Implications of the Geological Determination of “Grand Cycles” of the Milankovitch Band for Behavior of the Solar System

Attention has historically focused on the 21, 41, and 100 ky Milankovitch periods, but cycles of 405 ky and up to several million years are present in the orbital solutions. The latter I have previously termed "grand cycles" of the Milankovitch band. Laskar (1) has shown there is long-term chaotic evolution in planetary orbits that render grand cycles frequencies <1/405 ky unpredictable over deep time, especially the g₄-g₃ cycle with a present frequency of ~1/2.35 m.y. While Cenozoic records (2) lack observable change in this frequency, I have shown that early Mesozoic paleotropical lake level records (199-235 Ma) provide a "geological interferometer" revealing that g₄-g₃ had a frequency of 1/1.75 m.y., consistent with chaotic diffusion (3). Wavelet analysis shows this 1/1.75 m.y. frequency was stable over at least 25 m.y. The g₁-g₅ and g₂-g₁ frequencies are also present. The Triassic 1/1.75 m.y. frequency is consistent with multiple marine ²⁰⁶Pb/²³⁸U ash ages tied to the lacustrine records by magnetostratigraphy. Because the tropical lake sequences show no obliquity signal, their spectral properties can be used as a template to identify grand cycles in obliquity from contemporaneous higher latitude records. With obliquity records, s₄-s₃ can be determined, and through this the resonance state of the Earth-Mars system. If this can be done for the rest of the Jurassic and Cretaceous, the grand cycle "geological interferometer" will allow the development of a high-precision solution for the behavior of the Solar System over 235 million years and a robust test of general relativity derived from the quadrupole moment J₂ of the Sun as has been noted by Laskar (1). References: 1, Laskar, 1999, Phil. Trans. R. Soc. Lond. A, 357:1735; 2, PŠlike et al., 2004, Geology 32: 929; 3, Olsen & Kent, 1999. Phil Trans. R. Soc. Lond. A, 357:1761.