For the first time, authigenic dispersed biotite was discovered in Pleistocene terrigenous sediments of the Central Hill, located in the Escanaba Trough in the southern part of the Gorda Ridge (northeastern sector of the Pacific Ocean), which accounts for almost the entire content of fine fractions 1 μm of some samples from ODP 1038B hole. The authigenic nature of biotite is associated with the metasomatic effect of hydrothermal solution on terrigenous clay minerals after intrusion of basaltic magma in the form of laccolith with a temperature of ~1200°C. The mineral composition of fine fractions of sediments was studied using complex analytical methods, including modeling of their diffraction patterns. It has been established that the dispersed micaceous mineral (biotite) is trioctahedral, high-iron, does not swell when saturated with glycol, but contracts after heating at 550°C. It is shown that in its structure there are no foreign layers, the height and composition of which differ from the micaceous layers. The decrease in the height of micaceous layers upon heating biotite to 550°C is mainly due to a decrease in the height of 2:1 octahedra due to the difference in the Fe2+–O and Fe3+–O bond lengths as a result of the oxidation of Fe2+ cations It has been established a limit value for the coefficient of variation CV, characterizing the absence of mixed-layering in a regular structure, which should not exceed a value of 0.10.

A new approach is proposed to assess the degree of defect density of kaolinite minerals using their IR spectra in the OH-stretching vibration region. Three linear equations were obtained that relate the ratios of spectroscopic parameters to each other: A( ν_3)/A( ν_3) + A( ν_2) = - 1pt 0.2177FWHM( ν_1)/FWHM( ν_4) + 1.247; FWHM( ν_3)/FWHM( ν_2) = - 0.5804FWHM( ν_1)/FWHM( ν_4) + 2.8696; FWHM( ν_3)/FWHM( ν_2) = 2.636A( ν_3)/A( ν_3) + A( ν_2) - 0.4437 , where: FWHM(νi) is a full width at half maximum and A(νi) is the integral intensity of Lorentzian absorption bands at ν1 3697 cm–1, ν2 3670 cm–1, ν3 3652 cm–1 and ν4 3620 cm–1, respectively. These equations made it possible to establish criteria for decomposing the IR spectra into individual bands (νi) and determining the optimal values for the FWHM(νi) and A(νi) parameters used for calculating the contents of high-ordered kaolinite (HOK) and low-ordered kaolinite (LOK) phases in natural samples with an accuracy of 5

Using a complex of analytical methods, clay minerals were studied in Pleistocene sediments from Hole ODP 1038B (120.50 m deep), drilled on the northwestern edge of the Central Hill (Escanaba Trough, Gorda Ridge) near the hydrothermal source with a temperature of 108°C, as well as in Pleistocene background terrigenous sediments from reference Hole ODP 1037B, drilled in the Escanaba Trough 5 km south of the Central Hill. The terrigenous clay mineral assemblage in sediments from Hole 1037B consists of the mixed-layer smectite-illites, smectite, chlorite, illite, and kaolinite. Sediments from Hole 1038B in the interval from the bottom surface to a depth of 5–7 m are composed of terrigenous clay minerals. In the rest of the sedimentary section, clay minerals are represented by the newly formed biotite, chlorite, and dioctahedral smectite. They were formed during the basaltic melt intrusion into the Escanaba Trough with the formation of a laccolith and the subsequent rapid cooling of its flank. The intrusion was accompanied by the ascent of high-temperature hydrothermal fluid in the central discharge channel, interacting with the adjacent sediments. As a result, the fine-dispersed biotite was formed in sediments at the high-temperature stage of this interaction due to the primary terrigenous clay minerals, K-feldspar, and amphiboles. The rapid cooling of the hydrothermal fluid to a temperature of presumably 270–330°C promoted the partial replacement of biotite by chlorite. The further rapid cooling of the hydrothermal fluid to 200°C and lower and its mixing with seawater seeping into sediments of the Central Hill fostered the formation of smectite.

Clay minerals were studied in Pleistocene sediments from Hole 1038А (114.50 m deep) and Hole 1038Н (192.80 m deep) drilled near a hydrothermal vent with a temperature of 217°C on Central Hill, 275 m east of Hole 1038B. In sediments from Hole 1038A, at a depth of 8.52 m, <0.001-mm fraction consists completely of chlorite. In the rest of the sediment section in Hole 1038A, clay minerals consist of chlorite (from 64 to 98

At the current level of research, a generalization of previously studied and new lithological-mineralogical, structural, and crystal-chemical characteristics of globular layer silicates (GLS) of the Mg-rich glauconite–illite series from Upper Proterozoic sections of eastern and northern Siberia (Uchur–Maya region, Anabar uplift) has been carried out. The classification of glauconite–illite minerals was carried out in accordance with recommendations of the International Nomenclature Committees for Mica and Clay Minerals, as well as based on the available literature and our own data. The Al index, i.e., (KAl = VIAl/[VIFe3+ + VIAl]), in minerals of the glauconite–illite series varies from 0.40 to 0.85; the content of Mg and K cations varies, respectively, from 0.51 to 0.75 and from 0.63 to 0.80 f.u. Application of the X-ray modeling method for diffraction patterns of the oriented and unoriented specimens of Upper Proterozoic GLS made it possible to determine the following properties: the content of swelling layers (4–10

At the current level of research, a generalization of previously studied and new lithological-mineralogical and structural-crystal-chemical characteristics of globular phyllosilicates (GPS) of the glauconite-illite series with a high Mg content from Upper Proterozoic sections of Eastern and Northern Siberia (Uchur-May region, Anabar uplift) has been carried out. The classification of glauconite-illite minerals was carried out in accordance with the recommendations of the International Nomenclature Committees for mica and clay minerals, as well as on the basis of literature and our own data. The degree of aluminum content of minerals (КAl = VIAl / [VIFe3+ + VIAl]) of the glauconite-illite series varies from 0.40 to 0.85, the content of Mg and K cations varies from 0.51 to 0.75 and from 0.63 to 0.80 f.u. (formula units), respectively. Using X-ray modeling method of diffraction patterns of oriented and non-oriented preparations of Upper Proterozoic GPS, the following were determined: the content of swelling layers (4–10%), their types (mica, smectite, chlorite), the nature of the alternation (short-range order factor R = 0), unit cell parameters csinβ, ccosß/a, average value of parameter b (9.018–9.074 Å). The conditions of glauconite formation in the Upper Proterozoic basins are considered, their influence on the structural and crystal-chemical features of magnesian hydrocarbons is discussed.

The mineralogical, structural and crystal-chemical features of seven samples of globular phyllosilicates of the glauconite-illite series (GPS) from the Lower Cambrian of Northern Estonia and Western Lithuania, from the Middle Cambrian of Western Latvia, and also from the Lower Ordovician of Northern Estonia and Western Latvia are considered for the first time. The Al index GPS (КAl = VIAl/ [VIFe3+ + VIAl]) varies from 0.27 to 0.59, which allows us to attribute them to the glauconite-illite series, in which GPS are represented mainly by glauconites (the Al index is КAl = 0.27–0.46) and one sample of Al-glauconite (КAl = 0.59). The content of K2O in minerals is from 7.12 to 7.90%. For the first time, the content of expandable layers (4–13%), their types (smectite, vermiculite) and the character of their alternation (R = 0, R = 2) were determined in the studied samples by simulation of experimental X-ray diffraction patterns from oriented preparations. Simulation of X-ray diffraction patterns obtained from nonoriented preparations made it possible to reveal the degree of three-dimensional order, and mean values of the unit-cell parameter b (9.056–9.094 Å) as well as the features of the distribution of their individual micaceous varieties and to establish the heterogeneity of the samples. Based on these data, the microheterogeneity of the Cambrian and Ordovician GSSs was established and compared with the heterogeneity in the previously studied Riphean GPS [Drits et al., 2013]. The obtained Rb-Sr и K-Ar ages for the Middle Cambrian and Lower Ordovician samples, as well as the earlier published dates for the Lower Cambrian samples, are “rejuvenated” compared to age limits accepted for the Cambrian and Lower Ordovician [Gradstein et al., 2020]. The dependence of the Cambrian and Lower Ordovician “rejuvenated” isotopic dates and the discovered GPS heterogeneity, as well as possible reasons for its occurrence, are discussed.

To overcome the existing uncertainty in the interpretation of “crystallinity” indices of kaolinites, HI [Hinckley, 1963], IK [Stoch, Sikora, 1966; Stoch, 1974], QF [Range, Weiss, 1969], AGFI [Aparicio, Galán, 1999; Aparicio et al., 2006], WIRI [Chmielová, Weiss, 2002], their values obtained for a representative collection of 30 kaolinite samples were compared with the results of modeling the corresponding X-ray diffraction patterns. It is shown that all the studied samples consist of a mixture of almost defect-free high ordered HOK and defective low-ordered LOK kaolinite phases, and that there are relationships between the HOK content and the values of the “crystallinity” indices, which are described by different regression equations. The relationship is most pronounced for HOK and the Hinckley index, HI, which is described by the quadratic equation HOK (%) = 12.236 HI2 + 25.464 HI ‒ 1.2622 with the correlation factor R2 = 0.993. The resulting equations can be used to find concentrations of HOK and LOK in natural kaolinites. Comparison of structural parameters of defective kaolinites obtained by modeling of their X-ray diffraction patterns with those of Expert System [Plançon, Zacharie 1990] showed that the latter sometimes predicts: 1) single-phase highly defective kaolinites, while their diffraction pattern modeling establishes a mixture of HOK and LOK phases; and 2) in two-phase samples, the content of the low-defect phase (ldp) is greater than 100%.

Illite-smectite (I-S) minerals from the Upper Jurassic oil-source shales of Denmark and the North Sea were studied by a complex of diffraction and spectroscopic methods. Detailed structures were identified to reveal the mechanism of postsedimentary transformations of these shales. Usually, oil is generated in the oil-source rocks of sedimentary basins simultaneously with the diagenetic and catagenetic I-S transformations. The results obtained demonstrate the relationship between these two reactions: NH3 molecules released from kerogen during the maximum oil formation are fixed as NH4 cations in smectite or vermiculite interlayers, forming mica or tobelite structural fragments. This solid-phase transformation produces the mixed-layer structures consisting of illite, tobelite, smectite, and vermiculite (I-T-S-V) layers.

Illite-smectite (I-S) minerals from the Upper Jurassic oil-bearing rock shales of Denmark and the North Sea were studied by a complex of diffraction and spectroscopic methods. Detailed structures were identified to reveal the mechanism of diagenetic transformation of these shales. Usually, in oil-bearing rocks of sedimentary basins, oil generation occurs simultaneously with the I-S diagenetic transformation. The results obtained demonstrate the relationship between these two reactions: NH3 molecules released from kerogen during ma-ximum oil formation are fixed as NH4 ammonium cations in smectite or vermiculite interlayers, forming mica or tobelite structural fragments. As a result of this solid-phase transformation, mixed-layer structures are formed, consisting of layers of illite, tobelite, smectite and vermiculite (I-T-S-V).

Traces of extremely powerful explosive volcanic eruptions are documented in the southern Moscow Syneclise; the eruptions occurred in the Moscovian Age about 309 million years ago in Variscan orogenic regions adjacent to the East European Platform. Interbeds of altered volcanic ash, 5–15 cm thick, can be traced over the distance of tens of kilometers in the sediments referring to the Podolskian and Myachkovian substages of the Moscovian Stage. These interbeds are composed of calcareous clays of montmorillonite composition and contain grains of zircon, apatite, ilmenite, biotite, K-feldspar, and quartz. Two types of K-feldspar (authigenic and volcanic) referring to the sanidine group are identified. U–Pb SIMS dating of pyroclastic zircons from the tuffaceous bed at the boundary between the Podolskian and Myachkovian showed an age of 308.9 ± 2.3 Ma, and 40Ar/39Ar dating of volcanic sanidine at a higher level showed the age of 305.5 ± 2.7 Ma, which agrees well with the available age estimates for the stage boundaries in the Pennsylvanian. Analysis of the Late Paleozoic volcanism in the nearby regions showed that the most likely area where catastrophic explosions took place, with subsequent transportation of volcanic ash to the southern Moscow Syneclise, is the zone of the North Caucasus.

Clay minerals in Holocene–Pleistocene sediments from Hole 858B DSDP drilled at 20 m from the black smoker in the Dead Dog hydrothermal field, axial valley of the Juan de Fuca Ridge, were scrutinized for the first time by modeling the X-ray diffraction patterns in combination with the splitting of 060 reflection profiles into individual maximums. In the section of the sedimentary cover drilled to a depth of 38.6 mbsf, we can distinguish three sediment groups, with successive transformation of clay minerals reflecting a high temperature gradient. Terrigenous clay minerals (dioctahedral illite, mixed-layer smectite-illite, and trioctahedral chlorite) are preserved in the 1.97–7.2 mbsf interval. Terrigenous illite and chlorite were preserved and trioctahedral mixed-layer chlorite-smectite and corrensite were formed in the 7.2–16.7 mbsf interval. At 16.7–38 mbsf, all terrigenous clay minerals were transformed into a new assemblage of trioctahedral phases: corrensite minerals, mixed-layer talc-smectite, and chlorite. Chlorite alone was found at 38.4 mbsf. Structural transitions of clay minerals imply their formation at each stage by the dissolution and synthesis. Metalliferous sediments in the 0–1.97 mbsf interval comprise a mixture of partially altered terrigenous clay minerals and the indicator Fe-rich dioctahedral mixed-layer mica-smectite, which was formed from a hydrothermal fluid mixed with seawater. The composition of clay minerals in the 11.65–12.60 mbsf interval was transformed by high temperature of the hydrothermal fluid penetrating from the discharge channel of the hydrothermal convective system into the tectonic horizontal fracture of the sedimentary cover in the 10.41–11.65 mbsf interval.

To resolve the existing ambiguities in the interpretation of the OH-stretching vibrations of kaolinites, relationships were, for the first time, established between the structural and Fourier-transform infrared (FTIR) spectroscopic features for a set of kaolinite samples which differed in terms of their relative amounts of coexisting high- and low-ordered phases. For this purpose, a representative collection of kaolinites differing in origin, particle size, and degree of disorder was studied by powder X-ray diffraction (XRD) and FTIR spectroscopy. Modeling of the experimental XRD patterns based on the orthogonal layer unit cell having a mirror plane showed each sample to be a mixture of nearly defect-free high-ordered (HOK) and low-ordered (LOK) kaolinite phases, with HOK varying from 86 to 4%. The wavenumbers, heights, areas, and full widths at half-maximum (FWHM) were determined for the OH-stretching bands at ~3697 (ν1), ~3670 (ν2), ~3652 (ν3), and 3620 cm–1 (ν4) by decomposition and fitting of the FTIR spectra. The FWHM(ν1)/FWHM(ν4) and FWHM(ν3)/FWHM(ν2) values were related linearly to the HOK content, which may be associated with the in-phase and out-of-phase character of the corresponding pairs of vibrations, respectively. A novel interpretation was suggested for the variations in the relative integrated intensities of the OH bands with the amount of the HOK phase. The intensity distribution of the ν2 and ν3 bands is controlled by the triclinic structure symmetry in the defect-free kaolinite and the mirror symmetry of the layers in low-ordered structures, in agreement with the observed evolution of the corresponding band intensities. The ν1 and ν2 band positions for the low-ordered samples are within the wavenumber range for the high-ordered samples. In contrast, the ν3 and ν4 band positions for the low-ordered samples are shifted toward higher wavenumbers, indicating that some of the low-ordered kaolinites should contain dickite-like structural fragments distributed among kaolinite layers.

The mineralogical, structural, crystal-chemical, and isotope-geochronological data were obtained for the first time in two samples of globular phyllosilicates (GPS) of the glauconite–illite series collected from terrigenous rocks in two sections of the lower part of the Lower Vendian Maastakh Formation (Khorbusuonka and Ulakhan-Sololi rivers, northwestern slope of the Olenek Uplift). Simulation of experimental X-ray diffraction patterns for both samples in the air-dried and ethylene glycol-solvated states was used to determine the expandable layer contents (9, 10%), types of expandable layers (smectite- and vermiculite-type), their ratios in a three-component mixed-layer structure, parameter csinβ (9.98 Å) of mica layers, and the short-range order factor describing the alternation of different layer types (R = 2, 3). Values of the unit-cell parameter b (9.027, 9.039 Å) correspond to the dioctahedral Al, Fe-bearing micas. The mica components in the studied mixed-layer minerals are shown to be represented by Fe-illites (KAl = VIAl/(VIFe3+ + VIAl) = 0.71, 0.82) with the K2O content of 7.77 and 8.40%. The Rb–Sr dating of the Maastakh GPS was carried out for the first time in combination with the calculation of theoretical patterns in the cation distribution in the mineral structure and comparison of the calculation results with the Mössbauer and IR spectroscopy data using the Optima software package supplemented with the new Irmes software. The Rb–Sr data obtained for two Fe-illites (Khorbusuonka and Ulakhan-Sololi rivers: 1033, 913 ± 12 Ma, respectively) are “older” relative to the Vendian Maastakh Formation (~640 ± 5), indicating a terrigenous origin of the studied grains. Globular phyllosilicates from the Maastakh Formation are similar in age and composition to the previously studied Lower Khaipakh (Middle Riphean) GPS (1172 ± 18 and 1112 ± 24 Ma, respectively). The age of GPS samples from the Maastakh Formation is younger (1033–913 Ma), probably, due to the initial cationic disordering in the GPS structure and partial loss of radiogenic elements during secondary alterations (rewashing and redeposition of Fe-illite grains in sediments of the Maastakh Formation) and, probably, during their catagenetic changes as well.

For the first time, mineralogical, structural, crystal-chemical and isotope-geochronological data were obtained for a glauconite sample from the Lower Riphean Ust-Il’ya Formation on the Magan River (western slope of the Anabar Massif, northern Siberia). It has been established that glauconite from the lenticular layer of friable glauconitite (glauconite grains ≥80%) contains two populations of mixed-layer crystals, in which mica layers (93%) alternate with either smectite-type (7%) or vermiculite-type layers (7%) with the short-range order factor R = 3. The ratio KAl = (VIAl / (VIFe3+ + VIAl) equal to 0.45 allows identifying the micaceous mineral as glauconite with the unit-cell parameter b = 9.065 Å and K2O content of 8.29%. Comparison of new data with the previously obtained mineralogical and crystal-chemical characteristics of Ust-Il’ya glauconites from the Kotuikan River section (2.5 km above the Il’ya River mouth), located 65 km south of the Magan River section, showed both similarities and differences. Analysis of the crystal-chemical heterogeneity of Kotuikan glauconite samples from rocks of different lithological types revealed peculiarities in the distribution of individual mica varieties composing the glauconite globules. Isotopic dating of glauconite from the Magan River section was performed in combination with simulation of the distribution of octahedral cations and comparison of the results obtained with Mössbauer and infrared (IR) spectroscopy data. Such an approach combined with the mineralogical and crystal-chemical analyses contributes to correct interpretation of the stratigraphic significance of isotope data. The results obtained provide grounds for the conclusion that isotopic dates of glauconite from the Magan section (1474 ± 21 Ma) coincides within the error limit with the earlier Rb–Sr and K–Ar dating of the Ust-Il’ya Formation (1485 ± 13 and 1459 ± 20 Ma, respectively) based on the glauconite in the Kotuikan section (Zaitseva et al., 2016). The former value marks the stage of early diagenesis of sediments and is suitable for estimating the age of this formation.