The Toarcian Oceanic Anoxic Event (T-OAE) of the early Jurassic period involves one of the largest perturbations of the carbon cycle in the past 250 Ma, recorded by a pronounced negative carbon-isotope excursion (CIE). Numerous studies have focused on potential causes of the T-OAE and CIE, but are hampered by an uncertain timescale. Here we present high-resolution (!2 kyr) magnetic susceptibility (MS) measurements from the marine marls of the Sancerre-Couy drill-core, southern Paris Basin, spanning the entire Toarcian Stage. The MS variations document a rich series of sub-Milankovitch to Milankovitch frequencies (precession, obliquity and eccentricity) with the periodic g 2 -g 5 (405 kyr) and quasi-periodic g 4 -g 3 (!2.4 Myr Cenozoic mean periodicity) eccentricity terms being the most prominent. The MS-related g 4 -g 3 variation reflects third-order eustatic sequences, and constrains the sequence stratigraphic framework of the Toarcian Stage. In addition, MS variations reveal a modulation of g 2 -g 5 by g 4 -g 3 eccentricity related cycles, suggesting that sea-level change was the main control on the deposition of the Toarcian Sancerre marls, in tune with the astro-climatic frequencies. The stable 405 kyr cyclicity constrains a minimum duration of the Toarcian Stage to !8.3 Myr, and the well documented CIE, associated with the T-OAE, to !300 to 500 kyr. The 405 kyr MS timescale calibrates the periodicity of the prominent high-frequency ! 13 C cycles that occur in the decreasing part of the CIE to 30 to 34 kyr, consistent with the Toarcian obliquity period predicted for an Earth experiencing sustained tidal dissipation.

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Climatic and palaeoceanographic changes during the Pliensbachian (Early Jurassic) 2 inferred from clay mineralogy and stable isotope (C-O) geochemistry (NW Europe

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Cyclostratigraphic analysis of the Maastrichtian limestone-marl alternations of Bidart (SW France) allows the hypothesis of orbital control on lithological cycles to be evaluated. Magnetic Susceptibility (MS), oxygen and carbon isotope measurements, sampled at a high resolution, are analyzed using various cyclostratigraphic tools. A statistically significant orbital signal is detected, with a remarkable record of the precession corresponding to the limestone-marl couplets. This well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the MS and !13C records based on the 100 kyr eccentricity cycle. The total duration of the section is estimated at 1.44 ± 0.22 Myr. Correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled Bidart !13C record to the astronomically calibrated !13C signal of ODP hole 762C shows that the studied section extends from-71.5 to-70 Ma, covering the upper part of Chron C32n.1n and 2/3 of Chron C31r. Oxygen isotope data suggest a 2°C cooling of sea-surface temperatures during the studied interval. When placed on the long-term !18O trend of the Bidart section, this interval is here recognized as the onset of the early Maastrichtian cooling event. With its excellent record of the precessional forcing, the Bidart section, along with other sections of the Basque country, is a useful tool for the refinement of the Maastrichtian timescale.