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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The structural, thermal, and fluid evolution of the Livingstone Range anticlinorium, and its regional significance to the southern Alberta foreland thrust and fold belt

Cooley, Michael Ames 08 April 2008 (has links)
The Livingstone Range anticlinorium (LRA) is a long (>65 km) narrow (<5 km) structural culmination that coincides with a major hanging-wall ramp across which the Livingstone thrust cuts ~1000 m up-section eastward from a regional décollement in the upper part of Devonian Palliser Formation to another regional décollement within Jurassic Fernie Formation. The presence of Precambrian basement fluids prior to thrusting and folding is recorded in the LRA by deformed jasper+/-fluorite+/-sphalerite veins, and adjacent haloes of altered dolomitic host rock with high 87Sr/86Sr ratios (0.7094 to 0.7100) relative to most host rocks. Basement fluids are a possible source for anomalously radiogenic strontium that occurs in the diagenetically altered Paleozoic carbonate rocks in the LRA and throughout the Western Canada Sedimentary Basin, but underlying thick shale strata such as the Exshaw Formation are also a possible source. The earliest stages of thrusting deformation involved the development of distinctive chevron-style, flexural-slip thrust-propagation folds that have conspicuous blind thrust faults along their hinge zones. The hinge-zone thrust system of the Centre Peak anticline consists of a series of stacked detachment thrusts, each of which emerges from a different zone of interbed slip in the backlimb of the anticline and deflects the hinge zone eastward. Each successively higher detachment thrust dies out in the hinge zone at approximately the same stratigraphic level at which an overlying detachment thrust fault emerges from a bedding detachment zone in the backlimb. Fluid flow during thrust-propagation folding is recorded by dolomite+/-calcite veins with isotopic compositions that are similar to those of host rocks. Fluid flow occurred along faults related to thrust-propagation folding, and also along many tear faults and larger thrust faults. Veins in these fault zones have slightly higher 87Sr/86Sr ratios relative to adjacent host rocks and are interpreted to have formed from a mixture of formation fluids and hotter basement fluids in a rock-dominated system. Oxygen isotope thermometry of four syn-folding veins indicates they precipitated at anomalously high temperatures (>250°C). The youngest episode of fluid flow along thrust faults and tear faults is recorded by calcite veins with very low δ18O values (-18 to -9‰ PDB), which are interpreted to have precipitated along faults that were active while the LRA was being transported eastward and elevated by underlying thrust faults, and cooled by infiltrating meteoric water. The conduits along which significant meteoric fluid circulation occurred are marked by visibly altered host rocks that have anomalously low δ18O values and slightly lower δ13C values relative to most host rocks. Rapid cooling due to deep infiltration of meteoric water into the shallow brittle surface of the deforming earth is almost certainly not restricted to thrust and fold belts, nor is its thermal effect necessarily restricted to the upper few kilometers. This model for fluid flow has significant implications for predicting thermal conditions in deep metamorphic rocks that lie beneath the brittle crust, the most obvious effect being to push down the brittle/ductile transition zone, which would enhance even deeper meteoric fluid circulation and cause the deflection of underlying isotherms. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2007-11-01 15:25:23.854
2

Assessing the anthropogenic impact on soil redistribution processes using radionuclides (10Be, 210Pb, 137Cs and 7Be) : a case study from the Christina River Basin, USA

Marquard, Julia January 2015 (has links)
Anthropogenic driven soil erosion has increased drastically within the last few centuries. Accelerated removal of topsoil degrades soil characteristics, decreasing the agricultural capacity to sustain food production for future human generations. In order to reduce sediment erosion to a minimum, soil movement dynamics have to be understood over relevant timescales. Emphasis is required on human land use, which has changed over time, altering erosion and deposition processes in the landscape. This thesis aims to understand the development of erosion with time and studies the effects of the anthropogenic impact on the Earth’s surface. A case study was conducted in the Christina River Basin in south-eastern Pennsylvania (USA) to evaluate the anthropogenic impact on sediment redistribution before and during European colonisation of the US East Coast. The Christina River Basin is focus of the Christina River Basin Critical Zone Observatory, where researchers of many disciplines (e.g. hydrology, geochemistry, geology, biology, geomorphology, soil science) study the interactions of the water, mineral and carbon cycle in relation to different land uses. This site is particularly suitable for this study due to the sudden change in land use with the arrival of European Settlers and the well-recorded history of land use in the area since. Besides sediment processes related to the European colonisation, special emphasis was placed on the last century and the particular impact of land management practices on the landscape. For the approach of this study, upland and depositional sediment profiles, as well as suspended sediment collected from rivers at different times were analysed for radionuclide activity. In particular, a combination of the short-lived radionuclides 7Be, 210Pb, and 137Cs with the long-lived meteoric nuclide 10Be was used to allow detection of sediment erosion as well as tracing of sediment source to streams over different time frames. Natural sediment processes were studied by investigating meteoric 10Be in different upland and valley hollow soil profiles in the Christina River Basin. Natu-ral sediment erosion rates of 17 to 18 mm per 1000 years and soil residence time of 26,000 to 57,000 years in upland sites classify the region to be characterised by slowly eroding soils. Valley hollow study sites indicate an alteration in sediment supply due to climate change within the last 80,000 years. Analysis of meteoric 10Be on suspended sediment in rivers with time (from pre-colonial to present times) and a comparison to the historical background of land use management indicated drastic changes in the sediment sources to the streams during the colonisation of the US East Coast. Such profound changes in the soil movement dynamics can be tied to a complete deforestation of the watershed during that time. However, a slow recovery of sediment sources to pre-colonial conditions within the last 100 years was observed, which may be related to the afforestation in parts of the watershed and change in farming practises. Examination of floodplains in recent history (last 100 years) using 210Pb and 137Cs identified a correlation between changes in land use and floodplain development. In particular, deforestation led to channel migration within the watershed, whereas afforestation reduced the flood magnitude. A discrimination of different sediment sources (agricultural and forest surface, channel migration) was detected on present suspended sediment by using a combination of tracers: 7Be, 137Cs, 210Pb and 10Be. About 50 % of sediment in the stream was attributed to channel migration classifying the stream as relatively unstable, whereas the second major sediment contribution was agricultural soil (32 %). As both sources are closely related to human activity in the study area, appropriate land management practices and stream channel stabilisation are of great importance for a hydro- and morphodynamic balance in future times. Results presented in this study provide evidence of the powerful impact anthropogenic land use has had on sediment movement in the Christina River Basin. More importantly, this study has shown the usefulness of combining long- and short-lived radionuclides to identify soil redistribution at different time periods and scales. Radionuclide data does not only reflect the drastic impact during European colonisation but also detects gradual changes that occur due to human action to limit soil erosion within the last century. This study indicates that some of the best management practices may minimise anthropogenic induced soil erosion, whilst simultaneously signifying the need to further improve land use management and reduce sediment erosion.
3

Investigations of Macro and Micro Scale Void Spaces: Preservation, Modeling and Biofilm Interactions

Nagel, Athena Marie Owen 15 August 2014 (has links)
Dissolutional voids in the subsurface were examined from three different viewpoints. First, analysis of pseudokarst features on San Salvador Island, Bahamas, uncovered the involvement of organics in the cementation and porosity generation process. This organic material was analyzed using SEM, TEM, and in thin section. While the actual role of organics in the cementation process could not be determined using these tools, the abundance of the material was documented. Holocene samples appear to have more organics than Pleistocene samples. The abundance of this material should have an effect on isotope analyses and needs to be considered in future work on meteoric cements and the environments where they form. Second, work on Mallorca Island, Spain, demonstrated how the placement and abundance of exposed caves could predict subsurface cave distributions. This work measured caves along exposed coastlines and in protected areas known as calas. Results found that caves within the calas have larger volumes and aerial footprints than caves on the exposed cliffs. The cave distributions showed that calas had to form prior to cave formation. Several paleo-slump features were observed and are believed to be the result of collapsed Tortonian flank margin caves, which were later inilled with Messinian sediments, using the caves as limited accommodation space, resulting in these sediment layers unaffected by the collapse further up section. Third, the current method of cave data manipulation to produce cave areal footprints and volume was found to be incorrect and in need of a calibration mechanism. This calibration was determined by reviewing how Compass cave mapping software generates volume estimates, using shapes of known volumes. Cave surveying techniques were also reviewed to determine if survey protocol affected volume outputs. Surveying in straight lines, down the center of a passage, avoiding splay shots, and taking left, right, up and down measurements (LRUDs) were found to generate the most accurate volumes estimates using Compass. These protocols were used to remap caves from paper maps to generate correction factors. Propriety software was used that could “shrink wrap” a 3D cave map rendering to produced values for cave volume and porosity and rock porosity.
4

A Geochemical and Spatial Characterization of the Champagne Hot Springs Shallow Hydrothermal Vent Field, Dominica, Lesser Antilles

McCarthy, Kevin Thomas 12 July 2004 (has links)
Studies of seafloor hydrothermal activity and its associated geochemical and mineralogical effects have primarily focused on deep sea systems. These processes are not limited to deep sea locations. Numerous shallow hydrothermal systems have been identified along the submerged flanks of volcanic islands such as Vulcano Island, Italy and Ambitle Island, Papua New Guinea. This study investigates the Champagne Hot Springs shallow marine hydrothermal system, located along the submerged flank of the Plat Pays volcanic system on the southwest section of the island of Dominica, Lesser Antilles. The main objective is determine the source of the hydrothermal fluids and gases and their related effect on sediment and precipitate chemistry. A detailed map of the vent field will also be generated to accurately present vent locations and distribution. Geochemical and mineralogical analyses of vent waters, pore waters, gases, sediments and precipitates were determined by High Pressure Liquid Chromatography (HPLC), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), Neutron Activation Analysis (NAA), Scanning Electron Microscopy (SEM), Electron Dispersive X-Ray Analysis (EDX), Powder X-Ray Diffraction (XRD), Gas Chromatography and Mass Spectrometry. These analyses have revealed the following: (1) The vent waters and pore waters are mixtures of seawater and meteoric derived hydrothermal fluids in varying proportions. The relative input of each component is both temperature and flow rate dependent. (2) The simultaneous increase in pH and Eh caused by mixing between Fe2+ rich vent fluids and seawater forms precipitates and sediment coatings of hydrous ferric oxides. The elevated concentrations of As and Sb in the precipitates and sediments relative to average Caribbean seafloor sediments is a function of adsorption to the surface of the hydrous ferric oxide, (3) Pore waters in the immediate vicinity of sediment covered vents carry Fe2+ rich fluid to the sediment/seawater interface, where rapid oxidation of soluble Fe2+ to insoluble Fe3+ leads to precipitation of hydrous ferric oxide coatings on sediment grains and subsequent formation of hydrothermally altered sand patches, (4) The gas samples are typical arc-type gases and have both meteoric and magmatic signatures.
5

Rocket-borne in situ measurements in the middle atmosphere

Hedin, Jonas January 2009 (has links)
The Earth's mesosphere and lower thermosphere in the altitude range 50-130 km is a fascinating part of our atmosphere. Complex interactions between radiative, dynamical, microphysical and chemical processes give rise to several prominent phenomena, many of those centred around the mesopause region (80-100 km). These phenomena include noctilucent clouds, polar mesosphere summer echoes, the ablation and transformation of meteoric material, and the Earth’s airglow. Strong stratification and small scale interactions are common features of both these phenomena and the mesopause region in general. In order to study interactions on the relevant spatial scales, in situ measurements from sounding rockets are essential for mesospheric research. This thesis presents new measurement techniques and analysis methods for sounding rockets, thus helping to improve our understanding of this remote part of the atmosphere. Considering the need to perform measurements at typical rocket speeds of 1 km/s, particular challenges arise both from the design of selective, sensitive, well-calibrated instruments and from perturbations due to aerodynamic influences. This thesis includes a quantitative aerodynamic analysis of impact and sampling techniques for meteoric particles, revealing a distinct size discrimination due to the particle flow. Optical techniques are investigated for mesospheric ice particle populations, resulting in instrument concepts for accessing smaller particles based on Mie scattering at short ultraviolet wavelengths. Rocket-borne resonance fluorescence measurements of atomic oxygen are critically re-assessed, leading to new calibration concepts based on photometry of O2 airglow emissions. The work presented here also provides important pre-studies for the upcoming PHOCUS rocket campaign from Esrange in July 2010. PHOCUS will address the interaction between three major mesospheric players: meteoric smoke, noctilucent clouds and gas-phase chemistry.
6

The Stable Isotopic Variations and the Hydrogeology of the Coronet Peak Skifield, Queenstown.

Belcher, Danielle Marie January 2009 (has links)
This study aims to investigate the stable isotopic characteristics of meteoric and ground waters, and to obtain spring flow rates in the Coronet Peak Skifield, Queenstown. Spring flows were gathered during the winters of 2008 and 2009, whilst water samples were collected from precipitation, springs, reservoirs and groundwater during July, August and September 2009. The spring flows were examined and the water samples were analysed for δD and δ¹⁸O values using the CF-IRMS at the University of Canterbury. A database has been gathered from all natural water sources to give a local meteoric water line (LMWL) for the area that fits clearly with the global meteoric water line. The LMWL has an R2 value of 0.97 and the equation is δD = 8 δ¹⁸O +10. An understanding of evaporation as it occurs in the water storage reservoirs of the mountain has also been obtained, giving rise to a local evaporation line. The stable isotope ratios of hydrogen and oxygen within precipitation have been used extensively to characterise the hydrogeology with emphasis on altitude effects, storm duration and variations in storm track trajectories. Of these three phenomena, it is the trajectory of the storm track that is best shown to affect the composition of precipitation in this area. The air masses advancing on the study area from the north being more depleted in their isotopic signatures, with approximate δD and δ¹⁸O values of –130‰ and -16‰. The air masses approaching from a southerly direction are more positive in comparison, having approximate δD and δ¹⁸O values of –65‰ and -9‰. The altitude effect in precipitation on the Skifield has led to an altitude gradient being found: for every 100-metre increase in elevation, δ¹⁸O decreases by 0.71‰. However there were some inconsistencies. The influence on precipitation from storm duration is also inconsistent in this area. The R2 values range from 0.14 to 0.99, but this method does not take into account the position of the individual samples. Some samples did not plot in the expected order that is governed by a decrease in stable isotopic ratios with storm duration. The stable isotopic compositions within meteoric waters can be used as tracers of water sources. The isotope date of the springs also infers an altitude effect. The springs gave an altitude gradient of a decrease –0.43‰ with each 100-metre increase in elevation. This indicates that precipitation is the main influence on the stable isotopic composition of the springs in this area. However, data shows differences between the current precipitation and the groundwater compositions, indicating that present precipitation is not flowing from the springs, past precipitation is. The stable isotopic compositions of the springs have also been correlated with groundwater isotope data and suggest the sources of the springs are groundwater dominated. Although some springs compositions indicate an influence by current precipitation. This is shown by a negative stable isotopic trend in the precipitation sampled in August, corresponding with a relatively negative stable isotopic composition in some springs during this time period. Monitoring of spring flows on Coronet Peak have led to an average winter flow rate being established of 26.5 litres per second. Spring flow rates range from 0.25 – 6 litres per second. This monitoring has indicated the springs of the greatest yield that are not already being utilised on the Skifield. It is these springs that should be further investigated as to whether they would provide a sustainable source of water on the mountain. This locally derived water would then be utilised for the purposes of artificial snowmaking and other activities and amenities that are currently operated by NZ Ski on Coronet Peak.
7

Meteoric Diagenesis of Plio-Pleistocene Reef Terraces in the Southern Dominican Republic

Hernawati, Yulaika 09 December 2011 (has links)
Four prograding reef terraces (6, 15, 30, and 50 m) have been repetitively exposed to marine and freshwater alteration during the Pliocene and Pleistocene periods. Prolonged freshwater alterations have resulted in many diagenetic overprints that obscure early diagenetic products. This study investigates the sequence of the diagenetic processes and products in the terrace deposits using five long cores and 14 short cores taken from these different reef terraces. The lithologic changes in the cores were documented for reconstruction of the original depositional frameworks prior to embarking on a diagenetic study. Both textural and geochemical changes were examined within all four different terraces in order to characterized the diagenetic history. The textural changes observed in the cores and thin sections, provided preliminary evidence of the diagenetic environment. Through the use of X-ray diffractometry, stable isotopes (C and O), and trace element data, the interpretation of the diagenetic environment can be constrained. The reef terraces were deposited as as shallowing upward units following a down-stepping carbonate sequence. The lithology of the cores is dominated by reefal facies, which consist of the back reef, reef crest, front, and fore reef facies. The exposure surfaces, observed at various depths, constrained the interpretation of early diagenetic environments (met. vadose and phreatic). Three major diagenetic environments can be characterized from the cores, these are meteoric vadose, meteoric phreatic, and dolomitizaton. These diagenetis environments produced different geochemical signatures, which can be quantified through analysis of the stable isotopes and trace elements incorporated into the cements. The different reef terraces represent different duration of exposure, with the higher terraces having been exposed longer than the lower ones. This study enables the documentation and comparison of the processes and products of the meteoric diagenesis that occurred within these different terraces. In addition, this study also constrain the early dolomitization observed in sigmoidal reef deposits. In order to further quantify the process of early dolomitization, mineralogy, isotopes C and O, trace elements, and the Sr-isotopes were examined as well.
8

Diagênese meteórica e relacionada a domos de sal em reservatórios turbidíticos terciários da bacia do Espírito Santo

Oliveira, Daniel Martins de January 2018 (has links)
A evolução diagenética de dois reservatórios turbidíticos terciários da porção offshore da Bacia do Espírito Santo, foi influenciada tanto por processos meteóricos como por processos relacionados a domos salinos adjacentes aos reservatórios, que tiveram diferente impacto sobre sua qualidade. A precipitação de pirita framboidal, dolomita microcristalina e siderita ocorreram sob condições eodiagenéticas marinhas. A percolação por água meteórica ocorreu ainda durante a eodiagênese, e promoveu extensiva caulinização (δ18OSMOW=+15.3‰ a +18.2‰; δDSMOW=-51‰ a -66‰) e dissolução de feldspatos, micas e intraclastos lamosos. Durante o progressivo soterramento da sequência (profundidades atuais: 2600-3000m) e consequente compactação, fluidos oriundos dos lutitos circundantes, modificados por reações com a matéria orgânica e carbonatos, deslocaram gradualmente os fluidos salobros marinhos-meteóricos, levando à precipitação de calcita poiquilotópica (valores médios: δ18OVPDB= -6.6‰; δ13CVPDB= -1.2‰). A composição dos fluidos mesodiagenéticos foi progressivamente modificada pela proximidade dos domos de sal, promovendo ubíqua albitização dos feldspatos e precipitação localizada de quartzo, calcita (valores médios: δ18O= -10.2‰; δ13C= -3.9‰) e dolomita em sela (valores médios: δ18O= -10.2‰; δ13C= -4.2‰). A análise de inclusões fluidas nos crescimentos de quartzo indicou que os fluidos precipitantes tinham salinidade predominantemente entre 9 e 13 % de NaCl (em peso) e temperaturas de homogeneização na faixa de 1050 a 1450 C Estes valores são mais altos do que aqueles esperados para o gradiente geotérmico normal da área. A distribuição da albitização dos feldspatos sugere que as fraturas ao longo das margens dos domos de sal atuaram como caminho preferencial para a circulação das salmouras quentes. Os valores de δ13C e δ18O dos cimentos de calcita e dolomita seguem um padrão de covariância, mostrando um declínio desde daqueles representativos da água do mar (~0%), para δ13C =-5.9‰ e δ18O = -10.9‰ para a calcita, e δ13C = -5.4‰ e δ18O = -11.7‰ para a dolomita, o que sugere a progressiva participação da descarboxilação térmica da matéria orgânica dos lutitos com o soterramento. A compactação mecânica foi mais importante do que a cimentação na redução da porosidade, e a dissolução de feldspatos foi o processo mais importante na geração de porosidade nos reservatórios. Apesar da proximidade dos domos de sal, a intensidade dos processos diagenéticos foi moderada, já que não ocorreu autigênese de ilita, e a cimentação de quartzo foi limitada. Estas características podem estar relacionadas com o soterramento relativamente recente destes reservatórios. Este estudo mostra que a predição da diagênese e qualidade de reservatórios relacionados a domos de sal é uma função de múltiplas variáveis, incluindo as dimensões dos domos, o regime térmico regional da bacia, a condutividade térmica e de fluidos, e a composição mineral e propriedades geomecânicas dos reservatórios e litologias associadas. / The diagenetic evolution of two tertiary turbidite reservoirs from the offshore portion of the Espírito Santo Basin, eastern Brazil, was influenced by meteoric and salt dome-related processes, which had different impact on their quality. Marine eogenetic processes included the precipitation of framboidal pyrite, microcrystalline dolomite and siderite. Meteoric water influx during eodiagenesis occurred in response to relative sea-level falls that promoted extensive kaolinization (δ18O=+15.3‰ to +18.2‰; δD= -51‰ to -66‰) and dissolution of framework silicate grains. During progressive burial (present depths – 2600 m – 3000 m), connate marine fluids modified by reactions with organic matter and carbonates presented in the surrounding mudrocks gradually displaced brackish fluids generated by the meteoric influx and led to concretionary cementation by poikilotopic calcite (average δ18O= -6.6‰; δ13C= -1.2‰). Mesogenetic fluids were progressively modified by the proximity of salt domes, which led to ubiquitous feldspar albitization and localized quartz, calcite (average δ18O= -10.2‰; δ13C= -3.9‰) and saddle dolomite precipitation (average δ18O= -10.2‰; δ13C= -4.2‰). Fluid inclusion analysis in quartz overgrowths indicate that the precipitating fluids had salinities predominantly in the range 9-13 wt% NaCl equivalent and temperatures largely in the 105 – 145oC range These values are higher than those expected considering the normal geothermal gradient for the area. The distribution of feldspar albitization suggests that the fracture systems along the salt domes margins acted as preferential pathways for such hot, saline diagenetic fluids. Isotopic values for calcite and dolomite cements follow a co-variance trend of decreasing δ13C and δ18O from close to marine (~0‰) towards negative values (δ13C and δ18O down to -5.9‰ and -10.9‰ for calcite; -5.4‰ and -11.7‰ for dolomite), suggesting increasing contribution from thermal decarboxylation with increasing temperature and depth. Mechanical compaction was more important than cementation in reducing depositional porosity, and the dissolution of framework silicate grains is the most important processes for enhancing reservoir quality. Despite the proximity to the salt domes, the intensity of the influenced diagenetic processes is relatively mild, as illite authigenesis is lacking, and quartz cementation is limited, features that may be related to the recent burial of the reservoirs.
9

Diagênese meteórica e relacionada a domos de sal em reservatórios turbidíticos terciários da bacia do Espírito Santo

Oliveira, Daniel Martins de January 2018 (has links)
A evolução diagenética de dois reservatórios turbidíticos terciários da porção offshore da Bacia do Espírito Santo, foi influenciada tanto por processos meteóricos como por processos relacionados a domos salinos adjacentes aos reservatórios, que tiveram diferente impacto sobre sua qualidade. A precipitação de pirita framboidal, dolomita microcristalina e siderita ocorreram sob condições eodiagenéticas marinhas. A percolação por água meteórica ocorreu ainda durante a eodiagênese, e promoveu extensiva caulinização (δ18OSMOW=+15.3‰ a +18.2‰; δDSMOW=-51‰ a -66‰) e dissolução de feldspatos, micas e intraclastos lamosos. Durante o progressivo soterramento da sequência (profundidades atuais: 2600-3000m) e consequente compactação, fluidos oriundos dos lutitos circundantes, modificados por reações com a matéria orgânica e carbonatos, deslocaram gradualmente os fluidos salobros marinhos-meteóricos, levando à precipitação de calcita poiquilotópica (valores médios: δ18OVPDB= -6.6‰; δ13CVPDB= -1.2‰). A composição dos fluidos mesodiagenéticos foi progressivamente modificada pela proximidade dos domos de sal, promovendo ubíqua albitização dos feldspatos e precipitação localizada de quartzo, calcita (valores médios: δ18O= -10.2‰; δ13C= -3.9‰) e dolomita em sela (valores médios: δ18O= -10.2‰; δ13C= -4.2‰). A análise de inclusões fluidas nos crescimentos de quartzo indicou que os fluidos precipitantes tinham salinidade predominantemente entre 9 e 13 % de NaCl (em peso) e temperaturas de homogeneização na faixa de 1050 a 1450 C Estes valores são mais altos do que aqueles esperados para o gradiente geotérmico normal da área. A distribuição da albitização dos feldspatos sugere que as fraturas ao longo das margens dos domos de sal atuaram como caminho preferencial para a circulação das salmouras quentes. Os valores de δ13C e δ18O dos cimentos de calcita e dolomita seguem um padrão de covariância, mostrando um declínio desde daqueles representativos da água do mar (~0%), para δ13C =-5.9‰ e δ18O = -10.9‰ para a calcita, e δ13C = -5.4‰ e δ18O = -11.7‰ para a dolomita, o que sugere a progressiva participação da descarboxilação térmica da matéria orgânica dos lutitos com o soterramento. A compactação mecânica foi mais importante do que a cimentação na redução da porosidade, e a dissolução de feldspatos foi o processo mais importante na geração de porosidade nos reservatórios. Apesar da proximidade dos domos de sal, a intensidade dos processos diagenéticos foi moderada, já que não ocorreu autigênese de ilita, e a cimentação de quartzo foi limitada. Estas características podem estar relacionadas com o soterramento relativamente recente destes reservatórios. Este estudo mostra que a predição da diagênese e qualidade de reservatórios relacionados a domos de sal é uma função de múltiplas variáveis, incluindo as dimensões dos domos, o regime térmico regional da bacia, a condutividade térmica e de fluidos, e a composição mineral e propriedades geomecânicas dos reservatórios e litologias associadas. / The diagenetic evolution of two tertiary turbidite reservoirs from the offshore portion of the Espírito Santo Basin, eastern Brazil, was influenced by meteoric and salt dome-related processes, which had different impact on their quality. Marine eogenetic processes included the precipitation of framboidal pyrite, microcrystalline dolomite and siderite. Meteoric water influx during eodiagenesis occurred in response to relative sea-level falls that promoted extensive kaolinization (δ18O=+15.3‰ to +18.2‰; δD= -51‰ to -66‰) and dissolution of framework silicate grains. During progressive burial (present depths – 2600 m – 3000 m), connate marine fluids modified by reactions with organic matter and carbonates presented in the surrounding mudrocks gradually displaced brackish fluids generated by the meteoric influx and led to concretionary cementation by poikilotopic calcite (average δ18O= -6.6‰; δ13C= -1.2‰). Mesogenetic fluids were progressively modified by the proximity of salt domes, which led to ubiquitous feldspar albitization and localized quartz, calcite (average δ18O= -10.2‰; δ13C= -3.9‰) and saddle dolomite precipitation (average δ18O= -10.2‰; δ13C= -4.2‰). Fluid inclusion analysis in quartz overgrowths indicate that the precipitating fluids had salinities predominantly in the range 9-13 wt% NaCl equivalent and temperatures largely in the 105 – 145oC range These values are higher than those expected considering the normal geothermal gradient for the area. The distribution of feldspar albitization suggests that the fracture systems along the salt domes margins acted as preferential pathways for such hot, saline diagenetic fluids. Isotopic values for calcite and dolomite cements follow a co-variance trend of decreasing δ13C and δ18O from close to marine (~0‰) towards negative values (δ13C and δ18O down to -5.9‰ and -10.9‰ for calcite; -5.4‰ and -11.7‰ for dolomite), suggesting increasing contribution from thermal decarboxylation with increasing temperature and depth. Mechanical compaction was more important than cementation in reducing depositional porosity, and the dissolution of framework silicate grains is the most important processes for enhancing reservoir quality. Despite the proximity to the salt domes, the intensity of the influenced diagenetic processes is relatively mild, as illite authigenesis is lacking, and quartz cementation is limited, features that may be related to the recent burial of the reservoirs.
10

Diagênese meteórica e relacionada a domos de sal em reservatórios turbidíticos terciários da bacia do Espírito Santo

Oliveira, Daniel Martins de January 2018 (has links)
A evolução diagenética de dois reservatórios turbidíticos terciários da porção offshore da Bacia do Espírito Santo, foi influenciada tanto por processos meteóricos como por processos relacionados a domos salinos adjacentes aos reservatórios, que tiveram diferente impacto sobre sua qualidade. A precipitação de pirita framboidal, dolomita microcristalina e siderita ocorreram sob condições eodiagenéticas marinhas. A percolação por água meteórica ocorreu ainda durante a eodiagênese, e promoveu extensiva caulinização (δ18OSMOW=+15.3‰ a +18.2‰; δDSMOW=-51‰ a -66‰) e dissolução de feldspatos, micas e intraclastos lamosos. Durante o progressivo soterramento da sequência (profundidades atuais: 2600-3000m) e consequente compactação, fluidos oriundos dos lutitos circundantes, modificados por reações com a matéria orgânica e carbonatos, deslocaram gradualmente os fluidos salobros marinhos-meteóricos, levando à precipitação de calcita poiquilotópica (valores médios: δ18OVPDB= -6.6‰; δ13CVPDB= -1.2‰). A composição dos fluidos mesodiagenéticos foi progressivamente modificada pela proximidade dos domos de sal, promovendo ubíqua albitização dos feldspatos e precipitação localizada de quartzo, calcita (valores médios: δ18O= -10.2‰; δ13C= -3.9‰) e dolomita em sela (valores médios: δ18O= -10.2‰; δ13C= -4.2‰). A análise de inclusões fluidas nos crescimentos de quartzo indicou que os fluidos precipitantes tinham salinidade predominantemente entre 9 e 13 % de NaCl (em peso) e temperaturas de homogeneização na faixa de 1050 a 1450 C Estes valores são mais altos do que aqueles esperados para o gradiente geotérmico normal da área. A distribuição da albitização dos feldspatos sugere que as fraturas ao longo das margens dos domos de sal atuaram como caminho preferencial para a circulação das salmouras quentes. Os valores de δ13C e δ18O dos cimentos de calcita e dolomita seguem um padrão de covariância, mostrando um declínio desde daqueles representativos da água do mar (~0%), para δ13C =-5.9‰ e δ18O = -10.9‰ para a calcita, e δ13C = -5.4‰ e δ18O = -11.7‰ para a dolomita, o que sugere a progressiva participação da descarboxilação térmica da matéria orgânica dos lutitos com o soterramento. A compactação mecânica foi mais importante do que a cimentação na redução da porosidade, e a dissolução de feldspatos foi o processo mais importante na geração de porosidade nos reservatórios. Apesar da proximidade dos domos de sal, a intensidade dos processos diagenéticos foi moderada, já que não ocorreu autigênese de ilita, e a cimentação de quartzo foi limitada. Estas características podem estar relacionadas com o soterramento relativamente recente destes reservatórios. Este estudo mostra que a predição da diagênese e qualidade de reservatórios relacionados a domos de sal é uma função de múltiplas variáveis, incluindo as dimensões dos domos, o regime térmico regional da bacia, a condutividade térmica e de fluidos, e a composição mineral e propriedades geomecânicas dos reservatórios e litologias associadas. / The diagenetic evolution of two tertiary turbidite reservoirs from the offshore portion of the Espírito Santo Basin, eastern Brazil, was influenced by meteoric and salt dome-related processes, which had different impact on their quality. Marine eogenetic processes included the precipitation of framboidal pyrite, microcrystalline dolomite and siderite. Meteoric water influx during eodiagenesis occurred in response to relative sea-level falls that promoted extensive kaolinization (δ18O=+15.3‰ to +18.2‰; δD= -51‰ to -66‰) and dissolution of framework silicate grains. During progressive burial (present depths – 2600 m – 3000 m), connate marine fluids modified by reactions with organic matter and carbonates presented in the surrounding mudrocks gradually displaced brackish fluids generated by the meteoric influx and led to concretionary cementation by poikilotopic calcite (average δ18O= -6.6‰; δ13C= -1.2‰). Mesogenetic fluids were progressively modified by the proximity of salt domes, which led to ubiquitous feldspar albitization and localized quartz, calcite (average δ18O= -10.2‰; δ13C= -3.9‰) and saddle dolomite precipitation (average δ18O= -10.2‰; δ13C= -4.2‰). Fluid inclusion analysis in quartz overgrowths indicate that the precipitating fluids had salinities predominantly in the range 9-13 wt% NaCl equivalent and temperatures largely in the 105 – 145oC range These values are higher than those expected considering the normal geothermal gradient for the area. The distribution of feldspar albitization suggests that the fracture systems along the salt domes margins acted as preferential pathways for such hot, saline diagenetic fluids. Isotopic values for calcite and dolomite cements follow a co-variance trend of decreasing δ13C and δ18O from close to marine (~0‰) towards negative values (δ13C and δ18O down to -5.9‰ and -10.9‰ for calcite; -5.4‰ and -11.7‰ for dolomite), suggesting increasing contribution from thermal decarboxylation with increasing temperature and depth. Mechanical compaction was more important than cementation in reducing depositional porosity, and the dissolution of framework silicate grains is the most important processes for enhancing reservoir quality. Despite the proximity to the salt domes, the intensity of the influenced diagenetic processes is relatively mild, as illite authigenesis is lacking, and quartz cementation is limited, features that may be related to the recent burial of the reservoirs.

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