The diagenetic history of the Upper Jurassic Fulmar Formation of the Central North Sea is described with emphasis on the Fulmar Field. The Fulmar Formation was deposited on a variably subsiding shallow-marine shelf under the influence of halokinetic and fault movements. The sediments are extensively bio-destratified although large-scale cross-bedding is locally preserved. The dominant mechanism of deposition is thought to have been storm-generated currents. Soft-sediment deformation structures are common and are attributed to syn- and post-depositional dewatering of the sandstones. The dewatering was associated with fractures and shear zones which reflect tectonic instability resulting from periodic salt withdrawal and/or graben fault movements. The dewatering may have been initiated by repacking of the sediments during earth movements or by the gradual build-up and sudden release of overpressures due to compaction and/or clay mineral dehydration during rapid burial at the end of the Cretaceous. The formation is composed of arkosic sandstone of similar composition to Triassic sandstones from which it was probably derived. The sandstones also contain limited amounts of marine biogenic debris including sponge solenasters, bivalve shells, rare ammonites and belemnites. Initial diagenesis began with an environment-related phase during which quartz and feldspar overgrowths and chalcedony and calcite cements were precipitated. These cements appear to form concretions adjacent to local concentrations of sponge debris and shell debris, respectively, and were disturbed after their formation by fracturing and dewatering. This was followed by an early burial stage of diagenesis which resulted in extensive dolomite cementation and minor clay mineral authigenesis (illite and chlorite). The last phase of mineral growth was probably pyrite. During early burial diagenesis, secondary porosity after feldspar and/or carbonate was produced, although the exact timing is not clear. The lack of both stylolitic developments and extensive illitization indicates that the late burial diagenesis stage was never reached, although sufficient clay diagenesis occurred to destroy all traces of mixed-layer illite-smectite (present in some shallower wells). The main control on reservoir behaviour is primary depositional fabric. Diagenesis only overprints these controls. Locally-cemented fracture sets act as baffles to fluid flow, but they are not extensive and the reservoir acts as one unit.

It is now generally accepted that species names can be given to regularly interstratified clay minerals, in accordance with the recommendation of the AIPEA Nomenclature Committee (Brindley & Pedro, 1970). In Part A of this report we suggest (i) criteria for defining the degree of regularity of alternation of different layer types that should merit a name, (ii) data that should be provided for documentation of a regular interstratification, and (iii) some examples of interstratifications that do not merit names. In Part B of the report we apply the suggested criteria to the analysis of regular interstratifications previously reported in the literature, and make recommendation regarding the usage of existing names.

Piper and Tartan Fields are Upper Jurassic reservoirs located in fault blocks on either side of the Witch Ground Graben. The reservoirs are divided into a series of structural units, each successively downthrown towards the graben, covering a total depth interval of 8500–15 000 ft. Mudrocks interbedded with and overlying the reservoir sequence show a progressive increase in illite content with depth from ordered I/S clays with around 40% smectite to almost pure illites with low expandibility. K-Ar analyses on 13 <0·5 µm illite separates from mudrocks covering this depth interval give ages that range from 153 to 68 Ma. Shallowest samples give the oldest ages which are considered to reflect clay neoformation in Jurassic weathering profiles. In the 40Ar/K Harper diagram this data set falls on a mixing line which reflects the amount of smectite present. Deepest samples give the youngest ages and show a major reduction of 40Ar* with increasing K content indicating formation of new illite. These data are considered to document that ‘illitization’ proceeds via a two-step reaction: initial destruction of smectite followed by neoformation of illite. According to decompacted burial curves, ‘illitization’ took place 60–50 Ma ago. Reservoir sandstones have undergone a complex diagenetic history, involving multiple illite authigenesis. K-Ar analyses of 21 <0·5 µm illite separates selected across the oil-water contact in each of the main structural units show progressively younger ages in the water zone and with increasing depth of burial. Oldest ages in the oil zone (144–120 Ma) reflect eogenetic illite authigenesis whilst progressively younger ages in the water zone result from successive mesogenetic illite generations. The youngest age of 29 Ma was obtained from an illite-rich zone at the present oil-water contact in the Tartan downthrown block. Assuming illite authigenesis in the Tartan downthrown block took place shortly after oil accumulation, ∼29–35 Ma can be considered as a maximum age for the present oil accumulation. A minimum age for oil accumulation is calculated as 22 Ma on the basis of contamination of the 29-Ma sample with up to 10% of 93-Ma authigenic illite.

Clays from the Ae and C horizons of five Podzol soil series in New Brunswick were examined by X-ray, chemical and infrared absorption methods. All the experimental evidence indicated that the Ae horizons contained predominantly a dioctahedral randomly interstratified mica-vermiculite-smectite clay, whereas the C horizons contained abundant dioctahedral mica (illite) and trioctahedral chlorite. Since no trace of chlorite as a separate phase or as one component of the interstratified structure was found in the Ae horizons, it was concluded that, while the inherited chlorite was decomposed in all of the Ae horizons, mica was differentially hydrated giving an interstratified structure. Fourier transforms of the three-component interstratified clay revealed different ratios of hydrated layers (vermiculite and smectite) to non-hydrated layers and different stacking sequences. The proportion of hydrated layers and randomness of stacking was related to the degree of weathering as measured by the accumulation of TiO2 in the Ae horizon and it was suggested that they may be related to the degree of podzolization.

Up until about 2005, the main application of halloysites had been as an alternative raw material to kaolinite for ceramics. Since then, however, there has been an exponential increase in studies aimed at applications of halloysite nanotubes, now widely referred to as HNTs. The readily available and relatively cheap nanotubular forms of halloysite have potential uses in nanocomposites with polymers, as carriers for active agents, e.g. in medicine, agriculture, cosmetics and environmental remediation, as well as in nanotemplating, as supports for catalyst immobilization and as heterogeneous catalysts.

The Taşoluk kaolinite deposits of Afyonkarahisar (western Anatolia) are hosted by both pre-Early Cambrian sericitic mica-chlorite schists and Neogene volcanites, the latter comprising tuffs and agglomerates. These units have been affected by hydrothermal alteration controlled by faults resulting in complex, irregular, lateral mineralogical zonation. The occurrence of a siliceous cap on altered schists and in claystone, of quartz veins in schists and tuffs, and the development of explosion cones and pit fillings indicate that alteration in both the schists and the volcanites is due to hydrothermal processes. Altered schists have generally large (locally small) Fe contents, and claystones are generally silicified and have small Fe contents. Kaolinite predominates south and west of Taşoluk, whereas high (Fe+Ti)-bearing illite + kaolinite predominate in other altered sections. The kaolinite exhibits a stacked micromorphology within altered schists, and the altered volcanites record in situ precipitation, derived from a mechanism of paired dissolution and precipitation. Illite fibres coexist with kaolinite, smectite, chlorite, mica and sericitized feldspar in markedly altered schists, revealing that the illite formed either authigenically or by conversion of smectite to illite. A relative increase in Cr+Ni and decrease in Sr+Ba in the kaolinite deposits and their schistose host rock relative to the upper level of the kaolinite deposits and their volcanic parent rocks came about by the alteration of chlorite, mica and feldspar in the sericitic mica-chlorite schists, and feldspar, glass shards and schist fragments in the volcanites as a result of extensive faulting, fracturing and hydrothermal activity during Late Miocene-Pliocene volcanism, which contributed to the development of kaolinite deposits under acidic environmental conditions. With regard to industrial applications, the low-Fe kaolinized schists are suitable for use in refractories and paper coatings, while the claystone is suitable for use in ceramics and in the white-cement industry.

The desorption of methanol and isopropanol by a series of charge-deficient Ca-montmorillonites (prepared by a partial Li-saturation and subsequent heat treatment of Camp-Berteau material) has been monitored gravimetrically and by XRD. The results indicate that about half the total adsorbed molecules do not occur within the interlamellar space of the montmorillonite but are occluded in micropores between particles.

The importance of a number of techniques (including 1H and 13C NMR, XRD and IR) in exploring the important catalytic properties of synthetic and natural clays is described. A clear distinction is observed between proven catalytically-active clays (e.g. Al-exchanged) and those which are generally less effective (e.g. Na-exchanged). 13C NMR spectroscopy is used to identify directly products formed within the interlayer regions, and temperature-controlled powder XRD serves as a useful tool for identifying whether or not intercalation occurs under variously defined conditions. High-pressure XRD is used to verify the formation of different products during reaction.

The present study investigated the efficiency and mechanisms of aqueous Pb(II), Cd(II), Zn(II) and As(V) adsorption on natural (H), calcined (HC), and acid-activated halloysite (HA). The XRD and FTIR measurements indicated that the aluminosilicate framework was not affected by high-temperature treatment, in contrast to acid activation, which led to structural changes mainly in the tetrahedral sheet. The sorption of cations on H sample was low, though it was most effective for As(V). The X-ray photoelectron spectroscopy results suggested that removal of As(V) might be related to its reduction to As(III) involving oxidation of Fe(II) present in the mineral structure and/or iron minerals. The calcination enhanced halloysite sorption capacity for cations, while the As(V) sorption decreased. This was due to partial dehydroxylation and the subsequent formation of additional active sites. The acid treatment induced selective adsorption of Pb(II).

Analytical electron microscopy of representative smectites from soils and sediments revealed that K was present in significant proportions. It was the major interlayer cation in soils from pelitic rocks, continental and marine sediments, independent of their diagenetic grade. Sodium was predominant only in soils from basic rock. Fluvial sediments contained smectites with both kinds of interlayer compositions. The octahedral composition of each sample ranged widely, covering various fields of dioctahedral smectites. The most important trend was the substitution of Al by Fe and Mg; the chemistry of each smectite particle was determined by the parent mineral from which it formed. The real interlayer composition has important implications for the diagenetic smectite–illite transformation. When considering a typical K content, the smectite–illite reaction, with chlorite and quartz as subproducts, needs only 0.21 K atoms. For more K-rich compositions, a reaction is possible without an external supply of K.

Some characteristics of the kaolin→metakaolin reaction have been studied by applying nuclear magnetic resonance, X-ray fluorescence, and acid dissolution techniques to samples at intermediate stages of dehydroxylation. Nuclear magnetic resonance spectra enabled the average distance between hydroxyl groups to be computed, while X-ray fluorescence provided information on changes in the co-ordination number of aluminium and acid dissolution demonstrated the reduction in cohesion between individual layers during dehydroxylation. The last technique appears to be useful in studying the development of new solid phases. The main conclusions are that the reaction proceeds in a stepwise manner by complete removal of constitutional water from octahedral sheets and not by the growth of randomly distributed nuclei, that six-fold coordinated aluminium is gradually transformed into four-fold coordinated aluminium, and that the internal surface becomes progressively accessible to the acid reagent as dehydroxylation proceeds. The ‘ring structure’ of the silica layer remains.

UV-visible light absorption spectra of dilute suspensions of standard and commercial montmorillonites (bentonites) and of nontronite, hectorite and pyrophyllite, were studied.

All montmorillonites exhibit either an absorption band or a shoulder at a wavelength of 245 nm. The absorption peak for nontronite is shifted to 260 nm and absorption intensity is very high. Hectorite exhibits a very slight shoulder whereas pyrophyllite shows almost none. Absorption intensity in the UV range was found to be in direct correlation to structural octahedral Fe(III) contents. Direct evidence for the role of Fe(III) in the specific UV absorption of smectites was obtained by the fact that reduction with hydrazine fumes resulted in the disappearance of the peak and reoxidation with H2O2 caused its reappearance with even stronger intensity than originally. Mössbauer spectra showed that the Fe(III) disappeared almost completely in the reduced clay.

The rocks of the palygorskite deposit at Bercimuel (Segovia, Spain) have been studied by transmission electron microscopy and microanalysis. These rocks correspond to the zone of convergence of two alluvial fan systems that have filled the small basin of the River Riaza and would originally have been composed of illite and quartz silts. Among the accumulations of palygorskite it is possible to observe surrounded particles of micromicas that have undergone dissolution and opening thereby giving rise to disordered illite-smectite mixed-layer clays. This process continued up to the individualization of structural relics formed of units of 1–5 layers. At the same time, the chemical composition was modified with a loss of K and Al and a relative increase in Si and Mg, progressively evolving towards the composition of palygorskite. The paleogeographic position of the deposits, and the climatic conditions (arid environment), appear to be the dominant factors in the neoformation of palygorskite by alteration of the original sediments. The basic mineralogical process could be referred to as ‘early diagenesis’ in the formation of calcretes.

The Cretaceous fuller's earth of Southern England has been studied using sedimentological, petrographical and X-ray diffraction techniques, and by 40Ar-39Ar radiometric dating. The results indicate that the ultimate sources of the fuller's earth were basic to intermediate, alkaline pyroclastic materials, perhaps stemming from volcanicity associated with the Mesozoic rifting of the North Atlantic. The Wolf Rock phonolite is considered as a potential pyroclastic source. Deposition occurred under normal sedimentary processes, with partial re-working of land-fall ash, and incorporation of orthoclastic debris.

Upper Jurassic Piper Formation sandstones of the Outer Moray Firth Basin, UK North Sea, form the main reservoir for the Piper and Tartan Fields, and are sealed by either the Kimmeridge Clay or Cretaceous marls. The main reservoir sandstones can be broadly considered as stacked coarsening-upward units that accumulated in a predominantly high-energy, shallow marine complex with depositional waters of inferred normal marine salinity, Eh and ionic composition. The amount of porosity and its distribution throughout these sandstones differs between the individual structural entities of the Piper and Tartan Fields. On the Piper structure all the sandstones are highly porous. Oil-zone porosities average 25% and are only slightly reduced in the water zone. Sandstones in the upthrown block of the Tartan structure are also generally porous but porosities are typically reduced to below 20%. Porosities are the most variable in the Tartan downthrown block and in the 15/17-9 well, off-structure Piper, where porous sandstones with between 14 and 18% porosity are associated with highly compacted and cemented sandstones with <5% porosity. Thin-section and SEM textural evidence indicate that much of the porosity in these sandstones is secondary, produced through the dissolution of an intergranular cement that provided support for the detrital framework, was peripherally replacive with respect to most detrital grains, and extensively replaced feldspars. Nodular concretions and sporadic, irregular crystals of ferroan calcite are inferred to be the remnants of this intergranular cement. The distribution of porosity zones in the Tartan downthrown block is related to the present structure and oil-water contact, supporting the interpretation of a secondary origin for much of the present porosity. Highly compacted sandstones interbedded with the porous sandstones result from a combination of early compaction, brittle framework collapse following the generation of secondary porosity and late grain-to-grain contact dissolution. Aggressive fluids responsible for the generation of the cement dissolution porosity are inferred to have been expelled from the Kimmeridge Clay in the adjacent Witch Ground Graben. The preservation of secondary porosity in Piper Formation sandstones is due to the relative timing of secondary porosity generation and subsequent hydrocarbon migration.

Nickel ions play similar roles to magnesium ions in nickel-containing hydrous layer silicates. The extent of the replacement of Mg by Ni ranges from small proportions to complete, or almost complete, replacement. Particular interest attaches to the micro-crystalline, clay grade, minerals formed by processes of lateritic weathering. The multiplicity of names proposed in pre-X-ray-diffraction times must be re-evaluated in terms of modern identification procedures. Many of these minerals can now be placed in series such as:

Garnierite is now used mainly as a field term, prior to more specific identification, and terms such as 7 Å- and 10 Å-garnierite are useful when identification can proceed no further than recognition of basal spacings. Further study is required of schuchardtite, and of nickel-containing smectites and sepiolites. Consideration also must be given to the composition ranges of the end-member names.

The purpose of this study was to investigate the clay mineral phases in a Rhodic Acrisol soil and to discuss their evolution in subtropical conditions. Prairie and forest soil profiles were sampled and clay fractions of the parent material and soil horizons analysed by X-ray diffraction (XRD) at the Federal University of Santa Maria, Rio Grande do Sul-Brazil. The XRD results show the presence of interstratified kaolinite-smectite and illite-smectite as well as illite in the parent material. These minerals were also found in the soil samples but with two new phases: hydroxy-aluminium interlayered vermiculite (HIV), which showed incomplete collapse with treatment at 550ºC, and a newly formed kaolinite (d = 7.17 Å). Under a subtropical climate and a sandy lithology, HIV and kaolinite appear to be a result of a specific pedogenic clay formation, related to the natural vegetation. Originally, under the prairie area, the intensity of the weathering processes was weak (within 2:1 clay minerals), as only small quantities of kaolinite and Fe oxides, and no evidence of gibbsite, were found.

The acid strength and the number of acid sites on various clays were determined by observing the colouration of Hammett indicators adsorbed on them and by titrating benzene suspensions of them with n-butylamine, respectively. H(Al)-saturated allophane behaves as a strong acid (Ho; −5·6 ∼ 1·5) in a relatively dry environment (relative humidity 10-55%), but its acid strength is very much reduced either by increasing its water content or by saturating it with alkali or alkali earth metal cations. Imogolite shows only a very weak acidity (Ho; 4·6 ∼ 6·8) under medium dry to moist conditions (relative humidity; 30-100%). Both allophane and imogolite show a marked enhancement of acidity (Ho; −8·2 ∼ 1·5) when they have been dried over P2O5 or heated to result in dehydroxylation. H(Al)-saturated montmorillonite, kaolinite and halloysite show stronger acidities (Ho; −5·6 ∼ 1·5) than allophane (Ho; 1·5 ∼ 6·8) in a relatively moist environment (relative humidity; >60%). The n-butylamine titre and CEC show a good agreement for montmorillonite, but a poor agreement for allophane. The latter discrepancy which is larger for allophane when it has been heated at 150 and 300°C, is also found for imogolite when similarly heated. In these titrations, excess butylamine is found in supernatants at end-points. Therefore, the n-butylamine titre as such can not be used for the estimation of the number of acid sites on imogolite and allophane. The origin, structure and transformation of the acid sites on these clays is discussed.

Kaolinites were modified by controlled hydrothermal deuteration. Both infrared and near infrared vibration spectra of deuterated kaolinite were investigated by Diffuse Reflectance Infrared Fourier Transform spectroscopy. The stretching vibrations (v) of deuteroxyl groups of the kaolinite were observed at 2726, 2709, 2697 and 2667 cm-1, respectively. The overtone bands (2n) of the deuteroxyl groups were visible in NIR regions at 5454, 5419, 5388 and 5342 cm-1, respectively. The lattice vibrations of the kaolinite taking part in deuteration included 937, 915, 792, 751 and 690 cm-1 which are assigned to hydroxyl group-related deformation or translation-vibration mode. The hydroxyl band at 3435 cm-1 with its deuteroxyl band at 2542 cm-1 resulted from unevenly distributed structural defects, either due to the isomorphous substitution of foreign cations or the imperfections of the kaolinite lattice structure.

Two outcrops were studied which showed granite in the early stages of weathering. Reactions between specific mineral species were observed, and especially the formation of an illite-like phase which is similar to that of sedimentary illite. This phase has a composition distinct from that of the initial micas in the rocks, notably in its iron and magnesium content. This suggests solution-solid equilibria which involve ionic transfer beyond the grain bondary region where the mineral is found.