The Alano Section: The Candidate GSSP for the Priabonian Stage

Abstract

The deep-water hemipelagic Alano section is located in the Southern Alps of northern–eastern Italy close to the village of Alano di Piave in the type area of the Priabonian. Since 2005, the section has been presented as the potential Global Boundary Stratotype Section and Point (GSSP) for the late Eocene Priabonian Stage at several meetings of the International Subcommission on Palaeogene Stratigraphy (ISPS). Because of the favourable qualities of the section, we have been asked to produce the data necessary for the formal definition of the GSSP. In 2011, Agnini et al. published most of the documentation needed (lithostratigraphy, calcareous plankton biostratigraphy, magnetostratigraphy, and chemostratigraphy, including oxygen and carbon isotopes and carbonate content). The Agnini et al. (2011) paper also contained a motivated proposal for the definition of the Priabonian at the base of a prominent crystal tuff layer, the Tiziano bed, located at the 63.57 m level in the Alano section. Following the publication of this proposal, a unanimous consensus on the Alano section as the GSSP of the Priabonian (i.e., Gradstein et al. 2012; Wade et al. 2012) has been reached during an ad hoc workshop held in Alano in June 2012. However, not unexpectedly, alternative criteria for the definition of the GSSP have been subsequently advanced (Gradstein et al. 2012; Wade et al. 2012; Less and Özcan 2012). During 2012, we further refined the stratigraphy of the Alano section by obtaining cyclostratigraphic data. Moreover, U–Pb dating of zircons from seven levels has been undertaken. Here, we present the new cyclostratigraphic data and discuss various proposals for the definition of the Priabonian at Alano. We reiterate that our original proposal is the most balanced and in better keeping with Hedberg’s (1976) principles of chronostratigraphy.