Arbetet handlade om att ta reda på om det går att byta ut natriumhydroxid mot natriumkarbonat som alkalikälla på CTMP-linjen, och gjordes på uppdrag av Stora Enso Skoghalls bruk. De områdena som studerades var impregnering och blekning av CTMP (kemitermomekanisk pappersmassa) samt hantering av natriumkarbonatlösning. Natriumkarbonatens löslighet vid olika temperaturer verifierades, blekning av CTMP med natriumkarbonat och natriumhydroxid utfördes, titrering av natriumhydroxid och natriumkarbonat mot natriumbisulfitlösning och en enklare laborationsimpregnering gjordes. Även aspekten av utrustning, kostnader och eventuell utfällning av kalciumkarbonat studerades. Resultaten visade att det krävs mer natriumkarbonat för att ersätta natriumhydroxid än vad man trott och att det totalt sett blir dyrare. Det finns dock en möjlighet att andra delar av bruket kan utföra bytet av alkali och gå med större vinst än vad CTMP-linjen går med förlust. Försöken visade även på temperaturökning vid tillredning av natriumkarbonatlösningen, utfällning av kristallsoda och behov av att den befintliga utrustningen kompletteras utifrån rekommendationer från kemikalieleverantören. Tidigare studier visade på eventuella försämringar av papperskvaliteten när natriumkarbonat används vid blekning av CTMP. Trots att natriumkarbonat är ett billigare alternativ till natriumhydroxid, och att det teoretiskt sett skulle fungera bra som en utbrytare, är det mycket som man behöver ta hänsyn till vad gäller natriumkarbonat och det krävs eftertanke för att saker ska görs på rätt sätt. Utifrån resultaten kan man dra slutsatsen att det inte ser ut som en bra ide att utföra bytet. / The objective of this project was to see if it is possible to replace sodium hydroxide with sodium carbonate as an alkali source on the CTMP line, and it was done on behalf of the Stora Enso Skoghall Mill. The areas that were studied were the impregnation and bleaching of CTMP and also the handling of sodium carbonate solution. The solubility of sodium carbonate at various temperatures was confirmed, bleaching of CTMP with sodium hydroxide and sodium carbonate, titration of the sodium hydroxide and sodium carbonate against sodium bisulfite solution and a simpler laboratory impregnation was performed. Aspects of equipment, costs and the possibility of precipitation of calcium carbonate were also studied. The results indicate that more sodium carbonate is needed than one thought for the substitution to be possible, and that it also becomes more expensive. There is a possibility that other parts of the mill can perform the replacement of alkali and go with greater profit than the CTMP line goes with loss. Experiments also showed an increase in temperature when preparing the sodium carbonate solution, precipitation of natron and the need for the existing equipment to be supplemented on the basis of recommendations from the chemical supplier. Previous studies showed possible deterioration of the paper quality when bleaching CTMP with sodium carbonate. Although sodium carbonate is a cheaper alternative to sodium hydroxide, and that it would theoretically work well as a substitute, it is much that one has to take into consideration in terms of using sodium carbonate and it is necessary to think things through before usage, so that things can be done properly. Based on the results, it is shown that the swap of alkali will be suboptimal.

[pt] Os reservatórios de hidrocarbonetos em rochas carbonáticas representam aproximadamente 50 por cento da produção mundial de petróleo e tem por característica marcante sua complexidade, uma vez que são bastante heterogêneos. No Brasil, as rochas carbonáticas ganharam uma grande importância com a descoberta dos reservatórios carbonáticos do pré-sal. Entender e caracterizar estes reservatórios, que apresentam baixas taxas de penetração, exigirá grandes esforços em pesquisa e desenvolvimento. Uma pequena contribuição neste sentido é proporcionada nesta dissertação, onde três distintas rochas carbonáticas, o travertino romano, o travertino turco e o travertino de Itaboraí, foram caracterizadas geológica e geomecanicamente. O programa experimental consistiu na caracterização mineralógica, química, textural e diagenética, bem como na realização de ensaios de resistência e de porosidade. De posse dos resultados do programa experimental buscou-se correlações entre os índices/propriedades/parâmetros determinados. Verificou-se que a resistência à compressão simples dos materiais é diretamente proporcional, a sua densidade, a sua velocidade de propagação de ondas e ao índice esclerométrico; e inversamente proporcional a sua porosidade. Constatou-se ainda que a velocidade de propagação de ondas dos materiais é diretamente proporcional a sua densidade e inversamente proporcional a sua porosidade. / [en] Hydrocarbon reservoirs in carbonate rocks represent circa 50 percent of all oil produced worldwide. Those reservoirs are very complex since they are quite heteregeneous. In Brazil, carbonate rocks gained a great importance with the discovery of the pre-salt reservoirs. Understand and characterize these reservoirs, that present low penetration rates, will require major efforts in research and development. A small contribution in this regard is provided in this dissertation, where three travertines (i.e., Roman, Turkish and Itaboraí) were geologically and geomechanically characterized. The experimental program consisted in the chemical, mineralogical, textural and diagenetic characterization, as well as strength and porosity tests. A comprehensive analysis of test results from the experimental program was carried out in order to seek correlations between the indexes/properties/parameters determined. It was found that the unconfined compression strength of materials is directly proportional to its density, its velocity of ultrasonic wave propagation and to Schmidt test hammer index; and inversely proportional to its porosity. It was also found that the velocity of ultrasonic wave propagation of materials is directly proportional to its density and inversely proportional to its porosity.

[pt] O travertino Romano é uma rocha ornamental, historicamente presente na arquitetura Romana, que mesmo nos dias de hoje é muito utilizada em decorações e fachadas. Porém no meio científico é considerada uma rocha análoga a reservatórios carbonáticos, em especial do pré-sal Brasileiro. O presente trabalho buscou realizar um estudo experimental do travertino Romano, com enfoque no comportamento geomecânico anisotrópico em duas direções (normal e paralela ao acamamento), sob valores de tensões condizentes com as que ocorrem em reservatórios. Para isto foram feitas diversas análises macro e microscópicas, incluindo microscopia eletrônica de alta resolução a fim de estudar propriedades do travertino e sua estrutura porosa. Análises químicas do material e medição em laboratório dos mais variados parâmetros para se obter uma satisfatória lista de índices físicos auxiliaram neste contexto. Ensaios de resistência complementares, como o ensaio de carga pontual e ensaio de tração indireta (Ensaio Brasileiro) enriqueceram o estudo com resultados de ruptura nas direções perpendicular e paralela ao acamamento. Por fim, buscou-se estudar o comportamento geomecânico anisotrópico do travertino, sob a ótica normal e paralela ao acamamento sedimentar, através de ensaios triaxiais com tensão confinante variando de zero (uniaxiais) a 40 MPa, intervalo este bastante próximo as tensões efetivas de reservatórios carbonáticos brasileiros. Devido à grande heterogeneidade, os corpos de prova foram separados em grupos com intervalos de porosidade total similares. Então, com resultados de curvas tensão-deformação e trajetórias de tensão, foram possíveis diversas comparações em termos de comportamento geomecânico e observar que nem sempre o incremento da tensão confinante e a menor porosidade resultarão em maior resistência mecânica. / [en] The Roman travertine is an ornamental rock, historically present in Roman architecture, which even in present days is much used in decorations and facades. However in the scientific community it is considered a rock similar to carbonate reservoirs, especially the Brazilian pre-salt. The present work sought to carry out an experimental study of the Roman travertine, focusing on the anisotropic geomechanical behavior in two directions (normal and parallel to the sedimentary bedding) under tension values consistent with those occurring in reservoirs. For this, several macro and microscopic analyzes were carried out, including high resolution electron microscopy in order to study the properties of travertine and its porous structure. Chemical analysis of the material and laboratory measurement of the most varied parameters to obtain a satisfactory list of index properties aided in this context. Complementary strength tests, such as the point load test and indirect tensile strength test (Brazilian Test) enriched the study with results of rupture in the directions perpendicular and parallel to the bedding. Finally, it was studied the anisotropic geomechanical behavior under normal and parallel optics to the sedimentary bedding through triaxial tests with confining stress ranging from zero (uniaxial) to 40 MPa, this interval very close to the effective stresses from Brazilian carbonate reservoirs. Due to the great heterogeneity, the specimens were separated into groups with similar total porosity ranges. Then, with results of stress-strain plots and stress trajectories, several comparisons were possible in terms of geomechanical behavior and observe that not always the increase of the confining stress and the lower porosity will result in greater mechanical resistance.

Fez-se a separação, enriquecimento e purificação de iantânio e ítrio partindo-se de um concentrado de terras raras empobrecido em cério, conhecido como LCC, \"low cerium carbonate\", um concentrado de ítrio designado como \"carbonato de ítrio\" e um terceiro concentrado designado como \"oxido de terras ítricas\". Os dois primeiros concentrados foram produzidos industrialmente pela NUCLEMON - Nuclebrás de Monazita e Associados Ltda, usando monazita brasileira. O \"oxido de terras ítricas\" é proveniente do processo de obtenção de Iantânio durante a execução do trabalho experimental desta tese. Fez-se uso das seguintes tecnologias: 1) precipitação fracionada com uréia; 2) lixiviação fracionada do LCC com carbonato de amônio e 3) precipitação dos peroxicarbonatos de terras raras usando-se seus carbonatos complexos. Obtidas frações enriquecidas em terras raras estas foram refinadas por meio de tecnologia de troca iônica em leito de resina catiônica sem uso de ion retentor e eluição com sais de amônio do ácido etilenodiaminotetraacético. Com a associação das técnicas acima mencionadas foram obtidos óxidos puros de ítrio (>97,7%), oxido de Iantânio (99,9%), óxido de gadolínio (96,6 %) e oxido de samário (99,9%). O processo aqui desenvolvido tem viabilidade técnica econômica para a instalação de uma unidade de maior porte visando a industrialização. / In this work, separation, enrichment and purification of lanthanum and yttrium were performed using as raw material a commercial low cerium rare earth concentrate named LCC (low cerium carbonate), an yttrium concentrate named \'yttrium carbonate\', and a third concentrated known as \'yttrium earths oxide. The first two were industrially produced by the late NUCLEMON - NUCLEBRAS de Monazita e Associados Ltda, using Brazilian monazite. The \'yttrium earths oxide\' come from a process for preparation of lanthanum during the course of the experimental work for the present thesis. The following techniques were used: fractional precipitation with urea; fractional leaching of the LCC using ammonium carbonate; precipitation of rare earth peroxycarbonates starting from the rare earth complex carbonates. Once prepared the enriched rare earth fractions the same were refined using the ion exchange chromatography with strong cationic resin without the use of retention ion and elution using the ammonium salt of ethylenediaminetetraacetic acid. With the association of the above mentioned techniques were obtained pure oxides of yttrium (>97,7%), lanthanum (99,9%), gadolinium (96,6%) and samarium (99,9%). The process here developed has technical and economic viability for the installation of a large scale unity.

Conchas do molusco Physa sp., um gastrópode (caracol) comum de aquários de água doce, serviram como modelo para o estudo de alguns aspectos envolvidos na biomineralização. A concha calcária é constituída por cristais de carbonato de cálcio depositados em associação com uma matriz orgânica. Os componentes cristalinos e a matriz, foram estudados por microscopia eletrônica de transmissão e de varredura, e caracterizados por métodos espectroscópicos e analíticos. A constituição cristalina, em geral, assemelha-se àquela existente na maioria dos moluscos, enquanto a camada nacarada, interna da concha, apresenta comparativamente maiores variações. A matriz orgânica consta de um componente insolúvel, essencialmente constituído por polissacarídeos, enxofre e fósforo; e outro componente solúvel, com predominância de serina, glicina, ácido aspártico e ácido glutâmico. A análise feita por ativação de nêutrons demonstrou maior concentração de cálcio, sódio e estrôncio; estes elementos estão geralmente relacionados à presença de aragonita, em outras conchas de moluscos. O estudo qualitativo da fase cristalina foi realizado por difração eletrônica e por espectroscopia de infravermelho. Para análise quantitativa, usou-se a difração de raios-X, sendo os dados refinados pelo método de Rietveld. Os resultados obtidos demonstram a existência de dois polimorfos do carbonato de cálcio, aragonita e calcita, na concha da Physa. A caracterização qualitativa dos componentes inorgânico e orgânico do material estudado, mostrou semelhanças com relação a outros gêneros de moluscos. Experimentos de cristalização do carbonato de cálcio in vitro produziram aragonita e vaterita em presença de ácido aspártico ou glutâmico. Sob ação de glicina, serina ou quitina, houve formação de calcita. Em presença da matriz orgânica insolúvel, houve cristalização de calcita, enquanto a matriz solúvel induziu a cristalização da aragonita. Analisou-se quantitativamente todas as fases cristalinas obtidas nestes experimentos e estudou-se a morfologia dos cristais formados através da MEV e por MO luz. O resultado comparativo das investigações usando a concha natural, e dos cristais sintetizados, permitiu confirmar o papel fundamental da matriz orgânica no processo de cristalização do carbonato de cálcio. / Shells of Physa sp., a common freshwater gastropod snail, were used as a model for mineralization studies of calcium carbonate. The shell is a biomineral that consists of organized crystalline deposits associated to an organic matrix, both of which were studied by transmission and scanning electron microscopy; they were further characterized by means of pectroscopic and analytical methods. As a whole, its structural organization does not differ greatly from that found in other mollusc shells, except for the innermost, nacreous layer, that lines the shell. The organic matrix in Physa was found to consist of an insoluble fraction, essentially containing a polysaccharide, sulphur and phosphor. In addition, another (soluble) fraction is present, in which serine, glycine, aspartic acid and glutamic acid residues prevail. Neutronic activation analysis demonstrates a high concentration of calcium, sodium and strontium, elements known to be related to the presence of aragonite in other molluscan shells. A qualitative study of the crystalline phase was obtained through use of electron diffraction and FTIR spectroscopy. For quantitative analysis X-ray diffraction was used, as refined by the Rietveld method. Results obtained demonstrate the existence of two calcium carbonate polymorphs, aragonite and calcite in the shell of Physa, Qualitative evaluation of both organic and inorganic material from Physa showed similarities to those found in other mollusk shells. In vitro experiments performed at similar-to-natural conditions, on crystallization of calcium carbonate, did also crystallize aragonite and vaterite, provided aspartic acid or glutamic acid were present; whereas calcite was formed in solutions containing glycine, serine or chitin. Aragonite did crystallize when the soluble organic matrix was added to the solution. All these crystalline phases obtained were quantitatively evaluated, their morphologies being studied through light and electron microscopies. A comparative study of the natural crystals from the shell, and those obtained in laboratory experiments, stresses the fundamental role of the organic matrix on calcium carbonate crystallization

A indústria da construção civil é conhecida como umas das atividades econômicas que causam os maiores impactos ambientais desde o processo de extração da matéria prima até a produção dos produtos, incluindo o transporte e manutenção do ambiente construído. A produção de um dos seus principais componentes, o cimento, é o maior contribuinte para a emissão de gases de efeito estufa, principalmente devido a queima de combustíveis fósseis. Por este motivo, pesquisas na área de biotecnologia sustentável são conduzidas para diminuir e até mitigar os efeitos danosos provocados pelos fatores que compõem a construção civil. Dentre estas pesquisas destacam-se as que se baseiam na Biomimética, que é uma ciência que busca na Natureza as soluções tecnológicas para os problemas que os desenvolvimentos humanos geralmente apresentam: a geração de resíduos poluentes, uso de produtos químicos tóxicos e processos que operam com energia e pressão elevadas. Com base nos conceitos biomiméticos, este trabalho se propôs a estudar a biomineralização, que é um processo que ocorre na Natureza a milhares de anos e é responsável pela formação de muitas estruturas biomineralizadas tanto no ambiente terrestre como aquático. A biomineralização é um fenômeno provocado pela ação de diversas espécies de microrganismos que durante o processo de obtenção de energia reciclam minerais presentes no solo e na água e os precipitam na forma de sais inorgânicos. Este material precipitado age como agente ligante de partículas como no caso de formações geológicas (estromatólitos) ou exoesqueletos de animais marinhos, por exemplo. Neste estudo foi avaliado a biomineralização por biodeposição de carbonato de cálcio precipitado na presença da espécie de bactéria ureolítica (Bacillus subtilis) em ensaios em escala laboratorial utilizando corpos de prova de areia, argamassa e concreto. Os corpos de prova em areia e argamassa foram observados em MEV e EDS permitindo a identificação de células de microrganismos, formação de biofilme e provável formação de cristais de carbonato de cálcio na região de biofilme. Os corpos de prova de concreto foram utilizados para avaliar as consequências da biodeposição na absorção de água por capilaridade do material. Resultados indicam redução de 20% na absorção de água por capilaridade. Com os resultados obtidos é possível concluir que a técnica de biodeposição pode ser uma alternativa ao tratamento superficial de estruturas de concreto, contudo requer estudos posteriores de aplicação técnica e viabilidade econômica. / The construction industry has been known as one of the economic activities that cause the major environment impacts since the process of raw material extraction until the products manufacturing including transport and maintenance of the built environment. The production of one of the main compounds, the cement, is the largest contributor to the greenhouse gas emissions, mainly due to burn fossil fuels. For this reason, researches in sustainable biotechnological area are conducted to minimize and even mitigate the damaging effects either promoted by construction industry factors. Among these ones, it stands out researches based on Biomimetic, which is a science that seeks in Nature the technological solutions for problems that human’s development usually presents: the generation of pollutant residues, the use of toxic chemicals and process that operates in high pressure and energy. Based on biomimetic concepts this research proposes to study the biomineralization, which is a process that has occurred in the Nature for thousands of years and it is responsible for the formation of many structures either in soil and water environments. The biomineralization is a phenomenon caused by several specimens of microorganisms that during the process of obtaining energy, they recycle minerals presents at soil and water inducing precipitation as inorganic salts. This precipitated material works as a binder of particles similar to geologic formations (stromatolites) or exoskeleton of sea animal for example. In this study the biomineralization was evaluated through biodeposition of precipitated calcium carbonate by specimen of ureolytic bacteria (Bacillus subtilis). Essays were held using samples made by sand, mortar and concrete. The samples made by sand and mortar were observed at MEV and EDS, allowing the identification of microorganism cells, biofilm formation and probable formation of calcium carbonate crystals at biofilm region. The concrete samples were used to evaluate the consequences of biodeposition on water absorption by capillarity of the material. The results show reduction of 20% on water absorption by capillarity. According the results achieved it possible to conclude that the biodeposition technique can be an alternative to superficial treatment for concrete structures. However, it will be required more studies to evaluate technical application and economical availability.

Rising concentration of CO2 in the atmosphere is attributed to increasing consumption of fossil fuels. One of the most effective mechanisms to store CO2 captured from power plants is via geological injection of CO2 into formations that contain calcium and magnesium silicate and alumino-silicate minerals and rocks. The mechanism that ensures permanent storage of CO2 within rocks is mineral carbonation. When CO2 is injected into mineral or rock formations rich in calcium or magnesium silicates, they react with CO2 to form calcium or magnesium carbonates, which is also known as carbon mineralization. Calcium and magnesium carbonates are stable and insoluble in water. However, the kinetics of in-situ mineral carbonation involve CO2 hydration, mineral dissolution and formation of carbonates, and the relative rates of these phenomena when coupled, are not very well understood. In this study, the coupled interactions of CO2-reaction fluid-minerals were investigated to determine the optimal conditions for carbon mineralization, and to identify the chemical and morphological changes in the minerals as they react to form carbonates. Carbon mineralization in various minerals and rocks such as olivine ((Mg,Fe)2SiO4)), labradorite ((Ca, Na)(Al, Si)4O8), anorthosite (mixture of anorthite (CaAl2Si2O8), and basalt (rock comprising various minerals) were studied at high temperatures (Tmax = 185 oC) and high partial pressures of CO2 (PCO2, max = 164 atm) which are relevant for in-situ conditions. These minerals and rocks differ considerably in their chemical compositions and reactivity with CO2. A systematic comparison of the effects of reaction time, temperature, partial pressure of CO2, and fluid composition on the conversion of these magnesium and calcium bearing minerals and rocks showed that olivine was the most reactive mineral followed by labradorite, anorthosite, and basalt, respectively. Previous studies at Albany Research Center (Gerdemann et al., 2007; O'Connor et al., 2004) reported that a solution of 1.0 M NaCl + 0.64 M NaHCO3 was effective in achieving high extents of carbonation in olivine, heat-treated serpentine, and wollastonite. However, the independent effects of NaCl and NaHCO3 and their role in mineral carbonation were not sufficiently explained. In this study, the role of varying concentrations of NaCl and NaHCO3 on carbon mineralization of various minerals was elucidated. NaHCO3 buffered the pH and served as a carbon carrier, resulting in higher carbonate conversions. Except in the case of olivine, NaCl had a negligible effect on enhancing mineral carbonation. Unlike NaHCO3, NaCl does not buffer the pH or serve as a carbon carrier, but Cl- may serve as a weak chelating agent can complex with Mg or Ca in the mineral matrix to enhance dissolution. The competing effects of ionic strength and pH swings as the mineral dissolves and carbonation further complicate the role of NaCl on mineral carbonation. Based on the experimental methodologies developed to study carbon mineralization in minerals and rocks at high temperatures and pressures, alternative applications such as the remediation of hazardous alkaline wastes such as asbestos containing materials were identified. Asbestos is composed of chrysotile, a fibrous hydrated magnesium silicate mineral and a form of serpentine known to cause respiratory illnesses. By treating asbestos containing materials with CO2 in the presence of 0.1 M Na-oxalate, dissolution of chrysotile and precipitation of newer phases such as glushinkite (Mg(C2O4)* 2H2O) and magnesite (MgCO3) occurred, which reduced the chrysotile content in asbestos. Based on the methodologies for studying mineral dissolution and carbonation kinetics, and coupled mineral dissolution and carbonation behavior, a scheme for connecting laboratory scale experiments with simulations to estimate the uncertainties associated with carbon mineralization was developed. The effects of temperature, different dissolution rates, and varying levels of surface area changes due to passivation or reactive cracking on the rates of carbon mineralization were simulated using PhreeqC, a computer program developed for geochemical speciation calculations (Parkhurst & Appelo, 1999). Various studies proposed that microfractures and cracks may occur in geologic formations due to the extensive growth of carbonate crystals (Kelemen & Hirth, 2012; Kelemen & Matter, 2008; Matter & Kelemen, 2009; Rudge et al., 2010). Other studies have suggested that the formation of carbonates may plug the pore spaces and limit further reactivity (Hövelmann et al., 2012; King et al., 2010; Xu et al., 2004). The effects of changes in surface area due to the formation of microfractures or passivation due to carbonate growth on the rates of carbon mineralization were also simulated. Overall the results of these studies demonstrate the effect of various parameters on carbon mineralization and how these parameters can be connected to predict CO2 storage in mineral formations. The frameworks to connect laboratory scale experiments with simulations to determine carbon mineralization rates and to assess the risks associated with CO2 injection in reactive formations, can be used to direct future research efforts to predict the fate of injected CO2 with greater accuracy for sensor placement and optimization of CO2 monitoring technologies.

Understanding how coral reefs have developed in the past is crucial for placing contemporary ecological and environmental change within appropriate reef-building timescales (i.e. centennial to millennial). On Australia’s Great Barrier Reef (GBR), coral reefs situated within nearshore settings on the inner continental shelf are a particular priority. This is due to their close proximity to river point sources, and therefore susceptibility to reduced water quality as the result of extensive modification of adjacent river catchments following European settlement in the region (ca. 1850 CE). However, the extent of water quality decline and its impact on the coral reefs of the GBR’s inner-shelf remains contentious and is confounded by a paucity of long-term (> decadal) datasets. Central to the on-going debate is uncertainty related to the impact of increased sediment loads, relative to the natural movement and resuspension of terrigenous sediments, which have accumulated on the inner-shelf over the last ~6,000 years. The main aim of this thesis was to characterise and investigate the vertical development of turbid nearshore coral reefs on the central GBR. This aim was achieved through the recovery of 21 reef cores (3 - 5 m in length) from five proximal turbid nearshore reefs, currently distributed across the spectrum of reef ‘geomorphological development’ within the Paluma Shoals reef complex (PSRC). The recovered reef cores were used to establish detailed depositional and palaeoecological records for the investigation of the (1) internal development and vertical accretionary history of the PSRC; and (2) compositional variation in turbid nearshore coral and benthic foraminiferal assemblages during vertical reef accretion towards sea level. Established chronostratigraphic and palaeoecological records were further used to assess the impact of post-European settlement associated water quality change in a turbid nearshore reef setting on the central GBR. Radiocarbon dating (n = 96 dates) revealed reef initiation within the PSRC to have occurred between ~2,000 and 1,000 calibrated years before present, with subsequent reef development occurring under the persistent influence of fine-grained (< 0.063 mm) terrigenous sediments. The internal development of the PSRC was characterised by discrete reef facies comprised of a loose coral framework with an unconsolidated siliciclastic-carbonate sediment matrix. A total of 29 genera of Scleractinian coral and 86 genera of benthic foraminifera were identified from the palaeoecological inventory of the PSRC. Both coral and benthic foraminiferal assemblages were characterised by distinct assemblages of taxa pre-adapted to sediment stress (i.e. low light availability and high sedimentation). At the genus level, no discernable evidence of compositional change in either coral or benthic foraminiferal assemblages was found, relative to European settlement. Instead, variations in assemblage composition were driven by intrinsic changes in prevailing abiotic conditions under vertical reef accretion towards sea level (e.g. hydrodynamic energy, light availability, and sedimentation rate). These findings therefore highlight the importance for considering reef ‘geomorphological development’ when interpreting contemporary reef ecological status. Furthermore, this research emphasises the robust nature of turbid nearshore reefs and suggests that they may be more resilient to changes in water quality than those associated with environmental settings where local background sedimentary conditions are less extreme (e.g. towards the inner/mid-shelf boundary). To this end, this thesis presents new baseline records with which to assess contemporary ecological and environmental change within turbid nearshore settings on the central GBR.

Parrotfish are a diverse and ubiquitous group found on coral reefs worldwide. They are categorised into three main feeding modes; the browsers, scrapers and excavators, which together perform a number of important functional roles on coral reefs. Scraper and excavator parrotfish are common on most Indo-Pacific coral reefs where their roles in bioerosion, sediment production, grazing pressure and sediment reworking have been shown to influence benthic community composition, reef growth potential and sediment supply to reef habitats and reef associated sedimentary landforms. However, despite the widely known importance of parrotfish on coral reefs, our understanding of how their roles in carbonate cycling vary among species and among whole parrotfish communities in different reef habitats remains limited. This thesis produces original contributions to knowledge in the areas of species specific bioerosion estimates for the central Indian Ocean, bottom-up controls of habitat type on parrotfish assemblages and how variations in parrotfish assemblages translate to contributions to carbonate cycling processes among different reef habitats. The study was carried out across eight habitats on an atoll-edge reef platform in the central Maldives, where it was found that parrotfish community composition was driven by reef structural complexity and substrate type. Parrotfish occurred in six of the eight habitats, comprising ~44% of the platform area. Among these habitats, overall grazing pressure, bioerosion rates, sediment reworking and sediment production varied markedly. These processes were also found to have different spatial patterns over the reef platform, showing that they are not necessarily tightly coupled. In addition, reef habitats can vary in their importance for both sediment supply, and the relative importance of reworked sediment. Parrotfish produced a wide range of sediment size fractions, from < 32 to 2000 μm and produced predominantly coral sands (>80%) between 125 and 1000 μm in diameter. This is comparable to the grain types found on local reef islands, and it is likely that the most significant supply of this material is from habitats on the atoll-edge side of the platform (which make up ~20% of the total platform area). Quantifying parrotfish functional roles and understanding the drivers behind these processes is important for informing future empirical and modelling studies, particularly as coral reefs undergo a time of dramatic environmental change.

Carbonate rocks are of global importance as they contain about 50% of the world’s remaining hydrocarbon reserves and are also a major host to the world’s groundwater resources. Therefore, understanding and modelling the fluid flow processes in carbonates are of great importance. A critical problem is that, unlike homogenous media (such as sandstones), carbonates often show features, including porosity, that span across a wide spatial range, from sub-micron porosity to fractures of meters length-scale. In this study X-ray computed micro-tomography (μCT) has been utilised as a tool to monitor two phase (oil-brine) flow in porous carbonate (dolomite) plugs at ambient temperature and pressures smaller than 690 kPa. A simple, low-cost and highly X-ray transparent core-holder was utilised for which the design is introduced. Capillary end effects were recognised and avoided in data analysis. Displacement processes that occur in the dolomite under water-wet, oil-wet, and partially mixed-wet states were investigated. The experiments consisted of a series of drainage and imbibition processes occurring under capillary and viscous dominated flow regimes. Pore-scale mechanisms of piston-like displacement and snap-off (or at least clear results of them), that were previously observed in sandstones and 2D micro-models, were observed in the dolomite under study. In addition, a new pore-scale mechanism was identified which occurred at high capillary numbers, referred to as droplet-fragmentation. This new pore-scale mechanism may provide an explanation to the capillary-desaturation process for heterogeneous media. In the experiments performed on the oil-wet plug formation of a stable water in oil emulsion was observed which appears to be the first 3D observation of in situ emulsion formation made using μCT. Direct visualisation of the oil-brine-rock configurations and measurement of the contact angles are presented. A comparison was made for the contact angle distributions measured for the water-wet and oil-wet conditions. Observation of fluid displacement processes as well as oil-brine-rock contact angle distributions demonstrate that pore-scale imaging provides a promising tool for wettability characterisation on both pore and core scales. Such detailed wettability data can also be used in pore-scale flow models. For the dolomite under study multiple-scale pore network models were constructed by integrating single-scale networks extracted from μCT images acquired at different length-scales. Mercury injection capillary pressure laboratory measurements were used to evaluate the capillary pressure (vs. saturation) curves calculated using single, two-scale, and three-scale network models of this dolomite. The integrated networks displayed an improved match to the laboratory measurements in comparison with the single-scale network model. The three-scale network provided the closest simulated curve, this result confirms that a more representative model displays closer properties. While simulated capillary pressure curves are close (converging) for the integrated networks the calculated relative permeability curves show variability for different multiple-scale networks. The present work demonstrates that the pore-scale fluid displacement processes occurring in heterogeneous porous media are more complex than those occurring in homogeneous media. In addition, successful fluid flow simulations require construction of multiple-scale models as well as consideration of the pore-scale processes (such as droplet-fragmentation) that are specific to such complex pore systems.