Globorotalia truncatulinoides (d'Orbigny) in the Mediterranean Upper Pliocene geologic record

Globorotalia truncatulinoides truncatulinoides (d'Orbigny) is recorded in Mediterranean sections for a short interval just prior to the Discoaster brouweri Tan Sin Hok extinction. While this occurrence is time-equivalent to its first evolutionary appearance in oceanic areas, it is recorded in levels that are Late Pliocene (Piacenzian) in age. Furthermore, in the Mediterranean this event is close to the Globorotalia inflata (d'Orbigny) first occurrence, which marks the base of the Upper Pliocene according to Mediterranean scholars, who use a three-fold chronostratigraphic subdivision of the Pliocene. Since Globorotalia truncatulinoides truncatulinoides is widely used in oceanic areas to recognize the base of the Pleistocene, the same time interval (around 2.0 to 1.7 Ma) is ascribed to the upper Pliocene by some Mediterranean scholars and to the Pleistocene by workers in oceanic sediments. The abandonment of the tripartition of the Pliocene generally used in the Mediterranean is suggested, since in this subdivision the 'Upper Pliocene' is a short-time interval whose duration is within the accepted error for recognizing the base of the Pleistocene in many areas. Since the Plio-Pleistocene boundary is close to the top of the Olduvai subchron and the Globorotalia truncatulinoides truncatulinoides first evolutionary occurrence is about 0.1 Ma below this subchron, the use of other biostratigraphic events, whenever possible, is recommended for a more precise recognition of this boundary outside the type area.