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51.
The typical for marine sediments decrease in the amount of sulfate ion in interstitial solutions with increasing depth owing to sulfate reduction and attenuation of the diffusion of near-bottom waters is manifested as the basic-to-acid zonation in the sulfur isotope composition of the diagenetic pyrite nodules (increase of δ34S values from the center to edge). In sandstones of the Early Carboniferous Emyaksin Formation, which is developed at middle reaches of the Vilyui River (Sakha-Yakutia), we detected a peculiar sulfide nodule. In contrast to common nodules, this nodule is marked by the δ34S value decreasing from 7.5…8.6‰ at the center to –30…–31.4‰ at the edge. Such acid-to-basic zonation is attributed to the origin of nodule in a freshened basin (delta) with a sulfate-depleted environment, which gave way to a sulfate-enriched environment owing to the expulsion brines from the underlying gypsiferous sequences. 相似文献
52.
The paper presents the results of study of the Sr, C, and O isotope compositions in Upper Jurassic carbonate rocks of the Baidar Valley and Demerdzhi Plateau in the Crimean Mountains represented by different facies of the carbonate platform at the northern active margin of the Tethys. The 87Sr/86Sr value in them varies from 0.70699 to 0.70728. Based on the Sr chemostratigraphic correlation, the age of massive and layered limestones in the western part of the Ai-Petri and Baidar yailas (pastures) is estimated as late Kimmeridgian–early Tithonian, whereas the age of flyschoids of the Baidar Valley are estimated as late Tithonian–early Berriasian. The nearly synchronous formation of carbonate breccias of the Baidar Valley and Demerdzhi Plateau in late Tithonian–early Berriasian is substantiated. A summary section of Upper Jurassic rocks is compiled based on the Sr chemostratigraphic data. It has been established that δ18O values in the studied carbonate sediments vary from–2.9 to 1.3‰ (V-PDB). At the same time, shallow-water sediments in the internal part and the edge of the Crimean carbonate platform are depleted in 18O (–2.9 to +0.1‰) relative to sediments on the slope and foothill (–0.5 to +1.3‰). It is demonstrated that δ13C values do not depend on the facies properties and decrease in younger carbonate sediments from 3–3.5‰ to 1–1.5‰ in line with the Late Jurassic general trend. The δ13C values obtained for the Crimean carbonate platform turned out to be 0.5–1‰ higher than the values typical of the deep-water marine setting at the western margin of the Tethys. These discrepancies are likely related to peculiarities of water circulation and high bioproductivity in marine waters of the northern Peri-Tethys. 相似文献
53.
A. Gélabert O.S. Pokrovsky J. Schott A. Feurtet-Mazel 《Geochimica et cosmochimica acta》2007,71(15):3698-3716
This work is devoted to the physico-chemical study of cadmium and lead interaction with diatom-water interfaces for two marine planktonic (Thalassiosira weissflogii, TW; Skeletonema costatum, SC) and two freshwater periphytic species (Achnanthidium minutissimum, AMIN; Navicula minima, NMIN) by combining adsorption measurements with surface complexation modeling. Adsorption kinetics was studied as a function of pH and initial metal concentration in sodium nitrate solution and in culture media. Kinetic data were consistent with a two-step mechanism in which the loss of a water molecule from the inner coordination sphere of the metal is rate limiting. Reversible adsorption experiments, with 3 h of exposure to metal, were performed as a function of pH (2-9), metal concentration in solution (10−9-10−3 M), and ionic strength (10−3-1.0 M). While the shape of pH-dependent adsorption edge is similar among all four diatom species, the constant-pH adsorption isotherm and maximal binding capacities differ. Measurements of electrophoretic mobilities (μ) revealed negative surface potential for AMIN diatom, however, the absolute value of μ decreases with increase of [Pb2+]aq suggesting the metal adsorption on negative surface sites. These observations allowed us to construct a surface complexation model (SCM) for cadmium and lead binding by diatom surfaces that postulates the Constant Capacitance of the electric double layer and considers Cd and Pb complexation with mainly carboxylic and, partially, silanol groups. In the full range of investigated Cd concentration, the SCM is able to describe the concentration of adsorbed metal as a function of [Cd2+]aq without implying the presence of high affinity, low abundance sites, that are typically used to model the metal interactions with natural multi-component organic substances. At the same time, Cd fast initial reaction requires the presence of “highly reactive sites” those concentration represents only 2.5-3% of the total amount of carboxylic sites. For reversible adsorption experiments, the dominating carboxylic groups, whose concentration is allowed to vary within the uncertainty of experimental acid-base titrations, are sufficient to reproduce the metal adsorption isotherms. Results of this study strongly suggest that laboratory experiments performed in a wide range of metal to biomass ratios, represent robust and relatively simple method for assessing the distribution of metals between aqueous solution and planktonic and periphytic biomass in natural settings. 相似文献
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55.
G. N. Baturin V. T. Dubinchuk B. G. Pokrovsky A. N. Novigatsky O. B. Dmitrenko N. S. Oskina 《Oceanology》2016,56(5):690-701
Trawling of the bottom in the northeastern Kara Sea during cruise 125 of the R/V Professor Shtokman in 2013 recovered a block of cavernous, partly phosphatized carbonate rock consisting of biogenic carbonate material and partly crystallized diagenetic calcite. The fauna remains are mainly Oligocene–Pliocene planktonic and benthic foraminifers, with less common Oligocene–Miocene coccoliths and single wormlike organisms. Part of the phosphatized material in caverns is impregnated by manganese and iron oxides and enriched in heavy and trace metals. According to the oxygen isotopic composition, this rock formed under moderate temperature conditions. In terms of morphology, mineralogy, and the abundance of organic remains, the block is comparable to methanogenic carbonates found in other parts of the ocean, but shows no isotopically light carbon signatures typical of methane activity. This indicates the diversity of the carbon isotope composition of the Arctic carbonates. 相似文献
56.
A. A. Makhnach S. A. Kruchek B. G. Pokrovsky G. D. Strel’tsova O. V. Murashko O. L. Petrov 《Lithology and Mineral Resources》2018,53(1):1-13
The paper describes the results of study of the Silurian clayey–carbonate rocks ranging from the Telychian Stage (Llandovery) to the Gorstian Stage (Ludlow) recovered by the Borehole Davtyuny 3k in northwestern Belarus. Rocks of the Sheinwoodian Stage demonstrate a positive excursion of δ13C with amplitude of 4.7‰, marking the Ireviken biotic event recorded in the global chemostratigraphic curve. Values of δ18O for the carbonate material in the studied section (25.5–29.2‰ SMOW) are close to those for Silurian rocks from the Baltic region, Scandinavia, Ukraine, Poland, and Canada. The whole section contains postsedimentary gypsum as nodules and the infilling of fissures and fenestrae. Values of δ34S in gypsum (21.3–26.7‰ CDT) are close to those for the Silurian rocks on the Phanerozoic isotope plot. The formation of gypsum was related to a partial development of the supralittoral environment over the sublittoral and littoral clayey–carbonate substrate. The seawater accumulated in lowlands of the supralittoral plain after storms was intensely concentrated during arid conditions and accumulated in the clayey–carbonate sediment. The subsequent underground evaporation promoted the formation of gypsum as nodules in the unlithified sediments and the infilling of fissures and fenestrae in the lithified rocks. 相似文献
57.
V. Yu. Lavrushin Yu. G. Israfailov B. G. Polyak B. G. Pokrovsky M. I. Bujakaite I. L. Kamensky 《Lithology and Mineral Resources》2018,53(1):53-75
It is shown that the gas and water phases of the thermal nitrogen–methane waters in the Talysh fold zone of the Lesser Caucasus mountain system contain helium and strontium with mantle isotope signatures (3Не/4Не from 200 × 10–8 to 401 × 10–8 and 87Sr/86Sr from 0.70490 to 0.70562). At the same time, clear signs of the mantle component in other gases (nitrogen, methane, and carbon dioxide) are absent. The δ15N value in nitrogen varies from +0.3 to +1.7‰, methane is mainly characterized by δ13C from–57.4 to–38.0‰, while δ13C(CО2) varies from–24.4 to–11.3‰. An increase of the CО2 content is accompanied by the decrease of δ13C in CО2, against the background of increasing SO4 content in the salt composition of waters. This indicates a microbial nature of CO2 in the studied gases. Thus, the presence of mantle helium and strontium in the thermal waters is likely related to their leaching from the Pleogene–Neogene host volcanic rocks. The studies of the oxygen and hydrogen isotope composition in water revealed quite different mechanisms for the formation of cold and thermal waters of the region. The cold waters are mainly fed by local infiltration, whereas the feeding of thermal nitrogen–methane waters is strongly provided by transit atmogenic waters (>50%), which are formed in the mountain ranges at altitudes no less than 1600 m and spaced at 20–40 km or more from the thermal discharge sites. 相似文献
58.
B. G. Pokrovsky A. V. Zaitsev A. V. Dronov M. I. Bujakaite A. V. Timokhin O. L. Petrov 《Lithology and Mineral Resources》2018,53(4):283-306
The 87Sr/86Sr ratio in gypsum and limestones of the Ordovician section of the Moyero River decreases from the bottom upward from 0.7091?0.7095 in the Irbukli Formation (Nyaian Regional Stage, ~Lower Ordovician Tremadocian Stage) to 0.7080 in the upper part of the Dzherom Formation (Dolborian Regional Stage, ~Upper Ordovician Katian Stage), which is well consistent with biostratigraphic subdivision of the section and existing concept concerning the strontium isotope evolution of the World Ocean. The most characteristic feature of the carbon isotope curve is decrease of δ13С values in carbonates from weakly positive values (0.5…1.1‰) in the Irbukli Formation (Nyaian Regional Stage) to sharply negative values (–5.4...–5.8‰) in the middle part of the Kochakan Formation (top of the Kimaian Regional Stage, ~end of the Dapingian–base of the Darriwilian Stage). Increase of δ18О from 20?22‰ to 26?28‰, the negative correlation of δ13С and δ18О, and decrease of δ34S in gypsum from 30?32‰ to 22?24‰ in this interval indicate that the 13С depletion of carbonates was not related to the sulfate reduction and oxidation of organic matter during diagenesis and that the negative δ13С excursion was of primary nature. The presence of negative δ13С anomalies at this stratigraphic level in Ordovician sections of the South and North America (Buggish et al., 2003; Edwards and Saltzman, 2014; McLaughlin et al., 2016) indicates the global or subglobal distribution of this event, which was possibly related to the emergence of the oldest ground vegetation. Against the general decrease of δ13С, the lower part of the section reveals three low-amplitude (1?2‰) positive excursions, the position of which in general confirms the existing correlation scheme of the Moyero River section with the international scale. The upper part of the section is characterized by the alternation of low-δ13С intervals (from–2 to–3‰) and brief positive excursions with amplitude of 0.5?1.3‰. The positive δ13С excursion terminating the Ordovician section of the Moyero River correlates with the δ13С excursion in the middle Katian Stage, while the δ13С excursion in the lower part of the Baksian Regional Stage correlates with the excursion marking the Katian–Sandbian boundary. 相似文献
59.
Gavrilov Yu. O. Shcherbinina E. A. Shchepetova E. V. Golovanova O. V. Pokrovsky B. G. 《Lithology and Mineral Resources》2019,54(6):429-446
Lithology and Mineral Resources - The results of integrated study of the Cretaceous/Paleogene transition in the northeastern Caucasus are reported. The lithological, geochemical and... 相似文献
60.
A. A. Makhnach B. G. Pokrovsky O. V. Murashko O. L. Petrov 《Lithology and Mineral Resources》2020,55(1):24-35
The behavior of stable carbon and oxygen isotopes in carbonates during the deposition and diagenesis of sediments in the bioproductive Upper Famennian Pripyat Trough (southern Belarus) is discussed. Limestones and clayey limestones (Corg 0.92 ± 0.11%) are characterized by very low δ13C values (–9.6 ± 0.3‰). Parental sediments of these rocks were deposited in the shallow-water zone during slow downwarping episodes of the seafloor. Lithification of the sediments took place in oxidative conditions of the diagenesis zone. Organic matter was actively oxidized by free oxygen. Carbon dioxide with isotopically light organic carbon formed in this process was used during the crystallization of diagenetic carbonates that are visually indiscernible from the sedimentational variety. Marls, clayey marls, and carbonate-bearing clays (Corg 6.02 ± 0.80%) are characterized by δ13C values as high as –3.5 ± 0.6‰. In combustible shales (Corg >10%), δ13C value is ‒1.2 ± 0.6‰). The clayey rocks mark the episodes of sedimentation in relatively deep-water conditions that appear during the uncompensated sagging of the basin floor. The diagenetic zone with free oxygen was significantly decreased or absent at all. Here, oxygen of marine sulfates was the main or single oxidizer of organic matter (sulfate reduction). The sulfate oxygen is a weaker oxidizing agent than free oxygen. Therefore, much more organic matter was retained and fossilized in clayey rocks than in carbonate rocks. Organic carbon released during the sulfate reduction and mobilized later for the diagenetic carbonate formation was insufficient for the significant decrease of δ13C values relative to the marine carbonate standard. Isotopic composition of carbonate oxygen in the studied rocks is invariable and does not depend on the content of clay and organic matter. In these rocks, δ18O values are at the level (approximately –5‰) shown for the Famennian in the Global Chemostratigraphic Chart. This fact is consistent with the supposition that oxygen isotope composition of atmospheric precipitates, which influenced the rock formation via continental flow, is close to that of sea water in low latitudes where the territory of Belarus was located in the Late Devonian. 相似文献