41. CALCAREOUS PLANKTON PLIOCENE-PLEISTO CENE BIOSTRATIGRAPHY IN THE TYRRHENIAN SEA (WESTERN MEDITERRANEAN, LEG 107) 1

The distribution of stratigraphically important calcareous nannofossils and planktonic foraminifera has been inves­ tigated in the Pliocene-Pleistocene sequences of ODP Sites 652, 653, and 654 (Tyrrhenian Sea-western Mediterranean). Semiquantitative and quantitative methods have been used, and an optimum relative sequence of bioevents based on the calcareous plankton groups has been established. About 30 bioevents in an interval of 5.0 m.y. are considered widely traceable in the area and reasonably synchronous. On the basis of those events, a correlation among the three investi­ gated sequences is presented. The drilling campaign of ODP Leg 107 in the Tyrrhenian Sea (western Mediterranean) had as one of its main target the Tyr­ rhenian Sea as a biostratigraphic type locality. The stratotype sections of all the chronostratigraphic units of the Pliocene and Pleistocene used are located in the circum-Tyrrhenian area. The recovery of a continuous and complete pelagic Pliocene-Pleisto­ cene sequence was considered extremely important as a deep-sea Mediterranean type section in which to cross-correla te various fossil group biostratigraphies with tephrochronology and stable isotopic stratigraphy. Hole 653A, drilled near DSDP (Deep Sea Drilling Project) Site 132 was specially dedicated to this strati­ graphic objective. Sites 652 and 654, respectively southeast and northwest of Site 653 (Fig. 1), also recovered fairly complete Pli­ ocene-Pleistocene sequences, useful for the same stratigraphic purpose. In this paper we present the results of an integrated study of calcareous nannofossils and planktonic foraminifers at Sites 653, 652, and 654. The succession of biostratigrap hic events provided by the two fossil groups is cross-correlated in order to check traceability and ranking of the events in the Tyrrhenian Sea and to establish an optimum sequence of calcareous plank­ ton events in the western Mediterranean basin.