GRAND MILANKOVITCH CYCLES RECORDED IN THE CRETACEOUS (ALBIAN) FUCOID MARLS, PIOBBICO CORE, ITALY, AND IMPLICATIONS FOR THE CHAOTIC EVOLUTION OF THE SOLAR SYSTEM

The Piobbico core, drilled in the Umbria-Marche Apennines, Italy by I. Premoli Silva, G. Napoleone, and A. Fischer in 1982, recovered a continuous cyclostratigraphic record of Tethyan pelagic sedimentation during the Albian Stage. A grayscale scan of digitized core photographs captured exquisitely preserved lithofacies cycles with astronomical forcing frequencies associated with Earth’s orbital eccentricity, obliquity and precession index [1]. Harmonic analysis of the scan identifies individual fundamental frequencies of the Solar System (gi, si, i=1,2…8, for each of the planets in order from the Sun). Prominent 405-kyr cycles related to the Earth’s g2-g5 orbital eccentricity variation serve as an “astronomical metronome” to tune the scan and to define an astrochronology for the Albian, from 100 Ma to 112 Ma. Quadrature analysis reveals long-period modulations that affect the orbital eccentricity and obliquity frequencies arising from the moving orbital perihelia and eccentricities, g4–g3, and variable orbital inclinations and ascending nodes, s4-s3, of Earth and Mars. These are so-called “Grand cycles of the Milankovitch band” [2]. The La2004 astronomical solution from 112 Ma to 100 Ma [3] predicts a chaotic transition in the resonance argument (g4-g3):(s4-s3), from 2:1 to 1:1 from 108 to 107 Ma, followed by prolonged 1:1 resonance from 107 to 100 Ma, and a chaotic transition back to 2:1 resonance in the early Cenomanian. By contrast, the Piobbico scan reveals four chaotic transitions between these same two resonance states from 112 Ma to 100 Ma. From 110 to 105 Ma, s4-s3 is not evident due to insufficient obliquity forcing, and the resonances and transitions are inferred from g4-g3. The sensitive cyclostratigraphic record of the Piobbico core should prove to be a valuable contribution to the recently proposed “Geological Orrery” for astronomical solutions prior to 60 Ma [4]. Importantly, the higher than predicted recurrence rate of chaotic transitions observed throughout the Albian, 100 Ma to 112 Ma, if confirmed, points to greater instability in the Earth and Mars orbits than suggested by existing astronomical solutions. References: [1] A. Grippo et al., in B. D’Argenio et al. (eds.), SEPM Spec Pub 81, 57, 2004; [2] P. Olsen, Eos Trans AGU 82, F2 (U11A-11), 2001; [3] J. Laskar et al., Astron Astrophys 428, 261, 2004; [4] P. Olsen et al., Proc Natl Acad Sci USA 116, 10664, 2019.