Note micropaleontologiche sulla successione miocenica del Torrente Morra e su quella Pliocenica del Bacino dei Fiumi Tora e Fine (Provincie di Livorno e Pisa)

The Neogene sediments of the northern-central sector of the Fine-Tora rivers basin, located in Southern Tuscany (about 15 km east of Livorno City) have been examined. The analyses have been carried out on 10 stratigraphic sections. The sections have been chiefly analyzed in order to their micropaleontolagical content (Foraminifers. Ostracods and calcareous nannaplancton). The aim of the work has been to reconstruct the stratigraphic evolution of this basin sector and to furnish the micropaleontological setting of the formations. The Miocene succession consists of deposits of three sedimentary episodes and it is well represented in the Morra Stram Section. The first episode is represented by sediments, mainly conglomerates, of fluvio-lacustrine environment : and it is Turolian in age (Upper Tortonian). This episode is related to the "Serie Lignitifera" (a group of deposits widespread in Southern Tuscany). In these sediments, only vegetal remains and rare Ostracods (Iliocypris sp. and Candona sp.) have been found. The second episode is unconformable on the former. Il is represented by early Messinian ("Non distinctive Zone" of Foraminifers, upper part of Amaurolithus delicatus – A. amplificus of the calcareous nannoplankton) reef limestones, calcareous or c1ayey marls sometimes laminated and diatomitic, and gypsum. With the exception of the barren gypsum and diatomitic marls, where rare diatoms have been found, the other lithology contains rests of various organisms: planktic and benthic Foraminifers, calcareous nannofossils, Ostracods, Radiolarians, Diatoms, Sponges, Bivalves, Gastropods, Echinoids, Bryozoans. The assemblages often have an olygotypical character (teratological specimens are not rare) and that testifies for a marine inner platform sedimentation with hypersaline conditions and poor bottom ventilation. These sediments are referred to the second Messinian transgression of the Southern Tuscany (the sediments of the first transgression only exist in the southern portion of the Tora-Fine basin und it is not examined here). As regards the gypsum, it represents the evaporitic phase resulting from the closure of the Mediterranean Basin. The third sedimentary episode of the late Miocene consists of sands, c1ayey sands and gypsums of late Turolian age that deposited in a lacustrine environment with fresh or brackish waters. The stratigraphic relationship between the third and second episodes is of uncertain resolution, even if a slight angular unconformity seems to be existing in some place. The third sedimentary episode is related to the well-known "lago-mare" facies that characterised the Messinian interval of Mediterranean salinity crisis. In fact, the micropaleontological assemblages are constituted by small Gastropods and Bivalves (Dreissena and mactra), benthic Foraminifcrs (Ammonia Beccarii tepida, Cribrononion articulatum, Cassidulina prima and Bolivina sp.) and by very abundant Ostracods (among the others, specimens of Loxoconca miilleri and Cyprideis gr. torosa are always present and very abundant) The Pliocene succession is in conformable contact on the Miocene succession and the transition from the first to the second one happens in an always submerged environment ("acqua su acqua" of the local literature) rapidly changing from lacustrine lo marine. The very rapid transition is closely linked to the reopening of the Mediterranean-Atlantic Ocean communications. The Pliocene succession is composed by one sedimentary episode of Zanclean-Piacenzian age (Sphaeroidinellopsis seminulina s.l. Zone - Globorotalia aemiliana Zone ,G. crassaformis crassaformis Subzone interval, Discaaster variabilis s.1. Zone - D. tamalis Zone, Coccolitus pelagicus Subzone). The deposits of this episode consist mostly of c1ays, sands and limestones. The clays have been deposited in the outer neritic- upper epibathyal environment In fact, they are very rich of calcareous nannofossils and Foraminifers (plankton > benthos). Three sandy levels are interbedded into the clays and they point out periods of turbiditic sedimentation. Sands and limestones are representative of less deep environment than c1ays (the micropaleontological assemblages are characterised mainly by benthic Foraminifers). In fact, they deposited in the inner shelf environment and represent the regressive facies of the Pliocene sedimentation.