Holger Lindgreen

Determination of illite-smectite structures using multispecimen X-ray diffraction profile fitting

A procedure for structural investigations by X-ray diffraction of mixed-layer structures incorporating swelling layers has been developed. For each sample, specimens saturated with different cations (Na, Mg, and Ca), are analyzed both as air-dried and as glycolated. One structural model fitting all the observed patterns then provides the structure of the sample. Samples tested include: Mite-smectite (I-S) minerals from Kazachstan (a rectorite), Dolna Ves in Slovakia, Kinnekulle in Sweden, the North Sea, and Scania in Sweden. The fitting of the patterns of the Kazachstan rectorite demonstrated that the instrumental parameters applied in the modeling were correct. For the I-S minerals from Slovakia and Kinnekulle the observed patterns were fitted with one two-component I-S model. However, the Ca-saturated and air-dried specimen of the Kinnekulle bentonites had two types of swelling interlayers. For the Slovakian I-S with Reichweite = 2, an alternative two-phase I-S plus I–V (V = vermiculite) model fitted the experimental X-ray diffraction patterns equally well. The I-S mineral from Scania is in fact a three-component I-T-S (T = tobelite) and the North Sea sample is a four-component I-S-V-V, one type of the swelling layers having swelling characteristics intermediately between smectite and vermiculite. In addition to layer types and distribution, interlayer compositions, such as the amount of interlayer glycol and water and of fixed and exchangeable cations, were determined.

Sequential structure transformation of illite-smectite-vermiculite during diagenesis of Upper Jurassic shales from the North Sea and Denmark

Abstract For mixed-layer clay fractions from the North Sea and Denmark, X-ray diffractograms have been recorded for specimens saturated with Mg, Ca, Na and NH4, both airdry and intercalated with ethylene glycol, and the patterns have been computer-simulated with a multicomponent program. The mixed-layer fractions consist of an illite-smectite-vermiculite (I-S-V) phase constituting -90% of the fraction and a kaolinite-illite-vermiculite (K-I-V) phase. For each I-S-V, the degree of swelling in swelling interlayers depends on both interlayer cation and glycolation, whereas the amount of non-swelling illite and swelling interlayers and the interstratification parameters are constant. Based on structural characteristics and the degree of diagenetic transformation, the samples investigated can be divided into three groups. The I-S-V of group one is predominantly detrital and has 0.69-0.73 illite, 0.26-0.20 smectite and 0.04-0.07 vermiculite interlayers, the illite, smectite and vermiculite interlayers being segregated. The I-S-V of group two has been diagenetically transformed and has 0.80 illite, 0.12 smectite and 0.08 vermiculite interlayers, the vermiculite interlayers being segregated whereas the illite and smectite have the maximum ordering possible for R = 1. The I-S-V of group three has been further transformed during diagenesis and has 0.84 illite, 0.08 smectite and 0.08 vermiculite interlayers. Statistical calculations demonstrate that the I-S-V transformation can be described as a single interlayer transformation (SIT) within the crystallites.

Illite-smectite structural changes during metamorphism in black Cambrian Alum shales from the Baltic area

Abstract Illite-smectite (I-S) from Cambrian black shale of both early diagenetic and anchimetamorphic grade was investigated to determine the mechanism of the clay transformation. The layer sequences, the distribution of thicknesses of coherent scattering domains (CSDs), and the three-dimensional ordering were determined by X-ray diffraction (XRD). The proportions of cis-vacant (cv) and transvacant (tv) 2:1 layers were determined by thermal analysis and the proportion and distribution of interlayer ammonium by XRD and by infared spectroscopy (IR). The structural formulae were determined from total chemical analysis, and Mössbauer and 27Al NMR spectroscopies, and the particle shape and size investigated by atomic force microscopy (AFM). In the early diagenetic samples, the I-S is composed of two phases, one of which contains 0.05 and the other 0.25 smectite (S) interlayers. The first phase does not change during metamorphism. In the second phase, 0.20 S are converted to tobelite (T) layers through fixation of NH4+, but the I layers are not changed. Simultaneously, the proportion of cv layers changes from 0.18 to 0.02, and the tetrahedral substitution of Al for Si is parallel to the increase in T layers. All I interlayers contain 0.75K per O10(OH)2. Furthermore, the metamorphism results in increasing mean thickness of CSDs from 5.1-6.8 nm for the lowdiagenetic samples to 6.7-8.4 nm for the anchimetamorphic samples. We conclude that the tobelitization was accompanied by transformation of cv to tv 2:1 layers adjacent to the smectite interlayers, and formation of tv layers adjacent to the newformed tobelite interlayers in otherwise intact crystallites. This mechanism only partly resembles the tobelitization previously observed in the Upper Jurassic North Sea oil source rocks. I-S in these rocks contained tv 2:1 layers and T interlayers formed through solid-state Al for Si substitution in the tetrahedral sheet and by ammonium fixation in the corresponding interlayers. These different mechanisms are probably because the North Sea I-S originated from weathered illite, like the Cambrian high-illitic phase, whereas the Cambrian low-illitic phase undergoing the transformation originated from cv smectite of volcanic origin. The results indicate that the illitization in oil source rocks is linked to oil generation, and that it deviates from the illitization in other rocks because of the supply of ammonium formed during oil generation and the fixation of this ammonium in the former smectite interlayers.

The structure and diagenetic transformation of illite-smectite and chlorite-smectite from North Sea Cretaceous-Tertiary chalk

Abstract Illite-smectite (I-S) mixed-layer minerals from North Sea oil fields and a Danish outcrop were investigated to determine the detailed structure and the diagenetic clay transformation. Clay layers in the chalk and residues obtained by dissolution of the chalk matrix at pH 5 were investigated. The phase compositions and layer sequences were determined by X-ray diffraction (XRD) including simulation with a multicomponent program. The structural formulae were determined from chemical analysis, infrared (IR) and 27Al NMR spectroscopies and XRD, and the particle shape by atomic force microscopy (AFM). A high-smectitic (HS) I-S phase and a lowsmectitic (LS) illite-smectite-chlorite (I-S-Ch) phase, both dioctahedral, together constitute 80 - 90% of each sample. However, two samples contain significant amounts of tosudite and of Ch-Serpentine (Sr), respectively. Most of the clay layers have probably formed by dissolution of the chalk, but one Campanian and one Santonian clay layer in well Baron 2 may have a sedimentary origin. The HS and LS minerals are probably of detrital origin. Early diagenesis has taken place through a fixation of Mg in brucite interlayers in the LS phase, this solid-state process forming di-trioctahedral chlorite layers. During later diagenesis involving dissolution of the HS phase, neoformation of a tosudite or of a random mixed-layer trioctahedral chlorite-berthierine took place. In the tosudite, brucite-like sheets are regularly interstratified with smectite interlayers between dioctahedral 2:1 layers, resulting in ditrioctahedral chlorite layers.

Diagenetic structural transformations in North Sea Jurassic illite/smectite

The Kimmeridgian-Volgian(-Ryazanian) clay stone is the principal oil source rock in the troughs of the North Sea. Randomly (R0) ordered mixed-layer illite/smectite (I/S) appears to have transformed to R1-(IS) or R3-(ISII) ordered simultaneously with oil generation. The proportion of illite layers in I/S increased to 95% during diagenesis in these claystones. Exceptions are three samples of I/S of probably bentonitic origin; these have apparently changed during diagenesis to R0-ordered I/S containing 40-50% illite layers. Fine fractions of the claystones dominated by I/S were analyzed by 27Al and 29Si magic-angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, 57Fe Mössbauer spectroscopy, and X-ray powder diffraction (XRD), and for total chemical composition. Si/Al ratios determined from MAS-NMR agree closely with those calculated from total chemical analysis; however, tetrahedral and octahedral Al occupancies were most accurately determined by NMR. An increase in the percentage of illite layers and in the ordering of the I/S was accompanied by fixation of K+ and NH4+ in the I/S, by tetrahedral Al-for-Si substitution, and by octahedral Al-for-(Mg + Fe) substitution, resulting both in an increase of charge in the 2:1 layers and in a migration of charge from octahedral to tetrahedral sheets. The I/S of probably bentonitic origin had a larger tetrahedral and a smaller octahedral charge than expected from its content of illite layers. MAS-NMR showed a significantly higher content of tetrahedral Al (most likely in smectitic sites) than expected from the percentage of illite layers calculated from XRD. Correspondingly, XRD of K+-saturated and glycolated specimens showed that several smectite layers possessed a significant charge. A constant b-dimension of the I/S and the presence of a significant charge in the smectite layers suggest that a transformation of smectite to illite layers in the I/S by tetrahedral Al-for-Si substitution followed by interlayer cation fixation and interlayer contraction is the most probable genesis for the I/S investigated.

Sequences of charged sheets in rectorite

The pT to IT phase transition in end-member anorthite, CaA12Si20g, has been reversed in-situ at high pressures and temperatures in an internally heated diamond-anvil pressure cell using single-crystal X-ray diffraction. The unit-cell parameters of anorthite were determined at 48 temperature-pressure points up to 255 OCand 2.6 GPa. At high pressures and temperatures, from room temperature up to -225°C, the transition is marked by a first-order step in the unit-cell volume and the complete disappearance of c and d reflections from the diffraction pattern. From room temperature to -195 °C and 2.1 GPa, the transition boundary is linear and nearly isobaric, with a slope, dP/ dT, of -0.003 GPa/°C. From 195 to 240°C and 1.5 GPa the boundary is curved, with increasingly negative dP/dT, and the magnitudes of 11V and the scalar strain associated with the transition decrease to about 75% of their high-pressure values of -0.2 and -0.011 %. From 1.5 GPa to room pressure, the boundary is isothermal at 240°C and is marked by the disappearance of the c and d reflections, although there are no detectable discontinuities in the unit-cell parameters. The phase transition remains unquenchable over the entire boundary. The distinct changes in character of the phase transition and the trajectory of the equilibrium boundary in P-T space are associated with a crossover in the IT phase field that is marked by a sudden change in cell parameters of this phase over the pressure interval of -1.5-2.0 GPa.

Structural and chemical heterogeneity of illite-smectites from Upper Jurassic mudstones of East Greenland related to volcanic and weathered parent rocks

Illite-smectites (I-S) in one Upper Jurassic mudstone core from East Greenland were investigated to determine their structural and crystal-chemical features and to find the relation between these features and source rocks. The phase composition and layer sequences were determined by X-ray diffraction (XRD), the distribution of octahedral cations over trans - and cis -octahedra by thermal analysis, the structural formulae by XRD, Mossbauer spectroscopy, and total chemical analysis, and the short-range order in isomorphous cation distribution by infrared (IR) and Mossbauer spectroscopies. For all samples (except one having maximum degree of ordering for R = 1), simulation of the experimental XRD patterns led to two different I-S models having indistinguishable diffraction patterns. For the first, single-phase model, expandability ( w S) is 0.45–0.60. For the second, two-phase model, two randomly interstratified I-S having w S equal to 0.40 and 0.85, respectively, are present in different proportions in different samples. The single-phase model was selected. A new approach for simulating the two-dimensional distributions of the isomorphous octahedral cations using IR and Mossbauer parameters revealed a tendency for Fe segregation into edge-shared octahedra that may form zigzag chains. Almost identical IR and Mossbauer parameters found for the I-S having different amounts of trans -vacant ( tv ) and cis -vacant ( cv ) layers (ranging from 0.08 to 0.80) demonstrate that these parameters are largely determined by local cation environments around Fe3+ and OH groups. Different levels in the Upper Jurassic Kimmeridgian core contain I-S having different structures. I-S of hemipelagic mudstones at the bottom (37 m depth) and in the middle (13 m depth) of the core, with a high proportion of cv layers and of smectite layers ( w S ~ 0.60), probably formed from volcanic material. The other four samples have a high proportion of tv layers and probably formed by weathering of micaceous material. One of these I-S, from a mudstone turbidite (at 27 m depth), having maximum degree of ordering for R = 1, probably originated from one type of parent rock, and three mudstones (at depths of 4, 12, and 13 m) with segregated I-S, probably originated from a second rock type.

TOBELITIZATION OF SMECTITE DURING OIL GENERATION IN OIL-SOURCE SHALES. APPLICATION TO NORTH SEA ILLITE-TOBELITE-SMECTITE-VERMICULITE

Illite-smectite (I-S) minerals isolated from Upper Jurassic oil-source rock shales from Denmark and the North Sea have been investigated by X-ray diffraction, thermal analysis, infrared, Mössbauer, and solid-state nuclear magnetic resonance spectroscopies and chemical analysis. Detailed structures have been determined in order to reveal the diagenetic transformation mechanism in these shales. Generally, in oil-source rocks of sedimentary basins, oil generation takes place simultaneously with the diagenetic transformation of I-S. We demonstrate a link between the two reactions: NH3 released from kerogen during maximum oil generation is fixed as NH4+ in the NH4-bearing mica or tobelite layers formed from smectite or vermiculite layers in I-S, in a diagenetic interval which we name the ‘tobelitization window’. Due to this solid-state transformation, mixed-layer structures have been formed consisting of interstratified illite, tobelite, smectite and vermiculite layers (I-T-S-V) and having maximum ordering of illite + tobelite and smectite layers for R = 1. The tobelitization of smectite in I-S is probably typical for all oil-source rock shales.

The detailed structure and origin of clay minerals at the Cretaceous/Tertiary boundary, Stevns Klint (Denmark)

Abstract The structure of an illite-smectite (I-S) sample (HSI) from the Tertiary-Cretaceous boundary layer at Stevns, Denmark, i.e. the so-called Fish Clay, is investigated in order to discuss the origin of this clay and its similarity to clays from Maastrichtian-Danian chalk of Denmark and the North Sea. The phase compositions and layer sequences have been determined by X-ray diffraction. The structural formulae are determined from chemical analysis and solid-state 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The octahedral vacancy pattern has been determined by thermal analysis and the particle shape by atomic force microscopy. The HSI sample I-S consists of two phases, a high-smectitic (HS) phase (70%) having 95% smectite and 5% illite (leucophyllite) layers, and a low-smectitic (LS) phase (30%) having 50% smectite and 50% illite (leucophyllite) layers. Both phases have trans-vacant dioctahedral sheets and contain only traces of IVAl, the charge of the illite (leucophyllite) layers being provided predominantly by octahedral Mg for Al substitution. The structure of the tetrahedral and octahedral sheets for the HSI are compared to the structure of an I-S sample (GRI) from the Maastrichtian chalk at Stevns below the Tertiary-Cretaceous boundary and to the standard smectite SAz-1 from Arizona. For all three samples the 27Al MAS NMR spectra show the presence of two resolved IVAl resonances, which indicate the presence of two different IVAl sites. The NMR, infrared spectroscopy and chemical data show that both HSI and GRI have highly ordered Mg for Al substitution in the octahedral sheet, each Al having one Mg and two Al neighbours, whereas substitution of Mg for Al in SAz-1 is random. For the HSI sample, both the HS and LS phases are probably formed from volcanic ash. The structural similarity of the phases in HSI and GRI shows that GRI formed from a material similar to HSI by illitization of the HS phase and chloritization of the LS phase.

Oxidation and reduction of structural iron in chlorite at 480 degrees C

An iron-rich chlorite, ripidolite, was oxidized by air-heating at 480°C, i.e., below the dehydroxylation temperature and subsequently reduced in hydrogen at the same temperature. On the basis of chemical, differential thermal, infrared, Mössbauer, and X-ray powder diffraction analyses, Fe(II) seems to be present only in the 2:1 layer of the original chlorite in a type of site similar to that of Fe(II) in biotite, with OH in cis-positions. These data also suggest that octahedral Al and Fe(III) are located in the hydroxide sheet of the original chlorite. The structural changes of the mineral due to the oxidation and the subsequent reduction appear limited to minor structural rearrangements and, perhaps, to the introduction of OH in both cis- and trans-positions. The results of the investigation are in agreement with a reaction of the form: [Fe(II)OH]+ ⇋ [Fe(III)O]+ + H(H+ + e−).РезюмеРезюме—Хлорит богатый в железо, рипидолит, был окислен путем нагрева в воздухе при 480°С, то есть ниже температуры дегидроксиляции. Окисленный хлорит был последовательно восстанов-лен в водороде при такой же температуре. По данным химического, термодифференциального, инфракрасного, Мессбауеровского, и рентгеновского анализов кажется, что Fe(II) существует только в 2:1 слоях исходного хлорита в местах, похожих на те, которые Fe(II) занимает в биотите, с группами OH в положениях cis. Эти данные указывают также на то, что октаэдрические А1 и Fe(III) расположены в гидроокисных пластах исходного хлорита. Структурные изменения минерала, возникающие в результате окисления и последовательного восстановления кажутся быть ограниченными до небольших структурных перестроек, и, возможно до введения групп OH в обоих cis и trans положениях. Результаты исследований согласны со следующей формой реак-ции: [Fe(II)OH]+ ⇌ [Fe(III)O]+ + H(H+ + e−). [E.C.]ResümeeEin eisenreicher Chlorit, Ripidolith, wurde durch Erhitzen auf 480°C an der Luft, (d.h. unter die Dehydratationstemperatur) oxidiert und anschließend im Wasserstoff bei der gleichen Temperatur reduziert. Aufgrund chemischer Analysen, Differentialthermo-, Infrarot-, Mössbauer- und Röntgendiffraktometer-Untersuchungen scheint das Fe2+ nur in der 2:1 Schicht des ursprünglichen Chlorites vorhanden zu sein, wobei die Art des Platzes, den das Fe2+ besetzt, dem des Fe2+ in Biotit ähnelt und das (OH) in cis-Stellung ist. Diese Ergebnisse deuten weiters darauf hin, daß oktaedrisches AI und Fe3+ in den Hydroxidschichten des ursprünglichen Chlorits sind. Die strukturellen Veränderungen des Minerals aufgrund der Oxidation und der darauffolgenden Reduktion scheinen auf geringe strukturelle Neuordnungen und, vielleicht, auf die Einführung von (OH) sowohl in eis- als auch in /rans-Stellung beschränkt zu sein. Die Ergebnisse dieser Untersuchung stimmen mit folgender Reaktion überein: [Fe2+OH]+ “ [Fe3+O]+ + H(H+ + e−). [U.W.]RésuméUne chlorite riche en fer, la ripidolite, a été oxidée par échauffement à l’air à 480°C, c’est à dire sous la température de déshydroxylation, et la chlorite oxidée a subséquemment été réduite dans l’hydrogène à la même température. Basé sur des analyses chimiques, thermales différentielles, infrarouges, de Mössbauer, et de diffraction poudrée aux rayons-X, Fe(II) ne semble être présent que dans la couche 2:1 de la chlorite originale, dans un genre de site semblable à celui de Fe(II) dans la biotite, avec OH dans les positions-cis. Ces données suggèrent aussi qu’Ai octaèdral et Fe(III) sont situés dans la feuille hydroxide de la chlorite originale. Les changements structuraux du minéral causés par T oxidation et la réduction subséquente semblent limités à des réarrangements mineurs, et peut-être à l’introduction d’OH dans les positions -cis et -trans. Les résultats de l’investigation s’accordent avec une réaction de la forme: [Fe(II)OH]+ ⇌ [Fe(III)O]++H(H+ + e−]. [D.J.]