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1.
Doklady Earth Sciences - Kyanite gneiss from the “New Barchinsky” locality (Kokchetav Massif) was studied in detail. This rock is characterized by zonal distribution of the C and SiO2...  相似文献   
2.
The profile comprising a series of lower Aptian sections from Ul'yanovsk to Saratov in the Russian Plate has been studied. It is shown that the unit of organic-rich rocks is characterized by the lack of bioturbation and elevated concentration of many chemical elements. The petrography and geochemistry of organic matter (OM) indicate the prevalence of basinal OM in carbonaceous sediments, while continental OM dominates in host rocks. Sedimentological, biotic, and geochemical data testify to the deposition of organic-rich sediments under anoxic conditions. The anoxic environment in the Aptian basin of the Russian Plate correlates with the global OASE-1a anoxic event. The mechanism of Aptian carbonaceous sedimentation is discussed.  相似文献   
3.
The paper reports lithological and geochemical data on the stratigraphic interval corresponding to the Paleocene/Eocene Thermal Maximum (PETM) event in the Paleogene section of Eastern Crimea (Nasypnoe section). The section is located on the western continuation of the sublatitudinal profile consisting of 15 PETM sections spanning the area from Crimea to Tajikistan (over 2500 km). It is shown that PETM sediments have the negative δ13C and δ18O isotope excursions and are enriched in kaolinite, which is typical of most sections of this interval around the world. At the same time, the extremely low content of organic matter (OM) in sediments of the Nasypnoe section makes them sharply different from the highly carbonaceous rocks of the PETM interval in Central and Eastern Caucasus, and Central Asian regions. This is correlated with the low contents of many chemical elements in the studied rocks, and their extremely high contents in the highly carbonaceous rocks of the easterly sections. Thus, Eastern Crimea in the end of the Paleocene?beginning of the Eocene was occupied by the low-bioproductive marine paleobasin, whereas the coeval paleobasin in Central Asia was characterized by extremely high bioproductivity owing to the presence of significant amount of phosphorus.  相似文献   
4.
Upper Eocene and Lower Oligocene rocks in the northeastern Caucasus were examined in the most representative Chirkei section (Sulak River basin). Sharp lithogeochemical distinctions between them were revealed. The results of the study of nannoplankton demonstrated that the Eocene/Oligocene interface occurs slightly below the boundary between the Belaya Glina and Khadum formations. The studied section revealed a series of nannoplankton bioevents facilitating its stratigraphic subdivision. It has been established that organic matter (OM) in rocks of the Khadum Formation is characterized by a relatively high degree of maturity. Probably, the material of mainly marine genesis contains a terrigenous OM admixture. Positive oxygen isotope anomaly in the upper part of the Belaya Glina Formation reflects global climate changes (cooling) near the Eocene/Oligocene interface. Limitation of the anomaly by the upper boundary of the Belaya Glina Formation is likely related to changes in water salinity variations in the Early Oligocene basin and intense early diagenetic processes in rocks therein. Lithological, geochemical, and paleoecological data suggest that the Khadum paleobasin was depleted in oxygen. Such environment was unstable with periodic intensification or attenuation. Paleoecology in the Belaya Glina basin was typical of normally aerated basins.  相似文献   
5.
Superimposed catagenetic transformations are sharply expressed at the Mikhailov deposit, Kursk Magnetic Anomaly. They are confined to the base of Devonian and Juarassic rocks, which transgressively overlap martite eluvium formed after jaspilites on the surface of a buried uplift. These processes resulted in the appearance of massive lenticular and domal bodies (sandstones and siltstones cemented by calcite or iron sulfides) among friable terrigenous rocks, ferruginization of limestones and their transformation into sideroplesite ores, and formation of carbonate and pyrite concretions. Secondary processes are likely to be related to both descending waters and confined solutions (often thermal) ascending from the aquiferous horizons in the lower part of the sedimentary cover and basement.  相似文献   
6.
Rare biogenic structures, after which diagenetic minerals are developed, are described from Paleogene rocks of southern Dagestan. It is shown that these minerals form tabular mica-like and colloform aggregates confined to fucoids. In terms of composition, they represent the glauconite group minerals. Tabular and colloform minerals are compared with globular glauconite occurring in host sandy rocks. It is demonstrated that the globular variety is characterized by higher K and Fe contents, whereas the tabular variety has a higher SiO2 content. The probable mechanism of the formation of tabular and colloform minerals in biogenic structures is discussed.  相似文献   
7.

The results of studying an aggregate of graphite-and-diamond crystal in tourmaline 5 μm of the Kokchetav massif by the method of transmission electron microscopy are presented. The detail studies of the interface between the crystals of graphite and diamond have revealed the absence of disordered graphite that is detail partially graphitized diamond. Intense deformation changes in the graphite crystal occurred after it was captured by tourmaline at the regression stage, which led to considerable kinking of the graphite crystal along the a-axis. Thus, the coexistence of graphite and diamond crystals cannot be unambiguously interpreted as a product of partial diamond graphitization. Graphite could have crystallized syngenetic with a diamond crystal or at the retrograde stage in the graphite stability field.

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8.
Lithological, geochemical, stratigraphic, and paleoecological features of carbonaceous sediments in the Late Jurassic Volgian Basin of the East European Platform (Kostroma region) are considered. The shalebearing sequence studied is characterized by greater sedimentological completeness as compared with its stratotype sections in the Middle Volga region (Gorodishche, Kashpir). Stratigraphic position and stratigraphy of the shale-bearing sequence, as well as the distribution of biota in different sedimentation settings, are specified. It is shown that Volgian sediments show a distinct cyclic structure. The lower and upper elements of cyclites consist of high-carbonaceous shales and clayey-calcareous sediments, respectively, separated by transitional varieties. Bioturbation structures in different rocks are discussed. Microcomponent composition and pyrolytic parameters of organic matter, as well as distribution of chemical elements in the lithologically variable sediments are analyzed. Possible reasons responsible for the appearance of cyclicity and accumulation of organicrich sediments are discussed.  相似文献   
9.
The lithology and geochemistry of upper Oxfordian sedimentary rocks enriched in marine organic matter (OM) have been studied. These rocks occur as a persistent unit of Upper Jurassic rocks exposed on the right bank of the Unzha River in the Kostroma district. The OM was investigated in detail in both the carbon-rich rocks and their hosts. It was established that the OMs from the Oxfordian rocks are characterized by a low degree of thermal (catagenetic) maturity and their geochemical signature reflects specific features of synsedimentary and early diagenetic processes. Kerogen in the carbon-rich sedimentary rocks is markedly enriched in Sorg, and its formation was related to the early diagenetic sulfate reduction (sulfurization of the lipid fraction of the initial OM). The composition of kerogen from the host clay is sharply distinct in many parameters. No derivatives of isorenieratene were revealed in the aromatic fraction of bitumen in the carbon-rich rocks. The Oxfordian carbonaceous rocks are distinguished by slightly enriched in S, Mo, V, and Ni. Anoxic conditions were unstable in the water column during the deposition of carbon-rich sediments (such conditions were probably episodic). The Corg-rich unit formed due to a short-term abrupt increase in the productivity of phytoplankton related to eutrophication of water, probably, as a result of the recycling and redistribution of biophile elements.  相似文献   
10.
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   
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