Isotopic signatures of deposition and transformation of Lower Cambrian saliferous rocks in the Irkutsk Amphitheater: Communication 3. Carbon and oxygen isotopic compositions in carbonates     

V. I. Vinogradov  G. A. Belenitskaya  M. I. Bujakaite  V. N. Kuleshov  M. A. Minaeva  B. G. Pokrovskii 《Lithology and Mineral Resources》2006,41(3):271-279

In previous communications based on the study of sulfur and strontium, we showed that Lower Cambrian rocks of the Irkutsk Amphitheater underwent a significant epigenetic transformation. All postsedimentary alterations of rocks are related to the influence of water solutions that provoke the direct (physical) dissolution of material and its chemical transformation. In particular, an appreciable portion of anhydrites disappeared from the section due to reduction. Probably, these processes took place several times in the past and they are continuing at present. A similar conclusion was deduced from the strontium isotopic composition of carbonate rocks. Their strontium isotopic composition is usually shifted relative to the primary composition, although the prevalence of sulfate and carbonate rocks in the section promotes the stability of strontium isotopic composition with respect to secondary alterations. The carbon isotope system is even more stable due to the abundance of carbonate rocks in the section. This circumstance is probably responsible for the incapacity of isotope data to serve as obvious evidence of the epigenetic transformation of carbonates. The major elements of the evolution of carbon isotope signature could be retained since the sedimentation stage.  相似文献   

Isotopic signatures of deposition and transformation of Lower Cambrian saliferous rocks in the Irkutsk amphitheater: Communication 1. Sulfur isotopic composition     

V. I. Vinogradov  G. A. Belenitskaya  M. I. Bujakaite  V. N. Kuleshov  M. A. Minaeva  B. G. Pokrovskii 《Lithology and Mineral Resources》2006,41(1):85-97

New isotope data on Lower Cambrian rocks of the Irkutsk amphitheater are reported in three communications. The first communication is devoted to the sulfur isotopic composition, which is most sensitive to ostsedimentary geochemical transformations of sulfate rocks in saliferous formations. It is shown that δ³⁴S values in Bel’sk and Zhigalovo boreholes are within 22–35‰ The lowest values are close to the sulfur isotopic composition of a halogenic basin, while the highest values are related to epigenetic sulfate reduction. This process was responsible for the elimination of 100 m of anhydrites from the Lower Cambrian section.  相似文献   

Isotope Evidences of the Paleozoic Stage of Epigenetic Transformation of Vendian Sediments of the Russian Platform     

V. I. Vinogradov  M. I. Bujakaite  V. I. Murav'ev  M. B. Burzin  A. F. Veis 《Lithology and Mineral Resources》2002,37(5):454-461

The Rb–Sr characteristics of whole-rock samples of Upper Vendian clayey rocks recovered by Gavrilov-Yam boreholes are studied. The Rb–Sr age versus sampling depth relationship has been revealed. Three sample assemblages are identified. The errorchron relationship of samples in the first interval (1760–2400 m) fits the age of 390 ± 40 Ma corresponding to the initial Hercynian history characterized by the transformation of platformal sediments. The other two assemblages (2410–2525 and 2528–2560 m) make up isochrons with slopes corresponding to 590 ± 50 and 690 ± 10 Ma, respectively. Their geochronological meaning is unclear.  相似文献   

The Influence of Geodynamic Factors on the Postsedimentary Lithogenesis of Jurassic Terrigenous Complexes of the Caucasus (Southern Dagestan)     

Simanovich  I. M.  Golovin  D. I.  Bujakaite  M. I.  Vinogradov  V. I.  Sakharov  B. A.  Matsapulin  V. U.  Sokolova  A. L.  Pokrovskaya  E. V. 《Lithology and Mineral Resources》2004,39(6):555-565

The influence of geodynamic factors on the postsedimentary lithogenesis of terrigenous sequences during the replacement of the passive continental-margin regime to the active regime is considered with the Toarcian–Aalenian complexes of southern Dagestan as an example. It has been established that clayey rocks were lithified under conditions of subsidence lithogenesis, whereas the orogenic catagenesis of sandy rocks was related to stress initiated by the initial (amagmatic) subduction phase. The Kübler index has been used to reveal the postsedimentary zonality that is consistent with the intensity of folding and cleavage. The metagenesis zone fits the cleavage zone. The Rb–Sr and K–Ar datings of clayey rocks from the metagenesis zone yielded 180–190 Ma that can be interpreted as the timing of the maximal manifestation of postsedimentary lithogenesis.  相似文献   

Isotopic compositions of C,O, Sr,and S and problem of ages of the Katera and Uakit Groups,western Transbaikal region     

B. G. Pokrovsky  M. I. Bujakaite 《Lithology and Mineral Resources》2016,51(4):262-282

The age of the Katera Group, which occupies a large area in the western North Muya Range and occurs 100–150 km east of the Uakit Group, is a debatable issue. Based on geological correlations with reference sections of the Baikal Group and Patom Complex, the Katera and Uakit groups were previously considered nearly coeval units and assigned to Late Precambrian (Khomentovskii and Postnikov, 2002; Salop, 1964). This was supported partly by the Sm–Nd model datings (Rytsk et al., 2007, 2009, 2011). Finds of the Paleozoic flora substantiated the revision of age of the Uakit Group and its assignment to the Late Devonian–Early Carboniferous (Gordienko et al., 2010; Minina, 2003, 2012, 2014). We have established that Sr and C isotopic compositions in carbonates of these groups differ drastically, as suggested by their different ages. Sediments of the Nyandoni Formation (Katera Group), which contains carbonates characterized by minimum values of ⁸⁷Sr/⁸⁶Sr = 0.7056 and maximum values of δ¹³C = 4.9‰, were accumulated in the first half of Late Riphean (800–850 Ma ago), whereas the overlying Barguzin Formation (⁸⁷Sr/⁸⁶Sr_min = 0.70715, δ¹³C_max= 10.5‰) was deposited at the end of Late Riphean (700–750 Ma). Judging from the isotope data, the Nerunda Formation (Uakit Group), which contains carbonates with characteristics matching the most rigorous criteria of fitness for the chemostratigraphic correlation (Sr content up to 4390 μg/g, Mn/Sr < 0.1, δ¹⁸O = 23.0 ± 1.8‰), was deposited at the end of Vendian ~550–540 Ma ago). The sequence includes thick typical carbonate horizons with very contrast carbon isotopic compositions: the lower unit has anomalous high δ¹³C values (5.8 ± 1.0‰); the upper unit, by anomalous low δ¹³C values (–5.2 ± 0.5‰]). Their Sr isotopic composition is relatively homogeneous (⁸⁷Sr/⁸⁶Sr = 0.7084 ± 0.0001) that is typical of the Late Vendian ocean. The S isotopic composition of pyrites from the Nyandoni Formation (Katera Group) (δ³⁴S = 14.1 ± 6.8‰) and pyrites from the Mukhtunny Formation (Uakit Group) (δ³⁴S = 0.7 ± 1.4‰) does not contradict the C and Sr isotopic stratigraphic data.  相似文献   

Strontium and oxygen isotopic systems in waters of mud volcanoes of the Taman Peninsula     

M. I. Bujakaite  V. Yu. Lavrushin  B. G. Pokrovsky  O. E. Kikvadze  B. G. Polyak 《Lithology and Mineral Resources》2014,49(1):47-54

Ten of eleven analyzed water samples from mud volcanoes of the Taman Peninsula are characterized by ⁸⁷Sr/⁸⁶Sr ratio within 0.70734–0.70957, which overlaps the values typical of the Mesozoic and Cenozoic sedimentary carbonates, but sharply differs from the value in the clayey sediments of the Maikop Group (0.7157 ± 0.0022). These data indicate that the strontium isotopic composition is mainly defined by carbonate reservoirs, with relatively little effect of elision solutions, input of which is noticeable only in the water of Gladkovsky Volcano (⁸⁷Sr/⁸⁶Sr = 0.71076). The high δ¹⁸O in mud volcanic waters (up to 14.2‰) can also be attributed to ionic exchange with sedimentary carbonates at temperatures around 150°C.  相似文献   

Rb-Sr and K-Ar indicators of the transformation of precambrian clayey rocks in the East European Platform     

V. I. Vinogradov  M. I. Bujakaite  D. I. Golovin  Yu. V. Kushcheva  Yu. A. Ivanov  V. N. Teslenko  O. I. Pashicheva 《Lithology and Mineral Resources》2009,44(2):174-182

Rb-Sr and K-Ar characteristics of Vendian and Upper Riphean sections in various structural units of the East European Platform are studied. It is shown that Neoproterozoic clayey rocks of the platform underwent postsedimentary transformations, primarily owing to processes of K accumulation (illitization). Their intensity decreases with depth and isotopic signatures of provenance rocks are partly retained in Riphean rocks. Stages of the most active transformations approximately 400 and 600 Ma ago are manifested in the Vendian clayey rocks. Events of approximately 1000 Ma ago are recorded in Riphean rocks of the East European Platform. The least altered rocks of the Pachelma aulacogen can retain ancient hydrocarbon pools.  相似文献   

The Rb–Sr and K–Ar Dating of Riphean Rocks from the Bashkir Meganticlinorium, Southern Urals: Results and Implications     

V. I. Vinogradov  V. M. Gorozhanin  A. F. Veis  V. I. Murav''ev  M. I. Bujakaite  D. I. Golovin 《Lithology and Mineral Resources》2001,36(5):419-428

Results of the Rb–Sr and K–Ar isotopic dating of Riphean rocks from the southern Urals are discussed. Epigenetic transformation stages corresponding to 930, 525, and 750–800 Ma for Lower, Middle, and Upper Riphean, respectively, are recorded. These three rock groups presumably represented individual blocks, which experienced different secondary alterations.  相似文献   

Isotopic evidence for postsedimentary transformation of rocks of the Lower Cambrian Angara Formation in the Irkutsk Amphitheater     

V. I. Vinogradov  G. A. Belenitskaya  M. I. Bujakaite  D. I. Golovin  V. N. Kuleshov  M. A. Minaeva 《Lithology and Mineral Resources》2006,41(6):588-600

The section of the Angara Formation (upper portion of Lower Cambrian) is composed of a complex combination of dolomites, anhydrites, marlstones, and salinastones. The occurrence of solution breccia, various types of metasomatism, and other indications testify to the substantial postsedimentary reworking of these rocks. Sulfate reduction, one of the most important processes of reworking, is clearly expressed in the sulfur isotopic composition. The ⁸⁷Sr/⁸⁶Sr ratio in carbonate and sulfate materials is more stable owing to the relatively high Sr content in these rocks. Nevertheless, most sulfate and carbonate rocks are contaminated with the radiogenic Sr. The carbon isotope ratio in carbonates is close to the “normal” value despite the evaporitic character of sedimentation basins and the possible participation of organic carbon, which is a product of the oxidation of hydrocarbons by sulfates, in the transformation of carbonates. The Rb-Sr analysis of the clayey component of marlstones and the K-Ar analysis of mudstones from the lower portion of the Lower Cambrian-Vendian section indicate that the rocks were mainly transformed during a time span corresponding to the Caledonian folding dramatically manifested at the platform margin.  相似文献   

Carbon, oxygen, strontium, and sulfur isotopic compositions in late Precambrian rocks of the Patom Complex, central Siberia: Communication 2. Nature of carbonates with ultralow and ultrahigh δ13C values     

B. G. Pokrovskii  V. A. Melezhik  M. I. Bujakaite 《Lithology and Mineral Resources》2006,41(6):576-587

The Patom Complex is characterized by a unique association of carbonate rocks with ultralow (≤8‰) and ultrahigh (>6‰) δ¹³C values. The thickness, stable isotopic composition along the strike, and lithological and geochemical parameters suggest that these rocks could not form as a result of short-term local events or epigenetic processes. Ultralow δ¹³C values (less than ?8‰) in carbonate rocks of the Zhuya Group, which substantially exceed all the known negative C isotope anomalies in thickness (up to 1000 m) and amplitude (δ¹³C = ?10 ± 2‰), point to sedimentation under conditions of extreme “contamination” of water column by oxidized isotopically light organic (hereafter, light) carbon. The decisive role in this contamination belonged to melting and oxidation of huge volumes of methane hydrates accumulated in sediments during the powerful and prolonged Early Vendian glacial epoch. The accumulation of δ¹³C-depleted carbonates was preceded by the deposition of carbonates with anomalously high δ¹³C values. These carbonates formed at high rates of the burial of organic matter and methane in sediments during periods when the sedimentation basin consumed carbon dioxide from the atmosphere and organic carbon was conserved in sediments.  相似文献