Seamounts play an important role in facilitating the exchange of elements between the oceanic lithosphere and the overlying seawater. This water-rock interaction is caused by circulating seawater and controls the chemical exchange in submarine and sub-seafloor rocks. The exchange mechanism plays a major role in determining the final composition of these submarine rocks. This investigation is designed to evaluate the (i) degree of alteration and element mobility, (ii) to identify relations between alteration types and (iii) to characterise the chemical processes that takes place during seafloor and sub-seafloor alteration in the Central Atlantic region. The investigated submarine rocks are typically altered. They are composed mostly of calcite and clay minerals in addition to original magmatic feldspar, olivine, pyroxene, quartz, biotite, and amphibole.  Elemental analyses show that submarine rocks with high water-rock ratio have experienced near complete loss of Silica and alkali elements to seawater but are enriched in calcium and phosphorous. In addition, there is a strong enrichment of trace elements such as Sr, Ti, Rb and trivalent REEs in altered submarine samples that are likely residual in character. Oxygen and hydrogen isotopic values indicate a low temperature alteration process at less than 50℃.  Nannofossils were present in one sample and investigation suggests that the seamount south of El Hierro evolved from a young Canary activity rather than the early Cretaceous magmatic events as has been argued previously. / Djuphavsberg spelar en viktig roll för att underlätta utbytet av element mellan den oceaniska litosfären och det överliggande havsvattnet. Interaktionen mellan vattnet och bergarterna orsakas av cirkulerande havsvatten och kontrollerar det kemiska utbytet i undervattensbergarterna och som även spelar en viktig roll för att bestämma de slutliga produkterna i dessa bergarter. Undersökningen syftar till att (i) utvärdera graden av kemisk omvandling och rörlighet av elementen, (ii) identifiera samband mellan olika omvandlingstyper och (iii) att karakterisera de kemiska processer som äger rum vid kemisk omvandling av bergarter vid och under havsbottnen i Centralatlanten. De undersökta undervattensbergarterna är generellt kemiskt omvandlade och består av kalcit och lermineral utöver ursprungligt magmatiskt fältspat, olivin, pyroxen, kvarts, biotit och amfibol. Elementanalyser visar att de undervattensbergarter med en hög vatten-berg kvot har förlorat i stort sett all Si och nästan alla alkaliska element till havsvattnet medan en anrikning har skett av kalcium och fosfor. Dessutom har det i de omvandlade undervattensproverna skett en tydlig anrikning av spårämnena Sr, Ti, Rb och av trivalenta sällsynta jordartsmetaller. Syre- och väteisotopvärden indikerar en omvandlingsprocess vid låga temperaturer mindre än 50 °C. I ett prov fanns nannofossiler och en undersökning av dessa tyder på att djuphavsberget söder om El Hierro bildades under en yngre vulkanisk aktivitet än den magmatiska aktivitet som tidigare föreslagits som ägde rum under perioden Krita.

Les coccolithophoridés sont des algues marines photosynthétiques et planctoniques qui produisent des plaques micrométriques de carbonate de calcium (CaCO3) appelés coccolithes. Ces algues sont apparues il y 210 Ma et produisent actuellement la majeure partie du CaCO3 dans les océans modernes, jouant ainsi un rôle majeur dans le cycle du carbone. Cependant, l’émergence de la production de CaCO3 océanique par les coccolithophoridés au cours du Jurassique, ainsi que son impact sur le cycle du carbone, restent très mal compris. Cette étude s’est donc focalisée sur une période du Jurassique Moyen (Bajocien inférieur, -170 Ma) enregistrant la diversification de Watznaueria, un genre de coccolithophoridé qui a ensuite dominé la production de CaCO3 océanique pendant plus de 80 Ma. L’analyse des assemblages de coccolithes du Jurassique Moyen du Portugal et du sud de la France, réalisée à l’aide d’une méthode de reconnaissance automatique appliquée pour la première fois aux coccolithes du Jurassique, a permis de quantifier l’importance de cette période de diversification sur la production de CaCO3 pélagique. En outre, la durée de cet intervalle clé a été réévaluée grâce à l’analyse cyclostratigraphique des séries sédimentaires du Sud de la France. Les variations de production de CaCO3 pélagique ainsi reconstituées ont été comparées aux perturbations du cycle du carbone enregistrées par les rapports des isotopes du carbone, et indiquent un lien probable avec une augmentation marquée de la fertilité des océans. Par ailleurs, l’analyse paléontologique montre que cette diversification correspond à l’apparition successive de différentes espèces vraisemblablement opportunistes du genre Watznaueria. Enfin, les flux obtenus de CaCO3 pélagiques, largement inférieurs à ceux observés dans les océans actuels, semblent insuffisants pour avoir eu une influence significative sur le cycle global du carbone du Jurassique Moyen. / Coccolithophorids are photosynthetic and planktonic marine algae that produce micrometric calcium carbonate (CaCO3) platelets called coccoliths. These algae appeared about 210 Ma ago and produce today most of the CaCO3 in the modern oceans, hence playing a major role in the carbon cycle. Nevertheless, the onset of oceanic CaCO3 production by these organisms during the Jurassic and its impact on carbon cycling remain poorly understood. This study therefore focused on the Middle Jurassic interval (Early Bajocian, -170 Ma) which records the diversification of Watznaueria, an evolutionary important coccolith genus that subsequently dominated oceanic CaCO3 production for more than 80 Myr. The analysis of coccolith assemblages from the Middle Jurassic of southern France and Portugal, based on an automaticcoccolith recognition device used for the first time on Jurassic coccoliths, allowed quantifying the impact of this diversification on CaCO3 production. In addition, the duration of this key interval has been revaluated by the cyclostratigraphic analysis of sedimentary strata from southern France. The reconstructed changes in CaCO3 production were compared to carbon cycle perturbations recorded by carbon isotope ratios and indicate a probable link with a marked increase of ocean fertility. Besides, paleontological analyses show that this diversification episode correspond to the successive appearance of different, probably opportunistic Watznaueria species. The obtained fluxes of pelagic CaCO3 production, by far lower than those recorded in modern oceans, seems too low to have significantly impacted theMiddle Jurassic carbon cycle.

Esta tese apresenta o registro de variações paleoceanográficas na superfície e em oceano profundo na porção oeste do Atlântico Sul, através de evidências de nanoplâncton calcário, durante os últimos 200.000 anos. Os principais parâmetros avaliados foram relativos à paleoprodutividade primária, através de estimativas de abundância e taxa de acumulação do nanoplâncton calcário, índices paleoceanográficos de produtividade, variação de carbonato de cálcio, contribuição relativa das espécies de nanoplâncton para o carbonato de cálcio total e análises de dados geoquímicos complementares. Os dados derivam de três testemunhos coletados na Bacia de Santos entre 1900 e 2200 metros de profundidade. Os resultados demonstram que as mudanças paleoceanográficas observadas no período analisado devem estar relacionadas, concomitantemente, a variações na dinâmica do oceano na camada superficial e em oceano profundo. As evidências de paleoprodutividade primária e a subsequente deposição do nanoplâncton calcário apontam que ambas são dependentes de condições favoráveis em superfície e no fundo, respectivamente. Estas condições ocorreram durante o período de aquecimento das águas superficiais no oeste do Atlântico Sul e a retração de águas profundas de origem sul devido à intensificação da célula de revolvimento meridional do Atlântico. Os últimos 200.000 anos foram divididos em sete intervalos definidos pela variação de paleoprodutividade primária com base no registro de nanoplâncton calcário. / This thesis presents a view of the paleoceanographic changes that occurred in the surface and deep ocean in the western South Atlantic by means of calcareous nannoplankton during the last 200,000 years. Data was obtained from three sediment cores collected in the Santos Basin between 1900 and 2200 meters water depth. Estimates of primary paleoproductivity from calcareous nannoplankton abundance and accumulation rates, paleoproductivity proxies calcium carbonate content, the relative contribution of nannoplankton species to total calcium carbonate and complementary geochemical data analyzes were performed. The results demonstrate that paleoceanographic changes observed in the analyzed period may be related to changes in ocean dynamics at surface and deep ocean. Primary paleoproductivity record and the subsequent calcareous nannoplankton deposition indicate that these are dependent on surface and bottom conditions, respectively. These conditions were recorded during sea surface temperature warming in the western South Atlantic and retraction of southern-sourced deep waters due to strengthening of the Atlantic meridional overturning circulation. The last 200,000 years were divided into seven intervals defined by the changes in primary paleoproductivity record of calcareous nannoplankton.

Este estudo apresenta indicações de mudanças paleoceanográficas ao longo dos últimos 25.000 anos na porção oeste do Oceano Atlântico Sul a partir do registro da variação de nanofósseis calcários em dois testemunhos de sedimento marinho da margem continental nordeste do Brasil. Outros indicadores foram incorporados às análises de nanofósseis calcários no intuito de melhor compreender as alterações observadas nas assembléias fósseis: 1) dados isotópicos de oxigênio de testas de foraminíferos planctônicos e bentônicos; 2) índice de temperatura e de nutrientes; 3) equação de paleoprodutividade e 4) análises estatísticas multivariadas. Os índices de temperatura e nutrientes foram, pela primeira vez, aplicados a nanofósseis calcários do Quaternário em amostras do Atlântico Sul. A integração dos resultados sugere que as principais características oceanográficas não sofreram alterações significativas nos últimos 25.000 anos, embora condições ambientais instáveis tenham sido registradas a partir da transição do Último Máximo Glacial - Holoceno. Durante o Último Máximo Glacial a região estudada sofreu pouca variação de temperatura, funcionando como um reservatório de calor. A variação da profundidade da termoclina/nutriclina foi considerada a principal resposta às oscilações climáticas, sendo relacionada às mudanças de intensidade dos ventos alísios. / This study focuses on changes in calcareous nannofossil assemblages as an evidence of paleoceanographic variability during the last 25,000 years in two deep sea piston cores from the northeastern Brazilian continental margin. To support reconstructing ancient marine environment others proxies have been applied along with the calcareous nannofossil analysis: 1) oxygen isotopic data from planktonic and benthic foraminifers\' tests; 2) temperature and nutrient indices; 3) paleoproductivity equation and 4) multivariate analysis. For the first time the temperature and nutrient indices were employed to Quaternary calcareous nannofossil from the South Atlantic Ocean. According to presented results major oceanographic features were stable in the last 25,000 years, although instable environmental conditions were recorded in the Last Glacial Maximum - Holocene boundary. During the Last Glacial Maximum the western tropical Atlantic seems to have experienced slight temperature changes and served as a heat and salt reservoir. Nutricline and thermocline depth variation was considered the most important response to climate changes largely related to Trade Winds strength oscillation.

Submitted by CARLA MARIA GOULART DE MORAES (carlagm) on 2015-05-08T18:55:43Z No. of bitstreams: 1 RodrigodoMonteGuerra.pdf: 19509141 bytes, checksum: 3e17b817d88748afa71b52b6e19e720c (MD5) / Made available in DSpace on 2015-05-08T18:55:43Z (GMT). No. of bitstreams: 1 RodrigodoMonteGuerra.pdf: 19509141 bytes, checksum: 3e17b817d88748afa71b52b6e19e720c (MD5) Previous issue date: 2011-08-08 / Nenhuma / Este estudo apresenta inferências bioestratigráficas e paleoecológicas baseadas na distribuição de nanofósseis calcários em três poços perfurados na plataforma continental da Bacia de Pelotas, sul do Brasil. Estudos bioestratigráficos na bacia foram realizados no final da década de 1980, porém nos últimos trinta anos o arcabouço bioestratigráfico com nanofósseis calcários para as bacias marginais brasileiras obteve um refinamento significativo, justificando a elaboração de um novo estudo. A sucessão é composta principalmente por rochas siliciclásticas provenientes de amostras de calha com pequenos intervalos de testemunhos. Foram reconhecidas onze biozonas atingindo a seção Albiano superior/Maastrichtiano, o resultado das análises bioestratigráficas produziram uma melhor resolução principalmente para o Turoniano e o Campaniano da bacia. Abundâncias relativas e absolutas de espécies do Cretáceo foram utilizadas para a determinação de inferências paleoecológicas, as primeiras com base em nanofósseis calcários para a Bacia de Pelotas. Estes dados sugerem o predomínio de condições de águas quentes com alguns eventos de esfriamento da água durante o Turoniano superior, Turoniano superior/Coniaciano inferior, Coniaciano superior e Santoniano superior/Campaniano inferior. / This study reports biostratigraphic and paleoecologic inferences based on the distribution of calcareous nannofossils in three wells drilled in Pelotas Basin continental shelf, southern Brazil. The first biostratigraphic study in the basin comes from late 1980s, however the Brazilian nannoplankton biostratigraphic framework reached a higher resolution in the last thirty years, justifying the development of a new study. The successions are composed mainly by siliciclastic rocks coming from cutting samples and short intervals of cored samples. Eleven biozones were recognized, within the upper Albian and Maastrichtian interval, the biostratigraphic analyses provided a higher resolution mainly for Turonian and Campanian strata in the basin. Absolute and relative abundances of some Cretaceous calcareous nannofossils species provided paleoecological proxies, pioneer in Pelotas Basin using this fossil group. The results suggest a prevalence of warm-water condition, with cooling events during the upper Turonian, upper Turonian/lower Coniacian, upper Coniacian and upper Santonian/lower Campanian.

[Truncated abstract] The Northern Bonaparte Basin and adjacent Darwin Shelf form part of a major petroleum province on the northwestern margin of Australia. The middle to Late Cretaceous Bathurst Island Group consists of siliciclastic and pelagic carbonate strata that form the regional seal to underlying Upper Jurassic and Lower Cretaceous reservoir sandstones. The Bathurst Island Group has previously been subdivided into four stratigraphic sequences or ‘play intervals’ bound by regional disconformities in the Valanginian (KV horizon), Lower Aptian (KA horizon), upper Lower Cenomanian (KC horizon), Middle Campanian (KSC horizon), and at the CretaceousPaleocene boundary (T horizon). Correlation of these sedimentary packages and stratigraphic surfaces requires high-resolution calcareous microfossil biostratigraphy, while palaeobathymetric determinations based on benthonic foraminiferal assemblages are important for determining the subsidence history of the area and relative sea-level changes. This study presents the first detailed stratigraphic distributions, taxonomic lists and illustrations of foraminifera and calcareous nannofossils from the Bathurst Island Group of the Northern Bonaparte Basin and Darwin Shelf. A biostratigraphic framework has been constructed for the study area incorporating ‘standard’ (Tethyan) Cretaceous planktonic foraminiferal and calcareous nannofossil events where applicable, and integrating locally defined events where necessary. This framework allows Cretaceous strata to be correlated regionally across the study area and to the global chronostratigraphic scale. Correlation of the Northern Bonaparte Basin and Darwin Shelf strata to the Cretaceous Stages and international time scale is based on recent ties of nannofossil and foraminiferal events to macrofossil zones and palaeomagnetic polarity chrons at ratified and proposed Global Stratotype Sections and Points (GSSPs). Calcareous nannofossil events recorded in the study area that are critical for defining stage boundaries include the lowest occurrences of Prediscosphaera columnata, Micula decussata, Lithastrinus grillii, and Aspidolithus parcus parcus, and the highest occurrences of Helenea chiastia, Lithastrinus moratus, Aspidolithus parcus constrictus, and Eiffellithus eximius. Important planktonic foraminiferal events for correlation include the lowest occurrences of Rotalipora gr. globotruncanoides, and Dicarinella asymetrica, and the highest occurrences of Planomalina buxtorfi, Rotalipora cushmani, and Dicarinella asymetrica. During the middle to Late Cretaceous the Northern Bonaparte Basin and Darwin Shelf occupied mid-high palaeolatitudes between 35ºS to 45ºS. These palaeolatitudes are reflected in the transitional character of the planktonic microfossil assemblages, which combine elements of the low-latitude, warm-water Tethyan Province to the north and the cool-water high-latitude Austral Province to the south. ‘Standard’ Tethyan zonations are most applicable for uppermost AlbianMiddle Campanian strata because equator-to-pole temperature gradients were weakly developed, and global climate was warm and equable during this interval. These conditions resulted in broad latitudinal distributions for Tethyan marker species, and consequently most UC calcareous nannofossil zones and European-Mediterranean planktonic foraminiferal zones are recognised. In contrast, the EarlyLate Albian and the late Middle CampanianMaastrichtian were intervals of greater bioprovinciality and stronger palaeotemperature gradients. In these intervals application of the Tethyan zonations is more difficult, and a number of the Tethyan biostratigraphic markers are absent from the study area (e.g. Ticinella species in the Albian and Radotruncana calcarata in the Late Campanian). Cretaceous palaeobathymetric reconstruction of the study area is based on comparison of the foraminiferal assemblages with those of previous Cretaceous palaeobathymetric studies. Marginal marine assemblages consist solely of low diversity siliceous agglutinated foraminifera (e.g. Trochammina). Inner and middle neritic water depths (0-100 m) contain rare to common planktonic foraminifera (mainly globigerine forms), robertinids (e.g. Epistomina), siliceous agglutinates, lagenids, buliminids (e.g. Neobulimina), and rotaliids. The outer neritic zone (100-200 m water depth) contains abundant planktonic foraminifera (keeled and globigerine), calcareous agglutinates (e.g. Dorothia), and diverse lagenids, buliminids, and rotaliids. Upper-middle bathyal water depths (200-1000 m) are characterised by abundant planktonic foraminifera, common siliceous agglutinated taxa (e.g. Glomospira), rare to common Osangularia, and globular species of Gyroidinoides, Pullenia, and Paralabamina.

Este estudo apresenta indicações de mudanças paleoceanográficas ao longo dos últimos 25.000 anos na porção oeste do Oceano Atlântico Sul a partir do registro da variação de nanofósseis calcários em dois testemunhos de sedimento marinho da margem continental nordeste do Brasil. Outros indicadores foram incorporados às análises de nanofósseis calcários no intuito de melhor compreender as alterações observadas nas assembléias fósseis: 1) dados isotópicos de oxigênio de testas de foraminíferos planctônicos e bentônicos; 2) índice de temperatura e de nutrientes; 3) equação de paleoprodutividade e 4) análises estatísticas multivariadas. Os índices de temperatura e nutrientes foram, pela primeira vez, aplicados a nanofósseis calcários do Quaternário em amostras do Atlântico Sul. A integração dos resultados sugere que as principais características oceanográficas não sofreram alterações significativas nos últimos 25.000 anos, embora condições ambientais instáveis tenham sido registradas a partir da transição do Último Máximo Glacial - Holoceno. Durante o Último Máximo Glacial a região estudada sofreu pouca variação de temperatura, funcionando como um reservatório de calor. A variação da profundidade da termoclina/nutriclina foi considerada a principal resposta às oscilações climáticas, sendo relacionada às mudanças de intensidade dos ventos alísios. / This study focuses on changes in calcareous nannofossil assemblages as an evidence of paleoceanographic variability during the last 25,000 years in two deep sea piston cores from the northeastern Brazilian continental margin. To support reconstructing ancient marine environment others proxies have been applied along with the calcareous nannofossil analysis: 1) oxygen isotopic data from planktonic and benthic foraminifers\' tests; 2) temperature and nutrient indices; 3) paleoproductivity equation and 4) multivariate analysis. For the first time the temperature and nutrient indices were employed to Quaternary calcareous nannofossil from the South Atlantic Ocean. According to presented results major oceanographic features were stable in the last 25,000 years, although instable environmental conditions were recorded in the Last Glacial Maximum - Holocene boundary. During the Last Glacial Maximum the western tropical Atlantic seems to have experienced slight temperature changes and served as a heat and salt reservoir. Nutricline and thermocline depth variation was considered the most important response to climate changes largely related to Trade Winds strength oscillation.

Esta tese apresenta o registro de variações paleoceanográficas na superfície e em oceano profundo na porção oeste do Atlântico Sul, através de evidências de nanoplâncton calcário, durante os últimos 200.000 anos. Os principais parâmetros avaliados foram relativos à paleoprodutividade primária, através de estimativas de abundância e taxa de acumulação do nanoplâncton calcário, índices paleoceanográficos de produtividade, variação de carbonato de cálcio, contribuição relativa das espécies de nanoplâncton para o carbonato de cálcio total e análises de dados geoquímicos complementares. Os dados derivam de três testemunhos coletados na Bacia de Santos entre 1900 e 2200 metros de profundidade. Os resultados demonstram que as mudanças paleoceanográficas observadas no período analisado devem estar relacionadas, concomitantemente, a variações na dinâmica do oceano na camada superficial e em oceano profundo. As evidências de paleoprodutividade primária e a subsequente deposição do nanoplâncton calcário apontam que ambas são dependentes de condições favoráveis em superfície e no fundo, respectivamente. Estas condições ocorreram durante o período de aquecimento das águas superficiais no oeste do Atlântico Sul e a retração de águas profundas de origem sul devido à intensificação da célula de revolvimento meridional do Atlântico. Os últimos 200.000 anos foram divididos em sete intervalos definidos pela variação de paleoprodutividade primária com base no registro de nanoplâncton calcário. / This thesis presents a view of the paleoceanographic changes that occurred in the surface and deep ocean in the western South Atlantic by means of calcareous nannoplankton during the last 200,000 years. Data was obtained from three sediment cores collected in the Santos Basin between 1900 and 2200 meters water depth. Estimates of primary paleoproductivity from calcareous nannoplankton abundance and accumulation rates, paleoproductivity proxies calcium carbonate content, the relative contribution of nannoplankton species to total calcium carbonate and complementary geochemical data analyzes were performed. The results demonstrate that paleoceanographic changes observed in the analyzed period may be related to changes in ocean dynamics at surface and deep ocean. Primary paleoproductivity record and the subsequent calcareous nannoplankton deposition indicate that these are dependent on surface and bottom conditions, respectively. These conditions were recorded during sea surface temperature warming in the western South Atlantic and retraction of southern-sourced deep waters due to strengthening of the Atlantic meridional overturning circulation. The last 200,000 years were divided into seven intervals defined by the changes in primary paleoproductivity record of calcareous nannoplankton.

L'étude biostratigraphique intégrée des ammonites et des nannofossiles calcaires de trois coupes du SE de la France (Vergol, Courchons et Berrias) a permis de proposer un nouveau schéma de biozonation solide pour l'intervalle Berriasien supérieur – Valanginien inférieur. Cette étude devrait permettre d'appuyer la proposition de la coupe de Vergol comme GSSP de la base du Valanginien. Pour ce qui concerne les ammonites, une exploitation intensive banc par banc et une révision taxonomique de l'ensemble des groupes ont montré un grand renouvellement faunique et ont amené à préciser le schéma zonal. Le Berriasien supérieur est caractérisée dans sa partie haute par une nouvelle zone, la zone à Alpillensis, qui remplace la partie supérieure de la zone à Boisseri sensu Le Hégarat. La zone à Alpillensis est subdivisée en deux sous-zones, à Alpillensis et à Otopeta. Pour le Valanginien inférieur, il a été reconnu la zone à Petransiens, pour laquelle deux nouvelles sous-zones, à Premolicus et à Salinarium, sont proposées, et la zone à Neocomiensiformis. Pour ce qui concerne les nannofossiles calcaires, plusieurs événements caractérisent la limite Berriasien/Valanginien, ainsi qu'un changement important des assemblages mis en évidence par une Analyse en Composante Principale. Ces changements sont liés probablement à une régression globale pendant la zone à Alpillensis suivie par une transgression pendant la zone à Pertransiens. Les Associations Unitaires ont mis en évidence une AU 1 dont le sommet se situe au dessus de la première apparition du nannofossile C. oblongata et de l'ammonite « Thurmanniceras » pertransiens. La succession de ces trois événements (« T. » pertransiens, C. oblongata et sommet de l'AU 1) m'ont amené à proposer l'identification de la limite Berriasien/Valanginien avec la première apparition de « T. » pertransiens / The integrated biostratigraphic study of ammonites and calcareous nannofossils in three sections from SE France (Vergol, Courchons, and Berrias) allowed a solid new biozonation scheme to be proposed here. This study should enable us to strengthen the proposition of the Vergol section as GSSP for the lower boundary of Valanginian. Concerning ammonites, an intensive exploitation bed by bed coupled to a taxonomic revision of all groups have shown a faunal renewal and brought to the proposal of a new zonal scheme. The Upper Berriasian is characterized in its upper part by a new zone, the Alpillensis zone, which replaces the upper part of the Boisseri zone sensu Le Hégarat. The Alpillensis zone is subdivided into two subzones, Alpillensis and Otopeta. For the Lower Valanginian, the Pertransiens (with the introduction of two new subzones, Premolicus and Salinarium) and Neocomiensiformis zones have been recognized. Concerning calcareous nannofossils, many events are recorded across the Berriasian/Valanginian boundary, underlying a major change in the assemblages as indicated by Principal Component Analysis. These changes are very likely linked to sea level changes. In fact, a major regression occurred in the Alpillensis zone, followed by a transgression in the Petransiens zone. Unitary Associations resulted in an UA 1 whose topmost part occurs just above the first occurrences of the nannofossil C. oblongata and of the ammonite « Thurmanniceras » pertransiens. The stratigraphic succession of these three events (namely, the FOs of « T. » pertransiens and of C. oblongata and the top of UA 1) allow us to identify the boundary between the Berriasian and Valanginian in this work with the FO of « T. » pertransiens

Le biome marin du Toarcien inférieur a subi une des crises les plus significatives de l'histoire de la Terre, qui a affecté les mers épicontinentales du globe. Ces bassins épicontinentaux sont également caractérisés par l'accumulation de grandes quantités de matière organique dans les sédiments de l'époque, ce qui a été interprété comme le résultat d'un Evénement Anoxique au Toarcien inférieur (T-OAE, ~183 Ma). Le nannoplancton calcaire, qui fait partie des organismes le plus sensibles aux conditions environnementales des eaux océaniques de surface, a été profondément affecté par cette crise et sa récupération se mit en place seulement à la fin du Toarcien inférieur. Si le T-OAE a été étudié en grand détail ces dernières années, la période de récupération est beaucoup moins bien connue. A ce stade, nous ne savons pas, notamment, si la récupération de la production carbonatée primaire est représentée par un épisode rapide ou par une suite d'événements (qui feraient partie d'un plus long processus) intervenus sur quelques millions d'années après le T-OAE. Pendant les perturbations environnementales qui ont eu lieu au Toarcien inférieur, des fluctuations importantes du niveau marin ont été interprétées ainsi que des variations de la température des eaux océaniques. Après le T-OAE, le niveau marin et les températures montrent des changements plus graduels pendant une grande partie du Toarcien supérieur-Aalénien inférieur et les niches écologiques occupées par le nannoplancton calcaire sont ré-établies. Ces conditions de relative stabilité sur le long terme (~10 Ma) sont idéales pour étudier les dynamiques de la communauté des nannofossiles calcaires et, notamment, comment les différents taxons réorganisent leurs relations synécologiques. Le Toarcien-Aalénien est une période clé dans l'évolution du nannoplancton calcaire, avec des nouveaux genres qui apparaissent. Les nannofossiles de cet intervalle restent relativement peu étudié dans le Bassin Lusitanien, malgré l'importance de cette région d'un point de vue paléocéanographique. En effet ce bassin, qui était à l'origine un rift avorté lié à l'ouverture de l'Atlantique, a permis les connections entre des masses d'eaux de provenance NW européenne et sud-téthysienne. C'est dans cette région que nous retrouvons donc des mélanges de taxons liés à des différentes provinces géographiques / At ~183 Ma when large amounts of organic matter was dumped onto the ocean beds (known as the Toarcian Oceanic Anoxic Event, T-OAE), the Early Toarcian marine biota experienced one of the most important biological crises in Earth history. Calcareous nannoplankton was deeply affected and started only to recover from the end of the Early Toarcian. After the T-OAE, as phytoplankton communities dwelling the oceans photic layer recover from the previous disturbing conditions, the ecological niches once occupied by calcareous nannoplankton are again replenished. Located in the westernmost part of the Tethyan ocean, the Lusitanian Basin acted as a seaway between the NW Tethys and the Mediterranean Tethys provinces, therefore been actively influenced by these two different water masses. Hence such a region stands as the perfect spot to study the calcareous nannoplankton community, as its fossil remains bears species typical of both provinces. In order to appraise the nannoplankton demise and subsequent recovery, absolute and relative abundances of nannofossils were determined from pelagic marl-limestone couplets from three sections of the Lusitanian Basin. Also brachiopods shells were investigated for stable carbon and oxygen isotopes analysis. In order to independently assess the morphologic evolution of Lotharingius coccoliths, a Toarcian section from south France was studied. Different statistic methodologies were used throughout this work, in order to screen for robust and significant information from the numerous datasets that were built / Há cerca de 183 milhões de anos atrás, a biota marinha sofreu uma das mais importantes crises biológicas na história do planeta, quando grandes quantidades de matéria orgânica foram depositadas nos fundos oceânicos. Este episódio que teve lugar durante o Toarciano, resultou de um Evento Anóxico Oceânico (T-OAE), e afectou os mares epicontinentais à escala global. O nanoplâncton calcário, um grupo de organismos extremamente sensível às variações nas condições ambientais que têm lugar na camada superficial das massas de água, foi profundamente afectado. Foi somente no final do Toarciano Inferior que a sua recuperação se iniciou. Apesar de já muito se ter escrito sobre o T-OAE, a previsível recuperação deste grupo nunca foi sistemática nem detalhadamente estudada. Até hoje, não se sabia ainda se esta recuperação teria sido relativamente rápida, ou resultado de um processo lento e gradual que teria durado milhões de anos. Durante o Toarciano Inferior, quando as condições ambientais eram extremamente instáveis, ocorreram importantes e drásticas oscilações na temperatura e no nível médio dos oceanos. Após o T-OAE e durante todo o Toarciano e Aaleniano Inferior, as oscilações do nível médio dos oceanos e de temperatura são bastante mais suaves. À medida que a comunidade fitoplanctónica instalada na zona fótica recupera das condições extremas anteriores, os nichos ecológicos antes ocupados por nanoplâncton calcário, começam novamente a ser preenchidos. Apesar das prolongadas e suaves variações abióticas, é num ambiente então mais estável, que melhor se pode observar a evolução deste grupo, e de que forma as suas relações sinecológicas se alteraram ao longo de aproximadamente 10 milhões de anos. Apesar de ser considerado como um período onde a comunidade nanoplanctónica sofreu importantes alterações, nada se sabe em concreto que alterações foram essas que tiveram lugar após o TOAE num local tão estratégico como a Bacia Lusitânica. Situada na extremidade Oeste do Tétis e fazendo parte de um rift originado pela abertura do Atlântico, a Bacia Lusitânica actuou como um corredor que ligava livremente as massas de água das províncias mediterrânica e NW do Tétis, sendo por estas, activamente influenciada. Por essa razão, tal situação geográfica constitui um local excepcional para se estudar a comunidade de nanoplâncton calcário, uma vez que o seu registo fóssil compreende espécies típicas destas duas províncias do Tétis