Foraminiferal record and astronomical cycles: An example from the Messinian pre-evaporitic Gello Composite Section (Tuscany, Italy)

A high resolution bio-magneto and cyclostratigraphical study has been carried out for the first time on Messinian pre-evaporitic marine deposits (Gello Composite Section) from the Volterra Basin (Italy). Since the investigated deposits manifest no evident lithological cyclicity, others records have been used to recognize the vidences of an astronomical periodicity. The distribution curves of planktonic and benthic foraminifera have been used for paleoenvironmental reconstruction. yclostratigraphical analyses have been based on: i) abundance fluctuations of Bolivina and Bulimina among the benthic foraminifera, Globigerinoides, Orbulina and Turborotalita among the planktonics; ii) CaCO3 content changes; and iii) Shannon-Weaver index variations relative to benthic assemblages. As a result, 18 precession-controlled cycles have been recognized. Moreover, the recognition of the C3An.1r, C3An.1n and C3r magnetozone and some biochronohorizons, have allowed the tuning of the studied section with the ATNTS (Astronomical Tuned Neogene Time Scale) using the Laskar 2001 (1,1.2) solution of the insolation curve. This multidisciplinary study strongly supports that the onset of evaporitic deposition in Tuscany and in other circum-Mediterranean type-successions, as the Abad Composite Section (Spain) and the Falconara Section (Sicily), was isochronous

First record of Bolivinita quadrilatera (Schwager) in Italian Pliocene (Southern Tuscany)

Bolivinita quadrilatera (Schwager) is recorded for the first time from Lower Pliocene (Globororalia puncticulata Zone) sediments of Southern Tuscany. Previously the taxon, known from Late Miocene to Recent, bas been recorded in the Mediterranean area only from Early Pleistocene. A complete description and a partial synonymy list of the species are given

Biostratigraphy and chronostratigraphy of the Maltese Lower Globigerina Limestone Member (Globigerania Limestone Formation): new preliminary data based on calcareous plankton

The preliminary results of the study carried out on calcareous plankton (foraminifera and nannofossils) assemblages from the Maltese Lower Globigerina Limestone are presented here. The Lower Globigerina Limestone (LGL) is the lowermost member of the Globigerina Limestone Formation, widely outcropping in the Maltese Archipelago; this member has been generally referred to the Early Miocene (Aquitanian). The investigation of 78 samples from 11 sections (encompassing the whole succession of the unit) on Gozo and Malta islands (one of them close to the type section of the formation) has allowed us to assign a Chattian age (Late Oligocene) to the Lower Globigerina Limestone Member (LGLM). Globigerinoides primordius, Paragloborotalia opima nana, P. pseudokugleri, Subbotina gortanii, Globoturborotalita angulisuturalis, G. anguliofficinalis, and Coccolithus miopelagicus, Cyclicargolithus abisectus, Dictyococcites bisectus, D. scrippsae, Helicosphaera recta, Sphenolithus cf. ciperoensis, S. dissimilis, Triquetrorhabdulus carinatus, Zygrhablithus bijugatus are taxa particularly significant of the foraminiferal and nannofossil assemblages respectively. In all the investigated sections, these taxa assure the assignment of the member to the lower part of planktonic foraminiferal P.22 Zone and nannofossil NP25 Zone. Thus, it has also been possible to estimate in biostratigraphic terms the hiatus between the Lower and the Middle Globigerina Limestone members, the latter being referable to the upper half part of the planktonic foraminiferal N4 Zone (upper part of N5 Zone-basal part of N7 Zone interval in Gozo) and to the nannofossil CN1 Zone (CN2 Zone in Gozo). This hiatus is emphasized also by the occurrence at the top of the LGLM of a hardground with overlying phosphatized elements such as nodules or pebbles. Calcareous plankton biostratigraphy, Chattian, Lower Globigerina Limestone, Maltese Island

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

Evoluzione tettonico-sedimentaria neogenica lungo una trasversale ai bacini di Volterra e della Val d’Elsa.

The tectono-sedimentary Neogene evolution of a key area of Southern Tuscany has been analyzed. The area is characterized by two extensional basins (the Volterra Basin to the west and Val d'Elsa Basin to the east) separated by a morphological and structural high (the "Dorsale Medio Toscana"). The analysis has been carried out along a cross section from the southwest edge of the Volterra Basin (Mazzolla-Castellina in Chianti) to the eastern edge of the Val d'Elsa Basin (Chianti Mountain). Six paleo-sections were reconstructed ranging in age from the Serravallian to the Recent. Biostratigraphic and paleoenvironmental information obtained from micropaleontological analyses has allowed the evaluaionn of fault activities in the two basins at the various stages of evolution. During Serravallian-early Tortonian the whole area was part of a single sedimentary basin: the Ponsano Basin. That is, there is no evidence to suggest that at that time the "Dorsale Medio Toscana" was a morphological high. During late Tortoian the "Dorsale Medio Toscana" developed and separated the basins of Volterra and Val d'Era. The separation was not complete, however, as indicated by identlcal ostracod assemblages in the two basins. The basins contain fluvial and lacustrine sediments. Rapid rise and partial emersion of the "Dorsale Medio Toscana" and possible presence of relatively steep slopes are suggested by conglomeratic debris flow deposits interbedded with lacustrine sediments. Furthermore, pebbles of conglomeratic layers of fluvio-lacustnne sequence were totally originated from the rocks of ligurian units and from the Ponsano Formation that formed the ridge bedrock. During early Messinian the "Dorsale Medio Toscana" was fully emerged, and separated completely the two basins. In fact, Messinian marine facies have been found in the Volterra Basin but not in the Val d'Elsa Basin. During late Messinian ("lago mare" phase) a connection was re-established between the two basins as indicated by identical microfaunistical assemblages. This connection must have developed elsewhere, because along the studied cross-section the "Dorsale Medio Toscana" remained a morphological high. During Pliocene the two basins behaved differently. The Volterra Basin experienced a continuous high rate of sedimentation, whereas the Val d'Era Basin experienced discontinuous, variable sedimentation. Furthermore during the early Mlddle Pliocene, subsidence affected the area studied and much of the "Dorsale Medio Toscana" was submerged except in the Spicchiaiola-Pignano region. Afterwards still in the Middle Pliocene, the whole area was affected by regional uplift, which led to a major marine regression everywhere in Southern Tuscany

Il plancton calcareo (Foraminiferi e nannofossili) del Miocene delle Isole Tremiti

The p1anktonic foraminifers and calcareous nannofossils assemblages of ten Miocene stratigraphic sections of the Tremiti Islands have been studied. The investigated succession includes the Cretaccio Formation (about 165 m thick) and the basal part (about 3 m thick) of the overling S. Nicola Formation. The first unit lies with angular unconformity on the S.Domino Formation (Oligocene in age) and its base (3-3.80 m) is composed of green (red when wheathered) glauconitic doloarenites which are often thinly stratified or laminitic and with Elasmobranch teeth and apatite grains. Carbonatic fraction is absent in the glauconitic doloarenites because of dissolution. They are followed by about 22 m of stratified ocraceous-yellow dolomitic limestones (the thickness of the strata is from decimetric to beyond 2 m), more arenaceous in the lower part and more marly in the upper part. The carbonates dissolution characterizes the lower part of this interval and decreases progressively upwards; so the calcareous plankton becomes abundant and well preserved from the upper part of the interval. However the major lithology of the Cretaccio Formation is represented by decimetric-metric light marly layers (in particular whitish and reddish bands are alterned) (about 140 m thick); the calcareous plankton is constantly abundan. In the uppermost part of the formation, an interval 3-5 m thick, rich in glauconite and fossils (especially Flabellipecten and Neopycnodonte) was observed. In the studied sections, the S.Nicola Formation conformably lies on the glauconitic calcarenites; previously, the Authors reported an unconformable boundary between the two formations. Only the lowermost part (3 m thick) of S.Nicola Formation has been studied; it is composed of yellowish calcarenites and the whitish limestones with Cardium and Serpulids assemb1ages (calcareous plankton is rare or absent, while microbenthos is abundant). In the succession all the planktonic foraminifers and nannofossils gones and subzones of the Langhian-Messinian interval were recognized; from the biostratigraphic point of view the succession encompasses the interval from Praeorbulina glomerosa s.l Zone (P. glomerosa sicana Subzone) and Discoaster exilis-Sphenolithus heteromorphus Zone (D. exilis-Helicosphaera ampliaperta Subzone) to ’Xon distinctive” Zone and Amaurolithus delicatus-A.amplificus Zone, respectively. For each biostratigraphic units we provide: the lower and upper boun- dary, the thickness, the reliability and the succession of the bioevents and a short description of the associations. In the S.Domino, Caprara and Cretaccio islands, the Cretaccio Formation is Langhian. A Burdigalian age (G. trilobus Zone and S. heteromorphus Zone of the foraminifers and calcareous nannofossi1s, respectively) for the lower part of the formation, glauconitic and barren of calcareous plankton could not be excluded. In the S. Nicola Island the Cretaccio Formation includes also the Serravallian, Tortonian and Messinian stages. In particular, the glauconite rich levels of the upper part of the unit belong to the last two stages representing a condensed and perhaps also discontinuous sedimentation, probahly due to strong currents effects. For the first time, a Messinian age for the upper part of the Cretaccio Formation and for the lowermost part of the S. Nicola Formation has been documented on the basis of the calcareous plankton. In the past, the S. Nicola Formation has been considered of Middle Pliocene age. The Messinian age of these sediments is also confirmed by the presence of the benthonic forarniniferal assernblages with Bulimina echinata, Bolivina dentellata and Rectuvigerina gaudrynoides. Through the new bio-chronostratigraphic framing, the Miocene sedirnentary succession of the Tremiti Islands is perfectly correlable to that of central-southern Salento Peninsula. Infact, the two areas are very similar for theirs lythologic, chronological and dynamic features. Also the closure of Miocene cycle sedimentation is synchronous in both localities and realized during Messinian. In appendix, the cornplete list of the taxa and their original references are added. Systematic, evolutionary, stratigraphic and bibliographic remarks have been carried out for many planktonic foraminifers