Age and driving mechanisms of the Eocene-Oligocene Transition from astronomical tuning of a lacustrine record (Rennes Basin, France)

• Main Authors: Boulila, Slah, Dupont-Nivet, Guillaume, Galbrun, Bruno, Bauer, Hugues, Châteauneuf, Jean-Jacques
• Other Authors: Sorbonne Université (SU), Géosciences Rennes (GR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Centre National de la Recherche Scientifique (CNRS), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Chercheur indépendant, Marie-Curie (CIG HIRESDAT), ANR-19-CE31-0002,AstroMeso,Solution astronomique pour le Mésozoïque(2019), European Project: 649081,H2020,ERC-2014-CoG,MAGIC(2015)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Eocene-Oligocene Transition; lacustrine record; astronomical tuning; Rennes basin (France); geo; archeo; Antarctic; The Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/cp-2021-46; https://hal.archives-ouvertes.fr/hal-03425440/file/BOULILA%20et%20al%20Climate%20Past%20pour%20HAL.pdf; https://hal.archives-ouvertes.fr/hal-03425440

International audience Abstract. The Eocene-Oligocene Transition (EOT) marks the onset of the Antarctic glaciation and the switch from greenhouse to icehouse climates. However, the driving mechanisms and the precise timing of the EOT remain controversial mostly due to the lack of well-dated stratigraphic records, especially in continental environments. Here we present a cyclo-magnetostratigraphic and sedimentological study of a ∼7.6 Myr-long lacustrine record spanning the late Eocene to the earliest Oligocene, from a drill-core in the Rennes Basin (France). Time-series analysis of natural gamma-ray (NGR) log data shows evidence of Milankovitch cycle bands. In particular, the 405 kyr stable eccentricity is expressed with strong amplitudes. Astronomical calibration to this 405 kyr periodicity yields duration estimates of Chrons C12r through C16n.1n, providing additional constraints on the middle–early Eocene timescale. Correlations between the orbital eccentricity curve and the 405 kyr tuned NGR time series and assumptions on their phase relationships, enable to test previously proposed ages for the EO boundary, indicating that 33.71 and 34.10 Ma are the most likely. Additionally, the 405 kyr tuning calibrates the most pronounced NGR cyclicity to a period of ∼1 Myr matching the g1-g5 eccentricity term. Such cyclicity has been recorded in other continental records, pointing to its significant expression in continental depositional environments. The record of g1-g5 and sometimes g2-g5 eccentricity terms in previously acquired sedimentary facies proxies in CDB1 core led us to hypothesize that the paleolake level may have behaved as a lowpass filter for orbital forcing. Two prominent changes in the sedimentary facies were detected across the EOT, which are temporally equivalent to the two main climatic steps, EOT-1 and Oi-1. Combined with previously acquired geochemical (δ15Norg, TOC), mineralogical (Quartz, clays) and pollen assemblage proxies from CDB1, we suggest that these two facies changes reflect the two major ...