Abstract

This international workshop aims to enable cyclostratigraphic researchers from
all countries to learn about the new "AstroGeoFit" method, developed at the LTE.
https://observatoiredeparis.psl.eu/astrogeofit-revolutionne-la.html
For the first time, this method makes it possible to identify elements of the orbits of the solar system’s planets in geological records spanning several million years, without the need for a prior astronomical solution.

The morning sessions will be devoted to instructional classes, data presentations, and presentations of results using AstroGeoFit.
The afternoon sessions will consist of hands-on workshops using original data provided by the participants, with the support of MesoPSL.

Scientific justification

AstroGeoFit is a new method developed as part of the European ERC AstroGeo project, coordinated by Jacques Laskar. This method, combined with open-source software, makes it possible to reconstruct both the timescale of geological deposits and the orbital evolution of our planet based solely on sedimentary records. https://www.astrogeo.eu/astrogeofit/

For a century, scientists have known that the Earth’s orbital cycles—eccentricity, inclination, and precession—modulate the distribution of solar energy received at its surface. These rhythms, linked to gravitational interactions with other planets, are recorded in geological layers, like a fossil record of past climates.

But a major challenge arises when we try to go far back in time. The Earth’s orbit is chaotic (Laskar, 1989, 1990): tiny initial uncertainties amplify exponentially, making any direct reconstruction imprecise beyond about 60 million years. Beyond that point, the sediments themselves become our only reliable clock.

That’s where AstroGeoFit comes in—it’s designed to extract astronomical cycles directly from geological deposits, even when orbital solutions become uncertain. Its uniqueness rests on two pillars:

• Genetic algorithms, which simulate multiple scenarios of sediment accumulation (taking into account variations in rate, hiatuses, etc.)
• A Bayesian statistical analysis, which selects the orbital parameters most consistent with the data, while evaluating the margins of error.
  This approach makes it possible to reconstruct the eccentricity of Earth’s orbit—a cornerstone of climate over millions of years—and to establish a comprehensive timescale for the analyzed sediments.

AstroGeoFit was applied to synthetic data and to three major reference oceanic drill cores (ODP 926, 1260, 1262). Result: The tool successfully identifies astronomical rhythms, accurately reconstructs variations in sedimentation, and proposes a chronology consistent with existing dates—and even refines them.

Beyond dating, AstroGeoFit also opens up a new perspective: using terrestrial archives to better understand the past evolution of the solar system. By comparing signals extracted from rocks with those calculated by astronomical models, it becomes possible to constrain past orbital parameters in cases where chaos makes simulations uncertain. This is a unique way to bring geology, climate, and celestial mechanics into dialogue.

The AstroGeoFit workshop aims to introduce cyclostratigraphers to the new "AstroGeoFit" method, developed at the LTE.
https://www.astrogeo.eu/astrogeofit/
For the first time, this method makes it possible to identify elements of the orbits of the solar system’s planets in geological records spanning several million years, without the need for a prior astronomical solution.

The morning sessions will be devoted to instructional lectures, data presentations, and presentations of results using AstroGeoFit.
The afternoon sessions will consist of hands-on workshops using original data provided by the participants, with the support of MesoPSL’s resources. The goal is for participants to be able to use AstroGeoFit by the end of the week and to have conducted an initial analysis of the sedimentary sequences they have brought with them.

Preliminary program

Scheduled Course:
Statistical Data Analysis (1-hour session every morning) (Nathan Hara, LAM)

Proposed Speakers (very preliminary list)

Paul Olsen (Lamont/Columbia, USA)
Christian Zeeden (Leibniz Institute for Applied Geophysics, Germany)
Yujing Wu (LTE/Obs. Paris)
Matthias Sinnesaels (University of Dublin)
Frits Hilgen (University of Utrecht)