CENOZOIC TIME SCALE AND SEA-LEVEL RECORDS: ASTROBIOGEOCLIMATOMAGNETOCHRONOLOGY? (Invited Presentation)

In 1976, Bill Berggren coined the sesquipedalian term astrobiogeoclimatomagnetochronology to illustrate that the future of correlation involved not just the integration of biostratigraphy, magnetostratigraphy, and radiometric age measurements, but also astronomically-paced climate proxies. He heralded the "astro" stratigraphy work of Hilgen et al. (1991) on Neogene Mediterranean sapropels and Olsen (1986) and Olsen and Kent (1999) on Late Triassic to earliest Jurassic lake-levels for developing a chronology grounded in Milankovitch cycles. Cyclostratigraphic work on ocean drilling cores began with astronomical tuning of physical property records (Shackleton, 1996) and has now provided astronomically tuned oxygen isotope records through the Cenozoic (Westerhold et al., 2020). These chronologies do not rely on precessional or obliquity tuning, but rather they tune to the 405 kyr very long eccentricity cycle that is interpreted to be the most stable astronomical forcing. Astronomical tuning to the 405 kyr eccentricity cycle cannot be assumed and still requires testing by comparison of cycle ratios and high-resolution radiometric dates. We have used astronomically tuned Pacific benthic foraminiferal oxygen isotope records and lower resolution Mg/Ca data to develop a Cenozoic global mean sea-level record that challenges the notion of an ice-free Eocene. Our barystatic (ice driven) sea-level shows amplitudes 20-60 m on the 1.2 Myr long tilt scale that have been independently verified by backstripping in New Jersey, Australia, and New Zealand. In contrast, a purported astronomically tuned update of the Exxon Production Research Company sea-level curve (Haq and Ogg, 2024) shows not only extremely high amplitudes (>100 m), but also 400 kyr cyclicity that is out of phase with other astronomically tuned cycles (Lisiecki and Raymo, 2005; Westerhold et al., 2020; Miller et al., 2020, 2024) and we question the legitimacy of this sea-level record. We conclude that simply claiming an astronomical time scale does not a chronology make.

Berggren, W.A., 1976, Astrobiogeoclimatomagnetochronology: The application of chronology to earth science: Geological Society of America, Abstracts, v. 8(6), p. 774.