Towards a robust and consistent middle Eocene astronomical timescale

• Published in: Earth and Planetary Science Letters
• Main Authors: Boulila, Slah, Vahlenkamp, Maximilian, De Vleeschouwer, David, Laskar, Jacques, Yamamoto, Yuhji, Pälike, Heiko, Kirtland Turner, Sandra, Sexton, Philip F., Westerhold, Thomas, Röhl, Ursula, Sexton, Philip
• Other Authors: Institut des Sciences de la Terre de Paris (iSTeP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Center for Marine Environmental Sciences Bremen (MARUM), Universität Bremen, Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Lille-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), School of Environment, Earth and Ecosystem Sciences Milton Keynes, Faculty of Science, Technology, Engineering and Mathematics Milton Keynes, The Open University Milton Keynes (OU)-The Open University Milton Keynes (OU)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: Middle Eocene; Newfoundland Ridge; obliquity; s3-s6 modulation cycle; astronomical timescale; [PHYS]Physics [physics]; [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]; Newfoundland; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-02320009; https://doi.org/10.1016/j.epsl.2018.01.003

International audience Until now, the middle Eocene has remained a poorly constrained interval of efforts to produce an astrochronological timescale for the entire Cenozoic. This has given rise to a so-called "Eocene astronomical timescale gap" (Vandenberghe et al., 2012). A high-resolution astrochronological calibration for this interval has proven to be difficult to realize, mainly because carbonate-rich deep-marine sequences of this age are scarce. In this paper, we present records from middle Eocene carbonate-rich sequences from the North Atlantic Southeast Newfoundland Ridge (IODP Exp. 342, Sites U1408 and U1410), of which the cyclical sedimentary patterns allow for an orbital calibration of the geologic timescale between ∼38 and ∼48 Ma. These carbonate-rich cyclic sediments at Sites U1408 and U1410 were deposited as drift deposits and exhibit prominent lithological alternations (couplets) between greenish nannofossil-rich clay and white nannofossil ooze. The principal lithological couplet is driven by the obliquity of Earth's axial tilt, and the intensity of their expression is modulated by a cyclicity of about 173 kyr. This cyclicity corresponds to the interference of secular frequencies s3 and s6 (related to the precession of nodes of the Earth and Saturn, respectively). This 173-kyr obliquity amplitude modulation cycle is exceptionally well recorded in the XRF (X-ray fluorescence)-derived Ca/Fe ratio. In this work, we first demonstrate the stability of the (s3-s6) cycles using the latest astronomical solutions. Results show that this orbital component is stable back to at least 50 Ma, and can thus serve as a powerful geochronometer in the mid-Eocene portion of the Cenozoic timescale. We then exploit this potential by calibrating the geochronology of the recovered middle Eocene timescale between magnetic polarity Chrons C18n.1n and C21n. Comparison with previous timescales shows similarities, but also notable differences in durations of certain magnetic polarity chrons. We present a revision of ...