Coccioni, Rodolfo

During the middle Eocene to early Oligocene Earth transitioned from a greenhouse to an icehouse climate state. The interval comprises the Middle Eocene Climatic Optimum (MECO; ~40 Ma) and a subsequent long-term cooling trend that culminated in the Eocene-Oligocene transition (EOT; ~34 Ma) with the Oi-1 glaciation. Here, we present a refined calcareous nannofossil biostratigraphy and an orbitally tuned age model for the Monte Cagnero (MCA) section spanning the middle Eocene to the early Oligocene (~41 to ~33 Ma). Spectral analysis of magnetic susceptibility (MS) data displays strong cyclicities in the orbital frequency band allowing us to tune the identified 405 kyr eccentricity minima in the MS record to their equivalents in the astronomical solution. Our orbitally tuned age model allows us to estimate the position and duration of polarity chrons (C18 to C13) and compare them with other standard and orbitally tuned ages. We were also able to constrain the timing and duration of the MECO event, which coincides with a minimum in the 2.4 Myr and 405 kyr eccentricity cycles. Our study corroborates the previous estimated age for the base of the Rupelian stage (33.9 Ma) and estimates the base of the Priabonian stage in the MCA section to be at 37.4 Ma. Finally, calcareous nannofossils with known paleoenvironmental preferences suggest a gradual shift from oligotrophic to meso-eutrophic conditions with an abrupt change at ~36.8 Ma. Besides, nannofossil assemblages suggest that enhanced nutrient availability pre- ceded water cooling at the late Eocene. Altogether, this evidence points to a poorly developed water column stratification prior to the cooling trend.

The GSSP for the base of the Chattian Stage (Paleogene System, Oligocene Series) is defined at meter level 197 in the Monte Cagnero section, which belongs to the pelagic succession of the Umbria–Marche basin (Urbania, central Italy: 43°38′47.81″N–12°28′03.83″E). This level with an astronomical age of 27.82 Ma coincides with the highest common occurrence of the planktonic foraminifer Chiloguembelina cubensis at the base of planktonic foraminiferal O5 Zone and falls in the upper part of calcareous nannofossil NP24 Zone, in the lower part of dinocyst Dbi Zone, and in the lower Chron C9n. The proposal was approved by the International Subcommission of Paleogene Stratigraphy in July 2015, approved by the International Commission of Stratigraphy in August 2016, and ratified by the International Union of Geological Sciences in September 2016.

Terrestrial laser scanner imaging is applied, together with calcimetry and lithofacies logging, for the cyclostratigraphic characterization of the Ypresian–Lutetian pelagites exposed in the Smirra section (Umbria–Marche Basin, Italy). The necessary chronostratigraphic framework is provided by detailed bio- and magnetostratigraphic analyses, which allow locating the Ypresian–Lutetian boundary in this section. Terrestrial laser scanner intensity is compared to carbonate content values obtained through calcimetric analyses carried out on samples taken from the same section, and is found to represent a good proxy for lithology in these pelagic homogenites. Time-series analysis highlights Milankovitch frequencies, particularly evident in the high-resolution terrestrial laser scanner intensity series. The recognition of distinctive low-frequency (> 1 Myr) features in the amplitude oscillations of short eccentricity as well as its ~ 400 kyr modulation (long eccentricity), promote a tuning of the Smirra series using the most recent astronomic solution (La2010 nominal), which provides insights on the ages of the Y–L boundary and of the main biostratigraphic and magnetostratigraphic events in the Umbria–Marche Basin. Results confirm the value of high-resolution (mm-scale) terrestrial laser scanning for scrutinizing pelagite successions in search of low-frequency cycles that may help in the refinement of the astrochronological time scale.

Earth's climate experienced a warming event known as the Middle Eocene Climatic Optimum (MECO) at ~ 40 Ma, which was an abrupt reversal of a long-term Eocene cooling trend. This event is characterized in the deep Southern, Atlantic, Pacific and Indian Oceans by a distinct negative δ18O excursion over 500 kyr. We report results of high-resolution paleontological, geochemical, and rock magnetic investigations of the Neo-Tethyan Monte Cagnero (MCA) section (northeastern Apennines, Italy), which can be correlated on the basis of magneto- and biostratigraphic results to the MECO event recorded in deep-sea sections. In the MCA section, an interval with a relative increase in eutrophic nannofossil taxa (and decreased abundances of oligotrophic taxa) spans the culmination of the MECO warming and its aftermath and coincides with a positive carbon isotope excursion, and a peak in magnetite and hematite/goethite concentration. The magnetite peak reflects the appearance of putative magnetofossils, while the hematite/goethite apex is attributed to an enhanced detrital mineral contribution, likely as aeolian dust transported from the continent adjacent to the Neo-Tethys Ocean during a drier, more seasonal climate during the peak MECO warming. Based on our new geochemical, paleontological and magnetic records, the MECO warming peak and its immediate aftermath are interpreted as a period of high primary productivity. Sea-surface iron fertilization is inferred to have stimulated high phytoplankton productivity, increasing organic carbon export to the seafloor and promoting enhanced biomineralization of magnetotactic bacteria, which are preserved as putative magnetofossils during the warmest periods of the MECO event in the MCA section. Together with previous studies, our work reinforces the connection between hyperthermal climatic events and the occurrence (or increased abundance) of putative magnetofossils in the sedimentary record.

The Eocene climatic system experienced an important transition from warm Paleocene greenhouse to icehouse Oligocene conditions.This transition could first appear as a long-term cooling trend but, at an up-close look, this period is a complex combination of climatic events and,for most of them, causes and consequences are still not fully characterized. In this context, a study has been carried out on the middle Eocene sedimentary succession of the Contessa Highway section, central Italy, which is proposed as the Global Stratotype Section and Point(GSSP)for the Lutetian/Bartonian boundary at the top of the Chron 19n, with an astronomically calibrated age of 41.23 Ma. Through a cyclostratigraphic analysis of the rhythmic sedimentary alternations and combination with the results of time series analysis of the proxy record, we provide an orbital tuning of the middle Eocene and astronomical calibration of the bio-magnetostratigraphic events (particularly for the C19n/C18r Chronboundary) recognized at the Contessa Highway section.

The Oligocene represents an important time period from a wide range of perspectives and includes significant climatic and eustatic variations. The pelagic succession of the Umbria-Marche Apennines (central Italy) includes a complete and continuous sequence of marly limestones and marls, with volcaniclastic layers that enable us to construct an integrated stratigraphic framework for this time period. We present here a synthesis of detailed biostratigraphic, magnetostratigraphic, and chemostratigraphic studies, along with geochronologic results from several biotite-rich volcaniclastic layers, which provide the means for an accurate and precise radiometric calibration of the Oligocene time scale. From this study, the interpolated ages for the Rupelian/Chattian stage boundary, located in the upper half of Chron 10n at meter level 188 in the Monte Cagnero section, and corresponding to the O4/O5 planktonic foraminiferal zonal boundary, are 28.36 Ma (paleomagnetic interpolation), 28.27 ± 0.1 Ma (direct radioisotopic dating), and 27.99 Ma (astrochronological interpolation). These ages appear to be slightly younger than those reported in recent chronostratigraphic time scale compilations. The Monte Cagnero section is a potential candidate for defining the Chattian Global Stratotype Section and Point (GSSP) and some reliable criteria are here proposed for marking the Rupelian/Chattian boundary according to International Union of Geological Sciences (IUGS) recommendations.

We have conducted high-resolution paleomagnetic and rock magnetic studies, in addition to stable isotope analyses of the Massignano sedimentary section, which is the Global Stratotype Section and Point (GSSP) for the Eocene-Oligocene boundary. Our research builds upon the many past studies of the Massignano section in seeking to understand the timing and nature of the paleoenvironmental variations that occurred during the transition for the Earth’s climate system from greenhouse to icehouse. The new paleomagnetic results provide a refined magnetostratigraphy of the section and new age for the Eocene-Oligocene boundary at 33.7 Ma. Abrupt and large alternations in magnetic, concentration, composition, and grain sizes that occur in the high-resolution rock magnetic record are interpreted to be the result of rapid bimodal shifts in deep-sea circulation that affect sediment sources or transport. We speculate that currents flowing through the gateway between the Atlantic and Indo-pacific Oceans may have turned on and off as the gateway was progressively closing, resulting in the deposition of two different assemblages of magnetic minerals at Massignano. Finally, stable isotope (δ18O and δ13C) data collected on ostracod valves also suggest significant changes in sea bottom circulation in the Neo-Tethys Ocean at and about 2 m.y. before the Eocene-Oligocene boundary.

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semi-quantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal Zone P11 to the lower part of Zone P15 and from calcareous nannofossil Zone NP15 to the upper part of Zone NP17, which results in refinement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity timescale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa Highway section, from Chrons C21n (47 Ma) through to Subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the first evidence in the northern hemisphere of the middle Eocene climatic optimum (MECO) that has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO2 levels during the late middle Eocene and a consequent global CO2-driven climate change.

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semi-quantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enables recognition of several biostratigraphic events from planktic foraminiferal Zone P11 to the lower part of Zone P15 and from calcareous nannofossil Zone NP15 to the upper part of Zone NP17, which results in refinement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity timescale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa 2 Highway section, from Chrons C21n (47 Ma) through to Subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the first evidence in the northern hemisphere of the middle Eocene climatic optimum that has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This should demonstrate a global response of carbon cycle to the proposed transient increased pCO2 levels during the late middle Eocene and a consequent global CO2-driven climate change.