A 9 million-year-long astrochronological record of the early–middle Eocene corroborated by seafloor spreading rates

Abstract

The early-middle Eocene (ca. 56-41 Ma) is recorded in the pelagic Scaglia Rossa and Variegata Formations of the Umbria-Marche Basin (central Italy). Geochemical and magnetostratigraphic alignment between the Bottaccione section (Gubbio, central Italy) and the Smirra core (Cagli, central Italy) allows us to generate a continuous and wellpreserved new record that, combined with previously published data from the same area, creates a continuous high-resolution record from the Paleocene-Eocene thermal maximum (ca. 56 Ma) to the lower part of chron C21n. Comparison with carbon isotope records from Ocean Drilling Program Sites 1258 and 1263 reveals a satisfactory match, providing further evidence of the global significance of the long-term trend and superposed perturbations captured by the d 13 C records. The identification of astronomically forced geochemical cycles allows us to develop a 405 k.y. tuned age model, thereby extending the astrochronology from ca. 56.0 to ca. 47.5 Ma. Marine magnetic anomaly profiles from major oceanic basins characterized by high seafloor spreading rates were used to independently test the astronomical polarity time scale associated with our tuning, as well as other polarity time scales. Our age model suggests the existence of periods of relatively constant seafloor spreading rates separated by rapid changes, while the other time scales generate more gradual variations and also include large and short-term deviations in spreading rates that occur simultaneously in different oceanic basins, implying errors in polarity reversal ages. The Umbria-Marche age model further contributes to the closure of the middle Eocene gap in the astronomical time scale.

A Late Cretaceous‐Eocene Geomagnetic Polarity Timescale (MQSD20) That Steadies Spreading Rates on Multiple Mid‐Ocean Ridge Flanks

“…During this time, spreading rates decreased by a factor of 2–3 in the Indian Ocean while they approximately doubled in the North Pacific and in the South Atlantic (Figure 9). These spreading rate changes coincide with a previously noted set of global tectonic events (Francescone et al, 2019; Sutherland et al, 2020; Wessel et al, 2006; Whittaker et al, 2007) that we summarize below.…”

“…For example, in the Paleogene, the GTS12 GPTS uses a combination of astrochronology (66–47 Ma) and a GPTS based on the CK95 BMDs (47–34 Ma), and there are significant discrepancies in the Eocene and Paleocene (Vandenberghe et al, 2012). Many astrochronology studies used the CK95 GPTS to initially match sedimentary cycles with astronomical periods (Herbert et al, 1995; Röhl et al, 2003), to decide between alternative tuning options (Röhl et al, 2003), to estimate the duration of hiatuses (Pälike et al, 2001), to provide age constraints to floating timescales (Jovane et al, 2010), and to compare ages and durations of magnetic polarity chrons (Billups et al, 2004; Francescone et al, 2019; Herbert et al, 1995; Husson et al, 2011; Westerhold et al, 2008, Westerhold et al, 2017).…”

A Late Cretaceous-Eocene Geomagnetic Polarity Time Scale (MQSD20) that steadies spreading rates on multiple mid-ocean ridge flanks

“…During this time, spreading rates decreased by a factor of 2-3 in the Indian Ocean while they approximately doubled in the North Pacific and in the South Atlantic (Figure 9). These spreading rate changes coincide with a previously noted set of global tectonic events (Francescone et al, 2019;Sutherland et al, 2020;Wessel et al, 2006;Whittaker et al, 2007) that we summarize below.…”

“…For example, in the Paleogene, the GTS12 GPTS uses a combination of astrochronology (66-47 Ma) and a GPTS based on the CK95 BMDs (47-34 Ma), and there are significant discrepancies in the Eocene and Paleocene (Vandenberghe et al, 2012). Many astrochronology studies used the CK95 GPTS to initially match sedimentary cycles with astronomical periods (Herbert et al, 1995;Röhl et al, 2003), to decide between alternative tuning options (Röhl et al, 2003), to estimate the duration of hiatuses (Pälike et al, 2001), to provide age constraints to floating timescales (Jovane et al, 2010), and to compare ages and durations of magnetic polarity chrons (Billups et al, 2004;Francescone et al, 2019;Herbert et al, 1995;Husson et al, 2011;Westerhold et al, 2008, Westerhold et al, 2017.…”

Reconstructing Eocene Eastern Indian Ocean Dynamics Using Ocean‐Drilling Stratigraphic Records

“…All other reversal ages reported in this study are the result of our cyclostratigraphic agedepth model for Hole 762C. Westerhold et al (2015Westerhold et al ( , 2017 and Francescone et al (2019) assume that proxy sensitivity, measurement error and dating error exerted little influence on the total noise level. Unstable sedimentation, from short-term tectonic activity, may lead to elevated noise at all frequencies (Li et al, 2018).…”