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PALEOCEANOGRAPHIC AND PALEOCLIMATICRECONSTRUCTIONS OF THE LATE ALBIAN ¿ EARLYTURONIAN (LATE CRETACEOUS) TIME INTERVAL:FROM AN UNSTABLE TO A STABLE OCEAN
No full textLa Terra durante il Cretaceo (145.5-65.5 Ma) ha sperimentato lunghi periodi di clima caldo con temperature molto più elevate rispetto ad oggi. Il continuo sviluppo di Grandi Province Ignee (LIP) e il riassetto globale dei confini di placca ha portato ad un aumento dei livelli atmosferici di gas serra (CO2 e in alcuni casi CH4) e fasi di limitata circolazione oceanica. Il riscaldamento globale e l'aumento abnorme di CO2 hanno cambiato sensibilmente gli equilibri del ciclo del carbonio, alterando così il ciclo idrologico, la distribuzione dei nutrienti, l'intensità dell’upwelling e la formazione di acque profonde. Il record geologico dell’intervallo di tempo compreso tra il tardo Albiano e il Turoniano basale (~ 104-92 Ma) rappresenta un laboratorio naturale particolarmente intrigante per comprendere i processi fisici, chimici e biologici che hanno agito nel corso di questo periodo, caratterizzato dall’alternarsi di fasi di relativo equilibrio e fasi di alterazione del ciclo del carbonio. L’intervallo tra il tardo Albiano e il Turoniano basale è caratterizzato da tre grandi anomalie geochimiche corrispondenti alle escursioni positive della curva isotopica del carbonio: l’Evento Anossico 1d (OAE1d), l’Evento Cenomaniano Medio (MCE) e l’Evento Anossico 2 (OAE2).
Questo studio, tramite l’integrazione di dati sedimentologici, geochimici (isotopi del carbonio e dell’ossigeno, geochimica inorganica e organica) e ciclostratigrafia ad alta risoluzione, offre un'indagine integrata delle dinamiche paleo-ambientali e climatiche che accompagnarono questi grandi eventi. Particolare enfasi è volta alla comprensione dell’interazione tra i cambiamenti che avvengono nelle acque superficiali e i processi che agiscono sul fondo mare, con lo scopo di meglio definire il comportamento delle masse d'acqua in condizioni ambientali /climatiche estreme.
Come archivi naturali delle passate condizioni oceanografiche e ambientali sono state scelte cinque sezioni pelagiche Tetidee chiave: quattro dal Bacino Umbro-Marchigiano (Furlo, Contessa, Le Brecce, Monte Petrano - Italia centrale) e una dal Bacino di Belluno (Cismon - Italia settentrionale).
La descrizione sedimentologica ad alta risoluzione delle cinque sezioni – dalla scala di terreno fino alla scala microscopica- ha condotto ad una migliore comprensione dei processi fisici che hanno agito sul fondo marino durante la deposizione delle sequenze studiate. La presenza di peculiari strutture e facies sedimentarie indica che la sedimentazione pelagica non è esclusivamente governata dalla decantazione di particelle biogeniche. Correnti di fondo di intensità crescente e calante in modo ciclico ridistribuiscono attivamente i sedimenti presenti, formando facies specifiche e riconoscibili. Al fine di considerare anche questo processo, è stato definito un nuovo modello deposizionale per le contouriti carbonatiche pelagiche.
Nuovi dati isotopici ad alta risoluzione dell’ossigeno e del carbonio sia su carbonato che su materia organica sono stati prodotti per le sezioni del Monte Petrano e del Cismon. Il profilo ad alta risoluzione di δ13C presenta tre escursioni positive in corrispondenza dell’OAE1d, MCE ed OAE2. Inoltre, la correlazione dettagliata con ulteriori profili isotopici editi ed inediti disponibili per le altre sezioni studiate ha permesso di definire con maggiore accuratezza l’inquadramento stratigrafico a scala di bacino.
Importanti variazioni litologiche sono associate alle escursioni isotopiche del carbonio (CIE). Alcuni strati spessi pochi centimetri di scisto nero sono associati all’Evento Pialli (OAE1d) mentre l'impressionante livello Bonarelli è l'espressione litologica dell’OAE2. L’evento MCE costituisce, invece, un enigma più sottile e intrigante. E’ stata così ricostruita la variazione verticale stratigrafica delle facies identificate e messa in relazione ai principali eventi geologici. L'interazione dei processi paleoceanografici che controllano la composizione dei sedimenti in combinazione con la distribuzione dei sedimenti da parte delle correnti ha generato caratteristici stacking pattern.
Per le sezioni del Cismon e del Monte Petrano sono stati prodotti anche dati geochimici degli elementi maggiori e in traccia (XRF), al fine di comprendere meglio i cambiamenti paleoambientali che hanno caratterizzato questi due bacini adiacenti tra loro.
Tutte le sezioni del Bacino Umbro-Marchigiano sono state analizzate con tecniche ciclostratigrafiche, che hanno potuto mettere in luce quanto le variazioni di produttività primaria, rappresentata dalla variazione ciclica di carbonato e litologie silicee, riflettano la risposta climatica, oceanografica e deposizionale ai cicli orbitali.
La caratterizzazione sedimentologica altamente dettagliata è stata fondamentale per comprendere appieno la sedimentazione pelagica nella Tetide occidentale, durante le fasi di condizioni sia stabili che perturbate. Sulla base dei dati bio-, chemo- e ciclostratigrafici, l’evoluzione delle facies è stata datata con precisione ed è stata stimata la durata degli eventi. Questo approccio multi-proxy è stato fondamentale per caratterizzare un ambiente sedimentario apparentemente omogeneo e monotono ma in realtà estremamente dinamico.
Questo studio fornisce un importante passo verso una più completa comprensione dei meccanismi all'origine degli eventi paleoceanografici del ‘Cretaceo medio’, tra cui i fattori che innescano i cambiamenti anossia-disossia e ristabiliscono condizioni stabili a varie scale temporali.Earth during the Cretaceous (145.5-65.5 My) experienced long-lasting periods of warm climate with temperatures much higher than today. The continuous development of Large Igneous Provinces and the global rearrangement of plate boundaries led to an increase in atmospheric levels of greenhouse gasses (CO2 and possibly CH4), and times of restricted ocean circulation. Global warming and the abnormal increase in CO2 changed the equilibria of the carbon cycle thus altering the hydrologic cycle, nutrients distribution, upwelling intensity and deep water formation. The geological record of the late Albian to early Turonian (~104-92 My) time interval represents a particularly intriguing natural laboratory to understand the physical, chemical and biological processes that acted during a period of alternated phases of relative equilibrium and carbon cycle perturbations. The late Albian to early Turonian time interval is characterized by three major geochemical anomalies corresponding to positive excursions of the stable carbon isotope profile: the Oceanic Anoxic Event 1d (OAE1d), the Mid-Cenomanian Event (MCE) and the Oceanic Anoxic Event 2 (OAE2).
This study, combining sedimentological, geochemical (C and O isotopes, inorganic and organic geochemistry) and high-resolution cyclostratigraphic data, provides an integrated investigation of paleoenvironmental and climatic dynamics accompanying these major events. The interplay of surface water changes and sea bottom processes are here discussed with the purpose of better defining how water masses react during highly stressed climatic/environmental conditions.
Five pelagic Tethyan key-sections, four from the Umbria-Marche Basin (Furlo, Contessa, Le Brecce, Monte Petrano – central Italy) and one from the Belluno Basin (Cismon – northern Italy), were chosen as natural archives of the past oceanographic and environmental conditions.
The extremely detailed field- to microscopic-scale sedimentological description of the five sections allowed a better comprehension of the physical processes that acted on the sea-floor during the deposition of the studied sequences. Peculiar sedimentary structures and facies indicate that settling of biogenic particles wasn’t the only physical process controlling pelagic sedimentation. Waning and waxing cycles of bottom currents actively redistributed sediments, forming specific facies. In order to account for this process, a new depositional model for calcareous pelagic contourites was established.
New high-resolution oxygen, carbonate- and organic-carbon isotope record were produced for Monte Petrano and Cismon sections. High-resolution δ13C record exhibits three positive excursions in correspondence of OAE1d, MCE and OAE2. The detailed correlation with published and unpublished isotopic data from the other studied sections better defines the basin-scale stratigraphic framework.
Important lithological changes are associated with the observed carbon isotopic excursions (CIEs). Few centimeter thick black shale layers are associated with the Pialli Event (OAE1d) and the impressive Bonarelli Level is the lithologic expression of the OAE2. The MCE corresponds, instead, to more subtle and intriguing conundrum. A stratigraphic vertical variation of the identified facies was reconstructed and linked to the major geologic events. The interplay of the paleoceanographic processes controlling the sediment composition combined with current-driven sediment distribution resulted in characteristic cyclic patterns.
Major and trace element geochemical data were produced for Cismon and Monte Petrano sections in order to better understand the paleoenvironmental changes that characterized these two adjacent basins.
The application of cyclostratigraphic techniques to all the studied sections from the Umbria-Marche Basin shows that primary productivity variations, represented by the cyclic alternation of carbonate and siliceous lithologies, reflect the climatic, oceanographic and depositional response to orbital cycles.
Highly detailed sedimentological characterization was central to fully comprehend the pelagic sedimentation in Western Tethys during times of stable and perturbed conditions. Based on bio-chemo- and cyclostratigraphy, facies evolution was precisely dated and event duration was estimated. This multi-proxy approach was proved vital to characterize an apparently homogenous and monotonous sedimentary environment that was indeed extremely dynamic.
This study provides an important step towards a more comprehensive understanding of the mechanisms at the origin of ‘mid-Cretaceous’ paleoceanographic events, including feedbacks to trigger anoxia-dysoxia and re-establish normal conditions at various time scales
Sedimentation in the Tethyan pelagic realm during the Cenomanian : monotonous settling or active redistribution?
No full textSea bottom processes of the pelagic realm are still not completely understood and represent an intriguing subject. This paper focuses on the relationships between “normal” settling processes, redistribution of sediments and oceanographic parameters in a pelagic setting, during the Cenomanian. Five key Tethyian localities in the Cenomanian Umbria-Marche and Belluno Basins have been studied in order to understand the interplay among sea bottom processes that acted on the sea floor. The dataset consists of the mm-scale sedimentological description of the sections complemented by microfacies analysis on selected samples. Different sedimentological indications, such as presence of intraclasts, lined forams, pervasive plane-parallel lamination, suggest a continuous reworking under action of bottom-currents with varying intensity and direction. All the identified facies are here illustrated in detail and organized in a comprehensive schematic facies framework, the “facies matrix”, that leads to recognize two depositional facies suites: the “settling dominated” and the “traction current dominated”, under different oxygenation conditions. Our results suggest that settling of biogenic and inorganic particles represents the main source of pelagic sediments, but not the unique depositional process: under the action of sea-bottom currents of different intensity, sediments are continuously redistributed on the sea floor. All the collected evidences contribute to the proposal of a comprehensive depositional model for these reworked and redistributed fine-grained sediments, that represent true calcareous pelagic contourites. The model suggests that the identified traction-related facies can be used as a proxy for bottom current intensity and, indirectly, as an indicator of changing ventilation regimes at the sea floor through time
Orbital forcing of carbonate versus siliceous productivity in the late Albian–early Turonian (Umbria-Marche Basin, central Italy)
No full textWe applied a cyclostratigraphic analysis to a late Albian – late Cenomanian Tethyan section (Monte Petrano) from the Umbria-Marche Basin. Starting from a high-resolution (mm-scale) lithological log, estimated calcium carbonate contents were used as input data for cyclostratigraphy. The orbital tuning was based on long and short eccentricity, obliquity and precessional components and was tied to a radiometric age of 93.9 ± 0.15 Ma (2σ) of the Cenomanian/Turonian boundary. The estimated variations in sedimentation rates allowed for constructing an anchored astrochronology of the composite Albian – Cenomanian δ13C record. Our estimates of the total duration of the Albian and Cenomanian stages are about 14.20 ± 0.86 Myr and about 4.94 ± 0.35 Myr, respectively. The Aptian/Albian boundary lies at 113.04 ± 0.94 Ma and the Albian/Cenomanian boundary at 98.84 ± 0.35 Ma. Moreover, according to our results, OAE1d lasted about 1.21 ± 0.17 Myr (from 100.11 ± 0.41 Ma to 98.90 ± 0.35 Ma). We obtained an astronomical tuned age of 96.28 ± 0.28 Ma to 96.12 ± 0.27 Ma for the MCE I with a total duration of the event of about 166 ± 20 kyr. Astronomical cyclicities and climatic conditions exerted a direct influence on the depositional style of the studied geological record. Orbitally-paced variation in insolation controlled the variability in monsoon intensity, with maximum in monsoon strength during insolation maxima. Under humid climatic conditions, the orbitally-paced variations in summer monsoon precipitation controlled the amount of runoff and transportation of fine-grained detrital sediments in the basin, thus modulating the alternate deposition of marls and carbonate-rich sediments. During arid climate periods, the fluctuations in winter monsoon intensity controlled the variations in wind-blown dust availability and the fluctuations in ocean fertilization with times of enhanced siliceous productivity under eutrophic conditions and carbonate productivity under oligotrophic conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Caratterizzazione cromatografica delle frazioni volatile e solubile di cagliate congelate.
No full textCalcareous nannofossil biostratigraphy of the late Albian : early Turonian time interval: implications for global correlations
No full textCalcareous nannofossil biostratigraphy is proven to be a reliable tool for dating and correlating Cretaceous sequences at regional to global. However, assessment of nannofossil event reproducibility
still demands detail investigations of different oceanic basins, paleolatitudes and settings. In this study we present the revision of nannofossil biostratigraphic events across the late Albian –
early Turonian time interval. We investigated pelagic and hemipelagic sections located in different sedimentary basins in order to estimate reproducibility and variability of nannofossil bioevents in
different paleoceanographic regimes and/or latitudes and to evaluate the applicability of the three major nannofossil zonations available for the mid Cretaceous. The studied sections are located in the
Tethys Ocean, Vocontian Trough, Moroccan basin, Western Interior Seaway, and Pacific Ocean and were selected on the basis of availability of chemo-bio-stratigraphic data to constrain the age of
nannofossil events relative to stages, C-isotope anomalies and Oceanic Anoxic Events (OAEs). Most of the observed taxa are unambiguously described in the literature, but some taxonomic revision
has been applied to cases of potential misidentification and discrepant attribution. Each zonal and subzonal nannofossil event was evaluated for assessing the reproducibility, sinchroneity or
diachroneity. Also, a few additional potential nannofossil events are discussed in comparison with zonal and subzonal markers. Nannofossil Biohorizons were also examined in the context of stage
boundaries definition, namely the Albian/Cenomanian and the Cenomanian/Turonian boundary, to provide further information about the applicability of nannofossil events and the achievable resolution.
Moreover, our investigation proved nannofossil events to be extremely useful to biostratigraphically constrain paleoceanographic events of the late Albian – early Turonian interval, namely the latest
Albian OAE 1d, the mid Cenomanian MCE I and the latest Cenomanian OAE 2, which were successfully characterized in all the studied sequences
Onset and demise of Cretaceous oceanic anoxic events : The coupling of surface and bottom oceanic processes in two pelagic basins of the western Tethys
Full text linkThe upper Albian-lower Turonian pelagic successions of the Tethys record processes acting during the onset, core, and recovery from perturbed conditions across oceanic anoxic event (OAE) 1d, OAE 2, and the mid-Cenomanian event I (MCE I) relative to intervening intervals. Five sections from Umbria-Marche and Belluno Basins (Italy) were analyzed at high resolution to assess processes in surface and deep waters. Recurrent facies stacking patterns (SP) and their associations record periods of bottom current activity coupled with surface changes in trophic level. Climate changes appear to have been influential on deep circulation dynamics. Under greenhouse conditions, vigorous bottom currents were arguably induced by warm and dense saline deep waters originated on tropical shelves in the Tethys and/or proto-Atlantic Ocean. Tractive facies postdating intermittent anoxia during OAE 1d and in the interval bracketed by MCE I and OAE 2 are indicative of feeble bottom currents, though capable of disrupting stratification and replenish deep water with oxygen. The major warming at the onset of OAE 2 might have enhanced the formation of warm salty waters, possibly producing local hiatuses at the base of the Bonarelli Level and winnowing at the seafloor. Hiatuses detected at the top of the Bonarelli Level possibly resulted from most effective bottom currents during the early Turonian thermal maximum. Times of minimal sediment displacement correlate with cooler climatic conditions and testify a different mechanism of deep water formation, as further suggested by a color change to reddish lithologies of the post-OAE 1d and post-OAE 2 intervals
Phenolic composition and antioxidant activity of Southern Italy monovarietal virgin olive oils
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