Volume 19, 3, 2000
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Volume 19, 3, 2000 |
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Stratigraphy and Sedimentology
A.S. Byakov. Interregional and transregional correlation of Permian deposits of the Boreal realm based on bivalves 3
T.D. Zonova, Ye.A.Yazykova. Layers with Tetragonites duvalianus in the Sikhote-Alin 12
Yu.G.Volokhin, Ye.V.Mikhailik, G.I.Buriy. Triassic cherty formation in the Anyui River basin (Sikhote-Alin) 18
O. V Dudarev, A. I. Botsul, V. V. Anikeev, L. P. Yakunin, G. M. Kolesov. Modern sedimentation in the estuary of the Amur River 30
A. V. Sorochinskaya, A. V. Mozherovskiy, A. I. Obzhirov. Calcium siderite (siderodot) in the sediments of the South China Sea 44
Petrology, Geochemistry and Minerageny
I. A. Tararin, B. Ya. Karp. The problem of composition and age of magmatic rocks of the Obruchev Rise (Pacific Ocean) 49
O.V. Avchenko, I.A. Alexandrov, V.O. Khudolozhkin, N.P. Konovalova. Composition and genesis of fluid phase in minerals from Stanovoi complex 55
V. A. Zlobin. Geochemical peculiarities of black shale complex from the Upper Selemdzha gold ore area (Amur region) 65
L.A. Izosov, Yu.I. Konovalova, A.A. Vrublevskiy, T.A. Yemelyanova. The perspectives of diamond potential of East Asia and marginal seas 78
Geophysics
F. G. Korchagin, L. A. Maslov, O. S. Komova. Geomechanical model of Priamurye and its seismotectonic consequences 97
A. S. Karetnikov, V. G. Gurovich. Petrophysical characteristics of ultrabasites at Konder and Chad Massives 105
Chronicles
G.L.Kirillova. Carbon cycle and biodiversity variation in East Asia in the Cretaceous 112
A.S. Byakov
Interregional and transregional correlation of Permian deposits of the Boreal realm based on bivalves
More precise paleontological characteristics of the Permian bivalve zones of Northeast Asia are presented. The author defined these zones in 1991. The possibilities for the use of this scheme are shown. For the first time an attempt was made to use the defined bivalve zones for correlation with extraboreal regions (North America, Australia, New Zealand, etc.).
T.D. Zonova, Ye.A.Yazykova
Layers with Tetragonites duvalianus in the Sikhote-Alin
A wide distribution of representatives of Tetragonites duvalianus in the Sikhote-Alin territory is established. This allows us to distinguish the Aptian-Albian sequences as the original stratigraphic unit - the Tetragonites duvalianus layers. In this paper, a scheme of fossil location is given with a numbers of outcrops, which were mentioned in the text, accompanied with a detailed enumeration of all collected faunal samples at each point of the region. Moreover, all collected representatives of zonal species are portrayed on paleontological plates together with other specimens from this faunal assemblage, which characterizes the suggested layers. The discrimination of these layers with Tetragonites duvalianus will aid a correlation of synchronous formations with a strong facial change and carrying out of geological work in the tectonically complex system of the Sikhote-Alin.
Yu.G.Volokhin, Ye.V.Mikhailik, G.I.Buriy
Triassic cherty formation in the Anyui River basin (Sikhote-Alin)
The Triassic cherty formation in the middle reaches of the Anyui River basin is a transgressive-regressive macrocyclothem that represents upsection a continuous lithologic succession of units: clayey chert (32-34 m, Middle-Upper Anisian), platy jasper and chert (136-172 m, Ladinian-Lower Carnian), limestone (25-27 m, Upper Carnian-Middle Norian), platy chert (above 4m, Middle Norian-Rhaetian ?). The units' boundaries are diachronic, and the thickness of the units are changeable. The sum thickness of the Middle Anisian- Middle Norian part of the formation is 199 to 258 m, and its total thickness could reach 300-320 m. A remarkable member of the Anisian carbonaceous chert and clayey chert (organic carbon up to 4%) is found between the clayey chert and the platy chert units near the bottom of the formation. The rate of sedimentation (lithified rock) in the Middle-Upper Triassic didn't exceed 9-10 mm/1000 y. The rate of biogenic silica accumulation (g SiO2/sm2/1000 y.) was 1.09-1.2 during the Anisian, and varied from 0.6 to 1.8 during the Ladinian. The formation rocks are mostly planktonic siliceous (radiolarian) and carbonate sediments with some benthic remnants: sponge spicules in Anisian clayey chert, benthic foraminifer in Norian limestone. The clay mineral of chert and limestone includes dioctahedral illite, chlorite, mixed-layer chlorite-smectite, chlorite-vermiculite, vermiculite, and kaolinite. The latter is abundant in the Anisian and the Ladinian-Carnian beds. The studied sections record boundary parts of the limestone-chert facies of the formation at its junction with the chert facies developed westwards (in Tormasu area). Cherty rock and limestone presumably deposited in the lower part of the continental slope (island chain slope ?) or at the adjacent sea bottom.
O. V Dudarev, A. I. Botsul, V. V. Anikeev, L. P. Yakunin, G. M. Kolesov
Modern sedimentation in the estuary of the Amur River
The unique geographical position of the Amur River estuary (at the junction of the Asian continent and Sakhalin Island) is responsible for the discharge of the water stream-flow and sediment discharge into the areas located to the north and south of the mouth. Incidentally, annual distribution of distribution of the stream-flow in the near-estuary areas in the Sea of Okhotsk and Sea of Japan is not equal in volume. As a result of interaction between river and seawater masses, a submeridional structure of hydrological fronts is formed there and also an analogous structure of the bottom sediment distribution. The latter is characterized by symmetry of spatial arrangement of the sediment fields, namely, areas of alluvial fans and near-coastal sediments within the Sea of Okhotsk part of the estuary in comparison with the analogous part of the Sea of Japan. The sediments are carbonate- and silica-free, they are assigned to the terrigenous clastic type. According to their Fe and Mn content, they cannot be assigned to the subgroups of weakly ferriferous or weakly manganese sediments; however, their organic carbon content is higher than in other estuaries, but generally still typical of high-productive marine areas. Hydrological and morphological features can classify marine parts of the estuary as fill delta, because it takes up to 95% of the annual sediment discharge volume of the Amur River. As a result, this estuary is defined as a transitive accumulative system for supplied weathering products; the sedimentogenesis in this system is the key part of the total near-continental sedimentary process with its cyclic character. The vast authors’ material from different oceanological scientific disciplines allows us to estimate (on a new qualitative level) the trends of the recent sediment accumulation within the estuary of the Amur River, which is one of the great rivers on the western coast of the Pacific Ocean.
A. V. Sorochinskaya, A. V. Mozherovskiy, A. I. Obzhirov
Calcium siderite (siderodot) in the sediments of the South China Sea
This paper presents results of investigations of unusual carbonate formations found in the bottom sediments of the South China Sea shelf. The sediments were taken from the deep fracture fixed by geophysical methods. According to the gas-geochemical data there were found high concentrations of methane, hydrogen and carbon dioxide in the bottom water of that region. The carbonate formations were defined as calcium siderite by X-ray, atomic-absorption, microprobe and thermal analyses, and by infrared spectroscopy. The formation of that mineral is conditioned by the carbon dioxide and methane flows passing through the sediments.
I. A. Tararin, B. Ya. Karp
The problem of composition and age of magmatic rocks of the Obruchev Rise (Pacific Ocean)
The analysis and critical assessment of data from the literature on the Obruchev Rise, located in the northern termination of the Hawaiian-Emperor volcanic chain, is evidence that the rise is built by strongly altered tholeiitic basaltoids of the shield stage of Hawaiian-type volcanism with a minimal age of 61.9±5 Ma. This age is in agreement with Maastrichtian (hole 192, Meidzi guyot) and Campanian (hole 883, Detroit plateau) age of sedimentary rock occurring on the erosion surface of the basal basement. The subalkaline basalts - hawaiities and mugearites, detected by dredging of subordinated craters of the Detroit plateau, signify the post-shield stage of Hawaiian-type volcanism.
It is assumed that tholeiitic basalts with an Rb-Sr radioisochrone age of 49.0 Ma, derdged at hole 2649 on the Meidzi guyot, are geochemically distinct from tholeiites of the shield stage of Hawaiian type, show a great similarity to the Eocene tholeiites of the complex from the basement of the Attu Island, Aleutian island arc, and may belong to products of glacial delivery.
O.V. Avchenko, I.A. Alexandrov, V.O. Khudolozhkin, N.P. Konovalova
Composition and genesis of fluid phase in minerals from Stanovoi complex
The degree of mineral reduction and the composition of a gas phase (fluid) enclosed in them have been studied in the rocks of the Stanovoi metamorphic complex by methods of thermodegassing and electrochemistry. High carbon, hydrogen, and methane contents characterize the chemical composition of the gas phase. The gas phase is in disequilibrium state that is demonstrated by lack coincidence of lgfO2 values determined from H2O-H2 and CO2-CO relation. In high-temperature fractions, fluid is less disequilibrium than in low-temperature ones. On the whole, fluid oxidation potential is within the field of buffer reactions: ferrosilite-quartz-magnetite and wustite-iron; incidentally, the gas phase in plagioclase is more oxidized than that in hornblende. As regards the estimation of the degree of mineral reduction, data of electrochemical analysis do not contradict those of chromatography. Insignificant variation of the gas phase composition in minerals from different rocks may indicate that it was formed at a graphite buffer independently of the bulk composition of metamorphosed rocks. The upper temperature limit when a fluid is trapped by minerals (about 550-500°C) is determined by the intersection of lgfO2-T dependence trend in gas fractions with the C-CO buffer. This suggests that the fluid enters the minerals in the final stage of metamorphism. It has been shown that the degree of fluid reduction for the Sutam and Stanovoi complexes differs insignificantly.
V. A. Zlobin
Geochemical peculiarities of the black shale complex from the Upper Selemdzha gold ore area (Amur region)
On the basis of more than 1,500 analyses a distribution of rock-forming elements including S and Copx, and also many elements-admixtures is considered in a thick volcanogenic-sedimentary (black shale) complex of the Upper Selemdzha gold ore area.
A monotypic geochemical character of the main rock varieties from a stratigraphic section is shown. A conclusion was drawn on a rhythmic-cyclic transgressive-regressive structure of the ore-hosting units, an increase in the ascending order in the quantity of pelitomorphic deposits (phyllites) with high contents of Al2O3, K, radioactive (RE), REE, and other elements.
The characteristic geochemical peculiarities of the ore-hosting units - increased natrium content, predominance of protoxide forms of Fe over oxide forms, low concentrations of P, Mn, Copx, S, Au and Ag, clarke contents of RE and REE - give evidence of their formation at the expense of washout of plagiogneisses, characteristic of the basement of the eastern margin of the Siberian platform. Constant presence of feldspars is indicative of insignificant development of weathering crusts in the areas of removal of terrigenous material.
The formation of gold ores was likely to occur at the expense of post-magmatic processes, during two associated stages-periods with a minimal influence produced on the ore genesis of geochemical peculiarities of the ore-hosting rocks. The latter are enriched in S, As and sporadic W, Pb, Zn, Cu only in zones of intensive wallrock alterations. Gold mineralization is localized in hinge parts of various positive tectonic structures and in areas with the most pronounced lithological inhomogeneities.
L.A. Izosov, Yu.I. Konovalova, A.A. Vrublevskiy, T.A. Yemelyanova
The perspectives of diamond potential of East Asia and marginal seas
The Japan Sea Region is located in the East-Chinese Diamond-bearing Province, where large deposits of diamonds are known in kimberlite pipes and commercial diamond-bearing alluvial placers. Kimberlite manifestations, single native and placer diamonds and also extensive concentrate haloes of the kimberlite (lamproite) magmatism minerals-indicators are detected in the region. The authors of this paper have considered the main problems of geology and diamond potential of this part of the continent-ocean transitional zone, have carried out a tectonic zoning of the territory, have projected the geotectonic, structural, magmatic and mineralogical prerequisites for the forecasting of diamond deposits. They have also described and classified different-age. basic-ultrabasic rock associations. These associations are promising for detection of kimberlite and non-kimberlite diamond types. The statistic processing of a large volume of petrochemical information has been carried out according to the authors' methodology, which is based on a modification of factorial analysis (method of principal components). The method makes it possible to compare the multivariate chemical data with the main standards of the basic-ultrabasic formations, including the kimberlite and lamproite ones. It is very likely, that the Sea of Japan basin (especially shelf zones) and Japanese Islands have the definite outlooks for diamonds. There are fragments of Early Precambrian (?) granite-greenstone nuclears and potential-diamond-controlling fault zones in this region. Besides, an intensive basic-ultrabasic magmatism is widespread in Japan.
F. G. Korchagin, L. A. Maslov, O. S. Komova
Geomechanical model of Priamurye and its seismotectonic consequences
The paper considers geomechanical model of Priamirye based on density model with the account of data on seismicity and earthquake focal mechanisms. It is shown that boundaries between the Amur, Aldan-Stanovoy and Okhotsk Sea geoblocks, the Bureya Massif and the Sikhote-Alin fold system are continuously traced in the crust and upper mantle. The major seismic activity of the region is related to these boundaries. The distinctions in the structure of the upper mantle and the Earth’s crust are shown. The horizons are determined in the lithosphere which differ in the rate of the viscous substance flow. It is pointed out that as distinct from the Stanovoy lineament, those of the Mongolo-Okhotsk and Tan-Lu are not reflected in the structure of the viscous flow of the crustal substance. Probably, this is the indication of their young age.
A. S. Karetnikov, V. G. Gurovich
Petrophysical characteristics of ultrabasites at Konder and Chad Massives
Results of petrophysical investigation of ultrabasites from two alkaline-ultrabasic massives of central type -Konder and Chad, located in the south-east of the Aldan Shield, are shown.
There have been studied two thousand samples selected from the central parts of these two massives. Three petrophysical characteristics were studied in detail: the density r, the magnetic susceptibility k and the natural remanent magnetization - NRM. Based on the revealed peculiarities of these petrophysical characteristics, and also, on some distinctive features in the structure of the central parts of the Konder and Chad Massives, the assumption is stated that ultrabasites of only the Mesozoic Chad complex- are involved in formation of the core structure of the Chad Massif.