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.
La 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.
PALEOCEANOGRAPHIC AND PALEOCLIMATICRECONSTRUCTIONS OF THE LATE ALBIAN ¿ EARLYTURONIAN (LATE CRETACEOUS) TIME INTERVAL:FROM AN UNSTABLE TO A STABLE OCEAN / G. Gambacorta ; tutor: E. Erba ; co-tutor: R. Bersezio ; coordinatore: E. Erba. DIPARTIMENTO DI SCIENZE DELLA TERRA "ARDITO DESIO", 2014 Feb 12. 26. ciclo, Anno Accademico 2013. [10.13130/g-gambacorta_phd2014-02-12].
PALEOCEANOGRAPHIC AND PALEOCLIMATICRECONSTRUCTIONS OF THE LATE ALBIAN ¿ EARLYTURONIAN (LATE CRETACEOUS) TIME INTERVAL:FROM AN UNSTABLE TO A STABLE OCEAN
G. Gambacorta
2014
Abstract
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.File | Dimensione | Formato | |
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