Abstract
Abstract. To fully understand the global climate dynamics of the warm early Eocene with its reoccurring hyperthermal events, an accurate high-fidelity age model is required. The Ypresian stage (56–47.8 Ma) covers a key interval within the Eocene as it ranges from the warmest marine temperatures in the early Eocene to the long-term cooling trends in the middle Eocene. Despite the recent development of detailed marine isotope records spanning portions of the Ypresian stage, key records to establish a complete astronomically calibrated age model for the Ypresian are still missing. Here we present new high-resolution X-ray fluorescence (XRF) core scanning iron intensity, bulk stable isotope, calcareous nannofossil, and magnetostratigraphic data generated on core material from ODP Sites 1258 (Leg 207, Demerara Rise), 1262, 1263, 1265, and 1267 (Leg 208, Walvis Ridge) recovered in the equatorial and South Atlantic Ocean. By combining new data with published records, a 405 kyr eccentricity cyclostratigraphic framework was established, revealing a 300–400 kyr long condensed interval for magnetochron C22n in the Leg 208 succession. Because the amplitudes are dominated by eccentricity, the XRF data help to identify the most suitable orbital solution for astronomical tuning of the Ypresian. Our new records fit best with the La2010b numerical solution for eccentricity, which was used as a target curve for compiling the Ypresian astronomical timescale (YATS). The consistent positions of the very long eccentricity minima in the geological data and the La2010b solution suggest that the macroscopic feature displaying the chaotic diffusion of the planetary orbits, the transition from libration to circulation in the combination of angles in the precession motion of the orbits of Earth and Mars, occurred ∼ 52 Ma. This adds to the geological evidence for the chaotic behavior of the solar system. Additionally, the new astrochronology and revised magnetostratigraphy provide robust ages and durations for Chrons C21n to C24n (47–54 Ma), revealing a major change in spreading rates in the interval from 51.0 to 52.5 Ma. This major change in spreading rates is synchronous with a global reorganization of the plate–mantle system and the chaotic diffusion of the planetary orbits. The newly provided YATS also includes new absolute ages for biostratigraphic events, magnetic polarity reversals, and early Eocene hyperthermal events. Our new bio- and magnetostratigraphically calibrated stable isotope compilation may act as a reference for further paleoclimate studies of the Ypresian, which is of special interest because of the outgoing warming and increasingly cooling phase. Finally, our approach of integrating the complex comprehensive data sets unearths some challenges and uncertainties but also validates the high potential of chemostratigraphy, magnetostratigraphy, and biostratigraphy in unprecedented detail being most significant for an accurate chronostratigraphy.
Highlights
The consistent positions of the very long eccentricity minima in the geological data and the La2010b solution suggest that the macroscopic feature displaying the chaotic diffusion of the planetary orbits, the transition from libration to circulation in the combination of angles in the precession motion of the orbits of Earth and Mars, occurred ∼ 52 Ma
Our new bio- and magnetostratigraphically calibrated stable isotope compilation may act as a reference for further paleoclimate studies of the Ypresian, which is of special interest because of the outgoing warming and increasingly cooling phase
At Site 1262 the X-ray fluorescence (XRF) Fe record ends with the shoaling of the carbonate compensation depth (CCD) above the site in Chron C21r around 93 mcd (Zachos et al, 2004)
Summary
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 (Zachos et al, 2008), 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, 2015, 2016), and major faunal turnovers (Thomas and Shackleton, 1996; Gingerich, 2003; Clyde et al, 2007). Two major issues have to be solved to achieve a complete Ypresian astronomical timescale (YATS): (1) the “50 Ma discrepancy” in magnetostratigraphy (Vandenberghe et al, 2012; Westerhold et al, 2015) and (2) the exact number of 405 kyr eccentricity cycles in magnetochron C23 (Lauretano et al, 2016). The 50 Ma discrepancy arises from the short duration of magnetochron C23n.2n in Ocean Drilling Program (ODP) Site 1258 data (Suganuma and Ogg, 2006; Westerhold and Röhl, 2009) that results in a very unlikely abrupt global increase in spreading rate for this chron only at around 50 Ma (Vandenberghe et al, 2012). After revision of the composite record of Site 1258, the interpretation was improved (Westerhold and Röhl, 2009), but the interpretation for Chrons C22r, C23n, and C23r remained ambiguous
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