F.R. Likht
Nepheloid deposits as indicators of the sedimentary conditions, geodynamic and mineragenic peculiarities of near-continental basins

Major peculiarities of nepheloid material supply and distribution on the floor of the recent East Asia caldron type near-continental basins have been established. Accumulation occurs simultaneously on two spacially separated bottom areas – shallow-water and deep-water. In the shallow-water area there have been identified three typical natural environments of recent near-continental sedimentation, which produced three genetic types of ancient nepheloid deposits differing in specific features: 1) the near-river mouth, 2) transit-linear (transitional near-bottom flows, TNBF), and 3) silt-train. In the deep-water floor area there were deposited thin-bedded rhythmites, which according to their distinctive characteristics represented the nepheloid varieties of the flysch. Their formation is connected with the cyclic changing of meteoclimatic events resulting in a supply of extreme amounts of terrigenous material into sedimentary basins. Similar events as a trigger mechanism could also induce the formation of other flysch varieties.
Nepheloid deposits are an indicator of certain mineragenic environments in the recent and ancient basins. The location of one of the genetic types of nepheloid material in the shallow-water area of the sea (TNBF) reveals paleoriver valleys sunk on the shelf, which potentially contain ancient placers. Thin-bedded nepheloid rhythmites in the relatively deep-water area of the sea are paragenetically connected with other types of bottom sediments with related deposits, corresponding to black-shale geoformations of ancient basins. The latter often host different large mineral deposits, first of all those of the so called fine gold.

 S.A. Gorbarenko, A.V. Artyomova
Chronostratigraphy of the Upper Quaternary sediments of the Northwestern Pacific and the Bering Sea, change of the environment and productivity of the region

The isotope chronostratigraphy of the Upper Quaternary sediments of two cores from the NW Pacific and two cores from the Bering Sea is established by the oxygen isotope records in planktonic and benthic foraminifera. The main regularities of temporal changes in the calcium carbonate, organic carbon and opal content and magnetic susceptibility in sediments of the study region with regard to the climatic changes and productivity are established by means of isotopic-geochemical and lithophysical analysis of these cores and the ODP sites 882 and 883. The correlation of the volcanogenic interbeds in the sediments of the studied cores is carried out, and their stratigraphy and age are preliminarily ascertained. Correlation has been accomplished of A.P. Jouse diatom horizons determined by the analysis of the main ecological changes in the diatom assemblages in the Upper Quaternary sediments of the far NW Pacific, Bering and Okhotsk Seas [Jouse, 1962], and their comparison with similar changes in our columns with the standard oxygen-isotope stages. Also, changes in the lithology and content of biogenic components in the sediments of the region [Romankevich, 1963] and in the cores studied by us have been taken into account. A criterion of the ecological changes of diatom assemblages in the studied region it may be a ratio of frequency of the “neritic” species sum to the sum of the “neritic” and oceanic species (coefficient Id) which is determined by climate variability and mostly by the sea ice influence.
The schemes of the average sedimentation rate in the NW Pacific and Bering Sea for the periods of MIS 1 and MIS 2 (1-12.5 and 12.5-24 kyr BP, respectively) are plotted on the basis of the obtained results and correlation of the diatom horizons and lithological units in the early studied cores with the oxygen isotope stages. Closure of the Bering Strait and the aeration of the north-eastern shelf of the Bering Sea during the MIS 2 induced the growth of sedimentation rate in the Bering Sea, as compared with MIS 1 and the suspended material transfer from the Bering Sea through the Kamchatka Strait into NW Pacific and its accumulation in the south-eastern direction.

Yu.D. Markov, A.I. Botsul
The Late Quaternary deposits of the East Korean Bay (the Sea of Japan)

The comprehensive study of the Late Quaternary deposits from the East-Korean Bay shelf made it possible to reveal the ancient coastal lines being accompanied with facies of beaches, coastal slopes and of relatively deep parts of the shelf. The age of the bay sediments has been determined basing on faunal finds and absolute datings. It has been established that recent accumulation within the bay takes place in its inner parts and on the continental slope, whereas the middle and outer parts of this bay remain as the transit zones. This circumstance confirms the conception that the glacial eustatic fluctuations of the Japan Sea level occurred during the Late Pleistocene and Holocene.

Y.D. Zakharov, M.E. Melnikov, V.D. Khudik, T.A. Punina, S.P. Pletnev, O.P. Smyshlyaeva
A new find of ammonoids (Cephalopoda) in the oceanic floor deposits

Information about Cretaceous ammonites (Zelandites aff. japonicus Matsumoto and Tetragonitidae gen. et sp. indet.) of Magellan Rise in the Central Pacific is given for the first time. They were extracted by dredging on the IOAN guyot by the “Yuzhmorgeologiya” expedition in 2001. The age of the hosting carbonate cement is determined as Late Cretaceous (probably, Campanian-Maastrichtian). The detected ammonites are, most likely, emigrants from the Tethyan epicontinental basins of East Asia.

 V.V. Mishin, A.G. Nurmukhamedov, S.P. Belousov
Paleosuboceanic type of the Earth’s crust in Northeastern Kamchatka

This paper is based on complex geophysical investigations (seismic prospecting by the method of the converted waves, electrical survey by magnetotelluric sounding, gravity survey, magnetic survey) on the regional profile Lesnay settlement-Ossora settlement which crosses Kamchatka Peninsula near the Kamchatka neck. A brief characteristic is given of the methods of field work, information processing and interpretation. Sections basing on these methods and the summary geological-geophysical section are offered. Lithosphere’s mantle and the Earth’s crust layers are described, and their rock composition is estimated. The principal result of the work done was recognition of the unique structure of the eastern part of the territory through all the distinguished layers of the lithosphere. This resulted in recognition there of the paleosuboceanic type of the Earth’s crust, i.e. suboceanic crust, whose sedimentary cover is transformed into a metamorphic basement. The character of juncture of paleosuboceanic crust with continental crust is rated as obduction obscured at the level of lithospheric mantle; the obduction being accompanied by collision in consolidated crust. Possible variants of the origin of paleosuboceanic crust are discussed, and the position of the interpolate boundary in the studied territory, the peculiarities of regional seismicity, possibilities of the use of the data obtained for specification of metallogenic zoning and assessment of oil and gas potential are analyzed.

P.L. Nevolin, V.P. Utkin, A.N. Mitrokhin, S.V. Kovalenko, and T.K. Kutub-Zade
The Cretaceous intrusions of Southern Primorye: the tectonic position and dynamic conditions of their structure formation

The tectonic position of the Cretaceous granite intrusions in Southern Primorye is defined by fold and rupture deformations manifested in the formations hosting these intrusions. The structural patterns of the intrusions themselves are related to elements of fold and rupture parageneses as well. As exemplified by the Uspensky granite massif, it is shown that in conditions of a plastic environment, taxitic textures and layering of granitoid intrusions are organized into pseudofold syn- and antiforms elongated in the E-NE direction almost parallel to the intrusions extension. Geometrically, these structures are similar to folds observed in the enclosing rocks. They are also asymmetric and SE-verging. The same vergence style is typical of the system of counter-dipping thrusts. Brittle deformations are revealed in the paragenesis of strike-slip faults sensu stricto which control the dyke and vein facies location. The whole complex of fold and rupture dislocations typical of granitoids and surrounding formations was the result of lateral compression and left-lateral strike-slip geodynamic regime. The data obtained point out the substantial effects of geodynamic conditions (at least, strain fields and dominating block movement) produced on the studied igneous rocks formation and maybe on the entire magmatism.

M.D. Ryazantseva, I.I. Kupriyanova, B.V. Belyatsky, R.Sh. Krymsky, Ye.P. Shpanov
Age and genetic correlations between magmatic rocks and rare metal fluorite mineralization in the Voznesenka ore district (Primorye)

Basing on the previous and recent geological, isotope, petrochemical, and mineralogical data, the sequence and formation conditions of the Voznesenka granitic and mafic magmatic complexes as well as of various types of mineralization dated as Cambrian to Devonian have been specified. The position of the region at the intersection of deep-seated faults that belong to the global fault system superimposed on the continental margin may be considered as a tectonic factor contributing to the formation of major mineral deposits in this area. The magmatic control of mineralization relates to biotite and biotite-protolithionite granites that are the facies formed in different structural conditions. The latter circumstance resulted in a different degree of their differentiation and contamination by crustal and mantle material. Tin-ore deposits (456 Ma) are located in the еxocontact parts of biotite granites derived from a magma enriched in crustal material (452-462 Ma, ⁸⁷Sr/⁸⁶Sri - 0.708-0.720, e_Nd = 5). Related to the biotite-protolithionite by granites (452-462 Ma, ⁸⁷Sr/⁸⁶Sri - 0.707-0.708, e_Nd =-3.05), two stages of ore formation are recognized: (1) formation of struverite-columbite ores (440 Ma, U-Pb) in granitic domes; and (2) formation of large-scale Li-Be-fluorite mineralization with participation of deep fluids flows – a more extended stage:423 Ma, ⁸⁷Sr/⁸⁶Sri - 0.710-0.740 (upper levels) and 0.708-0.709 (lower levels), e_Nd=0.06– 0.69 (early generations of fluorite) and -0.37- -1.99 (late generations of fluorite). The long-lived openness of the channels that exposed the mantle-related fluid-magmatic centers is confirmed by emplacement of post-ore intrusions of the monzonitoid complex (415 Ma, ⁸⁷Sr/⁸⁶Sri - 0.708, e_Nd =-0.4-1.9) and various mafic and ultramafic dikes.

K.B. Bulnaev
Late Mesozoic volcanics and fluorite deposits in the Transbaikal region and Mongolia: age and genetic relations

Factors of possible genetic relationships between fluorite deposits in the Transbaikal region and Mongolia, and Late Mesozoic volcanics are considered. The special disconnection of most of fluorite-bearing belts and zones and areas of volcanics distribution is shown. New data are offered concerning the K-Ar and Rb-Sr age of the fluorite deposits and Late Mesozoic volcanics which give evidence of their formation in different times with an interval gap of 30-40 Ma. This is the basis for negating the genetic or paragenetic relationship between the deposits and volcanics, and the features of their distribution also negate it. The increased fluorine content as against the clarke found for alkali basalts and andesite basalts of the volcanic assemblage is related to the mantle origin of fluorine and its transfer into the Earth’s crust as part of basaltic magma.