Volume 28, 3, 2009 |
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V.L. Lomtev, V.N. Patrikeev, M.G. Gurinov. New data about the Sea of Okhotsk bottom structure 3 P.F. Volgin, L.M. Lyutaya, A.V. Kochergin. The geologic density section of the Earth’s crust in the Deryugin basin (Sea of Okhotsk) from gravity modeling results 12 V.P. Simanenko, A.N. Filippov, A.A. Chashchin. Basalts of the Panthalassa Ocean in the Samarka terrane, Central Sikhote-Alin 23 N.A. Nikolayeva, A.N. Derkachev, A.I. Obzhirov. Characteristic features of manifestations of gas-fluid emanations on the north-eastern slope of Sakhalin Island (Sea of Okhotsk) 38 N.G.Vashchenkova, M.T. Gorovaya, A.V. Mozherovsky. Composition and age of the mudstone unit (sedimentary cover of the continental slope, Sea of Japan) 53 V.Yu. Zabrodin. Reconstruction of the mesozoides structure of the eastern Amur-Okhotsk fold system (Far East) 64 V.V. Golozoubov, Dong Woo Lee, S.A. Kasatkin, B.I. Pavlyutkin. Tectonics of the Cenozoic Nizhnebikinsky coal-bearing basin (Northern Primorye) 74 V.S. Markevich, Ye.V. Bugdaeva. Pollen analysis basis for J/K age of the boundary deposits (in the Bureya basin (Russian Far East) 90 Ye.V. Perevoznikova, N.V. Miroshnichenko. Tausonite and fluorine-aluminiferous sphene in metamorphosed metalliferous sediments of the Triassic chert formation, Sikhote-Alin 100 S.V. Zyabrev. On biostratigraphy of accretionary complexes in the Russian Far East (critical review of several papers) 105 Anniversaries Galina L. Kirillova (70-th birth anniversary) 113 V.L. Lomtev, V.N. Patrikeev, M.G. Gurinov New data about the Sea of Okhotsk bottom structure The results of reinterpretation of time and deep sections of CDP 1632 profile revealed the following: 1) a submerged bar and the regional Late Pliocene unconformity at its level, Bol'sheretsky and Lebed' subaerial shield volcanoes, the Kony-Pyagina and Magadan megadikes; 2) morphological features of the Okhotsk arch nappe structure (monoclinal thrust slices of the acoustic basement with ramp semigrabens at the front, a tension zone with a solitary Quaternary diapir in the Kolsky trough, which divides the Okhotsk arch into two allochthonous megablocks with opposite vergence of thrusts), related to divergent sheet decollement, probably, at the M-discontinuity. P.F. Volgin, L.M. Lyutaya, A.V. Kochergin The geologic density section of the Earth’s crust in the Deryugin basin (Sea of Okhotsk) from gravity modeling results The geologic density section of the Deryugin basin located in the Sea of Okhotsk western part was studied from the profile Sakhalin I – Deryugin basin – Central Okhotsk rise. Methods of gravity modeling were applied which allow us to investigate laterally density variations of the Earth’s crust layers. Horizontal division of crustal layers of the basin regarding density was established, which suggests a stratified-block model of its structure. An assumption is made based on the established feature of the Earth’s crust in the Deryugin basin that it is located at the junction of the Sakhalin-Hokkaido microplate and the Sea of Okhotsk plate separated by a suture; the western and the eastern edge of the basin belong to the above plates, respectively. Accumulations of various mineral associations are conjectured in the suture zone, and hydrocarbon accumulations are supposed in the secondary reservoirs in the “granite” layer (basement) of the Deryugin trough sides of the Deryugin basin western side. V.P. Simanenko, A.N. Filippov, A.A. Chashchin Basalts of the Panthalassa Ocean in the Samarka terrane, Central Sikhote-Alin Basalts developed on the right bank of the Matai River in the Samarka terrane, a fragment of the Jurassic accretionary prism (Central Sikhote-Alin), are associated with Carboniferous-Permian riftogenic limestones, Permian pelagic cherts, Jurassic hemipelagic cherty-clay deposits, and terrigenous rocks of the continent-adjacent sedimentation area. Their petrogeochemical features give evidence of the volcanism character in different settings of the ancient Panthalassa Ocean. In terms of their chemical behavior, the Carboniferous-Permian basalts are similar to intraplate basalts of oceanic islands and are related to the plume mantle source. The area of formation was evidently an oceanic area with numerous islands and seamounts. The Permian basalts associated with cherts are tholeiitic; they were derived from depleted mantle in the spreading center located in the pelagic area. The Jurassic basalts have a plume nature and geochemically are intermediate between OIB and E-MORB. They are assumed to be formed in the area of the convergence zone in a geodynamic setting of rapid and extremely high-angle subduction. N.A. Nikolayeva, A.N. Derkachev, A.I. Obzhirov Characteristic features of manifestations of gas-fluid emanations on the north-eastern slope of Sakhalin Island (Sea of Okhotsk) Manifestations of cold methane seeps, gas hydrates and carbonate concretions are investigated within the north-eastern Sakhalin slope. Data on isotopic composition of carbon from methane, carbonate concretions and crust have shown that methane has mainly biogenic origin due to microbial reworking of the immature organic matter. Gas composition (including gas of gas hydrates) with a very small admixture of heavy methane homologues, light isotopic composition of carbon from methane and carbonate concretions, low temperature of near-bottom waters and sediments testify to the fact that the manifestations of numerous methane emanations are connected with gas generation within the upper part of the sedimentary rock series. The indicators of formation depth of gas have not been established on the investigated floor area. Typical mud volcano structures have not been recognized either. N.G. Vashchenkova, M.T. Gorovaya, A.V. Mozherovsky Composition and age of the mudstone unit (sedimentary cover of the continental slope, Sea of Japan) Comprehensive (petrographical, spore-and-pollen, and X-ray diffraction analyses) study of the rocks of the mudstone unit was carried out. The derived data give evidence of the terrigenous silt-clay sediments of the mudstone unit, which accumulated in a tranquil hydrodynamic environment, low sedimentation rates, and in shallow-water conditions. Two spore-and-pollen assemblages are distinguished in the mudstone: the Late Oligocene assemblage indicating a colder climate, and the Early Miocene assemblage reflecting a warmer climate in the Miocene. The global rise of sea level at the boundary of the Early and Middle Miocene along with tectonic processes in the region resulted in the expansion and deepening of sea basins. As a result the mudstone unit was overlapped by thick diatom-clay deposits of Middle Miocene age. Tectonic motions along the already existed faults at the end of the Late Miocene exposed in places on the sea bottom rocks of the mudstone unit which earlier occurred at depths of ?400–500 m. V.Yu. Zabrodin Reconstruction of the mesozoides structure of the eastern Amur-Okhotsk fold system (Far East) Based on the compositional similarity of the structure of the Upper Permian and Mesozoic assemblages in the Yankan-Dzhagdy and the Ulban structural and formational zone (SFZ) (Amur-Okhotsk fold system), reconstruction of the structure of the Ulban synclinorium is suggested for the end of the Jurassic period. It is presumed that the Unya-Bom subzone of the Yankan-Dzhagdy SFZ is a sheared and W-displaced for 400-600km fragment of the eastern Ulban synclinorium (the eastern centroclinal closing of the latter, inclusive). V.V. Golozoubov, Dong Woo Lee, S.A. Kasatkin, B.I. Pavlyutkin Tectonics of the Cenozoic Nizhnebikinsky coal-bearing basin (Northern Primorye) The Nizhnebikinsky basin located in the northern part of Primorye is infilled with Eocene-Lower Oligocene terrigenous continental coal-bearing deposits with a total thickness of 1500 m. The basin is the result of syn-strike-slip extension that occurred in the process of right-lateral displacements along the Alchan (Mishan-Fushung in NE China) fault of the Tan-Lu wrench fault system. The change of the left-lateral displacements along this system which dominated in the Cretaceous by the right-lateral ones in Cenozoic time is probably connected with Indo-Eurasian collision. V.S. Markevich, Ye.V. Bugdaeva Pollen analysis basis for J/K age of the boundary deposits (in the Bureya basin (Russian Far East) Pollen assemblages in the coal-bearing deposits of the Talyndzhan and the Dublikan Formation, Bureya basin, were studied The pollen assemblages from the upper part of the Talyndzhan Formation are dominated by gymnosperms, mainly those close to Pinaceae, and also Ginkgocycadophytus. Ferns are in small amounts; however, their taxonomical diversity is rather high. The last appearance of the spores Staplinisporites pocockii, Camptotriletes cerebriformis, C. nitida, and Cingulatisporites sanguinolentus, typical of the Late Jurassic palynofloras, is noted. Ferns prevail in the palynologicai assemblage of the Dublikan Formation. They are chiefly represented by Cyathidites and Duplexisporites. Among gymnosperms the role of Classopollis along with conifers rises. The first appearance of Stereisporites bujargiensis, Neoraistrickia rotundiformis, Contignisporites dorsostriatus, Duplexisporites pseudotuberculatus, D. rotundatus, Appendicisporites tricostatus, and Concavissimisporites asper is observed. These sporomorphs are characteristic of the Berriasian pollen floras. Thus, the boundary between the Jurassic and the Cretaceous most probably runs between the Talyndzhan and the Dublikan Formation. Ye.V. Perevoznikova, N.V. Miroshnichenko Tausonite and fluorine-aluminiferous sphene in metamorphosed metalliferous sediments of the Triassic chert formation, Sikhote-Alin A rare strontium mineral – tausonite, and also an unusual, very rich in fluorine and alumina variety of sphene, were found in metamorphosed metalliferous sediments of the Triassic chert formation of the Sikhote-Alin. These rocks are characterized by wide distribution of native elements, intermetallic compounds, and solid solutions of metals, and also by presence of diverse minerals of Au, Ag, and PGE. Tausonite was detected in manganese (metamorphosed siliceous-rhodochrosite) rocks of the Olginsky ore district and in “brown cherts” (siliceous rocks with manganese garnet and spessartine) of the Dalnerechensk district (Primorye). It forms rather abundant grains of 2–10 µm in diameter, usually placed in quartz or rhodonite. Microprobe analyses showed that in addition to Sr, Ti, and O only Fe3+ is present ( 0.20 f. u.) in this mineral. Fluorine-aluminiferous sphene was found in “brown cherts” of the Dalnerechensk district of Primorye (Gornaya River upper reaches). It forms crystals of 200200 µm in section. The recalculation of microprobe analyses for the crystallochemical formulae shows that about half of Ti positions in the structure of this mineral is often occupied by Al. A decrease in the total positive charge through the replacement of tetravalent Ti4+ by Al3+ was compensated by the decrease of the negative charge resulting from the replacement of oxygen by fluorine according to the pattern: Al3+F->Ti4+O2-. High content of fluorine in sphene, which occupied the position of missing oxygen in the structure, and, consequently (due to crystallochemical features of the mineral), high content of Al are related to the reduction nature of metamorphism of metalliferous deposits. | |
S.V. Zyabrev On biostratigraphy of accretionary complexes in the Russian Far East (critical review of several papers) Being a very simple geological discipline, biostratigraphy requires accuracy and robust logic to be observed. Failure in doing this leads to a distorted interpretation of regional tectonics. Common errors are analyzed with the examples from three recently published papers on biostratigraphy of the accretion complexes in Russian Far East. |