A critical re-evaluation of the Miocene/Pliocene boundary as defined in the Mediterranean

Abstract

A critical re-evaluation of the Miocene/Pliocene (M/P) boundary as defined--informally--in the Mediterranean is presented. We show that ages reported earlier for this boundary (ranging from 4.81 to 4.93 Ma) do not imply any diachroneity of the basal Zanclean lithohorizon which reflects the Pliocene flooding of the Mediterranean and defines the M/P boundary. These ages most likely represent an artefact resulting from intraformational variations in sedimentation rate and inconsistent interpretation of coluor variations in terms of sedimentary cycles. The best estimate for the age of this boundary arrives at 4.86 Ma if the conventional geomagnetic polarity time scale (GPTS) of Berggren et al. [1] is used, and at 5.16 Ma if the new GPTS of Cande and Kent [2] is used. An age of 5.32 Ma is obtained if the astronomically calibrated time scale of Hilgen [3] is adhered to. Because of its presumably global paleoclimatological significance, the M/P boundary as currently defined in the Mediterranean is preferred to a redefinition of this boundary at the Gilbert/Chron 5 boundary in a continuous open-marine sequence outside the Mediterranean. In addition, this redefinition would lead to unnecessary confusion in global chronostratigraphy.