Thesis (M.Sc.) -- Memorial University of Newfoundland. / Bibliography : leaves 198-207. Also available online.

Algal mats comprised primarily of Phormidium frigidum Fritsch, Lyngbya martensiana Menegh., and several species of pennate diatoms are found in the below-ice benthic regions of Lakes Bonney, Chad, Hoare, Fryxell, and Vanda, southern Victoria Land, Antarctica. Mats are also found in the littoral moats and ice-covers of several lakes, and in cryoconite holes on Canada Glacier. Variations in temperature, light, oxygen, salinity, and nutrient levels between lakes and different habitats in the same lake result in differences in species composition, morphology, biomass, and photosynthetic pigment content of the mats. Algal mats are trapping and binding sediment, and precipitating minerals, particularly calcite. Mats are removing organic and inorganic matter from the arheic lakes via transfer through the icecovers or by incorporation into the sediments. Some of the algal mats are laminated, organosedimentary structures and can be considered stromatolitic. Depending upon ambient and subsequent environmental conditions non-columnar, columnar, and pinnacle-shaped stromatolites are forming, some of which are partially lithified. If environmental variables (i.e. low light intensity, lack of burrowers or browsers, and relative lack of turbulence) associated with these stromatolites do not vary significantly, it is probable that they may result in a lacustrine carbonate sedimentary deposit. / Ph. D.

A unique assemblage of in situ microstromatolites, articulated intraclastic microstromatolites, and disarticulated stromatolites has been identified from drill cores of the 2.3 G.a. Transvaal Sequence, South Africa. These structures occur in organic-rich lenticular and nodular replacement black cherts which are associated with early diagenetic dolomite. Petrographic evidence indicates that the chert has formed via a primary carbonate and organic matrix--partial dolomitization--silicification paragenetic sequence; and that dolomitization and silicification were closely contemporaneous diagenetic events. Microstructures which resemble three dimensionally preserved microfossils are found in the majority of the silicified Transvaal cores. These fossil-like microstructures can be grouped broadly into three morphological types: (1) filaments, (2) ovoid or spheroidal forms, and (3) bacteria-like microstructures. Certain of the filamentous forms which are associated with pyrite mineral grains are clearly of abiological origin, and their formation can be explained in the context of sedimentary diagenesis and mineral paragenesis. The three dimensional association of the ovoid and bacteria-like microstructures to the microstromatolites is such as would be predicted from studies of modern cyanobacterial/microbial mat ecosystems. Hence, these microstructures are considered to be potential microfossils. The Transvaal microstromatolitic materials represent some of the smallest stromatolites yet described from either Proterozoic or Phanerozoic sedimentary rocks. Nearly all of the basic stromatolite growth forms (i.e. columnar, bulbous, nodular, and stratiform) are represented in the Transvaal assemblage. Thus, stromatolite diversity at the "basic growth form" level apparently did not evolve through geologic time. Physical and chemical environmental parameters probably controlled stromatolite morphogenesis only to the extent that they influenced the steady state balance of microstromatolite microbial communities. Indirect evidence suggests that the Transvaal microstromatolites grew via the precipitation of primary carbonate at some level within the structures and that a correlation exists between the degradation of primary producer organic carbon and the precipitation of a structurally supportive carbonate mineral matrix.

Microbial mats are important components of perennially ice-covered Antarctic lakes in the McMurdo Dry Valleys, where they often comprise the dominant biomass in this cold, shaded environment. These lakes represent some of the most extreme lacustrine environments on Earth, including a persistent ice-cover, stable, stratified water columns, with strong salinity related density gradients. In these low-disturbance environments, the microbial consortia develop macroscopic emergent structures such as pinnacles and ridges. Such structures are speculated to confer advantageous survival traits and have also been found in the Precambrian fossil record as “conophyton” stromatolites – arguably some of the earliest evidence of life – and it has been suggested that a better understanding of the growth dynamics of modern “conophyton” will inform our understanding of what was required for these early fossils to be produced. Despite decades of research, there are few studies of the structural basis of conophyton producing microbial mats in Antarctic lakes. To help address this gap, complex microbial mats along a transect established in Lake Fryxell, one of the McMurdo Dry Valley lakes, were examined; with the aim of documenting the distribution of different types of photosynthetic organisms and mat morphologies along environmental gradients such as light, conductivity, oxygen concentration and depth. Microbial mat samples were taken along the transect and analysed in New Zealand using confocal laser scanning microscopy, along with conventional pigment extraction techniques. Correlations between mat morphology, pigment content and lake properties were found. The appearance of bacteriochlorophylls, characteristic of green sulfur bacteria within and below the oxycline confirm a shift from aerobic to anaerobic metabolism that was consistent with mats taking on a prostrate appearance. The cyanobacterial pigment phycoerythrin was only found in the hyperoxic, relatively well lit region of the transect, and was associated with the mats forming a distinctive macroscale morphology with dense fields of cm-scale cuspate pinnacles. Between these, a hypoxic region was characterised by a relatively flat mat within which were many cm-scale pits. Structural investigations were focussed on two distinct morphologies, pinnacle and honeycomb mat. Nearly all photosynthetic organisms were located in the upper 2 mm of both pinnacle and honeycomb mats, mainly comprising diatoms and cyanobacteria. Pinnacle mats were dominated by a narrow cyanobacterium, probably a species of Leptolyngbya, which were mostly oriented vertically, which placed trichomes parallel to the direction of pinnacle extension. The honeycomb mat contained fewer narrow trichomes, rather the bulk of photosynthetic organisms were diatoms from the genera Muellaria, Navicula and Diadesmis, together with broad-trichome cyanobacteria that formed a thin skin on the surface of the mat, though absent from the pits. The type of emergent structure that is formed appears to be related to species composition, and this in turn appears to be related to the growth conditions. A model was developed to explain how species-specific growth mechanisms are involved in emergent structure formation for honeycomb and pinnacle mats.

Thesis (Ph.D.)--Memorial University of Newfoundland. / Typescript. Bibliography: leaves 420-456. Also available online.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 217-260).

A new method is presented here for petrophysical interpretation of heterogeneous carbonates using well logs and core data. Developing this new method was necessary because conventional evaluation methods tend to yield inaccurate predictions of pore connectivity and permeability in the studied field. Difficulties in the petrophysical evaluation of this field are related to shoulder-bed effects, presence of non-connected porosity, rock layers that are thinner than the vertical resolution of well-logging tools, and the effect of oil-base mud (OBM) invasion in the measurements. These problems give rise to uncommon measurements and rock properties, such as: (a) reservoir units contained within thinly bedded and laminated sequences, (b) very high apparent resistivity readings in the oil-bearing zone, (c) separation of apparent resistivity logs with different depths of investigation, (d) complex unimodal and bimodal transverse relaxation distributions of nuclear magnetic resonance (NMR) measurements, (e) reservoir units having total porosity of 0.02 to 0.26 and permeability between 0.001mD to 4.2D, (f) significant differences between total and sonic porosity, and (g) low and constant gamma-ray values. The interpretation method introduced in this thesis is based on the detection of layer boundaries and rock types from high-resolution well logs and on the estimation of layer-by-layer properties using numerical simulation of resistivity, nuclear, and NMR logs. Layer properties were iteratively adjusted until the available well logs were reproduced by numerical simulations. This method honors the reservoir geology and physics of the measurements while adjusting the layer properties; it reduces shoulder-bed effects on well logs, especially across thinly bedded and laminated sequences, thereby yielding improved estimates of interconnected porosity and permeability in rocks that have null mobile water saturation and that were invaded with OBM. Additionally, dynamic simulations of OBM invasion in free-water depth intervals were necessary to estimate permeability. It is found that NMR transverse relaxation measurements are effective for determining rock and fluid properties but are unreliable in the accurate calculation of porosity and permeability in thinly bedded and highly laminated depth sections. In addition, this thesis shows that low resistivity values are associated with the presence of microporosity, and high resistivity values are associated with the presence of interconnected and vuggy porosity. In some layers, a fraction of the vuggy porosity is associated with isolated pores, which does not contribute to fluid flow. An integrated evaluation using multiple measurements, including sonic logs, is therefore necessary to detect isolated porosity. After the correction and simulation, results show, on average, a 34% improvement between estimated and core-measured permeability. Closer agreement was not possible because of limitations in tool resolution and difficulty in obtaining a precise depth match between core and well-log measurements. / text

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.

As capas carbonáticas neoproterozóicas revestem-se de grande importância, uma vez que se formaram no meio a mudanças paleoclimáticas e evolutivas singulares, cujas origens e influências na história subsequente do planeta e da vida ainda não foram devidamente esclarecidas. Este trabalho procurou compreender parte desta história através do estudo da sedimentação estromatolítica associada à capa carbonática representada pela Formação Mirassol DOeste (base do Grupo Araras), que se formou há cerca de 635 Ma, imediatemente após a glaciação Marinoana, representada pela Formação Puga. A pesquisa foi realizada na região de Mirassol DOeste, Mato Grosso, na borda sudoeste do Cráton Amazônico junto a Faixa Paraguai. Foram estudadas características meso e microscópicas dos estromatólitos, bem como das feições sedimentológicas associadas (estruturas tubulares, megamarcas onduladas, megapeloides), em afloramento, amostras cortadas e lâminas petrográficas. A dois metros da base da formação, inicia-se uma sucessão de 10 metros de espessura de boundstones microbianos, caracterizados, petrograficamente, por lâminas alternadamente delgadas e espessas, compostas de peloides (restos micritizados de colônias microbianas) com micrita subordinada e fenestras. Constituem estromatólitos lateralmente contínuos e de morfologia simples. Estromatólitos estratiformes ocorrem ao longo de toda a sucessão, com formas dômicas, de dimensões métricas irregularmente espalhadas lateral e verticalmente, até dois ou três metros do topo da sucessão. Estromatólitos muito irregularmente ondulados, comumente assimétricos, com dimensões decímetros predominam a parte superior e estes estão recobertos por grainstones-packstones peloidais dolomíticos, com megapeloides milimétricos, em estratos marcados por megamarcas onduladas formadas por ondas. A sedimentação microbiana cessou na Formação Mirassol DOeste quando o ambiente de plataforma de baixa energia onde se desenvolvia começou a ser assolado pela ação de ondas de hipertempestades, que penetraram a região com o aumento do nível do mar. Estruturas tubulares verticais, de comprimento até decimétrico e diâmetro estreito (<3 cm), preenchidos, via de regra, por doloesparito maciço, perpassam a laminação estromatolítica principalmente das porções mais altas dos domos. Sugere-se que gênese dessas estruturas tenha sido pela percolação de gases e/ou líquidos derivados da decomposição de matéria orgânica nas esteiras microbianas. / Neoproterozoic cap carbonates are of great importance because they formed during a period of singular paleoclimatic and evolutionary changes, whose origin and influences upon subsequent geological and evolutionary history have yet to be unraveled. This dissertation sought to comprehend part of this story through the study of stromatolitic sedimentation associated with the cap carbonate represented by the Mirassol DOeste Formation (base of the Araras Group), deposited about 635 Ma ago, immediately following the Marinoan glaciation, represented by the Puga Formation. This research was carried out at Mirassol DOeste, Mato Grosso, on the southwest border of the Amazon craton next to the Paraguai fold belt. Meso and macroscopic characteristics of stromatolites and associated sedimentological features (tubular structures, megaripples, megapeloids) were studied in outcrop, cut specimens and petrographic thin sections. Two meters above the base of the formation a 10 m-thick succession of dolomitic microbial boundstones begins, characterized throughout by alternating thin and thick laminae made up of peloids (interpreted as the micritized remains of colonial microorganisms), subordinate dolomicrite, and fenestrae. They make up laterally continuous and morphologically simple stromatolites. Stratiform stromatolites occur throughout the succession, with irregularly scattered meter-sized domes till about two to three meters from the top. Above this point, very irregularly undulated, commonly asymmetric, decimeter-sized stromatolites predominate, and these, in turn, are covered by megaripple-marked dolomitic peloidal grainstones-packstones with millimetric megapeloids. Stromatolitic sedimentation ceased in the previously calm platform environment of the Mirassol DOeste Formation when wave action began to rework bottom sediments as extremely intense storms reached the locale with the rise in sea level. Narrow (<3 cm), vertical tubular structures of decimetric length and filled by massive dolosparite cut stromatolitic sediments, principally in the central portions of domal forms. These structures appear to have formed by the percolation of gas and/or liquids derived from the decomposition of organic material in the microbial mats.