Improving the Neogene Tuned Time Scale

Abstract

Orbital tuning and understanding climate response to astronomical forcing in the Miocene requires detailed knowledge of the accuracy of the astronomical solution used to compute insolation and orbital target curves for paleoclimatic studies. Initially, an algorithm to extract colour data excluding the effect of cracks is presented and applied to a drill core record from the western equatorial Atantic Ceara Rise from ca. 5 to 14.4 million years before present. It is demonstrated for some examples that tuned time scales can be tested using precession and eccentricity pattern. Quantitative colour records of precession-obliquity interference recorded in two successive 2.4 Myr eccentricity minima (9-9.6 and 11.5-12.1 Ma) in the Monte dei Corvi section in northern Italy are used to constrain the accuracy of the orbital solution, using the assumption of a direct response of sapropels to insolation. This quantitative approach results in an uncertainty of the astronomically tuned age models of ± 0.8 kyr for the 9-9.6 Ma interval, and of +4/‑1 kyr for the 11.5-12.1 Ma interval. This (un)certainty limits the precision of determining phase relations, but also improves our understanding of the limitations of tuned time scales and determining phase relations in the Miocene. Further, it is demonstrated that the tuning procedure can have a major impact of phases determined from tuned time scales. Finally, the well understood time scale is applied to determine response times of oxygen isotopes from the equatorial Atlantic Ceara Rise, potentials and pitfalls are discussed.