Roberto Mazzei

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.

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.

Geological map of the Pliocene succession of the Northern Siena Basin (Tuscany, Italy)

Abstract Please click here to download the map associated with this article. The late Miocene-Pliocene sedimentary fill of the Siena Basin (Tuscany, Italy) consists dominantly of clastics and has internal architecture that reflects the interplay of tectonics, relative sea-level changes and climate variations. Pliocene sediments are extensively exposed and overlay both late Miocene deposits and pre-Neogene bedrock. Specifically, Pliocene basin margin sediments consist largely of sand with gravel and mud intercalations, deposited mainly in nearshore settings with minor fluvial depositional episodes. They grade basinward to dominantly offshore fines with intervening turbiditic sand bodies. New fieldwork revealed that basin margin deposits, notwithstanding lithologically rather homogeneous, are made of a variety of sedimentary facies and bear several unconformities. They have been traditionally described and mapped using lithostratigraphic criteria, that have proven to be unfit to represent such complex stratigraphic architectures. The aim of this paper is to describe the allostratigraphic architecture of the Pliocene deposits exposed in a marginal key-area (45 km) of the northern Siena Basin by means of a 1:10,000 scale geological map. The recognized succession of allostratigraphic units and their bounding discontinuities, along with new biostratigraphic data from calcareous plankton, provides new insights into the geological history of the Siena Basin and represents valuable constraints for long-distance correlation.

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.

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.

The Scaglia Toscana Formation of the Monti del Chianti: new lithostratigraphic and biostratigraphic data

The Scaglia Toscana Formation (Scisti Policromi Auctt.) is one of the most investigated formation of the Tuscane Nappe. The Formation is widely exposed in the Chianti Mounts and despite the number of studies in this area, some aspects remain poorly known and debated. In this paper new litho- and bio-stratigraphic data from eight key-sections distributed over the entire area are provided and discussed in order to clarify the stratigraphic relationshpis among different lithostratigraphic members, as well as the depositional ages of each member. The Formation deposited in the Cretaceous-Oligocene time interval and it can be subdivided into five lithostratigraphic members: i) the Argilliti di Brolio (wine-red shales with sporadic siliceous calcilutites and rare interbedded cherts); ii) the Marne del Sugame (red and pink marls, calcareous marls and marly limestones with interbedded calcarenitic beds and ruditic lens-shaped bodies including calcareous-siliceous clasts); iii) the Argilliti di Cintoia (grey-green to black shales, locally with manganese-rich siliceous calcilutites and cherts); iv) the Calcareniti di Montegrossi (thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds); and v) the Argilliti e Calcareniti di Dudda (alternating thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds). These members deposited in a marine environment and have been interpreted as deposited in a turbiditic system, in which shaly and calcareous turbiditic members have been attributed to a basin plain below the CCD, whereas the marls and marly limestones of the Marne del Sugame Member can be settled in a slope/ramp environment above or close to the CCD. Furthermore, the combination of these new data with structural informations coming from literatures allowed to a better paleogeographic reconstruction of the paleobasin. In order to better explain these data, the paper is accompanied by two geological maps realized in the past but never distributed. The two geological maps, at the scale of 1:25,000, cover the whole area from the Cintoia (south of Florence) to the San Gusme (north of Siena) villages.