Lithology and Mineral Resources最新文献

The study of the distribution law and origin of groundwater in Quaternary sediments downstream of the Red River Delta is approached in the direction of research on sequence stratigraphy and the distribution law of lithofacies according to space and time. However, the distribution law of lithofacies and groundwater depends on global sea-level changes and tectonic activities as the two most important reasons. Quaternary sediments of the Red River delta downstream have 5 sediment cycles corresponding to 5 sequences: (1) sequence 1 with Early Pleistocene age (Sq₁–({text{Q}}_{1}^{1})); (2) sequence 2 with early Middle Pleistocene age (Sq₂–({text{Q}}_{1}^{{2{text{a}}}})); (3) sequence 3 with late middle Pleistocene age (Sq₃–({text{Q}}_{1}^{{2{text{b}}}})); (4) sequence 4 with early Pleistocene age (Sq₄–({text{Q}}_{1}^{{3{text{a}}}})); (5) sequence 5 with late Pleistocene–Holocene age (Sq₅–({text{Q}}_{1}^{{3{text{b}}}})–Q₂). Each sequence is composed of three sedimentary systems tracts. The lowstand systems tract (LST) is characterized by a lowstand alluvial muddy sand facies complex that acts as a primary freshwater aquifer (S_marLST). The transgressive systems tract (TST) is characterized by a coastal swamp sand mud facies (M_samtTST) and a maximum transgression bay-lagoon mud facies (MmtTST) acting as an aquifuge. The highstand systems tract (HST) is characterized by sand bar facies (SamhHST) and delta plain sandy mud facies (M_samhHST). Thus, vertically Pleistocene sediments have 5 aquifers, in which each aquifer is constituted by the superposition of two successive facies complex: (1) upper part: lowstand alluvial gravelly sand facies complex (LST) and (2) lower part: highstand dune sand bar facies complex (SarLST/SamhHST). The spatial distribution of freshwater aquifers in 3 provinces Northwest Thai Binh, Ninh Binh—southeast Nam Dinh, and northwest Nam Dinh demonstrate the absence of shallow marine-bay mud facies.

This paper, devoted to the mineral composition of ore-bearing sediments in the Pobeda hydrothermal cluster in the Mid-Atlantic Ridge (MAR), is a continuation of previous studies (Gablina et al., 2021). Rare zinc minerals (zinc phosphates, zincite, willemite, gahnite(?), and Zn-forsterite) are described. Most of these minerals were first established in bottom sediments of the MAR. The studies were carried out by several methods: scanning electron microscopy, X-ray spectral microanalysis, X-ray diffractometry, Raman spectroscopy, and electron backscatter diffractometry.

The paper analyzes the “bright spot” and “flat spot” anomalies of seismic data on the southeastern flank of the Knipovich Ridge associated with the accumulation of free gas in the sedimentary cover above the oceanic basement. The identified anomalies are associated spatially with negative values of the residual Bouguer anomaly and positive magnetic field (ΔТа) anomalies. This fact indicates the existence of decompaction zones in the crust and upper mantle related to serpentinization that can also provoke the superimposed, probably modern, chemogenic magnetization and distortion of the primary linear pattern of magnetic anomalies in the oceanic basement in the study area. Serpentinization was also responsible for vertical displacements of the crustal and upper mantle blocks on the flanks, leading to deformations of the sedimentary cover with the rock dilation. Off-axis seismicity indicates tectonic disruptions on flanks of the ridge with a higher access of water necessary for the serpentinization and the subsequent change in the physical properties of rocks reflected in geophysical fields. The eastern flank of the Knipovich Ridge underwent tectonic activation along the basement structures representing the northern extension of the Senja fracture zone, resulting in accumulations of free gas in the sedimentary cover.

The paper presents the results of studying the authigenic sulfide aggregates (pyrite) from sediments in the southwestern South China Sea. Materials for the study were obtained during a comprehensive geological-geophysical expedition aboard the R/V Akademik M.A. Lavrentyev (Cruise 88) (Shakirov et al., 2021). The morphology and microstructure of pyrite were studied. Isotopic studies of sulfur in pyrite were performed to elucidate the genesis of sulfides, and the abiogenic nature of their formation was substantiated for the first time in the Fu Han Basin. The biogenic origin of most other sulfide formations was confirmed by geomicrobiological investigations. The study of the composition and admixtures in pyrite revealed a high Ni content in this mineral.

Wide variations of ⁸⁷Sr/⁸⁶Sr (0.70825‒0.70924) have been established at the Porozhinsk deposit in manganese ores and carbonates ascribed to the Pod’’emsk Formation. These data, together with variations in the carbon (δ¹³C = –14.6…2.0‰, PDB) and oxygen (δ¹⁸О = 19.4…28.3‰, SMOW) isotope composition indicate different conditions of the formation of the studied rocks. The ⁸⁷Sr/⁸⁶Sr values in the studied dolomites of the Porozhinsk deposit are much higher than those of carbonate rocks (dolomites, limestones) of the Pod’’emsk Formation from the Chapa River section. The position of the ⁸⁷Sr/⁸⁶Sr values of dolomites from the Porozhinsk deposit on the secular ⁸⁷Sr/⁸⁶Sr variation curve for Late Proterozoic ocean (Kuznetsov et al., 2014) suggests that the carbonate rocks attributed to the Pod’’emsk Formation at the Porozhinsk deposit have younger age than carbonates of the Pod’’emsk Formation from the Chapa River section. The Mn/Sr values usually taken as a criterion for the degree of secondary alteration of carbonates (in interpreting ⁸⁷Sr/⁸⁶Sr variations and discussing the suitability of the material for chemostratigraphic constructions) are not suitable for rocks formed in manganese ore sedimentation basins.

Secondary dolomitization of reef formations is a fairly common phenomenon. Regardless of reef formation in the arid or humid climate, both isolated reefs and reefs of asymmetric reef systems are affected by this process. The article discusses the sources of Mg and methods of its input into reefs, as well as conditions of these processes and the removal of soluble reaction products. This element can be sourced both from relatively deep-water depression-filling sediments (synchronous to the reef) and from clay or salt rocks in the reef topography infill. The possibility of free filtration and removal of the dissolved reaction products is mandatory for this process. If the latter condition is absent, reefs retain their primary calcareous composition.

The lithological study of Recent sediments, as well as planktonic foraminiferal tests and macrobenthos therein, within transverse sections of four submarine canyons in the northern sector of the Argentine Patagonia gravitite–contourite system revealed a considerably more complex facies variability within the canyons than on the Perito Moreno Terrace between them. The facies variability in canyons is controlled by a combination of along-slope contour currents and down-canyon gravity flows. Two southern canyons contain the channel facies of terrigenous glauconite-rich sand that separate the flank facies of sand with a high content of foraminiferal tests. Two northern canyons include the facies of mixed sediments with a high content of <0.1 mm fraction, whose analogs are lacking on the surrounding terrace. They were likely deposited from the down-canyon gravity flows of dense suspension in the still-water bottom environment. Attached macrobenthos with calcareous skeletal elements (commonly corals) inhabits the mainly ice- or iceberg-rafted coarse rock fragments in all canyons and on the surrounding Perito Moreno Terrace.

The results of long-term studies of the heavy mineral composition in Neopleistocene basal moraines, carried out according to a unified technique in numerous outcrops in the European Russian Subarctic, are summarized. The heavy fraction of moraines was formed due to the transport of material from three different glacial feeding provinces: distal, transit, and proximal. With the activation of glacier dynamics and increase in the exaration activity of the mainland ice, local features of the underlying rocks had a decisive influence on the moraine composition. Taking into account other lithological data, the established age and spatial tendencies of regular variability in the mineral composition of different-age moraine horizons made it possible to identify reliably their stratigraphic position.

High-grade iron ores and bauxites of the Kursk magnetic anomaly (KMA) were formed in weathering crusts on the Early Precambrian ferruginous quartzites and shales, i.e., banded iron formation (BIF). Thus far, weathering crusts on the BIF were considered separately, although they formed simultaneously and represent a single sequence in each ore region. Therefore, it is of great interest to compare the coeval weathering crusts on rocks of the formation under consideration for a complex prediction of high-grade iron ores and bauxites. The obtained results showed that the BIF-hosted iron ores were formed during all stages of crust formation in the Paleozoic and such ores can be predicted throughout the KMA, whereas bauxites were only formed in inter-ore shales on the southwestern flank of the anomaly.

The article overviews concepts of the formation of sedimentary sequences of the Belt-Purcell Supergroup, a classical Upper Precambrian section of the Rocky Mountains (North America). Analysis of data on the bulk chemical composition of mudstones of the Belt-Purcell Supergroup (González-Álvarez, 2005; González-Álvarez and Kerrich, 2010) suggests that the overwhelming part of the fine-grained aluminosiliciclastic filling in the Belt Basin was delivered from complexes with non-Archean geochemical characteristics. During almost the entire period of sedimentary filling in the Belt Basin, the fine-grained aluminosiliciclastic material was delivered by large river arteries similar to modern rivers of category 1, i.e., major rivers draining large (>100 000 km²) continental areas (Bayon et al., 2015), and category 2 (rivers draining the “mixed/sedimentary” rocks). This fact confirms the concept of the formation of sedimentary sequences of the Belt-Purcell Supergroup inferred from both traditional geological methods and analysis of data on the U–Pb isotopic ages of detrital zircons and monazites from sandstones of various lithostratigraphic units.