HIGH RESOLUTION CHRONOLOGY FOR LATE MIOCENE MEDITERRANEAN STRATIGRAPHIC EVENTS

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ASTRONOMICAL CALIBRATION OF THE SERRAVALLIAN/TORTONIANCASE PELACANI SECTION (SICILY, ITALY)

We performed a cyclostratigraphic study of a sedimentary sequence (Case Pelacani section) outcropping in the south-eastern margin of Sicily (Italy) and covering the Upper Serravallian/Lower Tortonian stratigraphic interval. Calcareous plankton biostratigraphic data reported in another paper proved that all the sequence of bio-events generally reported from just below and above the S/T boundary is present in the section. They allowed a detailed correlation with the Gibliscemi section.  Preliminary paleomagnetic data suggest that a secondary remagnetization  component prevents the recognition of the correct sequence of paleomagnetic chrons along the studied interval. The sedimentary record has been compared, on the basis of an integrated calcareous plankton biostratigraphy, with that of the Gibliscemi section. Cyclostratigraphic analysis of the lithological patterns recognized throughout the succession and the application of spectral methodologies to the abundance fluctuations of the planktonic foraminifer Globigerinoides quadrilobatus highlighted the presence in the signal of the classic Milankovitch frequencies (precession, obliquity and eccentricity). Correlation of the lithological patterns and of the different frequency bands extracted by numerical filtering from the faunal record with the same components modulating the insolation curve provided an astronomic calibration of the sedimentary record and, consequently, a precise age for all the calcareous plankton bioevents recognized throughout the studied interval.&nbsp

ASTRONOMICAL CALIBRATION OF THE UPPER LANGHIAN/LOWERSERRAVALLIAN RECORD OF RAS IL PELLEGRIN SECTION (MALTA ISLAND, CENTRAL MEDITERRANEAN)

A high-resolution geochemical and micropaleontological data set has been obtained from the uppermost Langhian/lower Serravallian marly sediments of the Ras il Pellegrin section (Malta Island). A combination of the recorded stratal organization with the results of spectral analyses performed on CaCO3 data and faunal signals shows a dominance of the classic Milankovitch periodicities as modulating forcing of the studied succession. The application of band-pass filters allowed us to select the different Milankovitch frequencies (precession, obliquity and short- and long-eccentricity) from the original faunal and geochemical signals and to compare them with the same components of the astronomical curve. The reliability of the short-term astronomical tuning has been tested by using the larger-order cyclicity (100-400 kyr) as control. The good match of the different records with the selected insolation curve is consistent with the results of the cross-spectral analysis showing high coherency values in all the considered frequency bands. The calibration provided astronomical ages for the sedimentary cycles and consequently for all the bioevents recorded in the section. In particular, an age of 13.59 Ma has been obtained for the last occurrence (LO) of Sphenolitus heteromorphus, at present considered the best bioevent useful for recognizing the Langhian/Serravallian boundary. Moreover, an age of 12.62 Ma has been obtained for the first occurrence (FO) of Paragloborotalia partimlabiata.

PLIOCENE-EARLY PLEISTOCENE ASTRONOMICALLY FORCED PLANKTONIC FORAMINIFERA ABUNDANCE FLUCTUATIONS AND CHRONOLOGY OF MEDITERRANEAN CALCAREOUS PLANKTON BIO-EVENTS

The absolute age estimates for calcareous plankton events proposed by the writer in a recent paper are discussed according to the new proposed paleomagnetic time scales. A re-interpretation of the sequence of lithological cycles recognized in the "Rossello composite section" makes their number perfectly comparable with the number of planktonic foraminifera abundance fluctuations in the same stratigraphic interval. An absolute age of 5.33 MA is estimated for the base of the Pliocene, as defined in the Capo Rossello section. Periodicity of the relative abundance fluctuations of the planktonic foraminiferal assemblages during the Early Pleistocene stratigraphic interval is estimated at about 41 kyr, well comparable with the periodicity of the obliquiry astronomical cycles. By correlation of the sequence of biostratigraphic events recorded in the Early Pleistocene interval in the Mediterranean sections with the sequence of abundance fluctuations, their absolute ages have been obtained, as well as the absolute age of chronostratigraphic boundaries. The base of the Pleistocene is at 1.83 MA and the top of the Early Pleistocene, coincident with the top of the Sicilian, is at 0.89 MA. A re-evaluation of the Oxygen isotopic Stages of the upper Singa section is proposed, on the base of paleomagnetic and calcareous plankton biostratigraphic data reported for this section. Correlation with the North Atlantic Site 607 proved that rhe G. oceanica s.l. FO, the C. macintyrei LO and rhe Gephyrocapsa sp.3 FO are slightly diachronous between the Mediterranean and the mid-North Atlantic high latitudes

MEDITERRANEAN PLIOCENE BIOCHRONOLOGY: AN HIGH RESOLUTION RECORD BASED ON QUANTITATIVE PLANKTONIC FORAMINIFERA DISTRIBUTION

Quantitative analysis of planktonic foraminiferal assemblages from Mediterranean Pliocene sections evidenced several fluctuations in abundance which for 4 taxonomic units (Globorotalia inflata group, Globigerinoides ruber, Globigerinoides obliquus and Globigerinoides quadrilobatus) occur cyclically. Estimate of cycle periodicity, using paleomagnetically or biochronologically absolute dated calibration points, proves that abundance fluctuations display a periodicity of about 20 kyr in the lower part of the Pliocene and of about 40 kyr in the upper part of the Pliocene, thus correlatable to the precession and obliquity astronomical cycles respectively. Based on the sequence of abundance fluctuations a precise age estimate was obtained for several biostratigraphic events. Comparison of the ages estimated of the Late Pliocene bio-events between the Mediterranean and North Atlantic regions shows that possible diachroneities occur within a range not greater than 0.1 MA. A more detailed biostratigraphic scheme for the planktonic foraminifera, including four new subzones, is proposed for the Mediterranean area

PALEOCEANOGRAPHIC CONDITIONS AT THE BASE OF THE PLIOCENE IN THE SOUTHERN MEDITERRANEAN BASIN

Detailed quantitative analyses of the benthic foraminiferal assemblage from the base of the Pliocene sections (M Pl 1 biozone) at Eraclea Minoa and the Capo Rossello area (southern Sicily) documented fluctuating paleoecological conditions indicative of a dysaerobic bottom water environment. In particular, we identify the Uvigerina pygmaea-peregrina Event, which in the area studied covers the upper part of the M Pl 1 biozone. According to the integrated calcareous plankton biostratigraphy and to cyclostratigraphy based on fluctuations in the relative abundance of fauna in the planktonic foraminiferal assemblage, the base of the Uvigerina pygmaea-peregrina Event coincides with cycle 6a and its top coincides with cycle 10 in the Sicilian sections.A similar temporal correlation is seen in the Tyrrhenian basin (ODP Site 652). On the contrary, the Uvigerina pygmaea-peregrina Event covers a longer time interval in the Jonian basin, where it is recognizable from cycle 4 to cycle 12. The Uvigerina pygmaea-peregrina Event is time equivalent with an interval characterized by cyclically repeated sapropels in the eastern Mediterranean basin. As a matter of fact, 10 sapropels are present in the deep-sea sediments (ODP Site 969) and 10 Uvigerina pygmaea-peregrina peaks are present in the Roccella Ionica - Capo Spartivento composite section in the M Pl 1- lowest M Pl 2 biozones. The diachronous termination of the Uvigerina pygmaea-peregrina Event may indicate that well-oxygenated bottom conditions were established earlier in the western than in the eastern Mediterranean basin. Both the sapropels interval in the eastern Mediterranean and low-oxygen bottom conditions in the Jonian basin occurred during a time interval which straddles a minimum of eccentricity in the astronomical record.  &nbsp

HIGH RESOLUTION BIOCHRONOLOGY IN THE MONTE NARBONE FORMATION OF THE CAPO ROSSELLO SECTION AND THE MEDITERRANEAN FIRST OCCURRENCE OF <em>GLOBOROTALIA TRUNCATULINOIDES</em>

Quantitative analysis on the planktonic foraminiferal assemblages in the Late Pliocene - Early Pleistocene segment of the Capo Rossello section evidences the same number of relative abundance fluctuations of the Globigerinoides ruber taxonomic unit recorded in the same stratigraphic interval of other Mediterranean sequences. Between the Globorotalia inflata FO and the Discoaster brouweri LO 4 relative abundance fluctuations are present. Since the D. brouweri LO is recorded in the Mediterranean basin below the base of the Olduvai magnetic event and in coincidence of relative abundance fluctuation 73, the Gt. inflata FO is coincident with fluctuation 80. The first appearance ol Globorotalia truncatulinoides is recorded on the second fluctuation above the Gt. inflata FO and on the second fluctuation below the D. brouwueri LO. Therefore the Gt. truncatulinoides FO is coincident with fluctuation 77. The absolute age proposed for these 3 bio-events is 1.99,2.07 and 2.13 MA respectively. The most important calcareous nannofossil events, recognized by quantitative analysis, have been correlated to the abundance fluctuations of the Globigerinoides ruber taxonomic unit

THE GELASIAN STAGE: A PROPOSAL OF A NEW CHRONOSTRATIGRAPHIC UNIT OF THE PLIOCENE SERIES

A new Stage, the Gelasian, is proposed as the third upper subdivision of the Pliocene Series. The GSSP of the base of the Gelasian Stage and of the Middle Pliocene-Upper Pliocene boundary is coincident with a "sapropel" level which outcrops in the Monte San Nicola section, near Gela (Southern Sicily, Italy). This level corresponds to the Mediterranean Precessional Related Sapropel 250 of Hilgen (1991)and has an astrochronological age of 2.589 Ma. It correspondes to the oxygen isotopic Stage 103 of Raymo et al.(1989) and in the boundary stratotype section it outcrops 1 meter above the Gauss-Matuyama paleomagnetic boundary. Astrochronologic, magnetostratigraphic, biostratigraphic and climatostratigraphic elements to approximate the GSSP of the Gelasian outside the stratorype section are presented

CALCAREOUS PLANKTON HIGH RESOLUTION BIOSTRATIGRAPHY (FORAMINIFERA AND NANNOFOSSILS) OF THE UPPERMOST LANGHIAN – LOWER SERRAVALLIANRAS IL-PELLEGRIN SECTION (MALTA)

Results of an integrated biostratigraphic (calcareous nannofossils and planktonic foraminifers) study of the uppermost Langhian/lower Serravallian Ras il-Pellegrin section (Fomm ir-Rih Bay – Malta) are presented. This high resolution study allowed us to recognise several useful lower Serravallian bio-events in the Mediterranean and to provide a detailed distribution pattern of the recognised taxa. The astrochronological calibration, reported in a different paper of this volume, provided absolute ages of the bio-events of the studied section. The LO (Last Occurrence) of Globorotalia peripheroronda at 13.39 Ma, the Paragloborotalia partimlabiata FO (First Occurrence) at 12.62 Ma and the Paragloborotalia mayeri FCO (First Common Occurrence) at 12.34 Ma among the planktonic foraminifera, and the Sphenolithus heteromorphus LO at 13.59 Ma, the Cyclicargolithus floridanus LCO (Last Common Occurrence) at 13.39 Ma, the Reticulofenestra pseudoumbilicus FCO at 13.32 Ma, the Calcidiscus macintyrei FO at 12.57 Ma and the Calcidiscus premacintyrei LCO at 12.51 Ma among the calcareous nannofossils, were recorded. Moreover, our results confirm the LO of S. heteromorphus as a fairly synchronous event in the Mediterranean and in the Atlantic and Pacific Oceans. Therefore, we suggest a lithological level near or coincident with this event for the definition of the GSSP of the Serravallian. The Ras il-Pellegrin section may be considered a good candidate for this definition.&nbsp

ASTROCHRONOLOGICAL CALIBRATION OF THE UPPER SERRAVALLIAN/LOWER TORTONIAN SEDIMENTARY SEQUENCE AT TREMITI ISLANDS(ADRIATIC SEA, SOUTHERN ITALY)

A high resolution cyclostratigraphic study was carried out on a cyclicaly bedded succession of late Middle Miocene deep marine deposits from the Tremiti Islands, Adriatic sea (Italy). Astronomical calibration of the sedimentary cycles provides absolute ages for different calcareous plankton bioevents, widely used for intra Mediterranean correlation, in the interval between 11.12 and 12.60 Ma. The sedimentary record of the S. nicola composite section consists of an alternation of indurated, withish coloured, CaCo3 rich and grey less indurated, CaCo3 poor marly beds, at times replaced by red coloured CaCo3 poor marls. Results of direct correlation between the La 90 (1,1) solution of the insolation curve and the cyclic lithologic patterns occurring in the studied sections, combined with results of spectral methodologies applied on the climate sensitive data (CaCo3 and Globigerinoides) showed that the classic Milankovitch periodicity can be represented through the modulation forcing of the studied sedimentary records.&nbsp