Silvia Spezzaferri,2 Maria B. Cita,3 and Judith A. McKenzie2


Continuous sequences developed across the Miocene/Pliocene boundary were cored during Ocean Drilling Project (ODP) Leg 160 at Hole 967A, located on the base of the northern slope of the Eratosthenes Seamount, and at Hole 969B, some 700 km to the west of the previous location, on the inner plateau of the Mediterranean Ridge south of Crete. Multidisciplinary investigations, including quantitative and/or qualitative study of planktonic and benthic foraminifers and ostracodes and oxygen and carbon isotope analyses of these microfossils, provide new information on the paleoceanographic conditions during the latest Miocene (Messinian) and the re-establishment of deep marine conditions after the Messinian Salinity Crisis with the re-colonization of the Eastern Mediterranean Sea in the earliest Pliocene (Zanclean).

At Hole 967A, Zanclean pelagic oozes and/or hemipelagic marls overlie an upper Messinian brecciated carbonate sequence. At this site, the identification of the Miocene/Pliocene boundary between 119.1 and 119.4 mbsf, coincides with the lower boundary of the lithostratigraphic Unit II, where there is a shift from a high content of inorganic and non-marine calcite to a high content of biogenic calcite typical of a marine pelagic ooze. The presence of Cyprideis pannonica associated upward with Paratethyan ostracodes reveals that the upper Messinian sequence is complete. The stable isotope composition of C. pannonica indicates that this crustacean lived in a Lago Mare environment characterized by brackish water, distinctly different from the marine environment. At Hole 969B, the identification of the Miocene/Pliocene boundary coincides with a marked lithologic change between 97.1 and 97.2 mbsf. The marine sediments directly overlie latest Messinian Lago Mare facies deposits comprising dark gray clay. The presence of planktonic foraminifers associated with brackish water ostracodes in Hole 967A, and with the gray clay in Hole 969B, may indicate temporary incursions of Atlantic water into a fully Lago Mare environment. This interpretation is also supported by the trends in the isotopic composition of the ostracodes and planktonic foraminifers.

After the Messinian Salinity Crisis, benthic foraminifers slowly repopulated the Eastern Mediterranean seafloor during the Sphaeroidinellopsis acme event (Biozone MPl1). The gradual ingression of typical deep Atlantic benthic foraminifers, Parrelloides bradyi and P. robertsonianus, and the presence of Globorotalia menardii (planktonic foraminifer) coincident with the boundary between the biozones MPl1 and MPl2 indicate that an efficient connection between the Atlantic Ocean and the Eastern Mediterranean Sea was re-established in this interval.

1Robertson, A.H.F., Emeis, K.-C., Richter, C., and Camerlenghi, A. (Eds.), 1998. Proc. ODP, Sci. Results, 160: College Station, TX (Ocean Drilling Program).
2Geologisches Institut, ETH-Zentrum, Sonneggstrasse 5, 8092, Zurich, Switzerland. silvia@erdw.ethz.ch
3Dipartimento di Scienze della Terra, Universitá di Milano, Via Mangiagalli 34, 20133, Milano, Italy.