Annual Report 2004 of the Bartonian/Priabonian Boundary Stratotype Working Group

The Veneto region in the Southern Alps (NE Italy) is a classical area for the Paleogene Stratigraphy. In particular, the historical stratotype and the parastratotype of the Priabonian (Munier-Chalmas & De Lapparent, 1893) stage are located close to the Priabona and Possagno villages, respectively. However, in both areas, the transition from the middle to late Eocene is missing (Priabona) or poorly exposed (Possagno; Bolli, 1975). We report here preliminary results on the calcareous plankton biostratigraphy of an undescribed section (Alano Section) from the central-eastern Veneto region that contains an expanded record of the middle to late Eocene transition.

THE ALANO SECTION (pdf)
Location: On the left side of the Piave River Valley, in the Veneto Prealps (Belluno Province), some 8 km from the classical Possagno section, in the same region of the Priabonian historical stratotype.
Geologic setting: the section is exposed in continuity along a river cut within the northern limb of the Alano syncline; it belongs entirely to the “Scaglia Cinerea” Formation. It is easily accessible and shows a total thickness of 120-130 meters.
Lithology: grey marls and calcareous marls with numerous centimetric to decimetric silty to sandy intercalations some of which do represent useful marker beds in the field. The composition of these beds is variable (glauconitic, bioclastic and volcanoclastic). Noteworthy is the presence of a “black-shale” interval between 17 and 25 m level (upper part of the Bartonian).
Depositional setting: bathyal.
Fossil content: macrofossils have not been observed except for two badly preserved bivalves. Calcareous plankton is abundant. Planktonic foraminifera are fairly well preserved even if encrusted in the more calcareous lithologies. Calcareous nannofossils are well preserved. Benthic foraminifera are common, increasing in abundance in the upper part of the section. Dinoflagellate cysts.are also present and their detailed study is planned. Preliminary biostratigraphic data on calcareous plankton are reported in the attached Figure.
Sampling: 105 m of the section were sampled at high resolution every 20 cm; sampling of the uppermost 10-15 m is in progress. Some pilot samples for magnetic properties are now under examination.
Because of the excellent outcropping conditions, richness of planktonic fossils, easy access, amenability to radiometric dating, the Alano section might be a potential candidate for defining the middle/upper Eocene boundary. In addition, it is a key section for facing the climatic, biotic and chronologic problems associated with the middle to late Eocene transition.Investigations have been undertaken by researchers of the Universities of Padua, Ferrara, Urbino, Utrecht and Milan, and by the numerous scientists of the OLIS Working Group coordinated by Coccioni (University of Urbino), respectively.

Report by Isabella Premoli Silva, Chairwoman.