Solar system chaos and the Paleocene-Eocene boundary age constrained by geology and astronomy

Abstract: Astronomical calculations reveal the solar system's dynamical evolution, including its chaoticity, and represent the backbone of cyclostratigraphy and astrochronology. An absolute, fully calibrated astronomical time scale has hitherto been hampered beyond $\sim$50 Ma, because orbital calculations disagree before that age. Here we present geologic data and a new astronomical solution (ZB18a), showing exceptional agreement from $\sim$58 to 53 Ma. We provide a new absolute astrochronology up to 58 Ma and a new Paleocene-Eocene boundary age (56.01 $\pm$ 0.05 Ma). We show that the Paleocene-Eocene Thermal Maximum (PETM) onset occurred near a 405-kyr eccentricity maximum, suggesting an orbital trigger. We also provide an independent PETM duration (170 $\pm$ 30 kyr) from onset to recovery inflection. Our astronomical solution requires a chaotic resonance transition at $\sim$50 Ma in the solar system's fundamental frequencies.