International Geologiical Congress - Oslo 2008


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HPS-05 Recent developments in the Geologic Timescale


Towards an astronomical-tuned Cenozoic time scale


Frits Hilgen, Utrecht University (Netherlands)
Lucas Lourens, Utrecht University (Netherlands)
Klaudia Kuiper, Vrije Universiteit (Netherlands)
Heiko Palike, University of Southampton (United Kingdom)
Ursula Rohl, Bremen University (Germany)
Thomas Westerhold, Bremen University (Germany)


Recent progress demonstrates that an astronomical-tuned Geological Time Scale (AGTS) for the Cenozoic is now within reach. Critical are the development of a new numerical solution for the Solar System accurate over the last 50-60 million years, the recovery of deep-sea successions suitable for tuning and the intercalibration with the 40Ar/39Ar and U/Pb radio-isotopic dating methods, the latter providing tight constraints for the astronomical calibration of pre-Neogene successions.

The entire Neogene was tuned in GTS2004 and only underwent minor refinements and modifications during the last years. Significant progress has been made in the tuning of the Paleogene. Pacific ODP Site 1218 with an excellent magnetostratigraphy and calcareous plankton biostratigraphy was used to tune the entire Oligocene, while attempts have also been made to tune the Eocene-Oligocene boundary stratotype section at Massignano. Tuning of the (younger part of the) Eocene remains problematical but will be the subject of, e.g., scheduled IODP Expeditions 317/319 in the Equatorial Pacific. A preliminary tuning of the older part of the Eocene was presented in three papers and included both the Paleocene-Eocene boundary, and the PETM and ELMO hypothermal events.

The entire Paleocene was recently tuned and three options with a ∼400-kyr age difference were presented, resulting in ages of 65.28, 65.68, 66.08 Ma for the K/Pg boundary. Although option three is consistent with a revised 40Ar/39Ar age of 65.95 Ma for the boundary using the astronomical age of 28.201 ± 0.023 Ma for the FCT sanidine standard, the key question is whether the full error propagation will allow to constrain the astronomical tuning of the K/Pg boundary on the 400-kyr eccentricity scale. This problem may delay the construction of a full astronomical-tuned time scale for the Paleocene.


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