An early Eocene carbon cycle perturbation at ∼52.5 Ma in the Southern Alps: Chronology and biotic response

Abstract

[1] At least two transient events of extreme global warming occurred superimposed on the long-term latest Paleocene and early Eocene warming trend in the Paleocene-Eocene thermal maximum (PETM) (or ETM1 $55.5 Ma) and the Elmo (or ETM2 $53.6 Ma). Other than warmth, the best known PETM is characterized by (1) significant injection of 13 C-depleted carbon into the ocean-atmosphere system, (2) deep-sea carbonate dissolution, (3) strong biotic responses, and (4) perturbations of the hydrological cycle. Documentation of the other documented and suspected ''hyperthermals'' is, as yet, insufficient to assess whether they are similar in nature to the PETM. Here we present and discuss biomagnetostratigraphic data and geochemical records across two lower Eocene successions deposited on a continental margin of the western Tethys: the Farra and Possagno sections in the Venetian pre-Alps. We recognize four negative carbon isotope excursions within chron C24. Three of these shifts correlate to known or suspected hyperthermals: the PETM, the Eocene thermal maximum 2 ($53.6 Ma), and the informally named ''X event'' ($52.5 Ma). The fourth excursion lies within a reverse subchron and occurred between the latter two. In the Farra section, the X event is marked by a $0.6% negative carbon isotope excursion and carbonate dissolution. Furthermore, the event exhibits responses among calcareous nannofossils, planktic foraminifera, and dinoflagellates that are similar to, though less intense than, those observed across the PETM. Sedimentological and quantitative micropaleontological data from the Farra section also suggest increased weathering and runoff as well as sea surface eutrophication during this event.

Frequency, magnitude and character of hyperthermal events at the onset of the Early Eocene Climatic Optimum

“…During the PETM global temper-V. Lauretano et al: Frequency, magnitude and character of hyperthermal events ature rose by 5-8 • C, and massive amounts of carbon were released as evidenced by a significant negative carbon isotope excursion (CIE) of > 3 ‰ in the ocean/atmosphere carbon pools, and widespread dissolution of seafloor carbonate (Kennett and Stott, 1991;Dickens et al, 1995;Thomas and Shackleton, 1996;Zachos et al, 2005Zachos et al, , 2008Sluijs et al, 2007;McInerney and Wing, 2011). A series of similar events are recorded in carbonate records from marine and continental deposits from the early Paleogene, as expressed by negative excursions in δ 13 C and δ 18 O often accompanied by dissolution horizons (e.g., Cramer et al, 2003;Lourens et al, 2005;Agnini et al, 2009;Galeotti et al, 2010;Stap et al, 2010;Zachos et al, 2010;Abels et al, 2012Abels et al, , 2015Slotnick et al, 2012;Kirtland Turner et al, 2014;Littler et al, 2014). Orbitally tuned records for this geological interval provide evidence that the early Eocene hyperthermal events were paced by variations in the Earth's orbit, specifically in the long-and short-eccentricity cycles.…”

“…4). They correspond to the ETM2, H2, I1, I2, J, and ETM3 (or X/K) events, formerly recognized in deep-sea δ 13 C bulk carbonate records and land-based marine and continental sections (Abels et al, 2012Agnini et al, 2009;Cramer et al, 2003;Kirtland Turner et al, 2014;Littler et al, 2014;Lourens et al, 2005;Slotnick et al, 2012).…”

Identification of the Paleocene–Eocene boundary in coastal strata in the Otway Basin, Victoria, Australia

“…Furthermore, the PETM CIE has a distinct shape, consisting of a very rapid onset (1-5 kyr) (Kirtland Turner and Ridgwell, 2016;Zeebe et al, 2016) and a prolonged plateau phase termed the "body" (70-100 kyr) followed by a gradual recovery (∼ 100 kyr) (Abdul Aziz et al, 2008;Murphy et al, 2010;Röhl et al, 2007). Subsequent events in the early Eocene, such as the Eocene Thermal Maximum (ETM) 2 (∼ 54 Ma; Lourens et al, 2005) and ETM3 (∼ 52.5 Ma; Agnini et al, 2009) are typified by smaller CIEs and lack a plateau phase.…”

Astronomical calibration of the Ypresian timescale: implications for seafloor spreading rates and the chaotic behavior of the solar system?

“…The Ypresian stage, from 56.0 to 47.8 Ma, represents the first ∼ 8 million years of the Eocene epoch (Vandenberghe et al, 2012), an interval characterized by the warmest deep-sea temperatures of the Cenozoic era , multiple transient global warming events (Cramer et al, 2003;Lourens et al, 2005;Agnini et al, 2009;Galeotti et al, 2010;Leon-Rodriguez and Dickens 2010;Stap et al, 2010;Zachos et al, 2010;Sexton et al, 2011;Slotnick et al, 2012;Littler et al, 2014;Kirtland Turner et al, 2014;Lauretano et al, 2015Lauretano et al, , 2016, and major faunal turnovers (Thomas and Shackleton, 1996;Gingerich, 2003;Clyde et al, 2007). Climatic records from the Ypresian greenhouse are of special interest because they potentially capture the behavior of Earth's climate system under pCO 2 concentrations likely to be reached in the near future Meinshausen et al, 2011).…”