International Geologiical Congress - Oslo 2008

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HPS-05 Recent developments in the Geologic Timescale

 

In search of a criterion to define the Ypresian/Lutetian boundary

 

Silvia Ortiz, University College London (United Kingdom)
Juan Cruz Larrasoaña, Instituto de Ciencias de la Tierra Jaume Almera (CSIC) (Spain)
Eustoquio Molina, Universidad de Zaragoza (Spain)
Xabier Orue-Etxebarria, Facultad de Ciencia y Tecnología, Universidad del País Vasco (Spain)
 

 

An International Working Group of the International Subcommission on Paleogene Stratigraphy is searching for potential sections to define the Global Stratotype Section and Point (GSSP) for the base of the Lutetian Stage (middle Eocene). The Ypresian-Lutetian (Y-L) transition is poorly known and the events traditionally used to define the Y/L boundary, i.e., the planktic foraminiferal P9/P10 or E7/E8 zonal boundaries, the base of the calcareous nannofossil zone CP12b, and the shallow benthic foraminiferal SBZ12/SBZ13 zonal boundary, occur at different levels. The first occurrence of hantkeninids has been usually most accepted as the main event to identify the boundary, which has classically been correlated to the top of Chron C22n. A major sea-level fall has been reported to be coeval with the base of the Lutetian Stage.

The late Paleocene and specially the early Eocene was the warmest period of the Cenozoic. The Paleocene Eocene Thermal Maximum (PETM) is an extreme transient warming or hyperthermal event, superimposed on that greenhouse world. It is thought that it was not a unique event, but the most prominent of several hyperthermal events. Benthic and planktic foraminiferal assemblages turnover for the Y-L transition has been quantitatively analyzed in several bathyal sections such as, Agost section (southern Spain) and Gorrondatxe Beach section (northern Spain), which are suitable candidates to place the GSSP for the base of the Lutetian. They point to a possible hyperthermal event related to the first occurrence of hantkeninids and associated with an overall relative sea-level fall. Further studies on marine and terrestrial successions are needed to correlate the data available and provide a complete record of the climate evolution of the Y-L transition and a precise criterion must be chosen to define the base of the Lutetian Stage.

 

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