Lithology and Mineral Resources最新文献

The paper considers the composition of sandy rocks from the Upper Triassic deposits of the Mongugai Formation of southwestern Primorye and presents the results of its paleogeodynamic interpretation. It has been established that, according to their mineralogical and geochemical parameters, sandstones are petrogenic, correspond to graywackes and, only partially, to lithite arenites, are characterized by a significant degree of geochemical maturity of the clastic material, and their formation occurred due to the erosion of significantly weathered parent rocks of the source areas. Generalization and paleogeodynamic interpretation of the data obtained indicate that sedimentation in the southwestern Primorye in the Late Triassic occurred in basins related to the active continental margin settings probably complicated by strike-slip dislocations along transform faults. The dominant source of detrital material was continental land: cratons and crystalline basement inliers surrounding the rift zones or along transform faults. Felsic granite-metamorphic complexes were eroded with the participation of sedimentary rocks enriched with ancient components. A secondary source was a deeply dissected continental-margin igneous arc, which supplied an additional amount of sialic material, as well as a small amount of the basic–intermediate volcaniclastic rocks into the basin. The U–Pb geochronological studies of detrital zircons from sandy rocks of the formation made it possible to establish the age and the possible position of igneous complexes, destruction of which formed the sediments.

A comprehensive study of the Maastrichtian–Danian boundary rocks in the Klementyev Mountain section (eastern Crimea) was carried out. The lithological characteristics of carbonate, carbonate–clayey, and clastic rocks are scrutinized. The dynamic of changes in the benthic and planktonic foraminiferal assemblages is analyzed. The geochemical and isotopic data were obtained for this section for the first time. The stratigraphic range of the upper Maastrichtian and lower Danian has been specified. The late Campanian–early Maastrichtian age of the underlying rocks has been confirmed for the first time. Sediments of the Klementyev Formation were deposited in a deep-sea pelagic paleoenvironment on the submerged part of the outer shelf, whereas the overlying Lower Danian sediments were deposited in shallow waters of the inner shelf with terrigenous sedimentation and high hydrodynamic activity.

The results of studies of the regional structure of Solenovian deposits of the Early Oligocene Rupelian Stage in the Cisсaucasian–Caspian region, which represented the northern slope of Eastern Paratethys in the Cenozoic, are presented. The geological structure and paleogeographic conditions in the basin during the Solenovian (second half of Early Oligocene) were refined based on a comprehensive interpretation of geological and geophysical materials. The spatial consequences of the sea level drop in Eastern Paratethys during the Oligocene regressions are traced. The periodic draining of shelf areas is reflected in the structure of erosional unconformities and buried river incisions. It has been established that the most significant was the late Solenovian regression with a relative sea level drop by more than 500 m. Consequently, a prominent unconformity surface, complicated by river incisions, was formed in the sedimentary sequence in the shelf part of the paleobasin (Maikop seismic sequence). Erosion ledges and landslide bodies formed on the slopes, and basin-infill complexes were accumulated in depressions.

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.