Lithology and Mineral Resources最新文献

A new industrial genetic (“aphanitic”) type of phosphorite deposits has been identified. In terms of the genetic, tectonic, facies, and geochemical features, this type differs fundamentally from the known micrograined, granular, nodular, shelly, and pebbly phosphorite deposits. They are the first industrial accumulations of phosphorus matter in the history of our planet. Conditions for their accumulation existed only in the Ediacaran period, when mass phosphatization of sediments with the formation of phosphate nodules as ribbon-shaped layers took place under the influence of early diagenetic processes. Phosphates were accumulated in basins with synsedimentary block structure inherited from paleorift structures and seismically active tectonic environment. The multidirectional displacement of blocks generated a complex seafloor relief and facies heterogeneous complex of sediments ranging from reefogenic-stromatolitic sediments in the uplifting areas to pelitic sediments in the dipping areas. The latter areas were marked by a massive input of sedimentary material significantly enriched in the planktonic organic matter. Transformation of organophosphorus compounds during the sulfate reduction promoted the phosphatization of sediments and the formation of aphanitic phosphorites, which differ from other ore types by anomalously high concentrations of As, Sr, and Ba and by anomalously low contents of U and REE.

The first of two communications is devoted to the study of lithogeochemical features of the pilot collection of Upper Precambrian sandstone and siltstone samples taken from four boreholes: Bogushevskaya 1, Bykhovskaya, Lepel 1, and Kormyanskaya (Belarus). This article analyzes the general features of their bulk chemical composition and shows the possibilities and limitations for further reconstructions. It has been established that Riphean and Vendian rocks included in the pilot collection, visually identified as sandstones, are actually quartz, feldspar–quartz, and arkosic varieties with different cement types. In terms of geochemical characteristics, the Vendian “siltstones” correspond to the coarse- and fine-grained siltstones and, to a greater extent, mudstones with a predominance of illite, as well as various admixtures of berthierine, kaolinite, and smectite. Based on the comparison of enrichment factor (EF) of the trace element, these rocks are marked by several dissimilarities related to both variations in the source rock composition and sedimentary environment. Data points of the samples on the Zr/Sc–Th/Sc diagram indicate that all of the studied Riphean and Vendian rocks are dominated by the first sedimentation cycle material, suggesting that the lithogeochemical characteristics of the pilot collection rocks quite correctly reflect similar features of the source rock complexes. Therefore, they can be used to reconstruct the paleogeodynamic and paleoclimatic factors that controlled the accumulation of Riphean and Vendian sedimentary sequences in Belarus.

Iron oxyhydroxides extracted from present-day biofilms with the Fe-oxidizing bacteria Arthrobacter spp., Gallionella spp., and Leptothrix ochracea in the northwest of the East European Platform display a significant content of rare earth elements (up to 1100 ppm). The REE concentration in oxyhydroxides produced by active bacterial communities increases by one order of magnitude during 1 yr, suggesting a high sorption capacity of the newly formed iron mineral phases. Values of (La/Yb)_N, Ce, and Y anomalies in the iron oxyhydroxides are consistent with the REE distribution in surface waters accommodating the bacterial communities. The Nd isotope composition of the studied bacterial iron oxyhydroxides inherits the isotopic composition in the ambient water; ¹⁴³Nd/¹⁴⁴Nd values in the bacterial iron minerals vary from 0.511570 to 0.512220; and ε_Nd(0) from –21.8 to –9.2. The maximum proportion of radiogenic Nd is typical for the samples taken from areas marked by the presence of Paleozoic carbonate rocks in Quaternary glaciolacustrine sediments.

The age and depositional environments of Middle Jurassic terrigenous rocks crowning the Mesozoic section on the northeastern flank of the Nagondzha terrane within the Ulakhan-Sis Ridge are discussed. Based on our finds of retrocerams and the analysis of biostratigraphic data of predecessors, the Bajocian–Middle Bathonian age of these rocks is accepted. Three lithologically different sequences are identified in the section. Sandstones from the lower unit belong to feldspathic litharenites; from the upper sequences, to litharenites dominated by extrabasinal carbonate clastics (calclithites). The analysis of structural-textural features, mineralogical-petrographic composition, and distribution of trace elements in litharenites suggests that all these sequences were deposited in the shelf part of paleobasin associated with an active volcanic island arc, which presumably existed since the Early Jurassic on the Omulevka Craton terrane until the termination of the Kolyma–Omolon superterrane formation.

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.