Holocene terrace systems and isolated terraces have been identified on the Black Sea coast of the Caucasus, including the northwestern part of the Colchis Lowland. Their composition was studied using a combination of lithological and physicochemical methods. It has been shown that the fine fraction (<0.001 mm) of sediments consists predominantly of newly formed mixed-layer kaolinite‒smectite with a terrigenous admixtures of smectite, kaolinite, micaceous mineral, and occasionally chlorite. Using diffraction pattern modeling for air-dry and ethylene glycol-saturated natural samples, the structural parameters of clay minerals and their quantitative content were determined. No correlation was found between these parameters and the facies settings in which the terrace deposits formed. No correlation was also found between the structural parameters of kaolinite‒smectite and the depth of sediment occurrence or their location within the study area. All samples contain kaolinite‒smectite with a fairly narrow range of the ratio of kaolinite and smectite layers, Wk : Wsm, on average from 0.55 : 0.45 to 0.65 : 0.35. It is shown that the average crystallochemical formula calculated for kaolinite‒smectite with Wk : Wsm = 0.65 : 0.35 exactly corresponds to the dioctahedral structure of the mineral. The decomposition of this formula into smectite and kaolinite components indicates that the 1 : 1 layers in the studied kaolinite‒smectites differ in their crystallochemical structure from true kaolinite ones. A solid-phase mechanism for the formation of kaolinite‒smectites in a smectite matrix is proposed via the removal of fragments of tetrahedral sheets from 2 : 1 layers and adjacent smectite interlayers. The structural evolution of mixed-layer kaolinite-smectites is discussed. The authigenic origin of mixed-layer kaolinite‒smectite minerals in the studied sediments is substantiated.
The facies were studied and the sequence-stratigraphic model of the Zhuya Group in the Ura Uplift (Vendian reference section, southern area of Middle Siberia) was constructed. The whole Zhuya Group represents a single sequence bounded by unconformities. Sediments of the Kullekin member were accumulated in the high-energy coastal-marine environments during sea-level lowstand. The development of transgression initiated a carbonate ramp on the Siberian Craton. The rest of the Zhuya Group above the Kullekin member records the gradual progradation of the ramp and basin compensation of accommodation space during sea-level highstand. The trajectory of the negative C isotope excursion of the Zhuya Group, correlated with the Shuram–Wonoka excursion, follows the relative sea level changes, reaching its nadir close to the maximum of transgression. Elucidation of the reason for the coincidence of these trends requires additional regional and interregional studies. The occurrence of Neoproterozoic zircons in the Kullekin sandstones derived from a northern source reflects accretion of the Baikal–Muya terrane to the Siberian Platform and can be attributed to either pre-Zhuya inversion of the Patom basin (collision) or erosion of synsedimentary tuffs on the Siberian Platform (soft accretion).
Titanium and zirconium are critical metals in many products important to the world economy and technologies. Countries in the former Soviet Union (FSU), such as Russia, Ukraine, and Kazakhstan, have significant reserves of these metals sufficient for the development of own mineral resource base. While the world’s main resources of titanium and zirconium feedstock are concentrated mainly in the beach/marine and eolian dune deposits on the present-day coasts, resources in FSU countries are associated with ancient (Paleozoic, Mesozoic, and Cenozoic) coastal-marine and alluvial placer deposits. Genesis of some placers is discussed. There are two main metallogenic structures in the studied area: East European Megaprovince located within the East European platform (Russia and Ukraine) and West Siberian Megaprovince, which includes the West Siberian Platform (Russia) and North Kazakhstan.
The U–Th–Pb isotope age of detrital zircon populations from sandstones of the Bol’shoi Inzer and Yusha formations of the Burzyan Group (Lower Riphean) of the Yamantau Anticlinorium in the Southern Urals was analyzed. The presence of grains supplied to the sedimentation area from proximal and distal sources was demonstrated. The former likely included the Taratash Complex/Orogen and the Bak 1 complex of the Bakaly granitoid block of the Volga–Ural region, or rock associations similar in age and composition from other regions. The latter include the Volga–Don, Svecofennian, East Sarmatian, and other Early Proterozoic orogens of the East European Craton (Baltica). Considering the intracratonic nature of the Early Riphean sedimentation basin, it has been suggested that some of the detrital material could be delivered from non-Baltica/Siberian sources. Maximum sedimentation age of the Bol’shoi Inzer and Yusha formations has been established. The age of the Bol’shoi Inzer Formation is estimated at 1805 ± 30 Ma (according to the YSG algorithm) and 1870 Ma (according to the YPP algorithm). The Yusha Formation is characterized by the maximum sedimentation age of 1798 ± 10 and 1890 Ma, respectively.
This paper examines cupriferous sandstones and shales hosted in sediments of varying ages (from P2 to PR2) and altered to different degrees (from early catagenesis to the epidote–amphibolite stage). The formation of these rocks is associated with the removal of Cu and other metals by formation waters from the red-colored ore-hosting rocks and their precipitation as sulfides on hydrosulfuric biogeochemical barriers. After their formation, cupriferous sandstones and shales can undergo metamorphic and supergene alterations, which are reflected in the crystallochemical properties of sulfide minerals, the composition of their paragenetic assemblages, the mineral zoning of mineralization, the morphology of ore bodies, and other features. This paper focuses on sulfides of the Cu—S system formed under various conditions. Their composition, structure, physicochemical and thermobaric stability, and occurrence in natural ores are discussed. The composition of copper sulfide ores in cupriferous sandstones, shales, and hypergenesis zones is elucidated. In particular, the paper explains why only nonstoichiometric Cu‒S sulfides (djurleite, geerite, spionkopite, yarrowite) are present in unaltered cupriferous sandstone ores and hypergenesis zones, whereas stoichiometric copper sulfides (chalcocite, digenite, and tetragonal phase) occur in metamorphosed ores. This fact is explained from a physical and chemical perspective. It has been established that each stage of rock formation and transformation is characterized by specific typomorphic minerals of the Cu‒S system and their parageneses that are stable under the conditions of a given stage. With increasing metamorphic grade, the mineral composition of ores and mineral zoning of the deposits change consistently toward simplification due to the gradual disappearance of low-temperature compounds and associations. Indicator minerals of the Cu‒S system, reflecting the thermobaric and chemical conditions of ore formation and transformation, have been identified.
In the southwestern part of Primorye, the widespread Permian volcanosedimentary frocks are a part of the Paleozoic–Early Mesozoic Laoeling–Grodekovo terrane, a fragment of the eastern end of the Central Asian Foldbelt. The Middle Permian Barabash Formation is exposed fragmentarily in the southern part of the terrane, and the material composition of its terrigenous rocks is almost unstudied. The aim of the study was to investigate specific features of the material composition of sandy rocks of the Barabash Formation and, based on its interpretation, to identify paleogeodynamic environments of the formation of rocks, as well as to determine the composition and age of the sources of clastic material. The obtained results show that the sandstones (graywackes and, in part, lithic arenites) are petrogenic or “first cycle” rocks that underwent one cycle of redeposition, and they were deposited due to the destruction of moderately weathered rocks in source areas. A comprehensive analysis and paleogeodynamic interpretation of the mineralogical and geochemical composition of sandy rocks indicate that the rocks were deposited in a basin associated with an active continental margin environment and, in all likelihood, complicated by strike-slip dislocations along transform faults. The main source of clastic material was continental land – cratons and uplifted basement blocks composed of granite-metamorphic complexes and, in part, sedimentary rocks enriched with ancient clastic components. Additional source was fragments of an ancient, deeply eroded island arc composed of basic and ultramafic rocks. U–Pb dating of detrital zircon grains from sandstones of the Barabash Formation made it possible to determine the age of igneous rocks, which that served as the main sources of clastic material, and to reconstruct their probable location.
Some lithogeochemical features of surface bottom sediments (silty sands, silty pelites, and pelitic silts) in the Pechora River Delta are analyzed. It was found that their bulk chemical composition (calculated on the anhydrous basis) is similar to that of the Pechora River suspended matter. The previous assumption that the detrital material composing the surface bottom sediments are predominantly sourced from sedimentary and felsic igneous rocks of the Urals is confirmed. The preservation of a provenance signal from this distant provenance in the Pechora River Delta is probably associated with both the rather harsh climate in the drainage basin and the absence of any other clastic sources in the middle and lower reaches of the Pechora River. It is shown that the content of the overwhelming majority of trace elements in the studied samples is noticeably lower or comparable to that in the upper continental crust. Absolute concentrations of heavy metals in bottom sediments of the Pechora River and Bol’shaya Zemlya Tundra soils, sampled in different years using various methods, have a fairly high degree of convergence. The main carriers of both heavy metals and other trace elements in bottom sediments are feldspars, fine-grained/silty–clayey components, as well as iron oxides and hydroxides.
Phosphorite-bearing mudstone beds in the lowermost part of the Kotlin regional stage (East European Platform) display average Th/U and Ti/Al values of 7.2 and 0.06, respectively. Such values are significantly higher than in the lower and uppermost parts of the sequence and the NASC and PAAS values. The erosion of mature source rocks during the deposition of phosphorite-bearing beds could lead to Th/U and Ti/Al values observed in the fine-grained sediments, suggesting the continental source of phosphorus.
Quaternary sediment subsidence in the Red River Delta has been quietly occurring for 1600 ka BP. This paper introduces the causes, mechanisms, and rates of tectonic subsidence and subsidence due to sediment compression in three boreholes selected for detailed study: BH4-HN, BH02-HP, and BH56-ND, representing three key areas of the Red River Delta. The activities of the northwest-southeast co-sedimentary fault systems and the northeast-southwest post-sedimentary fault systems have created a weak subsidence zone in Hanoi and two strong subsidence zones in Hai Phong and Nam Dinh. The results of sequence stratigraphy analysis show that these 3 boreholes all have 5 sequences: (1) Q_1^1 : Early Pleistocene; (2) Q_1^2a : Early middle Pleistocene; (3) Q_1^2b : Late middle Pleistocene; (4) Q_1^3a : Early late Pleistocene; (5) Q_1^3b -Q2: Late late Pleistocene-Holocene. These 5 sequences are related to 5 glacial/interglacial cycles. Each sequence has 3 sedimentary systems tracts: lowstand (LST), transgressive (TST), and highstand (HST) systems tracts. The sequences and system tract of the 3 boreholes were calculated for the total of tectonic subsidence rate and sediment compression rate as follows: BH4-HN has Vav of 0.281 mm/year, BH02-HP: 0.63 mm/year, and BH56-ND: 0.799 mm/year. This has shown that the two strong subsidence zones of Hai Phong and Nam Dinh cause the strong estuaryization process at the Bach Dang estuary and the strong erosion of the Hai Hau coast.
Correspondence of the main hypotheses of the sedimentary fluorite genesis with the available experimental data is discussed. Data on the saturation degree of seawater and large continental water basins by CaF2 are summarized. It was established that the fluorite formation at the carbonate–gypsum stages of salinization in evaporite basins with purely marine nourishment is impossible, since this requires an additional supply of fluorine from external sources, exceeding the marine F contribution by at least 1.5–4 times. Authigenic fluorite can also form in arid continental water basins similar to the modern, greatly dried-up Aral Sea. It is shown that interaction of sedimentary carbonate minerals with the seawater leads to the dissolved F removal, which is more than an order of magnitude greater for dolomite than for calcite and aragonite. According to a new physicochemical mechanism proposed for the authigenic fluorite formation, recrystallization of the primary finely dispersed carbonate minerals with a defective crystalline structure (for example, protodolomite) promotes a partial self-purification of the solid phase from incoherent elements, accompanied by the accumulation of dissolved F in pore waters until the CaF2 saturation is achieved and fluorite is deposited.
This article presents the results of a comprehensive lithological, biostratigraphic, and isotope geochronological study of the Emsian Bolshaya Usa River section on the western slope of the Polar Urals. The study aims to characterize the boundary between the Vuchvozh and Shervozh formations, and to clarify their stratigraphic range, to reconstruct the depositional settings, and to identify the sources of clastics for the formations studied. The detailed bed-by-bed description and analysis of the lithological and paleontological data enabled us to perform a lithological and stratigraphic subdivision of the section. The boundary between the Vuchvozh and Shervozh formations is marked by the appearance of a bed of fine-grained quartz sandstone and calcareous argillite. This siliciclastic unit has been proposed as a marker horizon. The deposition likely occurred in the lagoonal part of a carbonate platform in a back-reef setting. Biostratigraphic analysis of conodont, stromatoporoid, and tabulate associations from the Vuchvozh Formation indicates an Emsian age for the rocks, corresponding to the upper part of the Vyazovaya, Koyva, and the lower part of the Biya regional stages of the regional stratigraphic scheme of the western slope of the Urals (approximately corresponding to the serotinus–patulus conodont zones). U–Pb dating of detrital zircons from sandstones at the base of the Shervozh Formation revealed the predominance of Meso- and Paleoproterozoic ages (1–2 Ga), with a subordinate amount of Neoarchean-Paleoproterozoic and Neoproterozoic zircons. The distribution of detrital zircons indicates that the main sources of detrital material delivered to the passive Arct-Laurussia margin during the Emsian were the formations of the Sveconorwegian and Svecofennian domains of the Baltica, exposed as a result of the Caledonian orogeny. The dating results are consistent with existing paleogeographic models of the region.
Results of the U‒Pb isotope dating of detrital zircon grains from sandstones in the typical section of the Lower Permian Aksaut Formation on the northern slope of the Greater Caucasus are presented. This formation represents a structural element of the Hercynian molasse that completes the Hercynide section in the Greater Caucasus. Results of the U‒Pb dating of detrital zircons from the Aksaut Formation sandstones are compared with the previously published similar data on metasedimentary rocks of various ages within the Hercynides of the Greater Caucasus, as well as with the date intervals of crystalline complexes that comprise the Hercynian basement of the Greater Caucasus. Prominent age peaks at about 309 and 385 Ma on the probability density curve characterizing the distribution of detrital zircon dates from sandstones of the Aksaut Formation are related to the widespread development of granite magmatism and metamorphism in the central part of the Greater Caucasus with dates closely corresponding to the above age peaks. The presence of numerous zircon groups with ages of 450‒750 Ma in the Aksaut sandstones is associated with: (1) erosion products of magmatic manifestations in the Cadomide blocks (peri-Gondwanan terranes) participating in the structure of Hercynides in the Greater Caucasus, (2) recycling detrital zircons from igneous complexes of the peri-Gondwanan terranes and/or rocks of Upper Precambrian and Lower Paleozoic sequences composed of erosion products of the peri-Gondwanan terranes into the Late Paleozoic Aksaut Formation rocks.
Modern techniques, approaches, and methods of chemostratigraphy (s. lato) are reviewed. Using clay rocks from Upper Riphean and Vendian (Neoproterozoic) sedimentary sequences of the Southern and Middle Urals (Karatau, Asha, Serebryanka, and Sylvitsa groups) as examples, the characteristics of changes in their bulk chemical composition and the possible relationship of these changes with subglobal events in the inner and outer shells of our planet are analyzed. The presented materials suggest that modern chemostrati-graphy (s. lato) represents a broader geological discipline than simply a section of stratigraphy that uses chemical element contents or stable isotope ratios and other elements in sedimentary rocks to subdivide and correlate sediments. Chemostratigraphy (s. lato) is a large-scale and multifaceted analysis of the chemical composition of sediments/sedimentary rocks, allowing the researcher to use numerical data to assess the main (paleogeodynamic, paleoclimatic, paleogeographic) patterns of their formation, as well as the contribution of various provenances to these processes.
Problematic Hydroidea of the genus Fistulella were found in ore-bearing rocks of the Saf’yanovo massive sulfide copper–zinc deposit. The systematic position of this genus has not been determined. Fistulella, classified as problematic Hydroidea in (Shuysky, 1970), resemble the algae-type tubular organisms. They are reef builders and quite common in Paleozoic reefs of the northern Urals, where they form a type of biohermal limestones in association with algae, in particular, Ikella vermicularis (Shuysky, 1970). The ore-hosting sequence of the Saf’yanovo deposit includes the Silurian (Przhidolian) volcanic rocks. Attenuation of reef formation was noted at the Przhidolian stage in the northern Urals. Predominantly autotrophic communities of reef structures (small banks and bioherms) are replaced by heterotrophic communities (including problematic Hydroidea), characterizing the shoal conditions of the open sea. Findings of the remains of problematic organisms of the genus Fistulella at the Saf’yanov deposit are of great importance, because they suggest that the ore-hosting sequence in the deposit, along with volcanic rocks and sedimentary carbonaceous–siliceous rocks, also includes the remains of biohermal buildups and indicates a shallow sedimentation environment. The buildups were probably pre-ore structures, because the detected organism remains were replaced by carbonates of the magnesite–siderite series.
The structure of the Fedorovka chromite-bearing placer cluster, located in the East European Platform adjacent to the Southern Urals, is divided into two facies-stratigraphic complexes of the Middle Permian Biarmian stage: the lower complex, represented by beach and shallow-water sediments of a marine or lacustrine basin, belongs to the Kazanian stage; and the upper alluvial complex, to the late Kazanian (according to other sources, early Urzhumian) stage. The main placer chromite deposits are confined to the beach and shallow water complex (Sabantui placer occurrence), where sedimentation conditions were most favorable for the concentration of heavy minerals. The low-chromite alluvial deposits can serve as a transition zone or intermediate host for basin sediments located to the west. Chemically, Cr-spinels are typical for ophiolite massifs. The nearest massifs (Kraka group) are approximately 200 km away from the Fedorovka cluster. Placer occurrences exhibit features of proximal transport, which can be explained by the overthrust nature of ultramafic massifs and the possibility of more westward ophiolite allochthon migration from the ophiolite suture zone toward the East European Platform during the Permian orogeny. The industrial potential of the Fedorovka placer cluster requires further study. Similar deposits can be discovered within the coastal zone of the Biarmian Basin, located west of folded structures of the Southern Urals.
Cupriferous sandstones contain fragments of chloritized volcanic rocks, silicified volcanic glasses and carbonized plant relics, grains of feldspars (K-feldspar and plagioclase), quartz, clays, chlorite, calcite, and accessory epidote, zircon, apatite, barite, ilmenite, silver sulfide, ilmenite and chromite. The Cu-bearing minerals include chalcopyrite, bornite, nonstoichiometric minerals of the chalcocite-covellite series (djurleite, spionkopite, yarrowite, covellite), malachite and mottramite. Two pyrite varieties are identified: microcrystals replaced by Fe-oxyhydroxides and framboids replaced by copper sulfides. Cupriferous sandstones are characterized by varying contents of major oxides depending on the ratio of the amount of detrital material and carbonate cement in the rock. The marker trace elements of sandstones are Ba, Sr, and REE with high contents and Cr, Ni, Zn, As, Mo, Sb, Pb, U, Th, V, and Zr. The δ18O and δ13C values in calcite vary from +22.24 to +29.35‰ (SMOW) and from –5.34 to –18.0‰ (PDB), respectively. Based on the structural-textural and mineralogical-geochemical features, the studied sandstones can be classified as the coastal-marine deposits.
The borehole “Lisino-10” was drilled on the Izhora Upland, approximately 90 km southwest of St. Petersburg. This study presents the first continuous carbon and oxygen isotope curves obtained from Ordovician carbonate rocks (Latorp–Rakvere regional stages) in the northwestern part of the Russian Plate. Despite relatively small deviations in δ13C values (from –2.5‰ to 1.8‰), two positive carbon isotope excursions are clearly identified in the borehole section: (1) the MDICE (Middle Darriwilian Isotopic Carbon Excursion), with a peak δ13C value of 1.0‰ in the Loobu Formation, and (2) the GICE (Guttenberg Isotopic Carbon Excursion) at the Sandbian–Katian boundary, with a peak δ13C value of 1.8‰ at the boundary between the Vruda and Izvara formations. In addition to these positive excursions, two negative carbon isotope events are also recognized: (1) the BDNICE (Basal Dapingian Negative Isotopic Carbon Excursion), with a minimum δ13C value of –2.5‰ in the lower part of the Volkhov Formation, and (2) the LSNICE (Lower Sandbian Negative Isotopic Carbon Excursion), with a minimum δ13C value of –1.0‰ in the upper part of the Viivikonna Formation. These results enable carbon-isotope chemostratigraphic correlation of the Lisino-10 section with other regional sections and establish it as a reference section for the Ordovician paleobasin of the Russian Plate.
Based on the data from DSDP, ODP, and IODP Legs, several schematic maps of the CaCO3, Al2O3, and SiO2 distribution in Pleistocene sediments of the Atlantic Ocean have been compiled. Their analysis made it possible to reveal the manifestation of sedimentation zonation types, such as circum-continental, latitudinal, vertical, and tectonomagmatic. Specific features of the similarity and dissimilarity with analogous zonation types described for the Recent epoch are compared. It is concluded that Recent zonation in the Atlantic Ocean is inherited from the Pleistocene epoch.
The bulk mercury concentrations were determined in samples of fresh mud volcanic clays from 31 mud volcanoes of the Kerch‒Taman mud volcanic province. Its concentration ranged from 20 to 640 μg/kg. It is shown that the mercury concentrations do not depend on the size of the mud volcanic edifice or its activity. At the same time, it was noted that mud volcanic clays with higher density are characterized by higher Hg concentrations, which may reflect an increase in the concentration of mercury-bearing sulfides. Correlations were established between mercury concentrations in the clays and estimated formation temperatures obtained using hydrochemical geothermometers, Tmax values for clay kerogen, concentrations of HCO3, Li, B, Si in water, as well as δ18O(H2O) and δ13C(CH4). These relationships show that the observed [Hg] variations in the clays can be explained by different depths of the volcanic “roots.”. A hypothesis is put forward that the observed variability in mercury concentrations may not only reflect differences in its concentrations in the vertical section of the Maikop deposits, as previously thought, but also be a consequence of the fluid enrichment with this element as a result of the lithogenesis of clay rocks. The latter can be provided by smectite illitization, which is activated at temperatures >80–100°C and, due to desorption from the clay material, enriches mud volcanic fluids with a complex of chemical elements, including mercury.
The work is devoted to the study of distribution patterns of the organic carbon/sulfide sulfur ratio (C/S) in Upper Jurassic–Lower Cretaceous Black Shale Bazhenov Formation in Western Siberia. Possibilities of using this indicator to clarify the genesis of black shales are considered. It was revealed for the first time that rocks subjected to silicification in diagenesis are characterized by increased C/S values (5 ± 1), while a significant linear C/S relationship, characteristic of normal marine sediments, is retained. It has been confirmed that the catagenetic pyritization, transformation, and thermal degradation of organic matter reduce this indicator (often <2). Together with the dolomitization and kaolinitization, these processes provoke changes in the initial C and S concentrations and violation of the linear C/S relationship. It has been established that the Bazhenov Formation sections, in which the maturity degree of OM in rocks corresponds to the beginning of the main oil generation zone (Treservoir = 60–70°C, R_vt^^∘ = 0.5–0.65) are characterized by a high linear C/S relationship (r = 0.75–0.9). Sections subjected to intense oil generation at the “oil window” stage (Treservoir = 90–120°C, R_vt^^∘ = 0.85–1.15) lack the C/S correlation. It is shown that the C/S ratio serves as an effective criterion for identifying groups of black shales subjected to transformations at different stages of lithogenesis, assessing the transformation degree of the material composition of sections during the catagenesis, and rejecting significantly altered rocks from the analysis during paleoreconstructions.
