Report 2011 of the Lutetian/Bartonian Boundary Working Group

In search of a possible candidate section for the base Bartonian GSSP, the Middle Eocene sedimentary succession of the Contessa Highway section (CHS, near Gubbio, central Italy), was re-visited. Historically, this section has been the focus of important biostratigraphic studies on calcareous plankton (foraminifera and nannofossils) and magnetostratigraphy (e.g., Lowrie et al., 1982; Napoleone et al., 1983; Monechi & Thierstein, 1985). In the new study (Jovane et al., 2010) the Middle Eocene interval at CHS was sampled at much higher resolution than in previous works (every 5 cm in average). The co-authors of the paper based on the available high resolution bio-, isotope-, magnetostratigraphy and the astronomical tuning of the sedimentary record, and according to IUGS recommendations, suggest the CHS as an excellent GSSP candidate for the Lutetian/Bartonian boundary. Jovane et al. (2010) concluded in proposing the top of Chron C19n as the most useful and best potential criterion (criterion 4) for global correlation and an astronomically calibrated age for that event of 41.25 Ma.

Report by Isabella Premoli Silva, no report was received from the chairman Richard Fluegeman.

Report 2010 of the Lutetian/Bartonian Boundary Working Group

Several scientists, coordinated by Coccioni (University of Urbino), re-investigated the Middle Eocene interval from the classical Contessa Highway section, near Gubbio, a possible candidate for the Bartonian GSSP. In search of a possible candidate section for the base Bartonian GSSP, the Middle Eocene sedimentary succession of the Contessa Highway section (CHS, near Gubbio, central Italy), was re-visited. Historically, this section has been the focus of important biostratigraphic studies on calcareous plankton (foraminifera and nannofossils) and magnetostratigraphy (e.g., Lowrie et al., 1982; Napoleone et al., 1983; Monechi & Thierstein, 1985). In the new study (Jovane et al., 2010) the Middle Eocene interval at CHS was sampled at much higher resolution than in previous works (every 5 cm in average). According to the different lithologies, washed residues were obtained following the standard procedures for the marly and soft marly-limestone samples, while planktonic foraminifera from the hard marly limestone and limestone samples were successfully extracted using ethanolic acid (highly concentrated acetic acid, ca. 80%) and all washed through a 40 ?m mesh sieve. Study of free specimens, instead of thin sections as in most previous works, allowed to a more accurate taxonomical identifications and more precise distribution of planktonic foraminiferal taxa. Then, the major planktonic foraminiferal bioevents have been directly re-calibrated to the magnetic chrons revised by Jovane et al. (2007). Through a cyclostratigraphic analysis of the rhythmic sedimentary alternations and combination with the results of time series analysis of the proxy record, an orbital tuning of the Middle Eocene and astronomical calibration of the bio-magnetostratigraphic events (particularly for the C19n/C18r Chron boundary) recognized at CHS was provided. The criteria proposed as reliable for the definition of the Lutetian/Bartonian boundary are: (1) the first occurence (FO) of planktonic foraminifer Turborotalia cerroazulensis, that occurs in the upper part of Chron C19r, (2) the last occurrence (LO) of planktonic foraminifer Guembelitrioides nuttalli which is found just below the base of Chron C19n, (3) the base of Chron C19n, (4) the top of Chron C19n or (5) the FO of calcareous nannofossil Reticulofenestra (= Cribrocentrum) reticulata, that falls in the lower part of Chron C18r. The lithologic cyclostratigraphy combined with the ~7 My-long astronomically driven climate proxy records, provided a first astronomical calibration of the Middle Eocene epoch, allowing refinement of Eocene biostratigraphic dating with minimal correction to chronostratigraphy. Based on both, the available high resolution bio-, isotope-, magnetostratigraphy and the astronomical tuning of the sedimentary record, and according to IUGS recommendations, it results that the CHS represents an excellent GSSP candidate for the Lutetian/Bartonian boundary.

Jovane et al. (2010) concluded in proposing the top of Chron C19n as the most useful and best potential criterion (criterion 4) for global correlation and an astronomically calibrated age for that event of 41.25 Ma. The following paper was published: Jovane L., Sprovieri M., Coccioni R., Florindo F., Marsili A., Laskar J., (2010). Astronomical calibration of the middle Eocene Contessa Highway section (Gubbio, Italy). Earth and Planetary Science Letters, v. 298, p. 77–88.

Report by Isabella Premoli Silva, no report was received from the chairman Richard Fluegeman.

Report 2007, 2008 and 2009 of the Lutetian/Bartonian Boundary Working Group:

The work of the Lutetian-Bartonian Boundary Working Group during 2007, 2008 and has continued its focus on the base of magnetic polarity chron 19N as a guide horizon for the base of the Bartonian. For the base of chron 19N to be a useful guide horizon for the base of the Bartonian Stage, its correlation potential must be demonstrated. The working group has continued to focus field and laboratory studies on the correlation potential of this horizon.
The section along the Contessa Highway near Gubbio, Italy remains the primary candidate for a GSSP. Historically, this section has been the focus of important biostratigraphic studies of planktonic foraminifera and calcareous nannofossils. The Contessa Highway section also contains an excellent magnetic stratigraphy record in the Paleocene and Eocene.
Results of a high-resolution geomagnetic, geochemical, and biostratigraphic study of the Contessa Highway section were published during 2007 (Jovane et al. 2007).
Studies of the Barton Clay at Alum Bay and Barton-on-Sea, U.K: Further study of the Barton Clay at Barton-on-Sea and at Alum Bay on the Isle of Wight is desirable to clarify the magnetic stratigraphy of the traditional “unit stratotype” of the Bartonian. Magnetic stratigraphy has been completed on the underlying Bracklesham beds on the Isle of Wight and correlated with polarity chronozones through the use of calcareous nannofossils. To date, no paleomagnetic data has been collected from the Barton Clay. Results from this work will enhance our understanding of the chronostratigraphy of the type Bartonian and enable better decision-making when selecting a final GSSP.
Future Work: Identifying reliable biostratigraphic horizons to serve as additional guides to the base of the Bartonian remains a challenge. Several important biostratigraphic events occur near, but not precisely at, this horizon and may assist with correlation. Several of these events are listed in Fluegeman (2007).
The working group hopes to complete its work and propose a GSSP for the Bartonian by 2011.
References: Fluegeman, R. H., 2007, Unresolved issues in Cenozoic chronostratigraphy. Stratigraphy, vol. 4, p. 109-116.
Jovane, L., Florindo, F., Coccioni, R., Dinarès-Turell, J., Marsili, S., Monechi, S., Roberts, A. P., and Sprovieri, M., 2007, The middle Eocene climatic optimum event in the Contessa Highway section, Umbrian Apennines, Italy: Geological Society of America bulletin, vol. 119, p.413-427; doi: 10.1130/B25917.1.

Report by Richard H. Fluegeman, Chairman


Report 2006 of the Lutetian-Bartonian Boundary Working Group

The work of the Lutetian-Bartonian Boundary Working Group during 2006 has continued its focus on the base of magnetic polarity chron 19N as a guide horizon for the base of the Bartonian. For the base of chron 19N to be a useful guide horizon for the base of the Bartonian Stage, its correlation potential must be demonstrated. The working group has continued to focus field and laboratory studies on the correlation potential of this horizon.
The Contessa Highway Section, Central Apennines, Italy:
The section along the Contessa Highway near Gubbio, Italy is the primary candidate for a GSSP. Historically, this section has been the focus of important biostratigraphic studies of planktonic foraminifera and calcareous nannofossils. The Contessa Highway section also contains an excellent magnetic stratigraphy record in the Paleocene and Eocene.
Detailed paleontologic and geochemical studies are underway on the Contessa Highway section by a research team within the framework of the International PALIS (Paleogene Integrated Stratigraphy) Project coordinated by Rodolfo Coccioni. This team is a working group of different specialists (foraminifera, calcareous nannofossils, magnetostratigraphy, geochemistry) and is involved in the study of the Lutetian-Bartonian Boundary at the Contessa Highway section. This working group at present includes Rodolfo Coccioni (Urbino) and Valeria Luciani (Ferrara) (coordinators), Rita Catanzariti (IGG and CNR, Pisa), Luciana Ferraro (CNR, Naples), Fabio Florindo (INGV, Rome), Fabrizio Frontalini (Urbino), Luigi Jovane (INGV, Rome), Mike Kaminski (UCL), Fabrizio Lirer (CNR, Naples), Andea Marsili (Urbino), Simonetta Monechi (Florence), Alessandro Montanari (OGC), Silvia Spezzaferri (Fribourg), Mario Sprovieri (CNR, Naples), and Giordana Uguccioni (Urbino). The Contessa Highway section has been sampled at a very high-resolution (every 5 cm). It is anticipated that a high resolution biostratigraphic framework and details of the paleoecological and paleoceanographic conditions that accompanied the deposition of the Contessa Highway succession will be the result of this work.
Studies at Barton-on-Sea, U.K:
Field work on the Barton Clay and adjacent beds at Barton-on Sea, southern England were conducted in 2006 by Andy Gale and colleagues. This section is the traditional Bartonian unit Stratotype. The primary purpose of this work was to collect paleomagnetic data from the Barton Clay. Magnetic stratigraphy has been completed on the underlying Bracklesham beds on the Isle of Wight and correlated with polarity chronozones through the use of calcareous nannofossils. To date, no paleomagnetic data has been collected from the Barton. Results from this work will enhance our understanding of the chronostratigraphy of the type Bartonian and enable better decision-making when selecting a final GSSP.
The working group hopes to complete its work and propose a GSSP for the Bartonian by 2008.

Report by Richard H. Fluegeman, Chairman

Report 2005 of the Lutetian-Bartonian Boundary Working Group

The work of the Lutetian-Bartonian Boundary Working Group during 2004 and 2005 has focused on identifying stratigraphic events which could serve as guide horizons for the base of the Bartonian. The early focus of the working group was on identifying a biostratigraphic event that could serve as a definition of this boundary and be recognized in marine sections worldwide. Examination of numerous biostratigraphic events associated with the late Lutetian and early Bartonian convinced the working group that there was not a single bioevent of global magnitude that could serve as a boundary definition and preserve the historical concept of both the Lutetian and Bartonian Stages. At the Symposium on the Paleogene in Leuven during August, 2003, the working group reported to ISPS that it was investigating the base of magnetic polarity chron 19N as a defining event for the base of the Bartonian. There were several practical and historical reasons to choose polarity chron 19N as the base of the Bartonian. On the practical side, a magnetic event is a truly a global event and in geological terms, an instantaneous one. Additionally, magnetic events can be recognized in both marine and non-marine sections. From an historical perspective, the base of the Bartonian has been associated with chron 19N for nearly 30 years (Hardenbol and Berggren, 1978) and the selection of the base of polarity chron 19N truncates neither the Lutetian or Bartonian “unit stratotypes” in northwestern Europe.
For the base of chron 19N to be a useful definition of the base of the Bartonian Stage, its correlation potential must be demonstrated. The working group has determined that the following biostratigraphic events may be useful for correlation to the base of the Bartonian:

Planktonic Foraminifera
Lowest stratigraphic occurrence of Hantkenina alabamensis
Lowest stratigraphic occurrence of Turborotalia pomeroli
Highest stratigraphic occurrence of Guembelitrioides higginsi

Calcareous Nannofossils
Lowest stratigraphic occurrence of Reticulofenestra reticulata (not the
extinction event of R. reticulata as reported in Gradstein et al., 2004)

Larger Foraminifera
The base of Tethyan Shallow Benthic Zone (SBZ 7) of Serra-Kiel et al.
(1998)
The lowest stratigraphic occurrence of the genus Lepidocyclina (Gulf of
Mexico and Caribbean regions) Recent field work in the Gulf Coastal Plain of the United States suggests that these biostratigraphic markers can be used to identify Bartonian aged rocks. In outcrops from Texas to Alabama, calcareous nannofossils, planktonic foraminifera, and larger foramifera permitted separation of the Bartonian aged rocks from the underlying Lutetian. Other biostratigraphic markers such as smaller calcareous benthic foraminifera may be useful in regional correlation.

The section along the Contessa Highway near Gubbio, Italy is of special interest to the working group. Historically, this section has been the focus of important biostratigraphic studies of planktonic foraminifera and calcareous nannofossils. The Contessa Highway section also contains an excellent magnetic stratigraphy record in the Paleocene and Eocene.
Field work in August, 2004 showed the section to be well exposed with the key marker beds and sample locations identifiable. The key part of the section with regard to the base of the Bartonian is behind a chain-link net to control slumping. Samples can still be collected from the Contessa Highway section and this exposure remains important to future work.
The working group hopes to complete its work and propose a GSSP for the Bartonian by 2008.

Report by Richard H. Fluegeman, Chairman