A high-resolution grayscale series of the pelagic Fucoid Marls (Piobbico core, central Italy) shows strong, pervasive lithological rhythms throughout the Aptian interval. A hierarchy of centimeter- to meter-scale cycles characterizes the rhythms; when calibrating ∼1 m cycles to Earth's 405 k.y. orbital eccentricity cycle, these rhythms correspond to the periods of the eccentricity, obliquity, and precession index. Tuning to orbital eccentricity cycles provides a high-resolution time scale for the Aptian. Correlation to the Cismon core (northern Italy) extends the tuning to the Aptian-Barremian boundary. The tuning indicates a minimum duration of 13.42 m.y. for the Aptian Stage, where previous estimates range from 6.4 to 13.8 m.y. The combined Aptian–Albian astronomical tuning of the entire 77-m-long Piobbico core (and part of the Cismon core) provides a 25.85-m.y.-long astronomically calibrated time scale for Earth history.

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