High-fidelity dating of deep-time records: Integrating Earth's dynamical ellipticity and tidal dissipation into astrochronology

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One way to determine the ages of seafloor sediments and sedimentary rocks is by using a “calendar” based on astronomical calculations. This time scale makes use of the fact that predictable changes in the orbits of the planets drive cyclic changes in Earth’s climate. For example, observed cycles in sediment composition can be matched to astronomical cycles. Those cycles are calculated by computing planetary orbits backward in time. Unfortunately, the use of certain orbital cycles remains challenging because Earth’s gravitational shape and rotation rate have changed in the past. These changes introduce uncertainty into the orbital calculations. This project will develop high-fidelity dating methods for sedimentary records by including Earth’s gravitational shape and rotation rate into the orbital calculations. All numerical tools will be made available as open source programs and as add-ons to software packages. The project broader impacts include support for a graduate student, and a training workshop in astrochonology methods. The project has the potential to transform our ability to date sediments from the last 55 million years. It will also improve our understanding of tidal dissipation and climate forcing in the past.Dating of sedimentary records using astronomical calculations has led to the astronomical time scale (ATS), today representing the backbone of cyclostratigraphy and astrochronology, widely used within and beyond marine geology and geophysics. Age models often rely on the imprint of astronomically calculated cycles of eccentricity and other solar system frequencies in sedimentary records (e.g., 405, 173, and ~100 kyr). However, use of obliquity and precession cycles (at present 41 and ~20 kyr) remains challenging, mostly due to past changes in Earth's dynamical ellipticity (gravitational shape) and tidal dissipation (slowdown of Earth's rotation), which affect the astronomical calculations. This project will develop high-fidelity dating methods for sedimentary records by integrating dynamical ellipticity and tidal dissipation into astrochronology, targeting specific time intervals that feature high-quality sedimentary records. Using selected geologic records, the study will also test the hypothesis that tidal dissipation was significantly reduced in the past. Numerical tools will be provided for users to derive age models, applicable to various published astronomical solutions (calculated planetary orbital parameters). All dating tools will be made freely available as open source stand-alone applications, as add-ons to astrochronological software packages, and introduced to users during a training workshop. The project has the potential to transform the accuracy of sediment dating, as well as our understanding of tidal dissipation and obliquity forcing in the past.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.