Lucilla Capotondi

Late Quaternary central Mediterranean biochronology

Jorissen, F.J., Asioli, A., Borsetti, A.M., Capotondi, L., De Visser, J.P., Hilgen, F.J., Rohling, E.J., Van der Borg, K., Vergnaud Grazzini, C. and Zachariasse, W.J., 1993. Late Quaternary central Mediterranean biochronology. Mar. MicropaleontoL, 21: 169-189. A high-resolution biochronology is presented for the Late Quaternary of the central Mediterranean. In the Late Pleistocene-Holocene successions three assemblage zones are distinguished on the basis of frequency patterns of planktic foraminifera. The age of these zones is determined by Accelerator Mass Spectrometry (AMS) t4C dating. The zonal boundaries are dated at 12,700 yr B.P. (the end of Termination la) and 9600 yr B.P. (the start of Termination Ib), respectively. The AMS dates show that major changes in the planktic and benthic realms occurred synchronously over wide areas, although records of individual species may show important regional differences. In the studied areas, resedimentation processes revealed by anomalous successions of 14C dates, play a far more important role than indicated by the sedimentological and micropaleontological data. Possibly these processes contribute to the very high accumulation rates in the glacial Zone IlL Although the AMS technique has increased the accuracy of laC-measurements, of older carbonate may still lead to substantial age differences between areas with different sedimentary regimes.

The Tyrrhenian stage in the Mediterranean: definition, usage and recognition in the deep-sea record. A proposal

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 theStrombus-raised beach. The term Eemian (defined in a well in Amsterdam) has the same significance and is largerly 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.RiassuntoIl piano Tirreniano del Quaternario fu proposto da Arturo Issel proprio in questa Accademia dei Lincei nel 1914. La sua posizione stratigrafica si estendeva dal Siciliano (definito da Doderlein nel 1872) all’Olocene. Mentre sia il Siciliano che il Calabriano che lo precede sono caratterizzati da associazioni fossilifere fredde, il Tirreniano si distingue per una fauna decisamente calda, associata a evidenze di alto livello del mare. Dopo una introduzione che riassume e inquadra le conoscenze locali sugli affioramenti, il lavoro contiene una nuova documentazione riguardante il record stratigrafico di mare profondo recentemente acquisito mediante perforazioni scientifiche in carotaggio continuo e lo studio integrato con metodiche diverse di carote di mare profondo. Il materiale studiato proviene dai bacini di Alboran, balearico, tirrenico, ionico e levantino e costituisce un transetto E-W di circa 3000 km. A differenza del record di terra, quello sottomarino è continuo e permette delle correlazioni precise, di carattere fisico, chimico e biologico. È quindi possibile inquadrare il Tirreniano osservato a terra in un contesto regionale e globale di ampio respiro. Nella discussione vengono proposte due opzioni, entrambe compatibili con la definizione originale di Issel: la prima privilegia la connotazione paleoclimatica, che identifica il Tirreniano con la spiagge aStrombus, legate a una grande trasgressione marina verificatasi nell’ultimo periodo interglaciale (substadio isotopico 5e) di breve durata e corrispondente all’Eemiano del nord-Europa. La seconda opzione privilegia il significato cronostratigrafico del Tirreniano, che viene proposto come piano regionale valido per la regione mediterranea per il Pleistocene superiore. Questa seconda opzione è preferita alla prima ed è consona con le direttive della Commissione Internazionale di Stratigrafia, che ha recentemente deciso di non riconoscere unità cronostratigrafiche globali, né di validare stratotipi di limiti di carattere globale (GSSP) per il Quaternario, ma di riconoscere formalmente limiti ben definiti fra il Pleistocene inferiore, medio e superiore. Questa proposta, che identifica il Tirreniano con il Pleistocene superiore, verrà presentata e discussa in unworkshop indetto dalla Commissione Italiana di Stratigrafia che si terrà a Spoleto nel prossimo settembre.

Past diatom blooms and benthonic foraminifera extinction detected in old Adriatic sediments

The finding in two cores, collected in the Southern Adriatic, of sediments rich in diatoms and radiolaria and almost completely lacking in benthic forams, testifies to an environmental situation comparable with that in the Northern Adriatic. This situation must have persisted for long enough to be registered in the sediment. It is interpreted as the Adriatics response to the extreme oceanographic conditions causing deposition of the Sapropel S1 in the Eastern Mediterranean.