Annual Report 2012 of the Priabonian GSSP Working Group

The candidate GSSP section for the base Priabonian, equated to the base of the Upper Eocene, was presented to the Task Group during a Workshop, organized by D. Rio and collaborators from Padua University, held in Alano di Piave (Belluno, N. Italy) in June 8-10, 2012. Twentyfive scientists attended the workshop, including Eustoquio Molina, Chair of the Subcommission, Simonetta Monechi, elected new Chair, and Marco Balini, Chair of the Italian Stratigraphic Commission. After the welcome by the authorities, Luca Giusberti (Padua) gave an overview on the candidate Alano di Piave section summarizing the major results of the multidisciplinary study published by Agnini et al. in 2011, in which these authors designated the base of the Tiziano bed, a prominent crystal tuff layer in the Alano section, as the GSSP of the Priabonian Stage. For approximating the base of the Priabonian in the marine stratigraphic records over large areas and depositional settings the following events can be considered, (1) the extinction of the large muricate planktonic foraminifera, (2) the beginning of the Acme of the distinctive nannofossilCribrocentrum erbae, (3) the base of Chron C17n that allows also correlation with the continental records. After Giusberti’s presentation the Alano section was visited by all participants.
The afternoon of June 9 was dedicated to presentations regarding the historical appropriateness and correlations of the potential Priabonian GSSP at Alano. The topics addressed have been (1) An Historical Perspective (Premoli Silva), (2 & 3) The Paleoclimatic and Paleoceanographic context and Planktonic Foraminifera and Radiolarians (Wade), (4) Calcareous nannofossils (Backman), (5) Dinoflagellate Cysts (data from Houben), (6) Magnetostratigraphy (Muttoni), (7) Cyclostratigraphy (Galeotti), (8) Larger Benthic Foramifera (Pignatti, Papazzoni et al.), and (9) The Mammalian record (Rook).
After the presentations, all matter was open to discussion. First, all participants agreed that the Priabonian GSSP should be placed in the Alano di Piave section. Second, the audience moved to analyse the criteria for identify the Priabonian GSSP. After a fruitful and animated discussion two criteria emerged for placing the GSSP, (1) at the base of the Tiziano Bed, a prominent and easily recognizable level in the field within the otherwise monotonous marly succession, as favoured by the Padua proponents and some other scientists, and (2) at the extinction levels of the muricate planktonic foraminifer Morozovelloides and of the large muricate acarininids, that at Alano fall 6.05 m and 6.25 below the base of the Tiziano bed, respectively. According to Wade et al. (2012) and some participants, these two events have a much greater correlation potential worldwide. An informal investigation among the attending scientists resulted in votes almost even for both criteria.
The Workshop ended on Sunday 10 June with the visit to the nearby Cunial Quarry section (near Possagno) of late Eocene age.
Currently, the GSSP proposal, to be submitted to the Paleogene Subcommission members for comments and eventual approval, is in preparation by Domenico Rio and his collaborators from Padua University. The proposal will take in consideration what have emerged from the Workshop discussion and it will possibly incorporate data on ongoing cyclostratigraphic study and isotopic dating of the Tiziano bed, aimed to ameliorating the time scale of the Late Eocene.

Agnini C., Fornaciari E., Giusberti L., Grandesso P., Lanci L., Luciani V., Muttoni G., Palike H., Rio D., Spofforth D.J.A., Stefani C., 2011. Integrated bio-magnetostratigraphy of the Alano section (NE Italy): a proposal for defining the Middle-Late Eocene boundary. Geological Society of America Bulletin, v. 123 (5/6), p. 841-872; doi: 10.1130/B30158.1.
Fornaciari E., Agnini C., Catanzariti R., Rio D., Bolla E.M., Valvasoni E., 2010. Mid-latitude calcareous nannofossil Biostratigraphy and Biochronology across the middle to late Eocene transition. Stratigraphy, v. 7 (4), p. 229-264.
Spofforth, D.J.A., C. Agnini, H. Pälike, D. Rio, E. Fornaciari, L. Giusberti, V. Luciani, L. Lanci, G. Muttoni, 2010. Organic carbon burial following the middle Eocene climatic optimum in the central western Tethys.Paleoceanography, 25, PA3210, doi:10.1029/2009PA001738
Wade B.S., Premec Fucek V., Kamikuri S., Bartol M., Luciani V., Pearson P.N., 2012. Successive extinctions of muricate planktonic foraminifera (Morozovelloides and Acarinina) as a candidate for marking the base Priabonian.Newsletter on Stratigraphy, v. 45 (3), 15 pp; doi: 10.1127/0078-0421/2012/0023

Report by Isabella Premoli Silva, Chairwoman