Modificações nas concentrações iônicas em substratos de água rasa provocadas por micro-orgnaismos vêm demonstrando valorosas relevâncias tanto em fossilizações quanto precipitações de calcita, aragonita, dolomita, pirita e minerais de sílica e fosfato. Dados micropaleontológicos, petrográficos e geoquímicos, comumente estudados separadamente, quando integrados, podem elucidar questões sobre a formação destes minerais. A Formação Assistência (Subgrupo Irati, Permiano da Bacia do Paraná, Brasil) apresenta células e estruturas normalmente associadas a atividades microbianas, como microesferas dolomíticas, quartzo microcristalino e pirita. Microfósseis foram reconhecidos e seus processos de fossilização reconstituídos. Sílex, dolomito e folhelho de diversos níveis e localidades foram estudados utilizando-se seções petrográficas normais e polidas; resíduos orgânicos extraídos por dissolução ácida (HF/HCl); superfícies corroídas com dissolução parcial com HF; microscopia petrográfica e eletrônica de varredura (MEV); espectroscopia Raman e de energia dispersiva de raio-X (Energy Dispersive X-ray-EDX) e florescência e difratometria de Raio-X. As prospecções iniciais revelaram alta variedade de microfósseis de parede orgânica (cianobactérias; grãos de pólen; clrófitas; acritarcos; fitoclástos; escolecodontes; palinoforaminíferos e raros grãos de esporos) e microesferas dolomíticas. Diferentemente das pesquisas tradicionais sobre palinoestratigrafia, que utilizam de resíduos de rochas siliciclásticas finas, a petrografia do sílex diagenético revelou uma microbiota fóssil composta principalmente por delicadas cianobactérias. Permitiu também o reconhecimento de estágios ontogenéticos e de feições tafonômicas tais como a morfologia tridimensional de vesículas orgânicas e agregações polínicas. Estas preservações excepcionais é resultado de silicificação extremamente eodiagenética. Todas as amostras examinadas por florescência e difratometria de Raio-X apresentaram predomínio de sílica e dolomita e menores quantidades de pirita. Ao contrário dos nódulos e lentes de sílex de outros níveis, conhecidos de outras posições estratigráficas, somente o sílex maciço da Camada de Brechas Evaporíticas (CBE) demonstrou abundantes células de parede orgânica e estruturas preenchidas (fenestras e fraturas) com bordas dolomíticas. A sílica deste nível, portanto, foi gerada por fluídos supersaturados que substituíram a dolomita pré-existente. Analises com MEV e EDX revelaram cianobactérias fossilizadas com invólucros orgânicos (paredes celulares e/ou bainhas extracelulares) e regiões protoplasmáticas preenchidas por quartzo microcristalino. Comparações com estudos laboratoriais e ambientais demonstraram, em primeiro lugra, como a interação entre moléculas nas superfícies das células e íons em solução retiveram os componentes dos invólucros celulares e mineralizaram as demais partes das células. Em segundo lugar, porque o sílex da CBE também concentra microesferas dolomíticas agregadas em grandes quantidades e associadas e materiais carbonosos. Camadas externas recobrem esferas individuais, pequenos conjuntos e superfícies arredondadas. Nem toda microesfera exibem interiores celulares preenchidos por dolomita. Além das afinidades biológicas, as análises permitiram deduzir como certas condições na interface água/biosedimento provocaram a precipitação deste tipo de dolomita. Tais condições são relacionadas a salinidade, oxido-redução, razões \'Mg POT 2+\'/\'Ca POT 2+\' e atividades biológicas pretéritas tais como acumulações de substâncias poliméricas extracelulares (EPS - extracelular polymeric substances) e processos microbianos anóxicos (e.g.redução de sulfato e metanogênese). Foi possível também se reconhecer a sequência de mineralização (dolomitização e silicificação) bem como certas etapas que levaram a preservação de bainhas e interiores celulares. Os dados obtidos lançam novas perspectivas às discussões globais sobre o \"problema da dolomita\". / Microbial modification on ionic concentrations of shallow=water substrates recently reached valuable results both on fossilization and precipitation of calcite, aragonite, dolomite, pyrite, and minerals of silica and phosphate. Data on micropaleontology, petrography, and geochemistry, which are often sudied separately, when treated together, improve the understanding of the formation of these minerals. The Permian Assistência Formation of the Irati Subgroup in the Brazilian Paraná Bassin bears preserved cells and structures commonly associated with microbial activities, such as dolomite microspheres, microcrystalline quartz and pyrite. Microfossils were recognized and their processes of fossilization reconstituted. Chert, dolostone and shale from many stratigraphic leves and locations were studied by the use of normal and polished petrographic section; estracted organic residues via HF/HCL attach, HF-etched surfaces; petrographic microscopy; scanning electron microscopy (SEM); Raman and Energy Dispersive X-ray (EDX) spectroscopy; fluorescence and diffraction of X-ray. The initial surveys revealed a large variety of organic-walled microfossils (cyanobacteria, pollen grains, chlorophytes, acritarchs, phytoclasts, scolecodonts, palynoroaminifers and rare spores) and dolomitic microspheres. Unlike traditional researhce on palynostratigraphy, which employ organic residues from fine siliciclastic rocks, the petropgraphy of diagenetic chert revealed abundant fossil microbiota composed principally of delicate cyanobacteria. This procedure allowed also the recognition of ontogenetic stages of micoorganisms and taphonomic features such as three-dimensional morphology of organic vesicles and the pollen aggregations. This excellent preservation results from extreme eodiagenetic silicification. Every chert sample examined by fluorescence and X-ray diffraction shows mostly silica and dolomite with a minor amounts of pyrite. Unlike the nodules and lens of chert from other levels,which are known in many stratigraphic sequence, only the massive chert from Brecciated Evaporite Beb (BEB) bears abundant organic-walled cells and filled structures (fenestrae and fractures) exhibiting dolomitic edges. Silica from this sequence, therefore, was generated from supersaturated fluid solutions replacing pre-existing dolomite, preserving the organic content. The SEM and EDX revealed fossilized cyanobacteria with organic involucres (cell walls and/or extracellular sheath) and protoplasmatic region filled by microcrystalline quartz. Comparison with laboratory and environmental studies show, firstly, how the interaction between molecules in the cell surfaces and ions in solution retained the organic components of cellular surfaces and mineralized portions at the other parts of cells, and secondly, why BEB chert is massive at the expense of others relatively smaller in size and the occurrence of chert in other sequences. The quartzitic matrix of the BEB chert also concentrate dolomitic microspheres, which are aggregated in large quantities and associated with carbonaceous material. Outer layers coat indivisual shperes, small clusters and rounded surfaces. Not every microsphere exhibit the filling of dolomite in the interior of cells. Beyond their biological affinity, this analysis allowed the evaluation of how certain conditions on water-biosediment interface led to the precipitation of this kind of dolomite. Such conditions are related to salinity, redox, \'Mg POT 2+\'/\'Ca POT 2+\' ratios, and ancient biological activities such as the accumulation of extracellular polymeric substances (EPS) and anoxic microbial processes (e.g. sulfate reduction, methanogenesis). It was also possible to recognize the mineralization sequence (dolomitization and silicification) as well as certain steps that led to the preservation of sheaths and some cell interiors. The acquired data launches a new prospect for global discussions on the \"dolomite problem\".

The Gorda Escarpment (40.4° N and from 126° W to 124.7° W) is a topographic high which is the eastern portion of the Mendocino Transform Fault. The Vizcaino Block is the anomalously shallow portion of the Pacific plate immediately south of the Gorda Escarpment. Sediments of the Vizcaino Block record a history of uplift and subsidence for itself and the Gorda Escarpment. Previous work on the Mendocino Ridge (the bathymetric expression of the Mendocino Transform Fault west of 126° W, where there is little sediment overlying basement) indicated that the ridge had been above sea level at some time in the past (Krause et al., 1964; Fisk et al., 1993). Assuming that the two bathymetric features have undergone the same response to tectonic forces, this study aims to constrain the timing of uplift and subsidence for the Gorda Escarpment, Vizcaino Block, and Mendocino Ridge by using the geological record of sediments of the Vizcaino Block. ODP Site 1022 drilling penetrated 379 meters into the Vizcaino Block's sediments. Age and lithologic constraints from the recovered cores, along with in-situ sampling by ROV and gravity cores, were integrated with a network of 25 seismic reflection lines. From these it is evident that uplift of the Gorda Escarpment and Mendocino Ridge began before 6 Ma, and was at a maximum at 2.7 Ma. Ocean circulation was likely altered by the uplift of the Gorda Escarpment and Mendocino Ridge. In turn, the altered ocean circulation regime may have had an impact on the regional climate in the Pliocene. From 2.7 Ma until the present the Gorda Escarpment, the Vizcaino Block and the Mendocino Ridge have been subsiding. / Graduation date: 2003

Thesis (doctoral)--Ludwig-Maximilians-Universität München, 2003. / Accompanying CD-ROM includes color images of all figures. Includes bibliographical references (p. 130-135). Original thesis in German available online via the Internet.

Bibliography: pages 45-55. / Eleven gravity cores from the continental margin off Eire and Land's End (SW England) were examined and found to document the major trends of the Late Pleistocene climate. Several stratigraphic indicators; - carbonate content, sediment texture, grain size, composition, nature of terrigenous components, ice-rafted debris and foraminiferal diversity were examined and show that the glacial history of the study area can be closely correlated with the palaeoclimatic evolution of the adjacent European shelf. Sediments deposited during Late Pleistocene glacial conditions show the following characteristics when compared to the surface sediments deposited under Holocene interglacial conditions: an increase in the quantity of ice-rafted debris and percentage of mica, and a notable increase in the degree of frosting and pitting of the quartz grains. Overall grain size was finer resulting in a silty sediment package. Sedimentologically the cores fall into two groups (1 and 2). The major difference being that Group 1 (located on the Pendragon Escarpment) received increased quantities of fine silts from a 'shelf spill-over' mechanism operating on the Fastnet and Western Approaches Basins, during glacial regressions. All sediment samples displayed polymodal characteristics reflecting the interaction of several different physical processes e.g. ice-rafting, contour currents etc. Striking variations in the populations of planktonic foraminifera were noted, alternating between Arctic and Sub-Arctic assemblages, reflecting the waxing and waning of glacial activity. The coccolith-carbonate minima correlate with the Arctic-fauna maxima and the ¹⁸O/¹⁶O maxima of the oxygen-isotope curves. Foraminiferal-test analysis (ratio of whole foraminifera fragmented foraminifera) revealed that no correlation existed with any of the other parameters analysed. However, the cores were severely affected by the presence of bottom currents which were strong enough to remove the fragmented tests. Parallellaminated contourites and evidence of erosion were noted in all cores. Ten cores penetrated sediments deposited during the last glacial maximum of 20,000 B.P - 18,000 B.P. near the 75cm depth mark (Core 1865 was too short to reach such sediments). However sediments reflecting the 11,000 B.P glacial readvance, detected at around the 25cm mark, were not as clearly represented. Bioturbation has smoothed the climatic record throughout the lengths of these cores and has also suppressed the high-frequency oscillations (<10³ B.P).

No description available.

L’objectif de ce travail était d’étudier la variabilité de la circulation océanique méridienne aux échelles de temps pluri décennales dans l’océan Atlantique nord au cours des deux mille dernières années, ainsi que son lien avec la variation de l’extension des gyres subtropicales et subpolaires. J’ai donc étudié, à partir de carottes de sédiments marins à fort taux de sédimentation, l’évolution de la température des eaux de surface et de la stratification de la colonne d’eau en lien avec le fonctionnement des gyres subpolaire et subtropicale.Compte tenu des difficultés spécifiques à la période de temps considérée, la première partie de mon travail a consisté à contraindre le milieu et la période de calcification des principaux foraminifères utilisés, à partir de la composition isotopique de l’oxygène analysée dans la coquille des foraminifères planctoniques. J’ai également précisé la calibration en Magnésium et en Calcium en fonction de la température. La deuxième partie de mon travail a consisté à reconstruire les conditions hydrologiques dans des zones clés de l’océan Atlantique Nord sur les deux mille dernières années. J’ai ainsi construit un index de la gyre subpolaire à partir d’un gradient de température Est-Ouest, qui traduit l’intensité dynamique de la gyre subpolaire et de la gyre subtropicale. L’apport de l’analyse des foraminifères planctoniques profonds a permis de reconstituer les variations de la colonne d’eau supérieure. La stratification plus ou moins marquée de la colonne d’eau est reliée directement à l’intensité des vents d’Ouest. Les similitudes entre les vents et l’index de gyre m’ont amené à proposer un couplage entre l’océan et l’atmosphère aux échelles de temps pluri décennales.La dernière partie de ma thèse s’est focalisée sur les conséquences des variations de la dynamique des gyres océaniques sur le transport de chaleur vers les hautes latitudes ainsi que sur l’impact des variations des vents d’Ouest sur le climat européen. / The purpose of this thesis was to study the surface oceanic circulation in the North Atlantic Ocean during the last 2,000 years, and its link with the intensity of the subpolar and the subtropical gyres. To fulfill these objectives, I studied sediment cores with a high sedimentation rate to reconstruct the multidecadal variability of the temperature and the water column stratification, controlled by the dynamic of oceanic gyres. To improve the marine paleoclimatic signal recorded from planktonic foraminifera, I constrained their growing season and their calcification depth by analyzing the oxygen isotopic composition of their calcitic shells. I also established calibrations between Mg/Ca ratio and temperature for the main species used.I applied these calibrations to reconstruct the hydrological conditions in key areas of the North Atlantic Ocean. I constructed an index of the subpolar gyre that traduces the dynamic intensity of the subpolar gyre and the subtropical gyre. I also studied the variability of the upper water column based on the analysis of deep-dwelling foraminifera. I interpret past changes in the water column stratification as resulting from changes in the intensity of Westerly winds. The similarities between the wind forcing evolution and the index of the subpolar gyre dynamics led me to propose a coupling between the ocean and the atmosphere on the multidecadal time scale. The consequences of the gyres dynamic on heat transport and the impacts of the change in westerly wind strength on European climate are studied in the last part of the manuscript.

O estudo de lâminas delgadas de sílex de origem diageneticamente precoce de diversos níveis estratigráficos e localidades da Formação Assistência no Estado de São Paulo revelou pela primeira vez uma assembléia de microorganismos orgânicos delicados, excepcionalmente bem preservados neste importante marco estratigráfico e paleontológico do Neopermiano da Bacia do Paraná. Esta assembléia consiste principalmente de organismos unicelulares, dominados por cianobactérias, tanto solitárias como coloniais, sem nenhum indício de filamentos. Inclui também uma provável clorófita cocoidal, grãos de pólen e fitoclastos, além de alguns microfósseis de afinidades incertas. Estudos paleopalinológicos de resíduos orgânicos desta formação nunca detectaram os elementos delicados desta microbiota. O exame petrográfico permitiu observar não somente todos os microorganismos fósseis em três dimensões no interior da rocha, mas também a distribuição espacial original dos microorganismos e suas relações com os outros componentes da rocha. Isto facilitou a avaliação da variedade morfológica dos microfósseis resultante da degradação e permitiu inferir padrões ontogênicos de alguns dos táxons descritos. Dentre eles, foram reconhecidos 14 morfotipos, reunidos em cinco espécies (todas novas) com afinidades biológicas conhecidas (quatro espécies de cianobactérias e uma clorófita) e cinco táxons incertae sedis (dois novos). A microbiota ocorre principalmente no sílex na base da formação. Constitui massas volumosas e densas preservadas in situ interpretadas como organismos originalmente bentônicos, capazes de formar esteiras microbianas e pequenos estromatólitos. A sedimentologia aliada à ampla extensão geográfica, ao hábito, à abundância e à natureza exclusivamente unicelular dos microorganismos fósseis, alem de exemplos atuais análogos, indicam um paleoambiente aquoso raso de salinidade alta, talvez hipersalina com salinidade variável. / The study of petrographic thin sections of early diageneteic chert from diverse levels and localities of the Assistência Formation in the state of São Paulo, Brazil, revealed for the first time an exceptionally well-preserved assemblage of delicate fossil microorganisms in this important stratigraphic and paleontological Early Permian marker unit of the Paraná Basin. This assemblage consists primarily of delicate colonial and solitary unicellular microfossils, dominated by cyanobacteria, without any evidence whatsoever of filamentous microorganisms. It also includes a probable cocoidal chlorophyte, pollen grains and phytoclasts, as well as several less common microfossils of uncertain biological affinity. None of the delicate microfossils of this assemblage have ever been detected in palynological analyses of organic residues from this formation. The study of thin sections made it possible to observe not only all of the fossil microorganisms in three dimensions within the rock but also their original spatial distribution and relationships with other components of the rock. This facilitated evaluation of the morphological diversity of the fossil microorganisms and permitted inferences as to possible ontogenetic patterns. Fourteen morphotypes were recognized among the more delicate microfossils and attributed to five species (all new) of known biological affinities (four species of cyanobacterias and one chlorophyte) and five taxa of Incertae Sedis. The fossil microbiota occurs principally at the base of the formation as dense, voluminous masses interpreted as remains of an in situ benthonic microbiota of photosynthetic microorganisms capable of forming microbial mats and small stromatolites. The sedimentology, together with the widespread distribution, habit, abundance and exclusively unicellular nature of the fossil microorganisms and the paleoenvironmental implications suggested by analogous modern examples, are consistent with a shallow aquatic habitat of high and perhaps variable salinity for the microbiota.

Der Südozean ist die Schlüsselregion zur Kenntnis der neogenen Klimaentwicklung. In diesem Zusammenhang ist die Untersuchung von planktonischen Gemeinschaften in Hinblick auf die Umweltentwicklung von großer Bedeutung. In antarktischen neogenen Sedimenten sind Radiolarien reichlich, in großer Diversität und einheitlich gut erhalten. Sie sind nicht nur perfekte Testobjekte für paläobiologischen Studien, sondern auch eine wichtige Quelle für eine verbesserte Biostratigraphie – bisher behinderte nämlich das Fehlen einer verlässlichen Geochronologie detaillierte Studien. Es wurde ein Datensatz aller Taxa von mehreren Standorten des Südozeans gesammelt: für alle der 98 Proben je ca. 7000 Radiolarien. Die Fauna enthält ca. 500 Arten (inclusive 120 neuer Taxa). Die Untersuchung der Makroevolutionsgeschichte dieser Fauna zeigt, dass eine wesentliche ökologische Umwälzung, ohne Aussterbeereignis, bezogen auf den Verlauf der Artengleichheit und den Anstieg der Gattung Antarctissa, bei ca. 8 Ma erfolgte. Dann, 3 My später, folgte ein wesentlicher Diversitätsverlust. Obwohl das ökologische Ereignis eventuell mit einer Änderung der Primärproduzenten assoziiert sein kann, ist der auslösende Faktor des Diversitätsabfalls unbekannt. Außerdem zeigt der Vergleich zwischen der Diversitätsgeschichte dieser Fauna und einer Paläodiversitätsrekonstruktion südozeanischer Faunen, beruhend auf der Neptune Datenbank, daß der generelle Verläufe mit den Probenteilungsmethodologien nachgezeichnet wird, jedoch diese Methodologien aufgrund grober Verzerrungen nicht geeignet für Detailstudien sind. Schließlich wurde eine biostratigraphische Analyse für die komplette Fauna vom Obermiozän bis Pliozän durchgeführt. Obwohl diese Analyse noch vorlaüfig ist, zeigt sich eine Angleichung des aktuellen Altersmodells um mehr als 1 My. Diese Studie zeigt auch 94 neue, sichere Ereignisse, die für die stratigraphische Einordnung der Antarktischen Sedimente genutzt werden können. / The Southern Ocean is the key to understand the Neogene climate evolution. Unfortunately the lack of a robust geochronological framework has hindered precise studies. Equally of interest is understanding how planktonic communities changed in relation with the evolution of these environments. Radiolarians are abundant in Antarctic Neogene sediments, diversified and consistently well-preserved. They should constitute not only an ideal testing ground for paleobiological studies but also a major resource for improved biostratigraphy. In this study, a quantitative, taxonomically-complete dataset have been collected in various sites of the Southern Ocean, using 98 samples and ca. 7000 specimens per sample. Ca. 500 species were uncovered in this fauna, including 120 new to science. The study of the macroevolutionary history of this fauna reveals that a significant, extinctionless ecological turnover, linked to a decrease in the evenness of the species'' abundances and the rise of genus Antarctissa to dominance, occured at ca. 8 Ma, followed 3 My later by a significant diversity loss. Although the ecological event can be tentatively associated with a regional change in the composition of primary producers, the triggering event of the diversity loss is yet to be found. The whole-fauna diversity history was compared to paleodiversity reconstructions computed using subsampling methodologies from the occurrences gathered in the Neptune database. The comparison shows that the main trends are retrieved by the subsampling procedures but also that substantial distortions make them poorly suited for detailed studies. Finally a biostratigraphical analysis was conducted on this whole-fauna dataset for the late Miocene - Pliocene sequence. Although this analysis is still very much preliminary, it shows a coherent readjustement of the current age models by more than 1 My. This study also shows that 94 events seem reliable enough to be used to correlate Southern Ocean sites together.

O estudo de lâminas delgadas de sílex de origem diageneticamente precoce de diversos níveis estratigráficos e localidades da Formação Assistência no Estado de São Paulo revelou pela primeira vez uma assembléia de microorganismos orgânicos delicados, excepcionalmente bem preservados neste importante marco estratigráfico e paleontológico do Neopermiano da Bacia do Paraná. Esta assembléia consiste principalmente de organismos unicelulares, dominados por cianobactérias, tanto solitárias como coloniais, sem nenhum indício de filamentos. Inclui também uma provável clorófita cocoidal, grãos de pólen e fitoclastos, além de alguns microfósseis de afinidades incertas. Estudos paleopalinológicos de resíduos orgânicos desta formação nunca detectaram os elementos delicados desta microbiota. O exame petrográfico permitiu observar não somente todos os microorganismos fósseis em três dimensões no interior da rocha, mas também a distribuição espacial original dos microorganismos e suas relações com os outros componentes da rocha. Isto facilitou a avaliação da variedade morfológica dos microfósseis resultante da degradação e permitiu inferir padrões ontogênicos de alguns dos táxons descritos. Dentre eles, foram reconhecidos 14 morfotipos, reunidos em cinco espécies (todas novas) com afinidades biológicas conhecidas (quatro espécies de cianobactérias e uma clorófita) e cinco táxons incertae sedis (dois novos). A microbiota ocorre principalmente no sílex na base da formação. Constitui massas volumosas e densas preservadas in situ interpretadas como organismos originalmente bentônicos, capazes de formar esteiras microbianas e pequenos estromatólitos. A sedimentologia aliada à ampla extensão geográfica, ao hábito, à abundância e à natureza exclusivamente unicelular dos microorganismos fósseis, alem de exemplos atuais análogos, indicam um paleoambiente aquoso raso de salinidade alta, talvez hipersalina com salinidade variável. / The study of petrographic thin sections of early diageneteic chert from diverse levels and localities of the Assistência Formation in the state of São Paulo, Brazil, revealed for the first time an exceptionally well-preserved assemblage of delicate fossil microorganisms in this important stratigraphic and paleontological Early Permian marker unit of the Paraná Basin. This assemblage consists primarily of delicate colonial and solitary unicellular microfossils, dominated by cyanobacteria, without any evidence whatsoever of filamentous microorganisms. It also includes a probable cocoidal chlorophyte, pollen grains and phytoclasts, as well as several less common microfossils of uncertain biological affinity. None of the delicate microfossils of this assemblage have ever been detected in palynological analyses of organic residues from this formation. The study of thin sections made it possible to observe not only all of the fossil microorganisms in three dimensions within the rock but also their original spatial distribution and relationships with other components of the rock. This facilitated evaluation of the morphological diversity of the fossil microorganisms and permitted inferences as to possible ontogenetic patterns. Fourteen morphotypes were recognized among the more delicate microfossils and attributed to five species (all new) of known biological affinities (four species of cyanobacterias and one chlorophyte) and five taxa of Incertae Sedis. The fossil microbiota occurs principally at the base of the formation as dense, voluminous masses interpreted as remains of an in situ benthonic microbiota of photosynthetic microorganisms capable of forming microbial mats and small stromatolites. The sedimentology, together with the widespread distribution, habit, abundance and exclusively unicellular nature of the fossil microorganisms and the paleoenvironmental implications suggested by analogous modern examples, are consistent with a shallow aquatic habitat of high and perhaps variable salinity for the microbiota.

L’intervalle Aptien-Albien inférieur de la marge sud-téthysienne est mal connu en raison de successions souvent incomplètes et de difficultés à les dater. Le Bassin d’Essaouira-Agadir (BEA), au Maroc, présente de nombreuses coupes, bien exposées et accessibles du Crétacé inférieur. Le but de ce travail est de (1) établir un cadre stratigraphique intégré de la série apto-albienne, basé sur (a) la biostratigraphy haute résolution des ammonites et des nannofossiles calcaires, (b) l’identification des discontinuités sédimentaires et (c) la stratigraphy isotopique du carbone; (2) reconstituer l’évolution paléoenvironnementale pendant cet intervalle, par l’étude des facies sédimentaires et l’analyse qualitative et quantitative des nannofossiles, et (3) proposer un modèle de fonctionnement de la plateforme-rampe mixte, carbonate-clastique, du BEA.Dans le BEA, le Barrémien supérieur est défini par la zone d’ammonites à sarasini et par la zone de nannofossiles NC5. La limite Barrémien-Aptien est définie par les ammonites. L’Aptien inférieur est déterminé par les zones d’ammonites à desahayesi jusqu’à furcata, et est limité par un premier minimum de 13C à la base, et par un premier maximum à la limite Aptien inférieur-moyen. L’Aptien supérieur est défini par quatre zones d’ammonites (martini, melchioris, nolani et jacobi), deux surfaces de discontinuité, quatre maxima et minima de 13C, et comprend la partie supérieure de NC6, NC7 et la base de NC8. La limite Aptien-Albien est placée dans la discontinuité D4 (base de la zone d’ammonites à Leymeriella tardefurcata), en accord avec la première occurrence (FO) des nannofossiles Prediscosphaera columnata et Hayesites albiensis, et par une diminution des valeurs de 13C. L’Albien inférieur est daté par les zones d’ammonites à tardefurcata et mammillatum, par la FO du nannofossile Hayesites albiensis, et par des valeurs minimales de 13C.Les faciès et environnements de dépôt des sédiments aptien à Albien inférieur ont été déterminés par leur lithologie, les figures sédimentaires, leur contenu faunique et les microfaciès. Ils ont permis d’identifier (1) quatre types de surface liées à des érosions subaériennes ou sous-marines, (2) quatre faciès sédimentaires carbonatés dans l’Aptien, correspondant à des environnements de rampe interne à distale, et (3) quatre faciès sédimentaires argilo-gréseux dans l’Albien inférieur, représentant des dépôts de rampe médiane à hémipélagiques. Ces faciès reflètent des milieux adjacents et passant de l’un à l’autre. L’intervalle Aptien-Albien inférieur du BEA a été subdivisé en deux cycles, soulignés par deux surfaces d’érosion majeures. Le cycle Barrémien terminal-Aptien est souligné par une surface karstifiée et erosive et comprend quatre séquences de dépôt de troisème ordre. Le cycle Albien surmonte une surface majeure d’érosion sous-marine, et contient au moins quatre sequences de dépôt. Dasns chaque cycle, l’évolution vertical des faciès indique un approfondissement ds milieux de depot liée à une hausse eustatique.Dans le BEA, production carbonatée est plus élevée à l’Aptien qu’à l’Albien inférieur, en raison d’un climat chaud, une lente montée du niveau de la mer, un milieu de dépôt peu profond et de faibles apports détritiques. L’abondance totale absolue des nannofossiles décroît entre l’Aptien et l’Albien inférieur, en raison d’un taux de sedimentation plus élevé associé à une subsidence plus rapide. L’apport en nutriments, la fertilité et la production primaire sont plus élevés à l’Albien inférieur qu’à l’Aptien, et sont principalement contrôlés par la montée du niceau de la mer et les courants d’upwellings. La transition Aptien terminal-Albien inférieur est marquée par l’abondance de taxons d’eau froide et par la migration de faunes cosmopolitaines du domaine boréal vers le domaine téthysien, qui pourrait traduire un événement climatique froid, voire glaciaire. / The Aptian-Early Albian interval of the southern Tethyan margin is poorly understood since sedimentary successions are frequently incomplete and dating is difficult. The Essaouira-Agadir Basin (EAB), Morocco, presents numerous, very good and accessible outcrops of the Early Cretaceous series. The aim of this work is to (1) establish an integrated stratigraphic framework of the Aptian-Albian series based on (a) high-resolution ammonites and calcareous nannofossil biostratigraphy, (b) identification of sedimentary discontinuities and (c) carbon isotope stratigraphy; (2) reconstruct the paleoenvironmental evolution during this interval through both sedimentary facies evolution and qualitative and quantitative nannofossil analyses, and (3) propose a functioning model for the sedimentation on the mixed, carbonate/clastic ramp of the EAB.In the EAB, the Late Barremian is defined by the sarasini ammonite zone and the NC5 nannofossil zone. The Barremian/Aptian boundary is defined by ammonites. The Early Aptian is defined by the deshayesi to furcata ammonite zones, and is bounded by a first minimum 13C value at the base and a first maximum value at the Early/Late Aptian Boundary. The Late Aptian interval, is defined by four ammonite zones (martini, melchioris, nolani and jacobi), two discontinuity surfaces, four maximum and minimum 13C values, and by the upper part of the NC6, the NC7 and the lowermost part of the NC8 nannofossil zones. The Aptian/Albian boundary is placed within the discontinuity D4 (base of the Leymeriella tardefurcata ammonite zone), supported by the First Occurrence (FO) of the Prediscosphaera columnata and Hayesites albiensis nannofossil taxa, and by decreasing 13C values. Early Albian times are represented by the tardefurcata and mammillatum ammonite zones, the FO of Hayesites albiensis, and by minimum 13C values.The facies and depositional environments of the Aptian-Early Albian rocks are identified based on their lithology, sedimentary structures, fossil content and microfacies. These allowed to identify (1) four types of key surfaces related subaerial or submarine erosion, (2) four sedimentary carbonated facies in the Aptian corresponding to outer to inner ramp depositional environments, and (3) four Early Albian sedimentary facies, represented by sandstones and shales, of basin to middle ramp depositional setting. These facies reflect deposition in adjacent and gradational paleoenvironments. The Aptian-Early Albian stratigraphic interval of the EAB, has been subdivided into two major cycles, floored by two major erosional surfaces. The latest Barremian-Aptian cycle is underlined by a major karstified-erosional surface and consists of four third-order depositional sequences. The Early Albian cycle, overlies a major submarine erosional surface, and also contains four depositional sequences. In each cycle, the vertical changes in facies indicates a deepening upward trend related to sea level rise.The carbonate production in the EAB is higher in the Aptian than during the Early Albian, due to warm conditions, slow rise of sea level, shallow depth of the basin, and little detrital influx. The nannofossil total absolute abundance decreases from the Aptian to the Early Albian, due to increasing sedimentation rate, associated with rapid subsidence. The nutrient input, fertility and calcareous nannofossil primary productivity is higher in the Early Albian with respect to the Aptian, and are mainly controlled by rising sea level and upwelling currents. The Latest Aptian-Early Albian period is characterized by a high abundance of cold taxa, and the migration of cosmopolitan biota from Boreal realm into the Tethyan realm, which may reflect the occurrence of a glacial climatic event.