1,721,070 research outputs found
Evoluzione sedimentaria e tettonica della parte centro-meridionale del bacino pliocenico di Radicofani
No full textFirst record of Bolivinita quadrilatera (Schwager) in Italian Pliocene (Southern Tuscany)
No full textBolivinita 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
Bio-cronostratigrafia a foraminiferi planctonici della Pietra Leccese (Miocene) nell’area tipo di Cursi-Melpignano (Lecce. Puglia)
No full textThis paper is a further contribution to the micropaleontological-stratigraphical studies on the Pietra leccese, a peculiar Miocene formation of the Salento Peninsula. The planktonic foraminiferal assemblages have been studied from seven sections, sampled in the quarries between Cursi and Melpignano (near Maglie, Lecce). This zone together with that of Lecce have been historically regarded as the type area of the Pietra leccese.
A modern scheme have been used to the bio-chronostratigraphical setting of the Pietra leccese. So, the formation has been established to range from the Globigerinoides trilobus Zone to Globorotalia conomiozea Zone and, therefore, from the upper Burdigalian to the lower Messinian. The formation has a thickness of few tens of meters, despite its wide stratigraphical extension and the detrital facies. This small thickness is due to at least three sedimentary gaps: the first (1.8 My at least) is located between the typical Pietra leccese (G. trilobus Zone, upper Burdigalian) and the lightly glauconithic one (Orbulina suturalis Subzone? – O. universa Subzone, upper Langhian); the second (2.5 My at least) is present between the lightly glauconitic facies and the first very fossiliferous level (labelled as “linea a cozze” by the local quarrymen) at the base of a glauconite-rich interval (Paragloborotalia siakensis Zone, upper Serravallian); the third gap (4 My at least) is located within the glauconite-rich interval and it is in correspondence to a second fossiliferous level (Globorotalia conomiozea Zone, lower pre-evaporitic Messinian).
The results deriving from this study confirms the stratigraphic and dynamic framework of the Salento Peninsula. Also in other area of the Salento, the Pietra leccese spans the Burdigalian-Messinian time interval and exhibits some sedimentary hiatuses. These hiatuses might be due to erosive/dispersive currents which affected the depositional basin and that varied in intensity in space and time
Globorotalia mariae mariae and G. mariae gratiae: Two new planktonic Foraminifera from the MiddleMiocene of the Mediterranean
No full textTwo new subspecies belonging to the genus Globorotalia, thatwe name G. mariae mariae and G. mariae gratiae, are here described and figured. They were found exclusively within the Middle Miocene and particularly from the early Langhian to the Serravallian of several Mediterranean sedimentary successions. The two subspecies have a slightly different stratigraphic range. Both were recorded from the Globigerinoides sicanus/Orbulina suturalis Zone (MMi4) to the Paragloborotalia partimlabiata Zone (MMi7). However, only G. mariae mariae is recorded from the Globorotalia praescitula Subzone (MMi4b), whereas G. mariae gratiae was found from slightly younger levels, corresponding to the Paragloborotalia siakensis-Praeorbulina glomerosa circularis Subzone (MMi4c). As far as their origin concerns, G. praescitula may have been the ancestor of G. mariae mariae. Subsequently, G. mariae gratiae evolved from G. mariae mariae. Both subspecies disappear in the Paragloborotalia partimlabiata-Globoturborotalita druryi Subzone (MMi7a). Concerning their stratigraphic range it is important to point out that in all the studied sections both subspecies were not found in the interval encompassing the Langhian/Serravallian boundary, and lasting from the upper part of the Praeorbulina glomerosa circularis Subzone (MMi4d) to the uppermost part of the Orbulina suturalis/Globorotalia peripheroronda Zone (MMi5)
Biostratigraphy and chronostratigraphy of the Maltese Lower Globigerina Limestone Member (Globigerania Limestone Formation): new preliminary data based on calcareous plankton
No full textThe 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
New data on the Middle Pliocene sedimentation in the southern Valdelsa basin (Siena, Italy)
No full textThe Valdelsa basin, one of the widest Neogene-Quaternary extensional basins of central Tuscany, is filled by dominantly clastic deposits of late Miocene and Pliocene age. Within the new regional project of geological cartography, sedimentological, stratigraphic and micropaleontological studies of the Pliocene marine sediments cropping out in the south-western area of the basin have been performed. The most important results are: a) the recovery of Globorotalia crassaformis, which allows to refer these sediments to the Piacenzian G. aemiliana Zone; b) the migration, during the Piacenzian, of the deeper areas of the Valdelsa basin from the central sector towards the eastern one; c) the recognition, during the same period, of a rapid transgression on the eastern margin. The analysis of these data, integrated with previous work from the surrounding areas, allows to outline the sedimentary evolution of the south-western sector of the Valdelsa basin during the Piacenzian
New data on the calcareous plankton biostratigraphy of the middle-upper Miocene of the Mediterranean area
No full textThe planktonic foraminifera of six sequences from middle to late Miocene are investigated. Five are located in the Mediterranean area and one in the Atlantic Ocean (Site 397). The aim of the research was to refine the biostratigraphy of the Serravallian to early Tortonian interval and to check the range of Neogloboquadrina acostaensis (Blow) and Paragloborotalia siakensis (Le Roy) which in the recent literature do have no more general consensus.
The study of planktonic foraminifera allowed us to recognize a succession of events part of which are new in the Mediterranean area and document an overlap in the distribution of N. acostaensis and P.lia siakensis.
Based on the new data, the zonal scheme of Iaccarino and Salvatorini (1982) and Iaccarino (1985) concerning the Serravallian to early Tortonian interval is emended. In particular it has been ascertained that the FO of N. acostaensis falls in the upper part of the Serravallian well before the LO of P.lia siakensis .
The new zonation has been calibrated with the calcareous nannofossil zonation and the geomagnetic polarity time scale. In the light of the new data it is pointed out that in the Rio Castellania-Rio Mazzapiedi-Tortonian type-section the closest events to its base are the LO of P.lia siakensis, the FCO of N. acostaensis, and the FO of Discoaster hamatus. Therefore these events are reccomended in selecting the GSSP Serravallian/Tortonian boundary.
Riassunto
Sono state esaminate e/o riesaminate le associazioni a foraminiferi planctonici di sei sezioni mioceniche delle quali 5 nell' area mediterranea e una in Oceano Atlantico (Site 397) con lo scopo di migliorare le conoscenze biostratigrafiche dell'intervallo Serravalliano-Tortoniano inferiore ed in particolare di controllare le distribuzioni stratigrafiche di Neogloboquadrina acostaensis (Blow) e Paragloborotalia siakensis (Le Roy) sulle quali secondo i dati bibliografici pi recenti non esiste pi un generale consenso. Lo studio delle associazioni ha permesso di riconoscere una successione di eventi in parte nuovi per l'area mediterranea ed in particolare, di documentare un intervallo di concomitanza tra le distribuzioni di P.lia siakensis e N. acostaensis.
I nuovi dati hanno consentito di emendare lo schema zonale di Iaccarino e Salvatorini (1982) e Iaccarino (1985) relativo all'intervallo Serravalliano-Tortoniano. In particolare Ž stato accertato che la comparsa di Neogloboquadrina acostaensis (Blow) Ž un evento di etˆ serravalliana, e che la scomparsa di P.lia siakensis (Le Roy) avviene dopo la comparsa di N. acostaensis.
La nuova zonazione Ž stata calibrata rispetto alla zonazione a nannofossili calcarei, alla scala cronostratigrafica e a quella geocronologica.
Alla luce di questi nuovi dati Ž emerso che nella sezione tipo del Tortoniano gli eventi pi prossimi alla sua base sono la LO di P.lia siakensis , la FCO di N. acostaensis e la FO di Discoaster hamatus. Pertanto si raccomanda di utilizzare questi eventi nella scelta del GSSP del limite Serravalliano-Tortoniano
New data on the Middle-Pliocene sedimentation in the southern Valdelsa Basin (Siena, Italy).
No full textMiddle Miocene high-resolution calcareous plankton biostratigraphy at Site 926 (Leg 154, equatorial Atlantic Ocean): paleoecological and paleobiogeographical implications
No full textHigh-resolution calcareous plankton (planktonic foraminifera and calcareous nannofossils) biostratigraphy is presented from the Middle to early Late Miocene interval (from 14.45 to 8.86 Ma) at Site 926 (ODP Leg 154, equatorial Atlantic Ocean). The main bioevents used in the low-latitude zonal schemes, and also auxiliary events revealing potential biostratigraphic value have been recognised. The investigated succession ranges from N.10 to N.16 Zones based on planktonic foraminifera, and from NN5 (CN4) to NN10 (CN8) Zones based on calcareous nannofossils. The evolution of the planktonic foraminiferal Globorotalia fohsi lineage appears to be environmentally controlled. The main diagnostic features of the species of this lineage are not always evident, rendering problematic the definition of the N.9/N.10, N.10/N.11 and N.11/N.12 zonal boundaries. Calcareous plankton events have been calibrated on the basis of the Astronomical Time Scale of Shackleton and Crowhurst [Shackleton, N.J., Crowhurst, S., 1997. Sediment fluxes based on an orbitally tuned time scale 5 Ma to 14 Ma, Site 926. In: Curry, W. B., Shackleton, N.J., Richter, C., Bralower, T.J. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program) 154, pp. 69-82]. The astrobiochronology obtained at Site 926 has been compared with that of the Mediterranean astronomically calibrated deep marine successions, allowing the evaluation of the degree of synchroneity and diachroneity of bioevents. Some bioevents, such as the last occurrence of Globigerinoides subquadratus dated at 11.55 Ma, the last occurrence of Sphenolithus heteromorphus dated at 13.51 Ma and the last common occurrence of Cyclicargolithus floridanus calibrated at 13.32 Ma, are near-synchronous events between the equatorial Atlantic and the Mediterranean area indicating their high biostratigratigraphic value in global correlation. The diachroneity of the last occurrence of Paragloborotalia siakensis, the first occurrence of Neogloboquadrina acostaensis and the last occurrence of Globorotalia peripheroronda between equatorial Atlantic and the Mediterranean reflect a different spatial and temporal distribution of these marker species probably due to a sharp definition of surface plankton provinces related to the latitudinal thermal gradient. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved
- …
