1,721,244 research outputs found
Climatically influenced interactions between the Mediterranean and the Paratethys during the Tortonian
No full textThe Paratethys was a separate branch of the Tethys Ocean that developed as a series of inland seaways, brackish lakes, and wetlands the interiors of central-eastern Europe and western Asia during the Oligocene-Neogene. A short-lived connection between the Mediterranean Sea and the Paratethys continental realm toward the very end of the Messinian salinity crisis is documented on the basis of the Paratethyan affinity of the brackish shallow water faunas in several Mediterranean localities. Nevertheless, there are at present only a few comparative studies on stratigraphy paleobiogeography and paleoceanography of these two contiguous Neogene provinces [e.g., Benson, 2000]. In this study we compare and integrate different stratigraphic data sets from middle-upper Miocene sequences of the central Mediterranean and the western Pannonian basins (central Paratethys) that are seen as parts of a complex paleoclimatic and paleoceanographic system. On the basis of this comparison we propose that the Paratethys had a long-lived influence on the large-scale oceanographic circulation of the eastern Mediterranean, at least since the Tortonian (between 9.7 and 7.5 Ma); that is, well before the onset of the Messinian Lagomare event (~5.5 Ma). The integrated stratigraphy of coeval marine (Tortonian) and continental (Transdanubian) strata presented here suggests that mutual interaction and interdependence of climate subsystems ostensibly developed over the Mediterranean area and central-eastern Europe continent and were orbitally forced. Long-eccentricity insolation forcing is hypothesized to have exerted a broad control on the freshwater budget of the brackish Pannonian Basin and the consequent oceanographic setting of the Mediterranean region
Surface and deep water conditions in the Sicily Channel (central Mediterranean) at the time of sapropel S5 deposition
No full textPeriodicità submillenarie registrate nei sedimenti marini degli ultimi 2000 anni (Tirrenio orientale)
No full textEarly Eocene hyperthermal events ETM2, H2 and I1 as recorded by Tethyan planktic foraminifera in the Terche section (northeastern Italy)
No full textIn the last years, several transient episodes of extreme warming, the so-called hyperthermals, have been recognized
in addition to the well-know Paleocene-Eocene Thermal Maximum (PETM; 55.5 Ma), superimposed on the
long-term Paleocene-early Eocene warming trend peaking in the Early Eocene Climatic Optimum (EECO). To
the present, perturbations produced by hyperthermals are well documented in terms of isotopic variations whereas
their influence on the biota is still largely unexplored.
The Terche section, located in the Venetian Pre-Alps (northeastern Italy), is an expanded latest Paleocene-lower
Eocene succession deposited in a bathyal setting of a continental margin of the central-western Tethys. This
section is particularly suitable to study post-PETM hyperthermals because it contains three well-exposed and
expanded marly-clayey units (MUs) corresponding to intervals of negative carbon isotope excursions (CIEs).
Calcareous plankton biostratigraphy allow us to refer them to the hyperthermals ETM2 (or H1; 53.7 Ma), H2
(53.6 Ma) and I1(53.3 Ma).
Here we present the first detailed quantitative analysis of planktic foraminiferal assemblages across these early
Eocene hyperthermals events. Quantitative analysis of planktic foraminiferal genera shows a long-term trend of
variation upon which higher frequency variations are superimposed. We interpret such long-term variation as the
response to the long–term warming trend since it highlights a slight increase of the warm indicators, such as the
acarininids, and decrease of the cold form subbotinids. The high frequency variations, instead, closely related to
the CIEs and to the MUs, record a pronounced increase in acarininids (up to 68%) and a parallel marked decline
in the abundances of subbotinids and other component of planktic foraminiferal assemblages. The MUs are also
associated with an increase of the eutrophic radiolarians. This aspect, together with the dominance of acarininids,
can be interpreted as a consequence of the extreme warmth coupled with eutrophic conditions of surface
waters. The surface-dwelling acarininids, able to temporarily colonize warmer deeper and nutrient-richer waters
previously occupied by Subbotina, better tolerated the relatively high eutrophic conditions which prevented the
warm indices Morozovella to thrive. The increased eutrophic conditions can be related to accelerate hydrological
cycle, in turn enhanced by the intense warming, as already observed for the PETM in the same area.
Calcareous plankton variations during the hyperthermals in a deep-water setting could be affected by selective
dissolution susceptibility due to the lysocline rise associated to these events. The planktic foraminiferal Fragmentation
Index calculated in correspondence to the MUs of the Terche section presents very low values compared
with those observed in other sections of the Belluno Basin across the PETM and the X-event. This indicates that
the planktic foraminiferal record is not biased by dissolution and the modifications of assemblages are genuine
and representative of the different genera real distributions. Our data on planktic foraminifera prove the strong
effect of the hyperthermals events on the biotic component of the upper water column and show that the most
intense perturbation was induced by the ETM2 that is characterized by the most pronounced CIE
Travertines as hydrologic archives: The case of the Pontecagnano deposits (southern Italy).
No full textCarbon-isotope stratigraphy and cyclostratigraphy of shallow-marine carbonates: the case of San Lorenzello, Lower Cretaceous of southern Italy
No full textA high-resolution (cm-scale) carbon-isotope stratigraphic study has been carried out at San Lorenzello (Matese Mountains, southern Apennines, Italy), on a shallow marine carbonate section, previously correlated with coeval sections by using a combination of biostratigraphic, cyclostratigraphic and sequence-stratigraphic criteria. This succession, deposited along the southern margin of the Alpine Tethys, is Late Valanginian - Early Hauterivian in age; it consists of a hierarchy of shallowing-upward cycles (elementary cycles, bundles and superbundles), linked to Earth’s orbital oscillations.
We estimate that the influence of the depositional environment and diagenesis on the δ13C signal is negligible and that the carbon-isotope composition of bulk carbonate, as well as individual grains, indicate a similar response to an original climate-ocean forcing. No clear relationship emerges between the δ13C variations and the sea-level changes.
The long-term δ13C oscillations have been correlated with the coeval curves from the emipelagic La Charce (Vocontian Basin, France) and from the pelagic Capriolo (southern Alps, northern Italy) sections. This comparison suggests that the C-isotope signature is well preserved at San Lorenzello, where only the upper part of the Valanginian carbon isotope global excursion is recorded in the outcrop. The available data allowed us: (a) to relate the shallow-marine stratigraphic record with the ammonite and nannofossil biozonation and the magnetostratigraphy; (b) to identify the Valanginian-Hauterivian boundary in the studied shallow-marine deposits on the basis of high-resolution carbon-isotope correlation with the La Charce and Capriolo sections; (c) to suggest that the time duration of about 2.9 my, estimated by orbital chronostratigraphy in the San Lorenzello section, is comparable with the ± 3 my reported for the same stratigraphic interval in Channell et al. (1995) and Gradstein et al. (2004)
A multidisciplinary approach for reconstructing the stratigraphic framework of the last 40 ka in a bathial area of the eastern Tyrrhenian Sea.
No full textA detailed integrated stratigraphic framework for the last 40 ka in the eastern Tyrrhenian Sea (central
Mediterranean) was obtained through quantitative analyses of planktonic foraminifera assemblages,
tephrostratigraphical studies and δ18O measurements on the basinal CET1 cored succession.
Relative abundance fluctuations in the planktonic foraminifera assemblages allowed the identification of nine
known eco-biozones and several bioevents recognized in the Tyrrhenian area and that are useful for correlations
between Mediterranean marine records. Compositional changes in the planktonic foraminifera assemblages
together with variations in the oxygen isotope record allowed us to detect the major climatic global fluctuations
and some of the minor events that occurred during the investigated time interval.
A total of 12 visible tephra layers and cryptotephras have been recognized and correlated with their volcanic
sources and/or with known explosive events of Campanian and Sicilian–Aeolian volcanoes.
A stratigraphic relationship between foraminiferal and climatic events and tephra layers has been highlighted.
For the first time ecostratigraphic and tephrostratigraphic methodswere combined to obtain a detailed integrated
stratigraphy for the last 40 ka in the Tyrrhenian area. The achieved stratigraphic framework provides a useful
stratigraphic reference record for the investigated area
Geochimica e petrografica di black shales del Livello Bonarelli, sezione di Novara di Sicilia (Monte Peloritani), Sicilicia nord-orientale: Implicazioni paleoambientali
No full textBlack shales ad alto potenziale petrolifero, alternati ritmicamente a marne e argilliti, affiorano in associazione con Argille Varicolori (Cretaceo-Paleogene) nei pressi di Novara di Sicilia (Monti Peloritani, Sicilia nord-orientale) costituendo l’espressione sedimentaria di un evento anossico con diffusione globale (OAE2), riferibile al Cenomaniano superiore. I depositi corrispondenti a tale evento sono individuati come “Livello Bonarelli”.
In detta successione, le alternanze black shales-marne-argilliti si estendono per uno spessore di circa 11 metri passando verso il basso ad alternanze irregolari di calcari marnosi, marne chiare, marne scure, argilliti e calcareniti (spessore ca. 9 m) che presentano l’intercalazione di un solo orizzonte di black shale.
Le caratteristiche petrografiche e geochimiche dei black shales (una millimetrica laminazione perfettamente preservata, abbondante e diffusa pirite in cristalli minuti, alte percentuali di TOC, valori negativi di Mn* e alti V/(V+Ni), accoppiati ad abbondanti radiolari e alti valori del rapporto Si/Al) offrono testimonianza di un ambiente di deposizione caratterizzato da condizioni di estremamente bassa disponibilità di ossigeno nelle acque di fondo associata ad elevata produttività delle acque di superficie. I traccianti geochimici di condizioni redox suggeriscono che le marne e le argilliti della parte inferiore della sezione segnano l'instaurarsi di condizioni disossico-anossiche che successivamente evolvono verso condizioni anossico-euxiniche, in coincidenza con l'aumentata frequenza nella deposizione di black shales.
Una comparazione con depositi del "Livello Bonarelli" affioranti in altre zone d'Italia (Appennino Umbro-Marchigiano e Prealpi Bellunesi) discrimina i black shales studiati per alti contenuti di smectite, bassi valori del rapporto K/Al e limitati contenuti di Ba.Organic-rich black shales rhythmically alternating with mar stones and mudstones crop out - in association with the Unit of Varicolourec Clays (Cretaceous-Palcogene) - in an area near the town of Novara di Sicilia (Pelorilani Mountains, northeastern Sicily). These deposits, belonging to the Upper Cenomanian, are identified as "Livello Bonarelli" representing the sedirr entary expression of the anoxic event OAE2. The alternances (about 11 m thick) pass downwards to more irregular alternances (about 9 m thick) of marly limestones, light marlstones, dark marlstones, mudstones, and calcarenites with only one black shale horizon intercalated. Geochemical and petrographic features of the black shales (a well preserved mm-lamination, common disseminated pyrite in very small crystals, high TOC percentages, negative values of Mn* and very high values of V/(V+Ni), together with abundant radiolarians and high values of the Si/Al ratio) identify a depositional environment characterized by very poor oxygen levels associated to high productivity of near-surface waters. Geochemical tracers of paleoredox conditions suggest an evolution from dysoxic-anoxic conditions, during the deposition of marlstones and mudstones from the lower part of the section, towards anoxic-euxinic conditions in coincidence with the enhanced frequency of black shale layers. A comparison with some deposits of the Livello Bonarelli cropping out in other areas in Italy discriminates the black shales studied for their high smectite proportions, low values of K/Al ratio and limited Ba values
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