Seeking an accurate astronomical solution from ~66-67 Ma Cretaceous-Paleogene boundary-interval cyclostratigraphy

The Earth’s ancient astronomical parameters are derived from high-fidelity cyclostratigraphic records in which observed cycles are dominantly controlled by two sets of factors: (1) orbital parameters involving the orbital motions of the planets, and (2) rotational parameters involving Earth’s spin, lunar separation and precession rate. A full astronomical solution (AS) for the Earth is thus comprised of an orbital solution (OS) and a precession solution (PS) [1].The OS is constrained to 0-60 Ma [2]; prior to 60 Ma chaotic behavior of planetary orbits results in a non-unique OS. The PS is constrained by geophysical modeling of dynamical ellipticity (De) and tidal dissipation (Td) [3, 4].

For times prior to 60 Ma, recovery of the AS relies on cyclostratigraphy. OS ZB18a and PS ZB18a(De=1,Td=0.9) have been proposed as candidates for a 58-66 Ma AS from ODP Site 1262 cyclostratigraphy [5], and OS (ZB20a) for a 66-71 Ma AS from Zumaia (Spain) cyclostratigraphy [6]. Here we examine an extension of Site 1262 cyclostratigraphy from the Cretaceous-Paleogene Boundary (KPB; 66 Ma) reaching back ~1 million years into the Late Maastrichtian [7]. The goal is to test the fit of various available OS (e.g., ZB20a, ZB18a) with cyclostratigraphy for this interval, and whether PS parameters appear to be consistent with post-KPB PS parameter values of De=1 and Td=0.9.

The sequence of XRF Core Scanner Fe area counts for Site 1262 (216.74-236.02 rmcd) was analyzed with TimeOpt [8] and AstroGeoFit [9]. TimeOpt identified a constant sedimentation rate of 2.13 cm/kyr, and constrained spectral power in two narrow-band lines consistent with short orbital eccentricity, and elevated power across the precession band. TimeOpt with a linearly increasing sedimentation rate template reorganized precession band power into four narrow-band lines consistent with precession frequencies. A close examination hinted that other variable sedimentation rates along the sequence remained undiscovered. AstroGeoFit confirmed the linear increase in sedimentation rate, and identified additional fluctuations that reorganized power into specific precession line frequencies.

The TimeOpt results indicate a close match between late Maastrichtian Site 1262 and OS ZB18a and PS ZB18a(De=1,Td=0.9), as was found previously for the post-KPB interval (58-66 Ma) [5]. The AstroGeoFit results improve on this finding. Finally, a KPB geochronologic anchor of 66.021 ± 0.024/0.039/0.081 Ma [10] for Site 1262 guides the assignment of an absolute timescale and precession-scale astrochronology for Site 1262.  

 

References:

• Zeebe, RE, Kocken, I, 2025, Earth-Sci Rev, 261, 104959
• Laskar, J, et al, 2011, Astron Astrophys, 532, L4
• Waltham, D, J Sed Res, 2015, 85, 990–998
• Farhat, M., et al, 2022, Astron. Astrophys. 665, L1
• Zeebe, RE, Lourens, LJ, 2022, Earth Planet Sci Lett, 592, 117595
• Kocken, I, Zeebe, RE, 2024, Paleocean Paleoclim, 39, e2024PA004954
• Westerhold, T, et al, 2025, Sci Adv, 11, eadr8584
• Meyers, SR, 2019, Earth-Sci Rev, 190, 190-223
• Hoang, N, et al, 2025, Paleoceanogr Paleoclimatology, 40, e2024PA005021
• Clyde, WM, et al., 2016, Earth Planet Sci Lett, 452, 272