difficult and long process. For the Lutetian Stratotype the process has lasted many years. For more than 20 years, the researchers involved in the project carried out many pilot studies worldwide and selected the sections that fulfilled the necessary requirements. Finally, all the specialists met in an international workshop held in Getxo in 2009, organized by the UPV/EHU group, and all the prospective stratotype sections were presented.
The Lutetian Working Group has investigated sections in Italy, Israel, Tunisia, Morocco, Mexico and Argentina, but unfortunately none of these was a good enough candidate for the Lutetian stratotype. In Spain many sections were visited and sampled in the Betic Cordilleras (Alamedilla, Agost, Fortuna, etc.) and in the Pyrennees (Anoz, Campo, Gorrondatxe, Guetaria, etc.). Most of the Pyrennean sections are not ideal and bear hiatuses, restricted facies, tectonic complications and other problems. At last, the research was focused on the study of the two more suitable sections to define the Lutetian GSSP: Agost and Gorrondatxe sections, in Spain. The results of the study of both sections were focused on the different events traditionally used to place the Ypresian/Lutetian boundary, previously thought to be almost simultaneous, to find out that they actually occur at very different levels. Events closest to the base of the Lutetian stage, as originally conceived, are the first occurrence of the calcareous nannofossil Blackites inflatus, at the base of Subzone CP12b, and the first occurrence of the planktic foraminifera Turborotalia frontosa. The integrated magnetobiostratigraphic studies carried out at the Agost and Gorrondatxe sections provide conclusive evidence that both sections are almost continuous and contain diverse and well-preserved fossil groups. However, the Gorrondatxe section was considered to be more suitable than the Agost section, and in 2011 the rock succession exposed at the cliff of the Gorrondatxe beach (Getxo, Biscay Province, Basque Country) was ufficially ratified as the Lutetian Stratotype.
The GSSP for the base of the Lutetian Stage (early/middle Eocene boundary) was defined at 167.85 meters in the Gorrondatxe sea-cliff section (NW of Bilbao city, Basque Country, northern Spain; 43º22’46.47″ N, 3º 00′ 51.61″ W). This dark marly level coincides with the lowest occurrence of the calcareous nannofossil Blackites inflatus (CP12a/b boundary), is in the middle of polarity Chron C21r, and has been interpreted as the maximum flooding surface of a depositional sequence that may be global in extent. The GSSP age is approximately 800 kyr (39 precession cycles) younger than the beginning of polarity Chron C21r, or ~47.8 Ma in the GTS04 time scale. The proposal was approved by the International Subcommission on Paleogene Stratigraphy in February 2010, approved by the International Commission of Stratigraphy in January 2011, and ratified by the International Union of Geological Sciences in April 2011. The official publication in Episodes was published in 2011.
In the web
Check out the video on the 2012 Ypresian/Lutetian boundary golden spike event:
The video at eitb.eus
Reference
Molina, E., Alegret, L., Apellaniz, E., Bernaola, G., Caballero, F., Dinarès, J., Hardenbol, J., Heilmann-Clausen, C., Larrasoaña, J., Luterbacher, H., Monechi, S., Ortiz, S., Orue-Etxebarria, X., Payros, A., Pujalte, V., Rodríguez-Tovar, F., Tori, F., Tosquella, J., Uchman, A. 2011. The Global Stratotype Section and Point (GSSP) for the base of the Lutetian Stage at the Gorrondatxe section, Spain. Episodes, 34 (2): 86-108. (Download)