Extending the astronomical (polarity) time scale into the Miocene

An astronomical time scale is presented for the late Miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the Mediterranean to the 65 degrees N summer insolation curve of La90 [1,2] with present-day values for the dynamical ellipticity of the Earth and tidal dissipation by the moon. This correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals, and planktonic foraminiferal and dinoflagellate events. The Tortonian/Messinian (T/M) boundary placed at the first regular occurrence of the Globorotalia conomiozea group in the Mediterranean is dated at 7.24 Ma. The duration of the Messinian is estimated at 1.91 Myr because the Miocene/Pliocene boundary has been dated previously at 5.33 Ma [3]. The new time scale is confirmed by 40Ar/39Ar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the Mediterranean Messinian.