Is there a normal magnetic-polarity event during the Palaeocene-Eocene thermal maximum (∼55 Ma)? Insights from the palaeomagnetic record of the Belluno Basin (Italy)

Abstract

SUMMARY In the lowermost Eocene sedimentary record of Ocean Drilling Program Site 1262 (Leg 208, Walvis Ridge, South Atlantic Ocean), the presence of a ∼53‐kyr‐long normal polarity event has been recorded within the ∼2.55‐Myr‐long reverse polarity Chron C24r (∼53.3–55.9 Ma) and termed Palaeocene–Eocene magnetic reversal (PEMR). The origin of the PEMR has been speculatively related to a change in the Earth's rotation rate that was in turn influenced by an abrupt overturning of the ocean‐atmosphere circulation that occurred during the Palaeocene–Eocene thermal maximum (PETM) at ∼55 Ma. Such provocative genesis for a magnetic‐polarity reversal demands the PEMR to be confirmed (or refuted) in additional PETM sections. Here, we present detailed palaeomagnetic and rock‐magnetic data from the Forada and Cicogna sections of the Belluno Basin in NE Italy, which contain an expanded and continuous record of the PETM termed clay marl unit (CMU). Our data indicate that these sediments were deposited during a continuous interval of reverse geomagnetic field polarity. We therefore conclude that no magnetic‐polarity reversals occurred throughout the PETM. In addition, we studied the origin of the high degree of flattening affecting the characteristic magnetic component directions of the sediments, which we interpret as due to a combination of depositional inclination shallowing typical of detrital haematite, and post‐depositional compaction of clays, particularly abundant in the carbonate‐depleted CMU.

Environmental perturbations at the early Eocene ETM2, H2, and I1 events as inferred by Tethyan calcareous plankton (Terche section, northeastern Italy)

“…At Terche, the intensity of the NRM ranges from 1.08 × 10 −4 to 1.14 × 10 −3 Am −1 , with an average value of 3.03 × 10 −4 Am −1 (Figure ), in agreement with the data from the coeval part of the Cicogna section [ Dallanave et al , , , ]. The unblocking temperature indicates a magnetization carried by hematite, in agreement with the results obtained from the Cicogna section sediments.…”

“…The magnetic mineralogy and rock‐magnetic properties of the Paleogene sediments of the Belluno Basin have been extensively investigated by Dallanave et al . [, , , ]. In particular, detailed paleomagnetic and rock‐magnetic study of the lower Eocene sediments of the Cicogna section [ Dallanave et al , , ] revealed that the dominant magnetic mineral is detrital hematite, which coexist with minor maghemite.…”

Eocene (46–44 Ma) Onset of Australia‐Pacific Plate Motion in the Southwest Pacific Inferred From Stratigraphy in New Caledonia and New Zealand

“…In fact, the IRM drop is interpreted as reflecting inversion of γ‐Fe 2 O 3 to α‐Fe 2 O 3 during heating in the magnetic field‐free furnace. Similar curves have been obtained from correlative sediments from southern New Caledonia (Dallanave et al, 2018) and coeval hemipelagic red beds from the Italian Alps (Dallanave et al, 2009, 2010, Dallanave, Agnini, et al, 2012, Dallanave, Muttoni, et al, 2012). In the latter cases, the maghemite‐hematite transition is observed at lower temperatures, approximately between 300°C and 400°C.…”

Benthic foraminifera at the Paleocene/Eocene thermal maximum in the western Tethys (Forada section): variability in climate and productivity

“…Detrital hematite sharply increased in concentration at the onset of Assemblage E Dallanave et al, 2010Dallanave et al, , 2012Fig. 4).…”

“…A common obstacle to performing detailed high-resolution studies of the PETM in deep-sea sediments is the fact that many records are condensed or discontinuous, especially across the few thousand years (Zeebe et al, 2014) of the onset of the carbon isotope excursion. The Forada section (northeastern Italy) represents an outstanding exception in that it contains an expanded deep-sea record of the PETM, which has been extensively studied because of its continuity and cyclostratigraphy (Agnini et al, 2007;Luciani et al, 2007;Tipple et al, 2011;Dallanave et al, 2012). Carbonate dissolution is less severe at Forada than in many other sections, with calcareous benthic foraminifera present for most of the interval characterized by the CIE (> 4 m; .…”