EARTH-MOON HISTORY AND ASTRONOMICAL PARAMETERS: CONSTRAINTS FROM THE PERMIAN AND PROTEROZOIC

Abstract

The cyclostratigraphic record of Milankovitch cycles serves as a chronometer for reconstructing geological time and allows evaluation of ancient climate change and depositional system history. However, direct calculation of astronomical solutions from theory is limited to the past ~50 Ma, due to the chaotic dynamics of the Solar System and to uncertainties in the Earth-Moon history. This study aims to overcome this limitation by leveraging high-quality cyclostratigraphic data and a recently improved Bayesian approach for astrochronologic evaluation (TimeOptB and TimeOptBMCMC; Malinverno and Meyers, 2024) to estimate and reconstruct the astronomical parameters and Earth-Moon history during the Permian and Proterozoic. We also develop and implement strategies for the application of the Bayesian method that account for sedimentary distortions of the astronomical signals, which are commonplace in cyclostratigraphic records. The two intervals we investigate are the ~290 Ma lacustrine deposits of the Permian Lucaogou Formation (China) and the ~2477 Ma Proterozoic banded iron formations (BIFs) from the Dales Gorge Member (DGM), Hamersley Basin (Australia). In agreement with prior work in the Lucaogou Formation, cyclostratigraphic analysis of natural gamma ray (NGR) geophysical log data provides evidence for the presence of astronomical signals, but also reveals sedimentation rate instability and noise that distorts the preserved astronomical signal, creating artifacts that must be considered when reconstructing the astronomical parameters and Earth-Moon history. Astrochronologic testing with TimeOptB identifies a statistically significant astronomical signal for the Lucaogou Formation. TimeOptBMCMC posterior estimates for the sedimentation rate, u, and axial precession frequency, k, of the Lucaogou Formation are 11.495 +/- 0.494 cm/kyr (2σ) and 57.180 +/- 2.386 arcsec/yr (2σ) respectively. These estimates correspond to an average lunar distance of approximately 373.291 × 10³ km and day length of 22.530 hours.

In the second case study evaluating Proterozoic BIFs, building on the work of Rodrigues et al. (2019) and Zhou et al. (2022), we refine and provide a best estimate for astronomical and Earth- Moon parameters from the analysis of high-resolution hyperspectral imaging data (quartz and ferric oxides abundance) from DGM BIFs (BIF 12 and 15). Astrochronologic testing with TimeOptB identifies a statistically significant astronomical signal for DGM datasets. For BIF 15, which yields the most well constrained result, the TimeOptBMCMC posterior estimates for the sedimentation rate and axial precession frequency are 1.675 +/- 0.086 cm/kyr (2σ) and 110.950 +/- 8.306 arcsec/yr (2σ) respectively, with an average lunar distance of 318.970 × 10³ km and length of day of about 16.856 hours. Our analysis resolves precessional forcing on smaller-scale lithologic cyclicity (15-cm Calamina cyclothems) and eccentricity forcing on longer-scale DGM BIF cycles. The results presented in this study yield new refined constraints on Earth-Moon history, and the improved methodologies provide robust strategies for addressing noisy datasets, which often complicate the reconstruction of astronomical cycles from paleoclimate proxies, thus expanding the utility and applicability of the TimeOptB and TimeOptBMCMC approaches.