Lithology and Mineral Resources最新文献

In order to determine the provenance areas of Cenozoic sedimentary basins in the Western Cis-Caucasia and to reconstruct the paleotectonic and paleogeographic environments of orogenic molasse formation in these basins, the sands and sandstones from Quaternary sequences corresponding to two stratigraphic levels were studied: (1) the lower part of the Belorechenskaya Fm section (Gelasian) (sample MK-29) and (2) sequences forming a series of adjacent terraces (Upper Neopleistocene) on the southwestern outskirts of the Maikop town (sample MK-30). U‒Th‒Pb isotope dating and morphological study of detrital zircons (dZr), as well as mineralogical analysis of garnet and tourmaline grains extracted from the heavy fraction of the samples have been performed. Density probability curves (DPC) characterizing the distribution of dZr ages from the studied samples were obtained. Together with previously published similar data on the Eopleistocene sands from the middle part of the Belorechenskaya Fm (sample K23-073) and the Holocene sands of the modern alluvium of the Belaya River (sample K22-032), this made it possible to obtain a summary characteristics for four successive stratigraphic levels of Quaternary deposits, demonstrating a temporal change in the provenance signal in the orogenic molasse of the Western Cis-Caucasia. The studied complex of clastic rocks participating in the Quaternary orogenic molasse contains well-defined signs of the “southern” (Caucasian) provenance signal presented in the sets of U‒Pb isotope ages of dZr grains. In the case under consideration, the “southern” signal is represented by peculiar components associated with the erosion of: (1) Lower and Middle Jurassic volcanogenic-sedimentary, volcanogenic, subvolcanic, and intrusive rocks of the Cimmerian structural level (Cimmerian provenance signal); (2) Early Paleozoic and Late Neoproterozoic igneous and metamorphic formations of the Cadomian complex (Cadomian provenance signal) as a part of the Hercynian basement. A tendency of a gradual decrease in the intensity of the Cimmerian and increase in the intensity of the Hercynian provenance signals in the stratigraphic units of the Quaternary sequence from the lower to the upper levels of the section has been established. This tendency characterizes a successive deepening of the erosion level of the Greater Caucasus orogen. In the beginning, at the early stages of the formation of the western segment of the orogen in Gelasian, erosion spanned rock complexes mainly of the Cimmerian structural stage. Later, starting from the Eopleistocene and up to the present time, the main source of detrital material became the exposed complexes of the Hercynian basement.

The genesis of oolitic carbonates among the lower Meotian sulfate–carbonate–clayey deposits in the Cape Kazantip sections was investigated. Laboratory studies were conducted using several analytical techniques, such as carbonate chemical analysis, optical polarization microscopy with the computer support for photography and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), isotopy, gas chromatography (GC), electron paramagnetic resonance (EPR), infrared (IR) spectroscopy, and X-ray diffractometry (XRD). The obtained results show that the chemical composition of oolitic carbonates is characterized by the constant presence of dolomite (11.93‒40.98%) and clayey (2.42‒19.40%) components, as well as the isotopically heaviest values of carbonate carbon (2.74‒5.40‰). These indicate the formation of oolites in saline water of an extremely shallow coastal lagoon. Gypsum is present in oolite cores and as cement in the oolitic carbonates and conglogravelites. Gypsification of sediments, which occurred at the stage of oolite formation during a sharp sea level fall, could be associated with the participation of sulfate ions from meteoric waters in the removal of sediments into the meteoric-vadose zone, possibly, together with the gas-fluid seepage. The occurrence of bottom gas-fluid seeps is corroborated by the detection of mineralized extracellular polymeric substance (EPS) in oolites, as well as the presence of bacterially induced halite, barite, and high-Mn kutnohorite of the dolomite group. Carbonate minerals in oolites are represented by low- and high-Mg calcites and Ca-dolomite. Distribution of the latter variety indicates the possibly primary sedimentary genesis of dolomite microcrystals in the oolite structure.

The results of studying the conditions of occurrence, morphological features, and material composition of coarse-grained rocks in the Cenozoic molasse of the Olyutorsky terrane (northeastern Kamchatka) are considered. The obtained data allows us to suggest the paleogeological conditions of their formation. Morphological studies revealed that conglomerates are usually medium-sized rocks, with fairly well-sorted and rounded pebbles. However, during the transition from marine to continental deposits, their dimension increases slightly, but the sorting and roundness deteriorate. Gravelites are medium-gravel sediments in marine deposits and coarse-gravel sediments in continental deposits. The gravel is marked by good sorting and roundness. Analysis of the obtained data shows that sediments of the Alugin and Pakhacha formations were deposited in narrow intermontane troughs in a shallow sea; sediments of the Korf Formation, in continental environments. The sediments were delivered from mountains surrounding the basins. A huge amount of coarse-clastic material was transported by ephemeral and permanent watercourses. The material composition of the psephite clasts indicates that the sediments were delivered mainly from local sources composed of the molasse-underlying volcanogenic-siliceous and terrigenous rocks. The secondary sources, which supplied the basin with clasts of feldspar–quartz sandstones and ancient siliceous and granite-metamorphic rocks, were represented by the Cretaceous–Paleocene turbidites of the Ukelayat terrane and the Late Paleozoic–Early Mesozoic rocks of the Koryak folded region located to the north.

The paper presents results of the U–Th–Pb isotope dating (LA-ICP-MS) of detrital zircons from sandstones of the Upper Cretaceous (Maastrichtian)–Lower Paleogene (Danian) boundary level sections, Klementyev Mountain section, Uzyn-Syrt Upland (eastern Crimean Mountains). The obtained data set from the Upper Maastrichtian Klementyev Formation (sample K22-001) contains the following number of dates: 5 Jurassic, 22 Triassic, 55 Paleozoic (including 10 Permian and 7 Carboniferous), 18 Neoproterozoic, 13 Mesoproterozoic (1014–1511 Ma), 27 Paleoproterozoic, and 10 Archean dates (including 1 Paleoarchean). The lower Danian Feodosiya Formation (sample K22-002) yielded the following number of dates: 2 Jurassic, 4 Triassic, 55 Paleozoic (including 11 Permian and 16 Carboniferous dates), 24 Neoproterozoic, 25 Mesoproterozoic (1008‒1525 Ma), 42 Paleoproterozoic, and 13 Archean dates. The very wide (Jurassic to Paleoarchean) age range indicates a diversity of primary provenances, including Archean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, and Paleozoic crystalline complexes. Such a provenance signal cannot be obtained during the accumulation of erosion products from one proximal local source. Thus, traditional paleogeographic schemes of Crimea are not confirmed for the Maastrichtian and Danian, according to which detrital material was delivered to the present-day Klementyev Mountain site from the south and/or southwest (present-day Crimean Mountains). The most probable sources of terrigenous material for the studied rocks were represented by the epi-Hercynian Scythian and ancient East European platforms located north of the Klementyev Mountain. Relative to the Danian sequences, the Klementyev Mountain section is marked by decrease in the share of the Triassic zircon and increase of the Neoproterozoic zircons in the Maastrichtian sequences.

This study investigates the glauconitic ooids of the Cambrian Gushan Formation at the Kelan section (Shanxi Province) through stratigraphic, microscopic, and geochemical analyses to unravel the paleoenvironmental conditions and sedimentary processes governing glauconite formation. The glauconite occurs within oolitic grainstone, which was deposited during the normal regression (highstand systems tract) of a third-order sequence, indicating a moderate to high sedimentation rate in a high-energy setting. Microscopic and geochemical data confirm the presence of glauconite in the form of pellets comparable in size to ooids and reveal their calcitic composition, suggesting simultaneous precipitation with calcite. A key finding of this study is the recognition of the Contrast Temperature Association (CTA), which highlights the coexistence of warm-water oolitic grainstone and traditionally cool-water glauconite, challenging the conventional paradigm of glauconite formation. The current sedimentological and geochemical investigations confirm that the glauconitic ooids of the Cambrian Gushan Formation (Miaolingian Series) at the Kelan section are autochthonous.

Rift formations of the Ishlya graben, widespread on the western slope of the Southern Urals (Bashkir meganticlinorium), are represented by alternating terrigenous rocks (carbonaceous shales, siltstones, and siltstones) of the volcanoplutonic association (gabbrodolerites and basic effusives with a small amount of pyroclastic material). Terrigenous rocks of the Ishlya graben contain rare-earth mineralization: allanite-(Ce), REE-bearing epidote, monazite-(Ce), xenotime-(Y), chevkinite-(Ce), fergusonite-(Nb), rare-earth fluorocarbonates (bastnaesite-(Ce), hydroxyl bastnaesite-(Ce), parisite-(Ce), and synchysite-(Ce) characterized by a wide variety of morphological types and the presence of complex associations. The chemical composition of metamorphic minerals was used to determine the P–T parameters of rock metamorphism (T = 250–600°C, P = 2–10 kbar), the chemical composition and temperature of the fluid phase (CaCl₂ + NaCl, T = 180–408°C for primary inclusions and FeCl₂, T = 121–248°C for secondary ones), as well as the hematization temperature (465–593°C) and re-equilibration of the ilmenite–titanomagnetite association (T = 501–576°C at oxygen fugacity from –23.15 to –21.25). It is shown that the processes of rare-earth mineralization in the natural environment are diverse and multifactorial, with the chemistry of the local-scale mineralization environment being of great importance. The comparative analysis of the chemical composition of monazite and xenotime revealed that the primary source of rare-earth phosphates in channel and alluvial deposits were represented by the Riphean–Vendian metamorphosed rocks in the eastern subzone of the Bashkir meganticlinorium.

Based on the analysis of the bulk chemical composition of sandstones that make up the Proterozoic sedimentary sequences, which unconformably overlie the basement (Ai and Prikamsk formations; Mukun and Valdai groups; Kerur Formation; Gwalior, Athabasca, Libby Creek, Wufoshan, and Birim groups, and others), it has been shown that the content of the major oxides and trace elements in them in the overwhelming majority of cases differs significantly from the chemical composition of the average Proterozoic cratonic sandstone. Their composition corresponds mainly to litharenites, sublitharenites, arkoses, and subarkoses according to the classifications proposed by F.J. Pettijohn with co-authors and M. Herron. Most of the sandstones from the analyzed set belong to rocks containing a significant or predominant part of the lithogenic component. The detrital material composing the sandstones was sourced from fairly mature substrates, with insignificant role of the basic igneous and metamorphic (?) rocks. The bulk chemical composition of sandstones and the paleogeodynamic nature of rocks suggest that the substrates were produced by various orogenic/collisional and rifting events. As with the fine-grained clastic rocks in the studied Proterozoic sedimentary sequences, obviously, not all of the discriminant diagrams used in this study yield consistent results.

The depositional environment of the Amasiri Sandstone within the Turonian Eze-Aku Group in the Lower Benue Trough, southeastern Nigeria, has remained controversial due to its lithological variability and complex facies architecture. This study combines detailed sedimentological observations derived from outcrop analysis, petrographic studies, and paleocurrent measurements to re-evaluate the depositional conditions and provenance of the Amasiri sandstone. Petrographic data indicate arkosic sandstone compositions, pointing toward potential source areas, including the Oban Massif, Calabar Flank, and the basement complexes around Ogoja. Analysis of sedimentological features and paleocurrent patterns supports a depositional scenario dominated by relatively dense gravity-driven sediment flows entering a marine or lagoonal basin. These findings suggest deposition within a hyperpycnal deltaic environment, providing a better understanding of the sedimentary processes that controlled the formation of the Amasiri Sandstone.

The article presents new information on the structure of Upper Precambrian sections in the eastern part of the Middle Tien Shan containing diamictites (tilloids). Identification of two lateral (Dzhetymtau and Akshiyrak) section types in the Vendian Dzhetym Group is substantiated. The Dzhetymtau type is characterized by the presence of rocks containing iron oxide compounds (ferruginous quartzites and hematite schists) in the section. The Akshiyrak type is marked by the presence of black shale layers with pyrite mineralization. At the same time, both types contain two (Dzhetymtau and Baikonur) regional stages (hereafter, horizons) of diamictite development. The paper presents materials indicating that the eastern part of the Middle Tien Shan includes a previously unknown (pre-Dzhetymtau) horizon of diamictite development in the Upper Riphean Boordu sequence, which is compared with the Bayisi Formation at the base of the Kurugtagh Group in northwestern China. In addition, the Kuilu–Sarydzhaz part of the Middle Tien Shan includes the Paleozoic diamictites.

Study of the internal structure of the recently described new species of sponge Gzhelistella cornigera (Davydov et al., 2023) and fusulinids from the Gzhelian stage (Moscow region) revealed numerous polymineral biomorphoses composed of mixed-layer clay minerals, goethite, chalcedony, and sanidine. A detailed structural and crystal-chemical study of clay minerals from biomorphoses and the host rock revealed a structural heterogeneity of the mixed-layer minerals. Using the X-ray diffraction pattern modeling method, it has been established that the clay material in the studied samples is represented by two authigenic mixed-layer (glauconite-nontronite) types with a contrasting relationship between the content of different layers and/or their alternation order, but identical structural and crystal-chemical characteristics of the crystallites. It is shown that such formations should be considered a single heterogeneous mixed-layer structure, with the relationship and/or alternation order of different layer types in crystals varying within certain limits. It has been established that the structural and crystal-chemical characteristics of mixed-layer minerals from brown biomorphoses and host rocks are almost indistinguishable, whereas these parameters are significantly different for green biomorphoses. It is assumed that the newly formed clay minerals from host rocks, like their brown analogs, were formed under similar physicochemical conditions. It is also obvious that during the formation of mixed-layer phases, brown biomorphoses were already deprived of the biogenic organic matter, while green biomorphoses retained it in sufficient quantity to change the environmental conditions within themselves in some places.