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Astronomical time scale for the Cenozoïc and Mesozoïc era. – ASTS-CM

Submission summary

Background: International project for a Cenozoic-Mesozoic Astronomically-Tuned Time Scale Due to planetary perturbations, the orbit of the Earth is slowly changing in time, as is the orientation of its spin axis. These changes induce variations of the insolation on Earth (Milankovitch, 1941) that affect the climate system, and are recorded in the sedimentary record. The revival of the Milankovitch theory follows the work of Hays et al., (1976). The agreement between astronomical computations and climate variations recorded in the sedimentary cores is now so well established that in the newly published geological time scale GTS2004 of the ICS (, (Grastein et al., 2004), the whole Neogene period (0-23 Ma) has been astronomically calibrated using the insolation solution of Laskar et al 2004. The GTS2004 results from a 10 years international effort and results in an unprecedented agreement for the establishment of Geological time scales over the Earth history. For this latest edition of a geological time scale, the ICS considered that for the Neogene period, the correlation of the sedimentary cores cyclicities to astronomical variations allowed a better accuracy than radiogenic measurements. Since, a large international effort has started in order to extent this astronomical calibration to older periods. One of the major goals for this next version of the GTS is the realization of an orbitally tuned Paleogene time scale (23-65.5 Ma) and to extend this tuning 'down' in Cretaceous (Gradstein and Ogg, 2004). This new time scale is expected to be in place at the time of the 33rd IGC in 2008 which will coincide with the International Year of Planet Earth that has just been proclaimed by the United Nation. The extension of the orbital tuning to the Paleogene period will be made possible by the high resolution sedimentary cores obtained during the recent ODP cruises. Indeed, IODP legs have been devoted to derive a time scale through the Paleogene and into the uppermost Cretaceous. The ICS also recognized the exciting prospect of an high resolution time scale for the past quarter-billion years and established a Task Group for a Cenozoic-Mesozoic Astronomically-Tuned Time Scale. Objective: The PI group has a leading position in the construction of long term astronomical solutions for paleoclimate studies. Their latest solution (Laskar et al., 2004) was used for the establishment of the new GTS2004. Apart from the PI, the french scientific community is singularly absent from the contributions to the GTS2004 book. One of the objective of this interdisciplinary proposal is to increase the french contribution in the forthcoming new time scale GTS2008. This is very timely, and the present proposal gathers several key points that appear to be mandatory for a proper establishment of an astronomically-tuned time scale for the Cenozoic and Mesozoic eras. Indeed, the two groups involved in this interdisciplinary proposal represent many aspects of this international project : - We propose to increase by two order of magnitude the accuracy of the astronomical solution of the Earth over the Cenozoic era (0-65Ma), with rigorous estimates of its precision, searching to meet the required standards for the establishment of an astronomically-tuned time scale for the Cenozoic. This will require an entirely new procedure as we will use the short term planetary ephemeris developed in the PI group (Fienga et al, 2007) in order to derive precise estimates of the accuracy of the astronomical long term solution. - We will undertake a detailed and complete cyclostratigraphic analysis of the Mesozoic sedimentary sections from the Vocontian Basin (South East of France), the Sancerre core (lower and middle Jurassic from the Paris Basin), the Betic Cordilleras (Spain), and the Umbria-Marche basin (Italy) that represent key elements for the establishment of a continuous stratigraphy of the Mesozoic era. - We will perform the analysis of some of the already acquired stratigraphic data in order to constrain some of the geophysical parameters of the Earth and to derive a better knowledge of the evolution of the Earth-Moon system in the past 250 Myr. For this phase of the proposal we request the support of the ANR for a two years postdoctoral position. The candidate will largely interact with the two groups and also with foreigns groups that have long standing interactions with the proposers (H. Pälike in England, F. Hilgen and L. Lourens in the Netherlands, U. Röhl in Germany, L. Hinnov in the US). References. Gradstein F. et al., 2004 – A Geologic Time Scale 2004. Cambridge University Press, 589 p. Laskar J. et al., 2004, A long-term numerical solution for the insolation quantities of the Earth. Astron. and Astrophys., 428, 261-285. Fienga A. et al, 2007- INPOP06. A new numerical planetary ephemeris (submitted,

Project coordination

Jacques LASKAR (Autre établissement d’enseignement supérieur)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


Help of the ANR 240,000 euros
Beginning and duration of the scientific project: - 48 Months

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