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编号 6 (2024)
Articles
Comparative analysis of geochemical peculiarities of pleistocene sediments from Indian and Atlantic oceans
摘要
We have compared the arithmetic average chemical composition of main types of Pleistocene sediments in the Indian and Atlantic oceans, and average chemical composition of the Pleistocene in both oceans as well. As the base for comparison we have used data from International project of deep-sea drilling reports (phases DSDP, ODP, IODP) and other references. It was revealed that results of comparative analyses of meanweighted chemical composition have been determined by masses of dry sediment matter. Domination of Atlantic mass accumulation rates over the Indian Ocean ones was due to larger ratio of watershed areas to areas of basin accumulation, more significant role of humid climate and enhanced primary production.
623–633
New data on the structure of the Laptev Sea flank of the gakkel ridge (Arctic Ocean)
摘要
The article provides new data on the structure of the Laptev Sea flank of the Gakkel Ridge. The intensive supply of clastic material from the shelf of the Laptev Sea leads to the development of a thick alluvial cone at the continental foot, which determines the structure of the bottom topography. In the northwestern direction, the influence of the fan decreases and tectonics becomes the main relief-forming factor. The bathymetric survey traced the asymmetrical rift valley of the Gakkel Ridge, the western side of which is complicated by terraces. The presence of fault structures, bottom subsidence and intensive sediment supply, and the widespread development of landslide processes indicate high neotectonic activity of the Laptev Sea flank of the Gakkel Ridge. For the first time in this region, numerous carbonate formations have been discovered, the authigenic cement of which is represented by magnesian calcite or aragonite with an admixture of terrigenous material. Palynological and micropaleontological analysis of carbonate formations indicates the Quaternary formation of authigenic carbonate cement. An important role in the formation of authigenic carbonates was played by diagenetic solutions coming from the sedimentary cover together with methane and products of oxidation of gases and organic matter. Authigenic carbonates were deposited mainly in isotopic equilibrium with bottom water at a temperature of about 0°C. The negative correlation between 87Sr/86Sr and δ13C indicates the presence of at least two different sources of carbonate-forming solutions.
634–647
Geochemical Characteristics of the Pelite Component of Bottom Sediments Deposited Near the Mouths of Modern Major Rivers. How Stable are They Upstream?
摘要
The article analyzes a number of geochemical characteristics (values (La/Yb)N and Eu/Eu*, Th content) of fine-grained silty and silty-pelitic gray silts of the Volga, particulate suspended matter of the Lena and silty-pelitic fraction of Yangtze bottom sediments. It has been established that in almost all cases, the indicated parameters of the lanthanide spectra normalized to chondrite and the Th content turn out to be comparable with their values determined for specially prepared (removal of non-terrigenous carriers of rare earth elements – carbonate minerals, Fe-Mn oxyhydroxides and organic components) pelitic fractions of bottom sediments deposited near the mouths of the named major rivers, and remain so thousands of kilometers up from their deltas/mouths. The regulation of the Volga and Yangtze flows does not have a significant impact on the parameters of particulate suspended matter and bottom sediments we are considering.
648–666
Peculiarites of clay minerals formation in the Pleistocene sediments under specific tectonomagmatic and hydrothermal conditions of the Central Hill (Escanaba Trough, Gorda Ridge, Pacific Ocean). Communication 2. Holes ODP 1038A and 1038H
摘要
Clay minerals were studied in Pleistocene sediments from Holes 1038А, 114.50 m deep, and 1038Н, 192.80 m deep, which were drilled near a hydrothermal spring with a temperature of 217°C on Central Hill, 275 m east of Hole 1038B. In the sediments from Hole 1038A, at a depth of 8.52 m, the fraction <0.001 mm consists completely of chlorite. In the rest of the sediment section from Hole 1038A clay minerals consist of chlorite (from ~64 to ~98%) and illite. In sediments from Hole 1038H clay minerals also consist of chlorite and illite. Their formation occurred under conditions that arose at the intrusion of a basaltic melt in the form of a laccolith into the Escanaba trough and the heating under its influence of a solution, during the interaction of which with sediments at a high-temperature stage biotite was formed. With the subsequent slow cooling of the laccolith and fluid, the newly formed biotite was completely replaced by chlorite. Illite was precipitated from a hydrothermal solution. At a depth of 183 m, in sediments from Hole 1038H, clay minerals consist of biotite, chlorite and dioctahedral smectite, just as in sediments from Hole 1038B when they were formed under conditions of rapid cooling of the laccolith flank and penetration of sea water into the sediments. The similarities and differences in the processes of formation of clay minerals are shown in the Pleistocene sediments of the Central Hill, located above the slowly cooling part of the laccolith (Holes 1038A and 1038H), and in sediments located above the rapidly cooling flank of the laccolith (Hole 1038B).
667–677
Triassic sediments of the Caspian region: composition, structure, paleogeography, oil and gas prospected
摘要
The article examines the structure and conditions for the formation of oil and gas bearing Triassic strata in the Caspian region.
It has been established that the Scythian and West Turanian plates in the Triassic were located on the active margin of the East European continent. Here a single thick (up to 3–5 km) cover of sedimentary and sedimentary-volcanogenic (mainly tuffaceous) rocks without the characteristic features of rifting was formed. In the north and east of the region, the Triassic is composed of variegated continental terrigenous rocks. In the eastern and southern parts of the Caspian basin, in the Eastern Ciscaucasia, on Mangyshlak, in the Middle Caspian, the Lower Triassic (Olenek) and Middle Triassic are represented by marine terrigenous-carbonate formations. The structural features of the Triassic strata in the Caspian basin are associated with salt tectonics.
The maximum thickness (up to 4.5–5 km) of Triassic deposits is developed in the zone of the Paleozoic Donbass-Tuarkyr rift and is caused by the Pre-Jurassic erosion of neighboring territories. The formation of graben-like troughs here is associated with later shear deformations, which is confirmed by their discrepancy with the facies zonation of Triassic deposits.
Currently, the Permian and Triassic deposits represent a folded complex, unconformably overlying the pre-Kungurian deposits. Triassic deposits of the Scythian and West Turanian plates are disturbed by faults with an amplitude of up to 2 km, and are dislocated in areas. Folding with faults and strike-slip faults is especially intense on the Karpinsky Ridge. Increased dislocation and Late Triassic magmatism on the Scythian and West Turanian plates are associated with collision processes during the closure of the Paleotethys ocean.
Oil and gas prospects are assessed positively.
678–699
Determination of the degree of structural heterogeneity of kaolinites by the decomposition of their IR spectra in the OH-stretching vibration region
摘要
A new approach to assessing the degree of defective structure of kaolinite minerals using their IR spectra in the region of stretching vibrations of OH groups is proposed. Three linear equations were obtained that relate the ratios of spectroscopic parameters to each other: = – 0.2177 + 1.247), = – 0.5804 + 2.8696), = 2.636 , where: FWHM(νi) – full width at half maximum and A(νi) – integral intensity of Lorentz absorption bands at ν1 ~3697 cm–1, ν2 ~3670 cm–1, ν3 ~3652 cm–1 and ν4 ~3620 cm–1, respectively. These equations made it possible to establish criteria for decomposing IR spectra into individual bands, νi, and determining optimal values for the parameters FWHM(νi) and A(νi), with the help of which it is possible to calculate the contents of high ordered kaolinite, HOK, and low ordered kaolinite, LOK, phases in natural samples with an accuracy of ~5%.
700–709
Features of chromite-containing placers of the Lukoyanovsky Placer district (Nizhny Novgorod region) and conditions of their formation
摘要
Chromites are a common component of the heavy fraction of sedimentary deposits of the cover of the platform areas, while their contents usually do not exceed the first percent. Placers of chromites of economic importance, as a rule, are formed in close connection of indigenous sources. Within the Lukoyanovsky placer area (Nizhny Novgorod region), high chromite contents (up to 100 kg/m3) were found in complex coastal-marine rare metal-titanium placers of the Middle Jurassic system, which is of economic importance. Placer bodies are localized on the periphery of the domed structures of the sedimentary cover. A possible source is the Upper Permian and Lower Jurassic sediments, which were eroded in the zone of positive tectonic structures of the cover and foundation of the platform and within the adjacent land. The studied patterns can serve as a basis for forecasting similar deposits within promising areas.
710–720