Neri Ciaranfi

Paleoclimatic record of a long deep sea core from the eastern Mediterranean

Abstract A deep-sea core over 16 m long from the crestal area of the Mediterranean Ridge has been investigated with different techniques, including quantitative micropaleontology, stable isotopes (measured on the epipelagic species Globigerinoides ruber and on the mesopelagic species Globorotalia inflata), and clay mineralogy. The resulting record of climatic fluctuations can be cross correlated to other Mediterranean cores by means of isochronous lithologies (tephra layers and sapropels). The climatic record of the Mediterranean is similar in character, phase, and chronology to the records investigated in the equatorial Pacific and in the Caribbean. Isotope stages 1 to 17 have been recognized. Cyclically repeated stagnant cycles resulting in sapropel deposition complicate both the isotopic and the faunal signal. The isotopic investigations reveal that the temperature change in the surface layers of the eastern Mediterranean was no greater than 8°C in the late “glacial” Pleistocene. The chronostratigraphic and biostratigraphic interpretation of Core KS09 indicate that the mean sedimentation rate was 2.4 cm/1000 years, a value very close to the 2.5 cm/1000 years calculated for the entire Quaternary section at DSDP Site 125, also located in the crestal area of the Mediterranean Ridge in the Ionian Basin. The base of KS09 is likely to be very close to the Brunhes/Matuyama boundary dated at 0.7 my.

CALCAREOUS NANNOFOSSIL EVENTS IN THE LOWER-MIDDLE PLEISTOCENE TRANSITION AT THE MONTALBANO JONICO SECTION AND ODP SITE 964: CALIBRATION WITH ISOTOPE AND SAPROPEL STRATIGRAPHY

We present quantitative data on calcareous nannofossil biostratigraphy in the section of Montalbano Jonico (Southern Italy). This is one of the candidate Global Statotype Section and Point (GSSP) of the Middle Pleistocene. The first common occurrence (FCO) and last common occurrence (LCO) of Reticulofenestra asanoi are well detectable in the section and are here proposed as additional events for improving biostratigraphic resolution in the interval corresponding to the transition between the small Gephyrocapsa Zone and Pseudoemiliania lacunosa Zone. The potential value of the bioevents is tested in a Mediterranean deep-sea core of ODP Site 964, located in the Ionian Sea. At Site 964 the FCO of R. asanoi occurs in the marine oxygen isotope stage (MIS) 30, and the LCO of the species correlates with MIS 23. The ages of the FCO and LCO of R. asanoi have been estimated at 1.06 Ma and 0.93 Ma respectively. The first occurrence (FO) of Gephyrocapsa sp. 3 has been correlated to MIS 25, both at Site 964 and at the Montalbano Jonico section. The age of the FO of Gephyrocapsa sp. 3 is estimated at 0.95 Ma, based on the astronomical datings of sapropels occurring at the Montalbano Jonico section. In addition, an interval of temporary disappearance of Gephyrocapsa sp. 3 has been identified within the P. lacunosa Zone. The beginning of this interval is correlated with MIS 20/19 and can be considered a reliable event in the Mediterranean area, occurring close to the Brunhes/Matuyama magnetic boundary. The recognized events provide a basis for interpreting the Montalbano Jonico section within a standard chronostratigraphic framework.

The Montalbano Jonico Section (Southern Italy): A Candidate for the GSSP of the Ionian Stage (Lower–Middle Pleistocene Boundary)

The Lower–Middle Pleistocene Subseries boundary and the Ionian Stage still lack formal ratification. The use of the name “Ionian” as a stage of the Middle Pleistocene follows Cita et al. (2006, 2008) and Gibbard et al. (2009). The GSSP of the Ionian Stage should be defined at a point close to the Matuyama–Brunhes (M–B) reversal, in a marine section exposed on land. However, magnetic reversal is considered as only one of multiple criteria that may be used for the definition of a GSSP (Head et al. 2008). The Montalbano Jonico section (Southern Italy) is a continuous marly–clayey marine succession, well exposed and astronomically calibrated, which extends from 1.24 to 0.645 Ma (Ciaranfi et al. 2009). It spans the interval from Marine Isotope Stage (MIS) 37 to 17/16 and covers, together with the Vrica section, the sedimentary record of the entire Calabrian Stage. The section encompasses MIS 19, whose base corresponds closely to the M–B boundary (Lisiecki and Raymo 2005); unfortunately, the M–B palaeomagnetic reversal was not identified in the Montalbano sediments (Sagnotti et al. 2010). The isotopic signals are considered acceptable for the definition of a boundary stratotype (Remane et al. 1996) and the practice has been recently adopted for the definition of the GSSP of the Serravallian Stage (Hilgen et al. 2010). The interval including MIS 19 is chronologically well constrained and is a maximum flooding surface, as shown by the occurrence of the Neopycnodonte palaeocommunity, and the mesopelagic tropical–subtropical Atlantic teleostean Bonapartia pedaliota marks the base of the interglacial. Evidence of glacio-eustatic sea level rise, correlated with MIS 19 and the M–B boundary, are well known in several geographical areas, supporting the wide traceability of this oxygen isotope shift. The onset of MIS 19 in the Montalbano Jonico section may represent an appropriate stratigraphic horizon for the definition of the GSSP of the Ionian Stage, also fulfilling the additional criteria of Remane et al. (1996) for boundary stratotype definition, such as continuous sedimentation, a high sedimentation rate, an absence of synsedimentary disturbance, and good preservation and protection of the section.