AstroGeoFit. A Genetic Algorithm and Bayesian approach for the Astronomical Calibration of the Geological Timescale

Variations in Earth's orbit and axial tilt induce climatic changes on its surface, which are recorded in sedimentary deposits. These cyclical variations are driven by the main secular frequencies of the solar system. Analyzing these cycles in sedimentary records can help establish an astronomical time scale for the geological record by correlating geological proxies with computed variations in insolation on the Earth's surface, in accordance with the laws of celestial mechanics. A critical aspect of this analysis is the estimation of the sedimentary deposition rate, which determines the time-depth transfer function, relating geological depth to relative or absolute time.

We propose a novel approach for constructing astronomical time scales for geological stratigraphic records. The AstroGeoFit method establishes a time-depth transfer function throughout the record, accommodating variable sedimentation rates, and extracts the primary astronomical signal from the geological sequence. This is achieved using a genetic algorithm that adapts to a wide range of sedimentation rate variations. This statistical analysis enables the reconstruction of an astronomical signal (e.g., eccentricity and/or precession) purely from the stratigraphic sequence with minimal personal bias. When this template is correlated with an astronomical solution, an absolute time scale is obtained for the entire record. In addition, we show that quantitative uncertainties can be estimated at each stage of the AstroGeoFit process with the Bayesian approach.

The publication of the AstroGeoFit approach will be associated to an open source python package that fully implement the AstroGeoFit algorithm.

Ref: J. Laskar, N. Hoang, N. Hara, Y. Wu, A.Sultanov, M. Sinnesael, T. Westerhold, P. Bujons, AstroGeoFit. A Genetic Algorithm and Bayesian approach for  the Astronomical Calibration of the Geological Timescale, 2025, in revision.