Lithology and Mineral Resources最新文献

Carbonate concretions in the region of Paramushir hydroacoustic anomalies are confined to the methane seep zones controlled by deep (tectonically weakened) bottom areas. Based on the structure, as well as chemical and mineral composition, the concretions can be classified as volcanosedimentary rock consisting of the vitro-, litho-, and crystalloclasts and buried microfauna cemented with the carbonate (aragonite) cement. The details and sequence of mineral formation of carbonate concretions are considered.

The article presents results of the biostratigraphic and U–Pb geochronological (detrital zircon) studies of the volcanoterrigenous lacustrine member of the upper subformation (Lower Paleozoic Oldynda Formation), which contains polymetallic massive sulfide ores of the Ozernoe deposit (Kurba–Eravna ore district, western Transbaikalia). The first, second, and “crystalline tuff” horizons of the first ore-bearing level of the Ozernaya member were studied. It is represented by an alternation of tuffs, calcareous, siliceous, carbonaceous tuffites, pelitomorphic limestones, calcareous gravelstones with interlayers and lenses of mineralized tuffaceous conglobreccia and layers of banded siderite pyrite ores. For the first time, bryozoans, algae, and palynoflora were recorded in calcareous tuffaceous siltstones and limestones of the second and “crystalline tuff” productive horizons. These data indicate the Early Carboniferous (Tournaisian) time of sediment accumulation. Results of the U–Pb geochronological studies of detrital zircons from the mineralized tuffaceous conglobreccia of the third productive horizon suggest that the lower boundary of rock formation is not older than Late Cambrian.

The article provides an overview of various indexes/indicators (Vogt, Parker, CIA, CIW, PIA, MIA, and others) used for studying weathering profiles/crusts and reconstructing paleoclimatic environments of sedimentary sequence accumulation. Their possibilities are demonstrated with Vendian–Lower Cambrian terrigenous rocks of Podolian Transnistria (southwestern slope of the Ukrainian Shield) as example. Distribution of index ba₁ values in this section indicates the presence of material subjected to intense transformation during the chemical weathering in mudstones of the Nagoryany Formation, the lower part of the Danilovka and the middle part of the Studenitsa formations. For mudstones of the Danilovka–Zbruch interval, the HM values are close to the HM_PAAS. The HM values are slightly higher for rocks of the Yaryshev–Nagoryany interval and comparable to those inherent in hot tropical continental clays for mudstones in the lower part of the Yaryshev Formation. Average value of index SA for mudstones of the entire section is 5.6 ± 0.7. Mudstones of the Grushka–Nagoryany interval, where SA < SA_PAAS, are composed of a more weathered material. The WIP values in mudstones of the Mogilev and Yaryshev formations, as well as in the upper part of the Zbruch Formation, correspond to the interval of their values between the PAAS and average Archean granite. Clay rocks of other formations have WIP ≤ WIP_PAAS. Average CIA value (71 ± 4) for mudstones virtually corresponds to the CIA value (70), which separates the sediments of cold/arid and warm/humid climates. Variations in the index CIW value along the section are oriented similarly as CIA variation. The vast majority of mudstones are characterized by PIA > PIA_PAAS. The average CPA value is 91 ± 4, which is also typical for PAAS. These and other data suggest the following point: based on a “direct” interpretation of the values of various chemical weathering indexes inherent in the fine-grained clastic rocks, paleoclimate in Podolian Transnistria was rather moderate or warm humid in the Vendian‒Early Cambrian. Comparison of the CIA values of mudstones with the values for the particulate suspended matter in modern rivers suggests that the Vendian‒Early Cambrian climate resembled the dry and humid subtropical or dry tropical type with elements of the humid climate.

Flat spot anomalies in the Quaternary part of the section of the Nansen Basin are imaged in seismic records and are interpreted to be related to gas-rich fluid accumulations. The flat spots are mainly located above basement highs between magnetic spreading anomalies C20 (~43 Ma) and C12 (~33 Ma). The complex morphometric analysis of flat spots show that serpentinization processes identified from modelling of gravity anomalies could be original gas source. This process also makes smoothing of the basement highs amplitudes. The depth of the top of the flat spots below the seafloor has an almost constant value of ~390 m indicating the ascent of gases from variable basement depths to a common subsurface fluid trap. The depth of the anomalies below the seafloor corresponds to a theoretical thickness of gas hydrate stability zone in the studied region. Gravity modeling along the Arktika-2011-03 section showed the position of the upper mantle blocks with lower (to 2.95 g/cm³) density within the highs of the acoustic basement. The flat spot anomalies occur above basement highs, below which blocks with lower density typical of serpentinized rocks are modelled. Thus, the serpentinization of the upper mantle ultramafic rocks is considered a main geochemical process, which can explain generation and accumulation of gas in oceanic abyss at a 1–3 km thick sedimentary cover, as well as small vertical movements of the basement blocks due to density reduction and expansion of serpentinized rock.

The article presents the results of sorption of rare earth metal (REM) cations on samples of deep-sea base metal sulfides in the Broken Spur and TAG hydrothermal fields (Mid-Atlantic Ridge). The studied samples contain the following major minerals: marcasite, pyrrhotite, pyrite, and sphalerite in the Broken Spur field; chalcopyrite, pyrite, and marcasite in the TAG field. It has been established that these Fe–Cu–Zn sulfide minerals are natural absorbents. The exchange capacity of sulfide minerals for REM cations is 0.006‒0.061 mg-equiv/g. The exchange complex of sulfide minerals comprises the cations of alkaline, alkali-earth metals, and main cations of metals in the crystal lattice – Fe, Zn, Cu (in very limited quantities). The mechanism of the REM cation absorption is ion-exchange equivalent to the exchange cations of sulfide minerals. It was found that REM cations occur in the sulfide minerals almost completely in the sorbed form (more than 90% of the total amount). Apparently, the chemically bound form is possible only for Lu and Dy cations. The mineral composition of sulfide deposits is preserved in the exchange reaction products, and new phases do not appear.

The article discusses the main directions of lithological studies in the oil-and-gas geology, continuing and developing the ideas and researches of L.V. Pustovalov. Several such studies are coordinated closely with other geological branches (tectonics, stratigraphy, and others). A wide range of such studies is devoted to analysis of the structure and development of sedimentary basins; elucidation of the structure of the internal structure of sedimentary complexes; prediction and prospecting for non-structural oil-and-gas traps; and study of natural oil-and-gas reservoirs at different hierarchical levels.

The mineralogical, structural and crystal-chemical features of seven samples of globular phyllosilicates of the glauconite–illite series (GPS) from the Lower Cambrian sequences of Northern Estonia and Western Lithuania, from the Middle Cambrian sequences of Western Latvia, and also from the Lower Ordovician sequences of Northern Estonia and Western Latvia are considered for the first time. Based on Al index (K_Al = ^VIAl/[^VIFe³⁺ + ^VIAl]) varying from 0.27 to 0.59, the globular phyllosilicates are attributed to the glauconite–illite series, most of which are represented by glauconites (the Al index is K_Al = 0.27–0.46) and one sample, by Al-glauconite (K_Al = 0.59). The K₂O content in minerals is from 7.12 to 7.90%. The content of expandable layers (4–13%), their types (smectite, vermiculite), and the character of their alternation (R = 0, R = 2) were determined for the first time in the studied samples by simulation of experimental X-ray diffraction patterns from oriented specimens. Simulation of X-ray diffraction patterns obtained from unoriented specimens made it possible to determine the degree of three-dimensional order and mean values of the unit-cell parameter b (9.056–9.094 Å), as well as the distribution of their individual micaceous varieties. Based on these data, the microheterogeneity of the Cambrian and Ordovician GPSs 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 studied Middle Cambrian and Lower Ordovician samples, as well as the earlier published dates for the Lower Cambrian samples, are “rejuvenated” relative to age limits accepted for the Cambrian and Lower Ordovician (Gradstein et al., 2020). The relationship of the Cambrian and Lower Ordovician “rejuvenated” isotopic dates and the discovered GPS heterogeneity, as well as possible reasons for its occurrence, are discussed.

The article presents the results of studying changes in the chemical composition of Pleistocene sediments from Hole 858B (depth 38.6 m, temperature gradient 10‒11°C/m) drilled in the Middle Valley, Juan de Fuca mid-ocean ridge (Northeast Pacific) in the Dead Dog hydrothermal field 20 m away from a “black smoker” (temperature 276°C). The content of macroelements in these sediments was studied by the XRD method. For the first time, data on a large set of trace elements were obtained from this object using the ICP-MS method. The chemical composition of sediments changed in the process of solution–sediment interaction during a rapid downsection increase of temperature. In the upper part of Sequence I (1.97‒10.41 m), the sediments are commonly altered slightly at a temperature of about 17°C. Changes in the content of macro- and trace elements are prominent in the lower part of Sequence I (12.70‒25.31 m, average temperature 112‒197°C). The chemical composition of sediments is most altered in Sequences IIB and IID (25.31‒38.6 m, temperature from 112‒197 to 320‒330°С). Changes in the content of the majority of macro- and trace elements in the sediments of Sequences IIB and IID are similar, except for a stronger decrease of chemical elements in the sediments of Sequence IID, which is marked by a significantly lower content of Cu, Zn, Ga, Rb, Sr, Ag, Cd, Sb, Cs, Ba, Tl, and Bi (i.e., the majority of detected elements except U) than in background sediments. Sediments in Sequence IID, as in Sequence IIB, contain less Ca, Na, K, and P, but more Mg. A lower content of the above-listed elements in these sediments can be attributed to their evacuation during the solution–sediment interaction and concentration in the solution, whereas a higher content of these elements is likely related to their input into sediments from the solution and, accordingly, their depletion in the solution. The results of studying the chemical composition of metalliferous sediments (Sequence III, 0‒1.97 m) and sulfide layer IV (10.41‒12.70 m), as well as the chemical composition of unaltered background sediments from Holes 855A, 855C, and 855D are presented.

New data on the C and O isotope composition in the Neoproterozoic carbonates of the Ballaganakh and Dal’nyaya Taiga regional stages (southeastern margin of the Patom paleobasin (hereafter, Basin) are presented. The negative δ¹³С anomaly, established in the upper part of the Ballaganakh regional stage, is comparable (in amplitude and stratigraphic position) to the Trezona anomaly, which preceded the Marinoan glaciation. The carbonate layers in glacial deposits of the Nichatka Formation of the Dal’nyaya Taiga regional stage have moderately positive δ¹³С values. The dolomite unit at the postglacial sequence base is characterized by moderately negative δ¹³С values that are typical for the cap carbonate sequence associated with the end-Marinoan glaciation. The lower part of the postglacial sequence (Barakun Formation) is characterized by a gradual increase of calcite in the carbonate component of rocks and a shift in the isotope composition corresponding to the difference in the fractionation coefficient of stable C and O isotopes for dolomite and calcite. This phenomenon, recorded in the postglacial sequences of Namibia and Canada as well, indicates that the carbonate mineral composition was governed by a global change in water chemistry rather than postsedimentary alteration. The overlying carbonate rocks of the Dal’nyaya Taiga regional stage in the epicontinental part of the Patom Basin (Sen Formation) are depleted in ¹³С compared to their shelf analogs in the Ura Uplift. Probably, the carbonates were accumulated asynchronously in the epicontinental and shelf facies of the Patom Basin. The reconstructed trend of variations in the carbon isotope composition for the Dal’nyaya Taiga regional stage is characterized by positive and low-amplitude negative δ¹³С anomalies similar to those in the Doushantuo Formation (China).

The article analyzes the distribution of datapoints of individual and averaged mudstones samples from almost 40 sedimentary successions of the Neoproterozoic–Ordovician (epoch lacking land plants) and the Devonian–Holocene (time of the appearance and abundance of land plants—“green epoch”) in the (La/Yb)_N–Eu/Eu*, (La/Yb)_N–(Eu/Sm)_N, and (La/Yb)_N–Th diagrams with classification fields of the silty–pelitic particulate matter in the estuary of different-category modern rivers. No fundamental differences between the “green epoch” and pre-Silurian rivers were revealed. In combination with other data, the above fact suggests the following conclusion: since the terrestrial vegetation is absent (and not only in the Neoproterozoic–Ordovician), the categories of rivers, which drained different (in area and composition) catchment areas and transported the fine-grained particulate material to the shelf zones were not fundamentally different from those at present.