Lithology and Mineral Resources最新文献

The results of a comprehensive lithological study of the Upper Neopleistocene polar (Ostashkovo) moraine (textural, structural, and mineral-petrographic features, as well as the chemical composition and typomorphism of garnets and zircons, carried out to identify its lithostratigraphic criteria and substantiate the division and correlation of Quaternary sections are considered. The moraine is widespread only in the northernmost part of the Pechora Lowland, where it forms the day surface relief. The study was carried out in lower reaches of the Pechora River and in coastal outcrops of the Kuya, Chernaya, and Shapkina rivers. The moraine, characterized by a high content of the pelite fraction, has a finer composition than the Middle Neopleistocene moraines widely developed here. The mineralogical spectra of the moraine in the studied area are of the same type and represented by epidote, garnets, amphiboles, siderite, and pyrite. Total amount of pyrite and siderite increases to 20–35% with the permanent dominance of siderite over pyrite. The petrographic spectrum of the polar moraine is characterized by the presence of single fragments of the crinoid–bryozoan limestones (guide boulders of the Novaya Zemlya demolition area), as well as a very consistent orientation of elongated rock fragments, suggesting their delivery from the north-northeast (Pai-Khoi and Novaya Zemlya). It was overlapped only in lower reaches of the Shapkina River by a glacial tongue extending from the northwest (Fennoscandinavia and northern Timan). The presence of garnets in the moraine is related to their supply from metamorphic and certain types of igneous rocks. Based on the ZrO₂/HfO₂ ratio, the predominant mass of zircon grains was formed in mafic and felsic igneous rocks. Zircons from the metamorphic rocks are subordinate.

The lithological features of Late Quaternary sediments deposited during the marine isotope stage (MIS) 3 in the Ura River valley on the Barents Sea coast (Kola region, northwestern Russia) have been studied. Seismo-induced soft-sediment deformation structures (SSDS) are preserved in the sandy–clayey deposits as five deformed layers separated by undisturbed deposits. These layers are marked by load casts, flame structures, injections, sedimentary breccia, and folds. The SSDS were produced by several processes: origination of debris flows in the subaqueous setting due to shear stress, gravity load of the overlying deposits, and liquefaction. The seismic shock and aftershocks could trigger the gravity flow activity and initiate the processes of liquefaction and fluidization of sediments. We believe that the main seismogenic zone was related to reactivation of the large Karpinsky oblique-slip fault, which separated the Baltic Shield from the Barents Sea Plate of the West Arctic Platform, contrast movements at the boundary of large structural elements, and development of strains at the front of the advancing Weichselian Ice Sheet at MIS 2.

The pyrolytic characteristics of dispersed OM were determined in clay pulp samples taken from 23 mud volcanoes of the Kerch–Taman area (Crimean–Caucasian region). The organic matter (OM) belongs to type III kerogen, and its alteration level corresponds to the earliest stages of oil generation. It is also shown that, in terms of the pyrolytic characteristics, the OM carried out by volcanoes is almost a complete analog of the dispersed OM present in clays of the Maikop Group. However, in comparison with the clays, the mud-volcanic pulp has a higher content of bitumoids. Relationship between the kerogen parameter Т_max and some temperature-dependent characteristics of the water (t(Mg-Li) and δ¹⁸O in H₂O) and gas (δ¹³C in CH₄) phases of mud volcanic ejecta was found for the first time in the mud volcanic systems of the Kerch–Taman region. These relationships reflect the general variation trend of fluid systems with the formation temperature increase and indicate the formation of solid, liquid, and gaseous phases of mud-volcanic ejecta in a single deep mud-volcanic formation. However, no discernible OM contamination of clay pulp from the surrounding sediments or walls of the mud-volcanic channel was found.

The results of a comparison of various ratios of trace elements-indicators of the composition of provenances for clay rocks of the Middle Riphean Avzyan Formation and the Upper Riphean Biryan Subformation of the Zilmerdak Formation (Bashkirian meganticlinorium, Southern Urals) are analyzed. The formation of these two objects is separated by a hiatus, with the maximum duration up to 250 Ma. The study is based on materials related to the content of trace elements in clay/fine-grained clastic rocks, respectively, of the Avzyan Formation (28 samples) and Biryan Subformation (16 samples) from the collections of E.Z. Gareev and the author, obtained by the ICP-MS method at the IGG Ural Branch of the Russian Academy of Sciences (Yekaterinburg). Distribution of individual and average data points of clay rocks of the named objects on La/Sc–Th/Co, Sc–Th/Sc, Eu/Eu*–Th/Sc, Ni–V–10Th, Th–La–Sc, Y/Ni–Cr/V, Cr/Th–Th/Sc, and Hf–La/Th diagrams are significantly comparable. The chondrite-normalized spectra of rare earth elements (REE) are also comparable. Only on the Th–Th/U diagram, the distribution of data points has a slightly different form, suggesting that either the provenance composition was invariable for almost 250 Ma, the duration of the pre-Upper Riphean hiatus was not so long, the author’s analytics are “lame”, or there are other reasons.

Chromites are a common component of the heavy fraction of sedimentary cover deposits in the platform areas, and their contents usually do not exceed some percents. Commonly, economic chromite placers are formed in vicinity of bedrock sources. Within the Lukoyanov placer district (Nizhny Novgorod region), high chromite contents (up to 100 kg/m³) were found in Middle Jurassic complex coastal-marine rare metal–titanium placers of economic importance. Placer bodies are localized on the periphery of domes in the sedimentary cover. The placers can be sourced from Upper Permian and Lower Jurassic rocks, which were eroded in the zone of positive tectonic structures of the cover and platform basement and within the adjacent land. The revealed patterns can serve as a basis for forecasting similar deposits within promising areas.

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: (frac{{Aleft( {{{nu }_{3}}} right)}}{{Aleft( {{{nu }_{3}}} right) + Aleft( {{{nu }_{2}}} right)}} = - {kern 1pt} 0.2177frac{{FWHMleft( {{{nu }_{1}}} right)}}{{FWHMleft( {{{nu }_{4}}} right)}}) + 1.247; (frac{{FWHMleft( {{{nu }_{3}}} right)}}{{FWHMleft( {{{nu }_{2}}} right)}} = - 0.5804frac{{FWHMleft( {{{nu }_{1}}} right)}}{{FWHMleft( {{{nu }_{4}}} right)}}) + 2.8696; (frac{{FWHMleft( {{{nu }_{3}}} right)}}{{FWHMleft( {{{nu }_{2}}} right)}} = 2.636frac{{Aleft( {{{nu }_{3}}} right)}}{{Aleft( {{{nu }_{3}}} right) + Aleft( {{{nu }_{2}}} right)}} - 0.4437), where: FWHM(ν_i) is a full width at half maximum and A(ν_i) 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 (ν_i) and determining the optimal values for the FWHM(ν_i) and A(ν_i) 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%.

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%) and illite. In sediments from Hole 1038H, clay minerals also consist of chlorite and illite. They were formed under conditions related to the intrusion of a basaltic melt as laccolith into the Escanaba Trough and the heating under its influence of a solution, during the interaction of which with sediments at a high-temperature stage biotite was formed. During the subsequent slow cooling of the laccolith and fluid, the newly formed biotite was replaced completely by chlorite. Illite was precipitated from a hydrothermal solution. At a depth of 183 m, in sediments from Hole 1038H, clay minerals consist of biotite, chlorite, and dioctahedral smectite, just as in sediments from Hole 1038B during their formation under conditions of rapid cooling of the laccolith flank and penetration of sea water into the sediments. The paper shows similarities and dissimilarities in the formation of clay minerals in Pleistocene sediments of the Central Hill, located above the slowly cooling part of the laccolith (Holes 1038A and 1038H) and in sediments located above the rapidly cooling laccolith flank (Hole 1038B).

The crystal chemical characteristics and causes of their variations in the weakly and strongly modified by epigenetic processes dolomites of the Middle Riphean Avzyan Formation in the Bashkir meganticlinorium have been determined. The studies were accomplished by the X-ray diffraction, X-ray fluorescence, and SEM/EDS analysis methods. The Avzyan dolomites are marked by increased parameters of the crystal lattice (a_av = 4.8105 Å, c_av = 16.0211 Å) and reduced values of the substructural reflection (K_av = 0.66) in comparison with stoichiometric dolomites. The average content of elements is as follows: Fe(II) 4545 ppm, Mn 423 ppm, and Sr 124 ppm. Increase in parameters of the crystal lattice of the Avzyan dolomites shows direct correlation with increase in the contents of Fe and Mn, whereas values of the substructural reflection have an inverse correlation. Rocks of all studied sections include two generations of dolomite and calcite. The calcite–dolomite veinlets were formed at 260–530°C and 0.3–2.3 kbar. In dolomites of different subformations, the average value of parameters of the crystal lattice a and c decreases from the early (Kataskin subformation) to the late Avzyan (Tyul’men subformation). In the same direction, average values of the coefficient K of the dolomite structure ordering increase. Dolomites of different stratigraphic levels of the Avzyan Formation underwent intense epigenetic transformations caused by the impact of medium- and high-temperature Fe- and Mn-containing fluids on rocks. Change in the crystal chemical characteristics of the Avzyan dolomites is associated not so much with the process of regional metamorphism, as with the activity of postmagmatic (sections near the Veselovka Settlement and on the Tyul’men River) and catagenetic (sections near the Islambaevo Settlement and on the Bol’shoi Avzyan River) of fluids, which percolated along the fracture zones.

The article provides new data on the structure of the Laptev Sea flank of the Gakkel Ridge. The intensive supply of clastic material from the Laptev Sea shelf leads to the development of a thick alluvial fan at the continental rise, which determines the structure of the bottom topography. In the northwestern direction, the influence of the fan decreases and tectonics becomes the main relief-forming factor. The bathymetric survey traced the asymmetrical rift valley of the Gakkel Ridge, the western flank of which is complicated by terraces. The presence of fault structures, bottom subsidence, extensive sediment supply, and the widespread development of subaqueous slump processes indicate the high neotectonic activity of the Laptev Sea flank of the Gakkel Ridge. For the first time in this region, numerous carbonate rocks have been discovered, the authigenic cement of which is represented by magnesian calcite or aragonite with an admixture of terrigenous material. The palynological and micropaleontological analysis of the carbonate rocks indicates the Quaternary formation of authigenic carbonate cement. An important role in the formation of authigenic carbonates was played by diagenetic solutions coming from the sedimentary cover together with methane and oxidation products of gases and organic matter. The authigenic carbonates were precipitated mainly in an isotopic equilibrium with bottom water at a temperature of about 0°C. The negative correlation between ⁸⁷Sr/⁸⁶Sr and δ¹³C indicates the presence of at least two different sources of carbonate-forming solutions.

We compared the arithmetic average chemical composition of main types of Pleistocene sediments in the Indian and Atlantic oceans, and average chemical composition of the Pleistocene in both oceans as well. As the base for comparison, we used data from the International project of deep-sea drilling reports (phases DSDP, ODP, IODP) and other references. It was revealed that the results of comparative analyses of the mean weighted chemical composition were determined by masses of the dry sediment matter. Domination of the Atlantic mass accumulation rates over the Indian Ocean ones was due to markedly larger catchment areas, influence of more significant humid climate, and enhanced primary production.