ISMAR, Italy

The Tyrrhenian stage of the Quaternary was introduced by Arturo Issel in this Academy over nineteen years ago, in 1914 for a time interval postdating the Sicilian and predating the Holocene. Largerly used in the past not only for the Mediterranean area, but worldwide, the term Tyrrhenian was abandoned in the last few years because it did not meet the strict requirements imposed by the international rules of stratigraphic nomenclature. A brief presentation of the original observational data and the significance of the fossil assemblage collected and investigated by Lovisato from the bay of Cagliari, ("Strombus-raised beach") containing a tropical fauna and related to a high sea-level stand, clearly shows that a strong climatic significance was given to the Tyrrhenian since the inception. The problem of the validation of the term Tyrrhenian is preceded by the presentation of a new data set arising from recent integrated investigations on a series of deep-sea cores and scientific drillings with continuous coring that form a 3000 km long E-W trans-mediterranean transect. Quantitative micropaleontology originating paleoclimatic and oxygen isotope curves, paleomagnetic reversals and astronomically driven sapropel cycles (in the eastern Mediterranean) are the proxies used to provide a well constrained stratigraphic framework and a series of independent correlation tools. It is now possible to discuss the Tyrrhenian as defined in land outcrops, where the stratigraphic record is necessarily discontinuous and correlations are often questionable, in the framework of a strongly and precisely correlated deep-sea record from the same area. Two options are considered, both plausible and consistent with Issel's original definition, that was formulated well before Milankovitch's discovery of orbital cycles and their influence on Quaternary climate. One option is to restrict the use of the term Tyrrhenian to the duration of isotopic substage 5e, i.e. the warmest part of the Last Interglacial, that corresponds to the Strombus-raised beach. The term Eemian (defined in a well in Amsterdam) has the same significance and is largely used in Europe. In this sense, the Tyrrhenian should be better defined as a climatostratigraphic unit, more than a chronostratigraphic unit. A second option is to define the Tyrrhenian as a chronostratigraphic unit (stage) for the Late Pleistocene, whose lower and upper boundaries have been internationally defined as coincident with Termination II (isotopic stage 6/5 boundary at approximately 130 000 yr BP) and Termination I (isotopic stage 2/1 boundary at 11500 yr BP). We prefer the second alternative, that will be discussed in an open forum setting at a Workshop planned for next fall in Spoleto, under the auspices of the Italian Commission on Stratigraphy. Since the International Commission on Stratigraphy recently decided not to use and formalize global stages and global stratotype sections and points (GSSP) for the Quaternary, but to use instead regional stages, we propose to use as regional stages for the Quaternary of the Mediterranean area the Calabrian for the Early or Lower Pleistocene, the Ionian for the Middle Pleistocene and the Tyrrhenian for the Late or Upper Pleistocene.