Astronomically calibrated cyclostratigraphy relies on correct matching of observed sedimentary cycles to predicted astronomical drivers such as eccentricity, obliquity, and climate precession. However, the periods of these astronomical cycles, in the past, are not perfectly known because: (i) they drift through time; (ii) they overlap; and (iii) they are affected by the poorly constrained recession history of the Moon. This paper estimates the resulting uncertainties in ancient Milankovitch cycle periods and shows that they lead to: (i) problems with using Milankovitch cycles for accurate measurement of durations (potential errors are around 25% by the start of the Phanerozoic); (ii) problems with correctly identifying the Milankovitch cycles responsible for observed period ratios (e.g., the ratio for long-eccentricity/short-eccentricity overlaps, within error, with the ratio for short-eccentricity/precession); and (iii) problems with verifying that observed cycles are Milankovitch driven at all (the probability of a random period ratio matching a predicted Milankovitch ratio, within error, is 20–70% in the Phanerozoic). Milankovitch-derived ages and durations should therefore be treated with caution unless supported by additional information such as radiometric constraints.

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