Lithology and Mineral Resources最新文献

The paper presents new data on a comparative analysis of sedimentary rocks from the Mendeleev Rise (Shamshura Seamount), presumably, of the Triassic age with the Aptian sandstones obtained by the underwater sampling of the Alpha–Mendeleev Rise during expeditions in 2012, 2014, and 2016. The geochemical characteristics of rocks are very similar, and the data from different-age samples form common fields on various diagrams. Petrographic studies revealed that the sandstones of presumably Late Triassic age, as well as the sandstones of Chukotka and Wrangel Island, are dominated by fragments of shale and felsic effusives. The Aptian samples are dominated by mafic rock fragments. In addition, sharp differences are observed in the age spectra of detrital zircon populations, indicating fundamentally different provenances for the Triassic and Cretaceous sandstones on the Alpha–Mendeleev Rise. Samples from the Shamshura Seamount are characterized by populations similar to those from Triassic rocks of Chukotka and Wrangel Island, suggesting the presence of Triassic rocks in this part of the Mendeleev Rise.

Authigenic dispersed biotite was discovered for the first time 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). It accounts for almost the entire content of fine fractions <1 μm of most samples from ODP Hole 1038B. The authigenic nature of the biotite is associated with the metasomatic effect of hydrothermal solution on terrigenous clay minerals of sediments after the 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 X-ray 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 its structure is devoid of foreign layers, the height and composition of which differ from those of micaceous layers. The decrease in the height of micaceous layers upon heating biotite to 550°C is mainly related 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 that a limit value for the coefficient of variation CV should not exceed 0.10 to characterize the absence of mixed-layering in a regular structure.

In the geochemical review based on records from cruises of the International Deep Marine Drilling Project (DSDP, ODP, and IODP phases) and other literature data on the main types of Pleistocene sediments in the Atlantic, tables of average arithmetic chemical composition, mean weighted chemical composition, accumulation rates, and mass accumulation rates of chemical components are presented. These tables can be used for the comparative analysis with sediments of the same or other stratons in different oceanic basins, as well as with paleoceanic sediments on the continents. The terrigenous matrix dominates within the lithogenic matter. Using methods of mathematical statistics, we revealed the main geochemical associations and major factors determining the chemical composition of studied sediments. Masses of oxides of petrogenic elements and several trace elements have been calculated for Pleistocene sediments. Average chemical composition of Pleistocene sediments is proposed for the Atlantic.

A technique to evaluate the degree of roundness of detrital zircons on a 5-point scale based on the preservation of crystal vertices, edges, and faces is presented. Based on measurements in individual grains, the integral roundness index R_s is calculated for a zircon grain set from various stratigraphic units. The obtained data make it possible to determine the proportion of different class grains in various sequences and to assess their similarity/difference degree, which can serve as an additional criterion for the differentiation of sedimentary sections. The proposed method is used to compare the roundness characteristics of detrital zircons from some Cimmeride sedimentary sequences in the Crimean Mountains. It is shown that relative to counterparts in the flysch sequences, sandstones of the Chenka sequence are characterized by a higher proportion of unrounded and weakly rounded zircons and a virtual absence of completely rounded grains. Value of R_s for the zircon grain set ranges from 3.41 and 3.95 for the Tauric Group to 2.55 for the Chenka sequence. Thus, R_s values in the sequences are marked by a significant difference, which is also confirmed by values of the mutual pair coefficient p calculated using the Kolmogorov–Smirnov test.

Lithogeochemical characteristics of limestones of the Uk Formation (uppermost unit of the Riphean stratotype section in the Southern Urals) are considered. Data points of limestones (40 samples), accumulated on the middle and inner ramps have a quite contrasting distribution on the (La/Sm)_sh, (La/Yb)_sh, and (Sm/Yb)_sh diagrams based on the systematization of numerous analytical data on carbonate sequences in various plate-tectonic (paleogeographic in the broad sense) environments, according to (Zhang et al., 2017). The data points of limestones of the Medved Member of the Uk Formation deposited on the middle ramp, according to a detailed lithofacies analysis, are shifted in these diagrams toward the field of limestones of open ocean, whereas limestones of the Manaysu Member (inner ramp) correspond to the near-coastal deposits in terms of their geochemical characteristics. Thus, the geochemical characteristics of the Uk limestones generally confirm the conclusions based previous reconstructions. In the described example, the distribution of trace elements in the inner ramp limestones was controlled apparently by the fine-grained aluminosiliciclastic material transported from the continent, whereas influence of the open ocean environment is already perceptible in geochemical features of the middle ramp limestones deposited in the deeper sea.

A set of 41 stream water samples of the Lo River catchment, Ha Giang province, collected in dry season was analyzed for pH, major cation and anion, trace element concentrations. The stream waters exhibits a midly acidic to alkaline, meanwhile, the Total Dissolved Solids (TDS) values have a wide range of 17.4–284.9 mg L^–1. Among major cations and anions, the stream water within the Lo River catchment is characterized by the predominant presence of Ca²⁺ and ({text{HCO}}_{3}^{ - }). This compositional pattern gives rise to the emergence of the Ca–Mg–HCO₃ water type as the most dominant species, followed by Na–Cl, Ca–Mg–Cl–SO₄ and Na–HCO₃–Cl types. However, the distribution of these water types corresponds closely with the geological conditions, with Na–Cl type prevailing in the watershed of granite complex, while watersheds characterized by lithologies such as Quaternary sediments, limestone, marble, shale, schist, and sandstone primarily exhibit the Ca–Mg–HCO₃ water type. The dominant reaction in the water system is the dissolution of carbonate minerals, like calcite and dolomite, followed by the contribution of modest rainfall during the dry season, and small-scale processes of mixing and cation exchange. Comparison of major ions and trace element with technical standard reveal the stream waters are generally deemed suitable for the routine activities of the local population in Ha Giang province. However, stream water of a few specific sites may require treatment before these waters can be safely utilized.

This article presents results of the comprehensive study (composition, reservoir properties, geophysical parameters, and age) of altered felsic volcanic rocks (rhyolites, dacites) associated with the Permian-Triassic intermediate structural level of the West Siberian. As a result of secondary alteration, oil and gas reservoirs can form in these volcanic rocks. Taking into account their occurrence depth (more than 2 km), they are available for study only from core and geophysical data. Based on the results of core studies, 25 petrographic varieties of felsic volcanics were established. The combination of such features as 1) structural and textural features, 2) degree of secondary alteration, and 3) peculiarities of logging curves made it possible to group these numerous petrographic varieties into six key rock types. At the same time, the distinguished rock types are characterized by different reservoir properties (porosity, permeability). All 443 samples representing various rock types are characterized by similar geochemical composition, and the U-Pb ages obtained by the zircons (254 ± 2–248.2 ± 1.3 Ma) indicate that the studied felsic volcanics belong to a single tectonic-magmatic stage at the Permian-Triassic boundary. According to seismic data, it was revealed that within the Frolov megadepression (the central part of Western Siberia), the studied volcanic rocks are distributed within grabens. In particular, the boundaries of a relatively large (70 km wide and 200 km long) graben-like Rogozhnikov-Nazym structure were adjusted, and several similar, but smaller structures were identified. A comprehensive analysis of core, log and seismic data made it possible to determine the morphology and spatial relationships of volcanic bodies composed of various types of felsic volcanic rocks, providing the basis for predicting intervals of the section with the best reservoir properties.

Data on the temperature and heat flow distribution in the sedimentary cover of the Astrakhan arch in the Caspian Basin are considered. Depth temperatures in 2D and 3D models with the thermal tomography technology are carried out. Parameters for this calculation are represented by original data on the thermophysical properties of sedimentary cover rocks and the concentration of long-lived isotopes in rocks. Palinspastic reconstructions of the sedimentation history of the cover served as the basis for calculating the temperature evolution over 400 Ma.

The paper reports original data on the isotopic composition (δ¹³С, δ¹⁸О) and major and rare earth element (REE) geochemistry of manganese ores in the Rodinauli section of the Kvirila deposit (Georgia). The δ¹³С (V-PDB) and δ¹⁸О (V-SMOW) values vary from –19.6 to –6.6‰ and from 21.1 to 29.1‰, respectively, in the carbonate ores; and from ‒14.9 to ‒5.5‰ and from 21.8 to 28.4‰, respectively, in the carbonate substance of cement of oxide ores. The studied ores are characterized by the presence of negative Ce anomaly (({{{text{Ce}}} mathord{left/ {vphantom {{{text{Ce}}} {{text{Ce}}_{{{text{PAAS}}}}^{*}}}} right. kern-0em} {{text{Ce}}_{{{text{PAAS}}}}^{*}}}) up to 0.51) in majority of samples (both carbonate and oxide ores); the prominent Eu anomaly is absent. A conclusion has been made that the ores were formed both under conditions of early diagenesis of sediments and later, during catagenesis, with the participation of metal-bearing elisional solutions.

Sedimentary material sampled in the southwestern Kara Sea both directly in ice scours and on background surfaces undisturbed by ice scouring has been studied. Based on studies of the physical properties and lithomineralogical features of bottom sediments in the ice scours, the boundary of ice scouring impact (exaration contact) was identified. Based on the X-ray diffraction analysis of <0.001-mm fraction, the chlorite structure is sensitive to temperature in samples taken below this contact, in contrast to the overlying samples. Together with the results of microscopic studies of thin sections, this fact indicates the neoformation of chlorite. The presence of secondary chlorite in near-surface conditions can suggest the glaciodynamic impact (pressure) of iceberg keels on bottom sediments. Microstructures of the ice scour sediments differ both in different test sites of the study area and within the same scour, depending on the location of sampling point on the transverse profile of morphosculpture.