Late Eocene impact-induced climate and hydrological changes: Evidence from the Massignano global stratotype section and point (central Italy)

Abstract

The Eocene-Oligocene transition marks the passage from "greenhouse" conditions to an "icehouse state" with progressive global cooling starting in the early middle Eocene. The late Eocene is also characterized by a high concentration of extraterrestrial impacts, the effects of which, on living organisms and climatic changes, are still not understood. We carried out a high-resolution investigation on planktonic foraminiferal assemblages in an 8-m-thick segment of the Massignano global stratotype section and point for the Eocene-Oligocene boundary with the aim of assessing the effects that the impacts may have had on the environment and this group of organisms. The studied interval is punctuated by three late Eocene iridium-rich layers, several cosmic signatures, and enhanced levels of 3 He. The two lower closely spaced iridium anomalies are possibly linked to the Popigai and Chesapeake Bay impact events, respectively, whereas no particular impact event can be assigned to the third anomaly, even if it might be correlated with some large craters. Interpretation of data suggests that all the impacts had no abrupt, dramatic effects on planktonic foraminifera. However, acting as forcing factors, they induced some environmental perturbations and may have contributed to remarkable climate changes superimposed on the general late Eocene cooling trend. The Popigai and Chesapeake Bay impact events triggered signifi cant changes in the water mass structure, in terms of stratifi cation and trophic resources, associated with some climatic excursions that took place within chron C16n.1n and chron C15r and at the transition between planktonic foraminiferal zones P15 and P16.The short-term warming pulse recognized after the Popigai impact might have been due to greenhouse effects produced by injection of CO 2 into the atmosphere and/or the release of methane hydrate after the impact itself. The dynamic between *cron@info-net.it.

Integrated stratigraphy (magneto-, bio- and chronostratigraphy) and geochronology of the Palaeogene pelagic succession of the Umbria–Marche Basin (central Italy)

“…At the Middle Eocene -Lower Oligocene Monte Cagnero section, which belongs to the Monte Montiego anticline and is located near Piobbico, three discrete portions have been selected Verducci & Nocchi 2004;Coccioni et al 2008;Hyland et al 2009;Pross et al 2010;Jovane et al 2012). Finally, we have considered the Upper Eocene -Lower Oligocene Massignano section, presently the official Global Stratotype Section and Point (GSSP) for the Eocene -Oligocene boundary, which is located on the west limb of the Monte Conero anticline, 10 km south of the city of Ancona (Bice & Montanari 1988;Coccioni et al 1988Coccioni et al , 2000Coccioni et al , 2009Brinkhuis & Biffi 1993;Premoli Silva & Jenkins 1993;Spezzaferri et al 2002;Jovane et al 2006Jovane et al , 2007bJovane et al , 2009Brown et al 2009). …”

“…According to Bice and Montanari (1988), Coccioni et al (1988Coccioni et al ( , 2000Coccioni et al ( , 2009, Brinkhuis and Biffi (1993), Premoli Silva and Jenkins (1993), Lowrie and Lanci (1994), Spezzaferri et al (2002), Jovane et al (2004Jovane et al ( , 2006Jovane et al ( , 2007bJovane et al ( , 2009), Tori and Monechi (2007) and Brown et al (2009), the Massignano section spans calcareous nannofossil Zones and Subzones NP18-NP21 of Martini (1971) and CP15a-CP16b of Okada and Bukry (1980), planktonic foraminiferal Zones P15-P18 of Berggren et al (1995) and Zones E14 to O1 of Berggren and Pearson (2006) and Wade et al (2011), dinocyst Zones Mps to Adi of Brinkhuis and Biffi (1993) and Chron C16n.2n to the lower part Chron C13n (Fig. 5).…”

Site U1403

“…F14). We tentatively conclude that this interval marks the Chesapeake Bay impact event, which occurred within Chron C16n.1n (Coccioni et al, 2009). We note that a lithologically similar gray-blue bed is present at Site U1404, but at that site the magnetochronology and biostratigraphy are consistent with deposition just above the Chron C17n.1r/C17n.2n boundary.…”

The planktic foraminiferPlanorotalitesin the Tethyan middle Eocene

“…The M. Cagnero section is a candidate for the GSSP for the Rupelian-Chattian boundary (Coccioni et al 2008) and is close to the Massignano section, the GSSP for the Eocene/Oligocene boundary (e.g. Premoli Silva & Jenkins 1993;Coccioni et al 2009). Sections a few kilometres away from the Alano and M. Cagnero outcrops, and thus likely to have a similar microfossil content, have been and continue to be extensively used in studies of Paleocene-Eocene hyperthermals, and in the refinement of Eocene biostratigraphy (e.g.…”