Alfred L. Salyn

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.

DETERMINATION OF THE CONTENT AND DISTRIBUTION OF FIXED AMMONIUM IN ILLITE-SMECTITE BY X-RAY DIFFRACTION : APPLICATION TO NORTH SEA ILLITE-SMECTITE

Abstract A new X-ray diffraction method for the determination of the amount and distribution of fixed NH+4 in illite-smectite has been developed. Illite-smectite was saturated with K+ and heated at 150 °C. The 002 and 005 reflections were recorded with steps of 0.01° 2θ, and the experimental d values and the values for full-width at half-height (FWHH) were determined using a peak-profile-fitting procedure. Peak profiles were calculated with the NEWMOD program for illite structures having different amounts of NH+4 and different patterns for the distribution of NH+4 in interlayers. For Upper Jurassic illite-smectite from North Sea oil source rocks, the amount and the distribution of NH+4 in illite interlayers were determined by comparing the experimental values for d005 and FWHH with the values calculated for the selected illite structures. The amounts of NH+4 determined in this manner correlate well with the amounts determined by an isotopic dilution method. The results demonstrate that these illite-smectite samples have K end-member illite and NH4 end- member illite (tobelite) layers and that the illite layers formed during diagenesis and oil generation actually are tobelite layers.

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.

Factors responsible for crystal-chemical variations in the solid solutions from illite to aluminoceladonite and from glauconite to celadonite

Abstract Several finely dispersed low-temperature dioctahedral micas and micaceous minerals that form solid solutions from (Mg,Fe)-free illite to aluminoceladonite via Mg-rich illite, and from Fe3+-rich glauconite to celadonite have been studied by X-ray diffraction and chemical analysis. The samples have 1M and 1Md structures. The transitions from illite to aluminoceladonite and from glauconite to celadonite are accompanied by a consistent decrease in the mica structural-unit thickness (2:1 layer + interlayer) or csinβ. In the first sample series csinβ decreases from 10.024 to 9.898 Å, and in the second from 10.002 to 9.961 Å. To reveal the basic factors responsible for these regularities, structural modeling was carried out to deduce atomic coordinates for 1M dioctahedral mica based on the unit-cell parameters and cation composition. For each sample series, the relationships among csinβ, maximum and mean thicknesses of octahedral and tetrahedral sheets and of the 2:1 layer, interlayer distance, and variations of the tetrahedral rotation angle, α, and the degree of basal surface corrugation, ΔZ, have been analyzed in detail. The transitions from illite to aluminoceladonite and from glauconite to celadonite are accompanied by a slight increase in the mean thickness of the 2:1 layers and a steady decrease in the α angles, whereas the interlayer distance becomes smaller. These results are consistent with the generally accepted model where tetrahedral rotation is the main factor for the interlayer contraction in muscovitephengite structures: the smaller the rotation angle (α) the larger the ditrigonal ring of the tetrahedral sheet and the interlayer pseudo-hexagonal cavity, allowing the interlayer cation to sink and thus shorten the c parameter. A new insight into the interpretation of the contraction of the mica layer thickness in dioctahedral micas has been achieved with the discovery that micas with the same or close mean interlayer distance, on one hand, have the same or nearly the same substitution of Al for Si; and on the other hand, they may have significantly different parameters of the interlayer structure, such as tetrahedral rotation, basal surface corrugation, ΔZ, and minimum and maximum interlayer distance. These results show that in dioctahedral 1M micas, the mean interlayer distance is determined by the amount of tetrahedral Al because the higher the Al for Si substitution, the stronger the repulsion between the basal O atoms and the larger the interlayer distance and csinβ parameter.

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.

Determination of the content and distribution of fixed ammonium in illite-smectite using a modified X-ray diffraction technique: Application to oil source rocks of western Greenland

Abstract The X-ray diffraction method previously developed for the determination of the amount and distribution of fixed NH4+ in illite-smectite has been modified to include the effects of layer thickness fluctuations of K-saturated and heated smectite and the effects of mean thickness of coherent scattering domains (CSDs). X-ray diffraction patterns and 002 and 005 reflection profiles are calculated for K-saturated and dehydrated NH4+-bearing I-S representing models having different distributions of K and NH4+ over mica-like interlayers, different proportions of interlayer types, different mean thicknesses of CSDs, and different degrees of thickness fluctuations for K-saturated and heated smectite layers. The diffraction criteria for identification of these models are discussed. The amount of fixed NH4+ can be determined accurately from the position of the 005 reflection. Diffraction methods have low sensitivity to different distributions of fixed K and NH4 over mica-like interlayers in NH4-bearing I-S containing a high amount of expandable interlayers and a low amount of fixed NH4. However, the interstratified nature of NH4-bearing illites or I-S can be determined unambiguously in two limited cases: first, when the structures have a low (<20%) content of expandable layers (WS) and, secondly, when NH4/(NH4 + K) ≥ 0.20 in the mica-like interlayers, even for WS > 0.20. The method is applied to I-S from western Greenland Cretaceous oil source rocks heated by intrusions. The samples contain I-T-S consisting of 13.33% tobelite layers. Two groups of samples are identified. One includes I-T-S structures in which dehydrated K-smectite layers have no significant thickness fluctuations. For these samples different broadening of 002 and 005 reflections is due only to interstratification of the 9.98 and 10.33 Å layers. In the other group a satisfactory agreement between the experimental and calculated positions and profiles of the 002 and 005 reflections is achieved only when thickness fluctuations for the K-smectite layers are taken into account.

Formation of flint horizons in North Sea chalk through marine sedimentation of nano-quartz

Abstract In the Upper Cretaceous-Danian North Sea chalk, silica composed of nano-size quartz spheres is dispersed in the chalk matrix, and quartz is present in bands and nodules of flint. In the present investigation of the North Sea Danian chalk the nano-quartz in the chalk matrix is compared with the silica in the flint. Samples of chalk and flint layers from four North Sea wells have been investigated. Atomic Force Microscopy (AFM) has been applied to image the quartz in the chalk and in the flint. X-ray diffraction (XRD), including analysis of the positions and profiles of hkl reflections in powder diffraction patterns, has been applied to characterize the lattice of the quartz in both the chalk matrix and in the flint. The quartz in the chalk matrix and in the flint is composed of nano-quartz spheres having identical cell parameters. Based on the results we propose a new model for formation of flint in North Sea chalk: (1) The nano-quartz in the flint, like the nano-quartz in the chalk matrix, has crystallized in the marine Chalk Sea environment. The colloidal quartz particles flocculated and were deposited on the sea floor mixed with calcitic bioclastic material. (2) Regional variations in the concentration of nano-quartz particles in the sediment reflect different degrees of acidification of the Chalk Sea. (3) This resulted in areas where practically all the calcite bioclasts were dissolved leaving a high concentration of nano-quartz particles to form flint layers; where there was less dissolution, indurated chalk with abundant nano-quartz particles is now preserved. (4) The acidification could have been caused by the effects of enhanced atmospheric CO2 linked to massive short-lived volcanic eruptions in the British Tertiary Igneous Province.