22 research outputs found
Spatiotemporal Characterization of Smectite‐to‐Illite Diagenesis in the Nankai Trough Accretionary Prism Revealed by Samples From 3 km Below Seafloor
No full textStructural characterization of the clay mineral illite-1M
No full textIllite is one of the major clay minerals found on the Earth’s surface, constituent of the soils, and araw material used for a variety of industrial applications. It is an Al-K mica-like, non-expanding,dioctahedral mineral that crystallizes in the monoclinic system. Its structure is very similar to that of2:1 mica, where two tetrahedral sheets sandwich an octahedral one, to build up the T-O-T sheet. Katoms, and possibly water molecules are hosted in the interlayer region.This work presents the results of the structural characterization of illite-1M from Northern Hungarywith the first attempt to refine the structure model and locate the interlayer water molecules. Thestructural characterization was accomplished using current state of the art analytical methodsavailable for the structural characterization of clays. The results illustrate the status of techniquesfor clay structure determination, as well as a structural model for illite.A chemical formula for the illite-1M under investigation can be written as:K0.78Ca0.02Na0.02(Mg0.34Al1.69Fe’’’0.02)[Si3.35Al0.65]O10(OH)2×nH2O.Structure simulations with WILDFIRE yielded a model with 30% of cis-vacant layers andexpandability percentage of 10 %. The value of the percentage of expandability was confirmed withNEWMOD whose best simulation was obtained with 90% of di-octahedral mica, 10% ofexpandable layers, and K = 0.8 in the interlayer region. The best structure simulation obtained withDIFFaX was obtained with a population of the K atoms of 80%. To obtain the best fit, 6 cells alongc (in agreement with the results of the TEM study) and an average dimension of the particles in thea-b plane of 300 nm were used.Besides the determination of the basic structure unit (the results are consistent with those obtainedwith the local information provided by the fit of the PDF data) and the model of disorder, therefinement with DIFFaX+ made it possible attempt to locate the interlayer water molecule and torefine its site population. Although physically sound, both the observed tetrahedral layercorrugation and the location of the water molecule need further experimental support, because thefinal fit of the observed pattern is still imperfect. The reasons for this misfit are thoroughlydiscussed
Illite in the Lower Paleozoic of the Illinois Basin: Origin, age, and polytype quantification
No full textIllite was first named in 1937 in Illinois by Ralph Grim, one of the founders of clay mineralogy. Illite is the most abundant clay mineral on the earth's surface. However, we know very little about the origin of illite in Illinois. This dissertation focuses on two aspects of illite in the Lower Paleozoic of the Illinois Basin: (1) illite polytype quantification, which explains the anomalies of the distribution of illite and smectite in the Illinois Basin, and (2) the origin and age of diagenetic illite, which is used to link illitization to fluid migration.Illite polytype quantification allows the differentiation of diagenetic and detrital illite. In Paleozoic shales from the Illinois Basin three polytypes 1M\rm\sb{d}, 1M, and 2M\sb1 are observed. 1M\rm\sb{d} and 1M are of diagenetic origin and 2M\sb1 of detrital origin. All three polytypes were quantified by mixing single polytypes and comparing the experimental XRD traces with traces calculated using WILDFIREIllite polytype quantification of different size fractions combined with K/Ar dates allows the extrapolation to apparent ages of detrital and diagenetic end-members. The extrapolated age of the diagenetic end-members dates episodes of diagenesis. Results show that the Upper Ordovician Maquoketa Group shales contain diagenetic illite (dominantly 1M\rm\sb{d} with minor 1M) with an age of 360 Ma, that was not formed solely by burial diagenesis but mainly through either a hydrothermal or K-rich brine event. Ordovician and Cambrian shale partings and sandstones, older than the Maquoketa Group, contain diagenetic illite (1M\rm\sb{d} in shales and 1M in sandstones) having an age of 300 Ma. This late Paleozoic age falls within the span of the Alleghanian orogeny.The conclusion is that the diagenetic illite of the Maquoketa Group and that of the underlying formations formed from different precursors in different hydrologic systems. The diagenetic illite in the Maquoketa Group formed mainly during a hydrothermal or K-rich brine event (100\sp\circC) from smectite or kaolinite. During the Alleghanian orogeny the Maquoketa Group served as an aquitard to fluids (140\sp\circC) that precipitated the diagenetic illite in the older and more permeable sandstones and carbonates.Made available in DSpace on 2011-05-07T14:12:00Z (GMT). No. of bitstreams: 2
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Illite in the Lower Paleozoic of the Illinois Basin: Origin, age, and polytype quantification
No full textIllite was first named in 1937 in Illinois by Ralph Grim, one of the founders of clay mineralogy. Illite is the most abundant clay mineral on the earth's surface. However, we know very little about the origin of illite in Illinois. This dissertation focuses on two aspects of illite in the Lower Paleozoic of the Illinois Basin: (1) illite polytype quantification, which explains the anomalies of the distribution of illite and smectite in the Illinois Basin, and (2) the origin and age of diagenetic illite, which is used to link illitization to fluid migration.Illite polytype quantification allows the differentiation of diagenetic and detrital illite. In Paleozoic shales from the Illinois Basin three polytypes 1M\rm\sb{d}, 1M, and 2M\sb1 are observed. 1M\rm\sb{d} and 1M are of diagenetic origin and 2M\sb1 of detrital origin. All three polytypes were quantified by mixing single polytypes and comparing the experimental XRD traces with traces calculated using WILDFIREIllite polytype quantification of different size fractions combined with K/Ar dates allows the extrapolation to apparent ages of detrital and diagenetic end-members. The extrapolated age of the diagenetic end-members dates episodes of diagenesis. Results show that the Upper Ordovician Maquoketa Group shales contain diagenetic illite (dominantly 1M\rm\sb{d} with minor 1M) with an age of 360 Ma, that was not formed solely by burial diagenesis but mainly through either a hydrothermal or K-rich brine event. Ordovician and Cambrian shale partings and sandstones, older than the Maquoketa Group, contain diagenetic illite (1M\rm\sb{d} in shales and 1M in sandstones) having an age of 300 Ma. This late Paleozoic age falls within the span of the Alleghanian orogeny.The conclusion is that the diagenetic illite of the Maquoketa Group and that of the underlying formations formed from different precursors in different hydrologic systems. The diagenetic illite in the Maquoketa Group formed mainly during a hydrothermal or K-rich brine event (100\sp\circC) from smectite or kaolinite. During the Alleghanian orogeny the Maquoketa Group served as an aquitard to fluids (140\sp\circC) that precipitated the diagenetic illite in the older and more permeable sandstones and carbonates.U of I OnlyETDs are only available to UIUC Users without author permissio
Micromilieu-controlled glauconitization in fecal pellets at Oker (Central Germany)
No full textABSTRACT: Although numerous models for the formation of glauconite have been presented, the precise process and micro-environment of glauconitization are still poorly constrained. We characterize the special micromilieu of glauconitization developed during early diagenesis and present a model for glauconite formation in fecal pellets. Glauconitization at Oker (Central Germany) occurred predominantly in fecal pellets deposited in a shallow marine-lagoonal environment during the Kimmeridgian. Within the fecal pellets, rapid oxidation of organic matter provides the post-depositional, physicochemical conditions favourable for glauconitization. Replacements of matrix calcite, dissolution of detrital quartz, K-feldspar, and clay minerals, and Fe redox reactions were observed within the early micro-environment, followed by the precipitation of euhedral pyrite, matrix-replacive dolomite, and megaquartz accompanied by I-S formation as thin section analyses and SEM observations show. Carbonate geochemical compositions based on ICP-OES and stable oxygen and carbon isotope signatures demonstrate that glauconite formation started in a suboxic environment at a pH of 78 and a temperature of 223ºC to 372ºC at maximum. TEM-EDX-SAED and XRD analyses on separated glauconite fecal pellets and on the <2 mm cla
Porosity and permeability determination of organic-rich Posidonia shales based on 3-D analyses by FIB-SEM microscopy
No full textThe goal of this study is to better understand the
porosity and permeability in shales to improve modelling fluid and gas flow
related to shale diagenesis. Two samples (WIC and HAD) were investigated,
both mid-Jurassic organic-rich Posidonia shales from Hils area, central
Germany of different maturity (WIC R0 0.53 % and HAD R0
1.45 %). The method for image collection was focused ion beam (FIB)
microscopy coupled with scanning electron microscopy (SEM). For image and
data analysis Avizo and GeoDict was used. Porosity was calculated from
segmented 3-D FIB based images and permeability was simulated by a Navier
Stokes–Brinkman solver in the segmented images.
Results show that the quantity and distribution of pore clusters and pores
(≥ 40 nm) are similar. The largest pores are located
within carbonates and clay minerals, whereas the smallest pores are within
the matured organic matter. Orientation of the pores calculated as pore
paths showed minor directional differences between the samples. Both samples
have no continuous connectivity of pore clusters along the axes in the x, y,
and z direction on the scale of 10 to 20 of micrometer, but do show
connectivity on the micrometer scale. The volume of organic matter in the
studied volume is representative of the total organic carbon (TOC) in the samples. Organic matter
does show axis connectivity in the x, y, and z directions. With increasing
maturity the porosity in organic matter increases from close to 0 to more
than 5 %. These pores are small and in the large organic particles have
little connection to the mineral matrix. Continuous pore size distributions
are compared with mercury intrusion porosimetry (MIP) data. Differences
between both methods are caused by resolution limits of the FIB-SEM and by
the development of small pores during the maturation of the organic matter.
Calculations show no permeability when only considering visible pores due to
the lack of axis connectivity. Adding the organic matter with a background
permeability of 1 × 10−21 m2 to the calculations, the total permeability
increased by up to 1 order of magnitude for the low mature and decreases
slightly for the overmature sample from the gas window. Anisotropy of
permeability was observed. Permeability coefficients increase by 1 order
of magnitude if simulations are performed parallel to the bedding. Our
results compare well with experimental data from the literature suggesting
that upscaling may be possible in the future as soon as maturity dependent
organic matter permeability coefficients can be determined
Plasma Spraying of Kaolinite for Preparing Reactive Alumino‐Silicate Glass Coatings
No full textThermally treated kaolinite is used to develop a range of alumino‐silicate‐based precursor materials but its behavior during plasma spraying has not been well‐researched. In this study, two types of kaolinite samples were investigated in the form of low defect (KGa‐1b) and high defect (KGa‐2) varieties. The extreme temperatures of the plasma stream (up to 20 000 K) induced flash melting to produce a highly porous alumino‐silicate glass without any crystallization of new Al−Si oxide minerals. The glass is comprised largely of intact or deformed spheres (average diameters 1.14–1.44 μm), which indicates rapid quenching and solidification before impact. The subspherical structures contain up to 40 % closed pore space caused by the rapid escape of water during melting. The low‐density, porous alumino‐silicate glass coatings with predicted specific surface areas (>0.95 m2/g) and hardnesses >1.8 GPa represent a potentially reactive but physically stable substrate ideal for further chemical functionalization
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Plasma Spraying of Kaolinite for Preparing Reactive Alumino-Silicate Glass Coatings
No full textThermally treated kaolinite is used to develop a range of alumino-silicate-based precursor materials but its behavior during plasma spraying has not been well-researched. In this study, two types of kaolinite samples were investigated in the form of low defect (KGa-1b) and high defect (KGa-2) varieties. The extreme temperatures of the plasma stream (up to 20 000 K) induced flash melting to produce a highly porous alumino-silicate glass without any crystallization of new Al−Si oxide minerals. The glass is comprised largely of intact or deformed spheres (average diameters 1.14–1.44 μm), which indicates rapid quenching and solidification before impact. The subspherical structures contain up to 40 % closed pore space caused by the rapid escape of water during melting. The low-density, porous alumino-silicate glass coatings with predicted specific surface areas (>0.95 m2/g) and hardnesses >1.8 GPa represent a potentially reactive but physically stable substrate ideal for further chemical functionalization
