Ediacaran phosphorites provide a principal record of the paleoenvironmental and paleoecological conditions of the oceans during Earth's second major oxygenation and the evolution of complex life. Although the fidelity of this record is high, diagenesis and metamorphism frequently alter or overprint primary minerals and structures, necessitating validation of results from mineralogical and geochemical analyses and determinations of fossil affinities. Therefore, it is imperative to unravel the complications of post-depositional alteration, and thus provide a strong foundation for environmental and biological interpretations, via an integrated sedimentological, stratigraphic, petrographic, and geochemical approach. Transmitted light, cathodoluminescence, and scanning electron microscope petrography in conjunction with Raman spectroscopic and X-ray diffraction analyses were employed to determine the origin of phosphorites from the early Ediacaran (632 – 614 Ma) Doushantuo Formation at the Wanjiagou section, near Zhangcunping, Hubei Province in South China. Results suggest granular phosphorites were deposited during one to two episodes of reworking of pristine phosphorite hardgrounds, which originated during redox-controlled and/or microbially-mediated phosphogenesis. Granular laminae were then cemented by a ferric iron-phosphate mineral, phosphosiderite. As a product of oxidative weathering and/or thermal stabilization of ferrous iron-phosphates (e.g., vivianite), this cement is suggestive of precipitation from ferruginous porewaters. This is the first direct evidence for iron-phosphate minerals in Ediacaran phosphorites and substantiates previous hypotheses of P burial beyond primary calcium phosphate. If accumulation and burial of phosphorites during this interval was rapid enough to have limited P availability and thus primary productivity, their formation may have governed oxygen production prior to the Neoproterozoic Oxygenation Event (NOE). Oxygenation of the oceans during the NOE and the appearance of complex, multicellular life are suspected to be causally linked within the Ediacaran. However, a fragmented fossil record with insufficient analogues and varied taphonomic modes leaves much of the Ediacaran fauna with uncertain taxonomic and phylogenetic affinities, leading to ambiguity regarding their life modes and environmental associations. Furthermore, demonstrating biogenicity is an often overlooked, yet fundamental component of Ediacaran fossil identification and interpretation, something that has particularly affected the morphologically simple discoidal group of fossils known colloquially as Aspidella. Petrographic observations supported by Raman and energy dispersive spectroscopy provide evidence that discoidal concretions from the Ediacaran Miaohe Member near Maxi, Hubei Province in South China are diagenetic in origin but superficially resemble Aspidella's morphology. Erosion of these syn-compactional concretions produced concentric rings on bedding planes caused by internally deformed laminae resulting in Aspidella pseudofossils. These results highlight the necessity for critical evaluation of the origin of discoidal structures observed in Ediacaran sedimentary successions. / Master of Science / Contemporary and ancient phosphorus-rich sedimentary deposits, known as phosphorites, precipitate within the oceans as a result of intricate chemical and biological interactions. The Ediacaran Period (635 – 539 million years ago) contains the first truly extensive occurrences of phosphorites in addition to a fossil record of the earliest animal organisms. Deposited after the end of Earth's last global glaciation, the origins of Ediacaran phosphorites are affiliated with these dramatic climatic and evolutionary transitions as well as the rise of atmospheric and oceanic oxygen concentrations to near modern levels. Deposition of phosphorites often occurs in low-oxygen oceanic environments and their formation constitutes the dominant mechanism by which phosphorus is removed from the phosphorus cycle on time scales greater than 1000 years. Therefore, phosphorite occurrences provide a record of phosphorus cycling, oxygen availability, and biological productivity. However, microscopic and chemical analyses of phosphorites from the Ediacaran Doushantuo Formation in South China demonstrate they are partially composed of phosphorus minerals that likely formed in non-oxygenated environments. The presence of these atypical phosphorus minerals has been previously hypothesized, with the implication that they further limited the availability of phosphorus for use by photosynthetic organisms. Such a limitation on photosynthesis would have resulted in decreased oxygen production and thus the formation of these phosphorites may explain the rate and trend of the change in oxygen concentrations observed during the Ediacaran. Ediacaran fossils also act as a proxy for environmental conditions of the ancient oceans through inferences about the preserved organisms' requirements for life. Although most fossils of this age are the first of their kind in terms of biological complexity, they are typically simple in terms of their morphology, making identification difficult. Furthermore, providing evidence that such simple structures actually represent a fossilized organism is often problematic due to the inability to compare them with modern organisms. Microscopic and chemical analyses of disc-shaped structures from the Ediacaran Miaohe Member in South China reveal that they are concretions that were not created by an organism, even though their morphology very closely resembles the Ediacaran fossil Aspidella. Identification of these concretions as pseudofossils suggests that close examination of fossils from Ediacaran rocks is necessary.

Dolomitos são rochas carbonáticas abundantes no registro sedimentar Pré-Cambriano, porém raras no registro Fanerozóico e sua gênese até hoje permanece como um enigma da geologia, conhecido como o \"Problema Dolomito\". As rochas sedimentares fosfáticas são amplamente estudadas por fornecerem dados importantes sobre a evolução sedimentar e condições físico-químicas e biológicas da água do mar durante a sedimentação e a diagênese, além de constituírem os maiores depósitos econômicos de fósforo do mundo. Os dolomitos e fosforitos da Formação Bocaina foram estudados com base na individualização de fácies sedimentares e petrografia, complementado com investigações geoquímicas (elementar e de isótopos de C e O), a fim de discutir os processos envolvidos na gênese destas rochas. As fácies sedimentares da Formação Bocaina, caracterizadas principalmente por grainstonesoolíticos, pisolíticos, e estromatólitos, indicam ambiente de águas rasas, límpidas e agitadas, interpretado como uma laguna, propícia à proliferação microbiana, com conexão restrita ao mar aberto. Estruturas tepeese pseudomorfos de cristais de gipsita sugerem condições evaporíticas para a bacia, com eventos de exposição subaérea dos sedimentos. Os dolomitos da Formação Bocaina são interpretados como secundários, originados da substituição de sedimentos calcíticos na eodiagênese, provavelmentedevido a elevada taxa de evaporação e refluxo das águas oceânicas. Modelos organogênicos para estes dolomitos não são descartados, devido à assinatura isotópica de C ser ligeiramente positiva (\'delta\' POT.13C IND.VPDB\' entre 0,95 e 3,15%o). A fosfogênese é interpretada como um processo eodiagenético, ocorrido em ambiente geoquímico anóxico, corroborado pelas anomalias positivas de Ce. O excesso de matéria orgânica permitiu a formação da apatita, provavelmente bioinduzida, durante eventos de subida do nível do mar, e desta forma, os fosforitos representam um marco estratigráfico para a bacia, como uma superfície condensada. Subseqüentemente, há rebaixamento do nível do mar, registrado nas fácies de fosfarenito e de conglomerado polimítico da base da Formação Tamengo, unidade que se justapõe à Formação Bocaina, marcando o fim do ambiente lagunar restrito e a instalação de uma plataforma francamente marinha. / Dolomites are carbonatic rocks abundant in the Precambrian but rarely found in the Phanerozoic sedimentary record. Their genesis has remained as a long-standing enigma in geology, often called the \"Dolomite Problem\". The phosphatic rocks, which represent the largest economic deposits of phosphorus in the world, have been studied to provide some important data about the sedimentary evolution and physical-chemical and biological condition of seawater during the sedimentation and diagenesis. The dolomites and phosphorites of the Bocaina Formation were studied based on sedimentary facies, petrography, geochemistry and carbon and oxygen isotopes investigations, to understand the process involved in the genesis of both rocks. The sedimentary facies of the Bocaina Formation are characterized by stromatolites, oolitic and pisolitic grainstones, which indicate shallow, clear and agitated water, favorable to microbial growth. The paleoenvironment was interpreted as a lagoon with restrict connection to the sea. Tepees structures and pseudomorphs of gypsum crystals suggest evaporitic condition to this basin, and also show evidences of aridity. The Bocaina Formation\'s dolomites have been interpreted as secondary, from replacement of limestones during eodiagenesis by reflux of oceanic waters. Organogenic models are also consideraded as a process to form these dolomites, based on the positive carbon isotope signature (\'delta\' POT.13 IND.CVPDB\' between 0.95 and 3.15%o). The phosphogenesis has been interpreted as eodiagenetic process occurred in anoxic geochemical environment, due to the excess oforganic matter, mediated by microbial process. The positive Ce anomalies support this interpretation. This process occurs during rising of sea level and the phosphorites represent a stratigraphic mark as a condensed surface. Subsequently, it is observed a sea level lowering, recorded in phospharenite facies and in basal polymict conglomerate of Tamengo Formation, unit which overlies the Bocaina Formation. This lowering event marks the end of the restrict lagoon environment and the installation of a marine platform.

Dolomitos são rochas carbonáticas abundantes no registro sedimentar Pré-Cambriano, porém raras no registro Fanerozóico e sua gênese até hoje permanece como um enigma da geologia, conhecido como o \"Problema Dolomito\". As rochas sedimentares fosfáticas são amplamente estudadas por fornecerem dados importantes sobre a evolução sedimentar e condições físico-químicas e biológicas da água do mar durante a sedimentação e a diagênese, além de constituírem os maiores depósitos econômicos de fósforo do mundo. Os dolomitos e fosforitos da Formação Bocaina foram estudados com base na individualização de fácies sedimentares e petrografia, complementado com investigações geoquímicas (elementar e de isótopos de C e O), a fim de discutir os processos envolvidos na gênese destas rochas. As fácies sedimentares da Formação Bocaina, caracterizadas principalmente por grainstonesoolíticos, pisolíticos, e estromatólitos, indicam ambiente de águas rasas, límpidas e agitadas, interpretado como uma laguna, propícia à proliferação microbiana, com conexão restrita ao mar aberto. Estruturas tepeese pseudomorfos de cristais de gipsita sugerem condições evaporíticas para a bacia, com eventos de exposição subaérea dos sedimentos. Os dolomitos da Formação Bocaina são interpretados como secundários, originados da substituição de sedimentos calcíticos na eodiagênese, provavelmentedevido a elevada taxa de evaporação e refluxo das águas oceânicas. Modelos organogênicos para estes dolomitos não são descartados, devido à assinatura isotópica de C ser ligeiramente positiva (\'delta\' POT.13C IND.VPDB\' entre 0,95 e 3,15%o). A fosfogênese é interpretada como um processo eodiagenético, ocorrido em ambiente geoquímico anóxico, corroborado pelas anomalias positivas de Ce. O excesso de matéria orgânica permitiu a formação da apatita, provavelmente bioinduzida, durante eventos de subida do nível do mar, e desta forma, os fosforitos representam um marco estratigráfico para a bacia, como uma superfície condensada. Subseqüentemente, há rebaixamento do nível do mar, registrado nas fácies de fosfarenito e de conglomerado polimítico da base da Formação Tamengo, unidade que se justapõe à Formação Bocaina, marcando o fim do ambiente lagunar restrito e a instalação de uma plataforma francamente marinha. / Dolomites are carbonatic rocks abundant in the Precambrian but rarely found in the Phanerozoic sedimentary record. Their genesis has remained as a long-standing enigma in geology, often called the \"Dolomite Problem\". The phosphatic rocks, which represent the largest economic deposits of phosphorus in the world, have been studied to provide some important data about the sedimentary evolution and physical-chemical and biological condition of seawater during the sedimentation and diagenesis. The dolomites and phosphorites of the Bocaina Formation were studied based on sedimentary facies, petrography, geochemistry and carbon and oxygen isotopes investigations, to understand the process involved in the genesis of both rocks. The sedimentary facies of the Bocaina Formation are characterized by stromatolites, oolitic and pisolitic grainstones, which indicate shallow, clear and agitated water, favorable to microbial growth. The paleoenvironment was interpreted as a lagoon with restrict connection to the sea. Tepees structures and pseudomorphs of gypsum crystals suggest evaporitic condition to this basin, and also show evidences of aridity. The Bocaina Formation\'s dolomites have been interpreted as secondary, from replacement of limestones during eodiagenesis by reflux of oceanic waters. Organogenic models are also consideraded as a process to form these dolomites, based on the positive carbon isotope signature (\'delta\' POT.13 IND.CVPDB\' between 0.95 and 3.15%o). The phosphogenesis has been interpreted as eodiagenetic process occurred in anoxic geochemical environment, due to the excess oforganic matter, mediated by microbial process. The positive Ce anomalies support this interpretation. This process occurs during rising of sea level and the phosphorites represent a stratigraphic mark as a condensed surface. Subsequently, it is observed a sea level lowering, recorded in phospharenite facies and in basal polymict conglomerate of Tamengo Formation, unit which overlies the Bocaina Formation. This lowering event marks the end of the restrict lagoon environment and the installation of a marine platform.

Étude stratigraphique, paléontologique et sédimentologique des dépôts silicoclastiques à glauconie et à phosphorites du Crétacé moyen de la zone delphino-helvétique entre Chambéry (Savoie, France) et Sion (Valais, Suisse). Ces dépôts riches en horizons fossilifères organisés en conglomérats phosphatés polyzonaux s'intercalent entre les calcaires urgoniens à rudistes et les calcaires à plancton de Seewen. La récolte de nombreuse ammonites et l'identification des foraminifères planctoniques en section ont permis la proposition d'un cadre stratigraphique nouveau. L'étude sédimentologique révèle un agencement des dépôts albiens et cénomaniens en aires sédimentaires plus ou moins pérennes contrôlées pour partie par des discontinuités souvent érosives d'origine sous-marine. L'interprétation des taphocénoses et des associations ichnologiques permet de proposer un approfondissement d'un facteur 10 entre l'Aptien supérieur et le Turonien. La confrontation des données sédimentaires avec les travaux structuraux publiés conduit à la proposition d'un cadre paléogéographique dans lequel sont reconnus deux types de bordure pour la plate-forme helvétique: l'une progradante en direction du bassin ultrahelvétique, l'autre structurale déterminée par un haut-fond, héritage probable du rifting jurassique. L'importante distribution des dépôts condensés à minéralisations sous marines sur les marges européenne et apulienne au Crétacé moyen permet de présenter en conclusion une reconstitution possible de la trajectoire des circulations océaniques de subsurface sur la bordure NW de la Téthys.