Gianfranco Salvatorini

CALCAREOUS PLANKTON HIGH RESOLUTION BIO-MAGNETOSTRATIGRAPHY FOR THE LANGHIAN OF THE MEDITERRANEAN AREA

High-resolution quantitative and qualitative analyses of the planktonic foraminifer and calcareous nannofossil content have been carried out on three Middle Miocene sections, from the Mediterranean area. Such sections (Cretaccio section, Tremiti Islands, Southern Italy; Moria section, Marche Region, Central Italy; DSDP Site, 372 succession, Balearic Basin), all well known in the literature, have been chosen because of their high-quality biostratigraphic potential. Remarkable magnetostratigraphic data were provided by the Site 372 succession where all chrons and subchrons of the interval C5Br-C5AAn have been recognised. The investigated interval falls between the First Occurrence (FO) of Praeorbulina glomerosa sicana and the Last Occurrences (LO) of Sphenolithus heteromorphus and Globorotalia peripheroronda. The LO of S. heteromorphus was detected in the uppermost part of the investigated sequence of Site 372 at the same stratigraphic level as the G. peripheroronda LO. A drastic decrease in abundance of S. heteromorphus (Last Common Occurrence -LCO) was detected slightly below its last occurrence; this event is well correlatable with the same event astronomically calibrated at Ras-il Pellegrin section (Malta Island), which has been recently ratified as the Global Stratotype Section and Point (GSSP) for the base of the Serravallian by the International Union of Geological Sciences. The stratigraphic correlation of the studied sections is based on first and last occurrences, abundance fluctuations of selected taxa and additional biohorizons. In particular the peculiar distribution pattern of some taxa, e.g. Paragloborotalia siakensis and Helicosphaera waltrans, offered the opportunity to increase the biostratigraphic resolution of the Langhian interval. The resulting integrated calcareous plankton bio-magnetostratigraphic scheme represents the downward extension of that one previously established for the Serravallian - Tortonian interval. The biostratigraphic correlation of the studied sections with the Langhian historical Stratotype pointed out its low degree of reliability. On the other hand, none of the sections here studied is suitable to be proposed as candidate for defining the Langhian GSSP. Thus the problem of finding, in the Mediterranean area, a valid section which could yield a new GSSP for the Langhian Stage is still open.

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.

NEW DATA ON MIDDLE TO LATE MIOCENE CALCAREOUS PLANKTON BIOSTRATIGRAPHY IN THE MEDITERRANEAN AREA

Planktonic foraminifera from one Atlantic Ocean (Site 397) and five Mediterranean sequences of middle to late Miocene age were investigated. The aim of the research was to refine the biostratigraphy of the Serravallian to early Tortonian interval and, since the recent literature provides no general consensus, to check the range of Neogloboquadrina acostaensis (Blow) and Paragloborotalia siakensis (Le Roy). Examination of planktonic foraminifera identified a succession of events which is, in part, new in the Mediterranean area, and documented an overlap in the distribution of N. acostaensis and P.lia siakensis . Based on the new data, the zonal scheme for the Serravallian to early Tortonian interval proposed by Iaccarino and Salvatorini (1982) and Iaccarino (1985) was emended. In particular, it was ascertained that the first occurrence (FO) of N. acostaensis falls in the upper part of the Serravallian, well before the last occurrence (LO) of P.lia siakensis . The new zonation was calibrated with the calcareous nannofossil zonation and the geomagnetic polarity time scale. In light of these new data, the events closest to the base of the Rio Castellania-Rio Mazzapiedi-Tortonian type-section are interpreted to be the LO of P.lia siakensis , the first common occurrence (FCO) of N. acostaensis , and the FO of Discoaster hamatus .. Therefore, the use of these events in selecting the GSSP of the Serravalian/Tortonian boundary is recommended.

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.

HIGH RESOLUTION CALCAREOUS PLANKTON BIOSTRATIGRAPHY OF THE SERRAVALLIAN SUCCESSION OF THE TREMITI ISLANDS (ADRIATIC SEA, ITALY)

The planktonic foraminifer and calcareous nannofossil content of two Middle Miocene sections of the Tremiti Islands (Southern Adriatic Sea) have been studied. The two sections are composed of marly limestones rich in calcareous plankton which show cyclic alternations of indurated (higher carbonate content) whitish and less indurated grey or reddish beds. The two sections represent a succession with a total thickness of 38 m. Samples have been collected at a mean spacing of 10-15 cm; qualitative analyses were performed on one sample per meter but quantitative analyses were made for each sample. The abundance fluctuations of several marker species proved to be a very useful tool to correlate the two sections. The astronomical calibration of the sedimentary cycles provided absolute ages for all the recognised calcareous plankton bioevents.

NEOGLOBOQUADRINA ATLANTICA PRAEATLANTICA , NEW SUBSPECIESFROM LATE MIDDLE MIOCENE

A new subspecies of Neogloboquadrina atlantica atlantica previously reported under different names, is here distinguished and named Neogloboquadrina atlantica praeatlantica . Its first occurrence into the Mediterranean dated at 11.78 Ma, is not evolutionary appearance but is related to a global climatic cooling which pushed southwards from high latitude this taxon; however, the area of its evolutionary appearance is not clearly defined; its extinction occurs within the Globigerinoides obliquus extremus Zone. N. atlantica atlantica which evolves from N. atlantica praeatlantica occurs in the Mediterranean at 11.15 Ma, just after the Mediterranean exit of Paragloborotalia siakensis (Le Roy).

NOTE GEOLOGICHE E STRATIGRAFICHE SULL'AREA DI PALMARIGGI (LECCE, PUGLIA)

The geological mapping and the biostratigraphic study of Neogene sediments outcropping near Palmariggi, a small area between Otranto and Maglie (Puglia), have been carried out. Above the dolomitic limestone units of the Cretaceous-Oligocene platform three sedimentary cycles have been recognized, one of Miocene and two of Pliocene age. The first cycle consists of two units: the Pietra leccese and the overlying Calcareniti di Andrano; the second cycle is represented by the Leuca Formation and the last cycle by the Uggiano la Chiesa Formation. The pre-Neogene units are affected by a folding episode with major structures trending NNW- SSE. A subsequent tectonic event characterized by folds with axial directions interferring with the previous one has been detected in the pre-Neogene units. The latter deformation affects also the Miocene successions. Both the previous deformative episodes control the outcrop distribution of the Neogene sediments, preserved in the low structural sites such as synclinal cores. In the Palmariggi area an extensional tectonics of pre-Pliocene age follows the folding related to the compressive episodes. The normal faults linked to this late extension, show a NNW-SSE trend.

The Miocene of Pianosa Island: key to understanding the opening of the Northern Tyrrhenian back-arc basin (Central Mediterranean)

The only place where Neogene–Quaternary rocks crop out for the entire Tuscan Archipelago in the Northern Tyrrhenian Sea is the island of Pianosa. In particular, the Miocene deposits record the depositional and tectonic evolution of the Northern Tyrrhenian region during this time period. These deposits are subdivided into two successions separated by a low-angle unconformity. The older, middle Burdigalian succession represents a calciturbidite shallow marine system, whereas the younger late Tortonian–early Messinian succession comprises a continental alluvial system that evolves upwards into a lagoonal–marginal marine environment. Here we present sedimentological, palaeontological and petrographical data that support a new stratigraphic and palaeogeographical framework for reconstructing the opening of the Northern Tyrrhenian back-arc basin. The early Miocene succession records a pre-rift marine depositional phase followed by a late Burdigalian–Langhian erosional phase. This was followed by a period of synrift continental-marginal deposition, as recorded by the late Miocene succession, terminated by an important phase of uplift, probably induced by the start of magmatic activity in the Tuscan Archipelago area.