AN OVERVIEW OF THE POST-MESSINIAN PALEOENVIRONMENTAL HISTORY OF THE WESTERN MEDITERRANEAN

A review of the Pliocene-Pleistocene paleoenvironmental history of the western Mediterranean is presented based on micropaleontological and geochemical studies of Ocean Drilling Program (ODP) leg 107 material and marine outcrops in southern Italy. The calcareous plankton biochronology proposed for the Mediterranean by Rio et al. (1990 and 1991a) provides the necessary age control for determining the timing of major climatic and oceanographic changes in the region. The early Pliocene period in the Mediterranean was not a time of warm, stable climate; rather, it was marked by relatively high-amplitude climatic oscillations. In marginal areas, these climatic oscillations resulted in the rhythmic deposition of limestone-marl couplets which have an average duration of approximately 19,000 years. It is proposed that these sedimentary couplets are the result of precessionally induced changes in monsoon intensity which in turn cause variability in coastal divergence and upwelling. The delta O-18 and the calcareous plankton (foraminifera and coccoliths) records for Tyrrhenian Sea ODP site 653 reveal a cooling of surface waters at similar to 3.1 Ma. Coincident with this cooling is an increase in the frequency of diatomite formation in southern Italy (Bianco section). The global cooling at similar to 2.4 Ma and the associated expansion of northern hemisphere glaciation resulted in a shift to more arid conditions in the Mediterranean region. This climate change may have altered the Mediterranean water balance, resulting in the establishment of anties-tuarine water exchange with the Atlantic at this time. The delta O-18 record for site 653 is also marked by a sharp cooling across the Pliocene/Pleistocene boundary. In the boundary stratotype section at Vrica, this cooling is manifested as an increase in the abundance of the planktonic foraminifer Neogloboquadrina pachyderma.