Improved Age Calibration of the O-25 Ma (Miocene- Pleistocene) Geomagnetic Polarity Time Scale

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9405347 Swisher This project is intended to greatly improve the temporal calibration of the geomagnetic polarity time scale (GPTS) in the O- 25 Ma age range (Miocene-Pleistocene). Currently, calibration of the GPTS in this time interval is based on three radioisotopic tie- points; 2.8 Ma, 14.8 Ma and 23.8 Ma. We propose to obtain between twenty and thirty high-precision 40Ar/39Ar dates for specific reversals in this time interval from a variety of lmcations and geologic settings, including the Mediterranean, East Africa, Iceland, and North America. This project is partly an outgrowth and synthesis of several ongoing research efforts by the PI's whose integration will increase the efficiency and timeliness of obtaining accurate radioisotopic tie-points will produce, for the first time, a GPTS based on the highest quality 40Ar/39Ar ages obtainable, one that is capable of rigorously testing orbitally- tuned time scales beyond the Miocene/Pliocene boundary. This intercomparison will help evaluate the causes and timing of global climate change, and will also be useful in assessing the ages of 40Ar/39Ar ages obtainable, one that is capable of rigorously testing orbitally-tuned time scales beyond the Miocene/Pliocene boundary. This intercomparison will help evaluate the causes and timing of global climate change, and will also be useful in assessing the ages of 40Ar/39Ar dating standards for application well beyond the time range covered by this project.