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1.
At present, Larix gmelini is a main component of taiga developed in north Sakhalin, northeast China and east Siberia. During the interval from ∼11.8 to 12.4 ka BP, pollen assemblages from north Hokkaido, Japan, are dominated by Larix. Pollen assemblages of this Lateglacial climatic reversal, known as the “Kenbuchi Stadial”, are similar to pollen assemblages from the Last Glacial Maximum in north Hokkaido. Vegetation of Hokkaido inferred from these pollen assemblages — open taiga composed of Larix gmelini, Pinus pumila and Picea jezoensis and/or Picea glehnii — may have been like that of north Sakhalin today. Comparison of these fossil pollen assemblages from Hokkaido with pollen assemblages from modern surface samples in Sakhalin suggests that ∼ 11.8 to 12.4 ka BP, temperatures relative to today were at least 9°C lower in January and 7°C lower in August, and that annual precipitation was at least 735 mm lower than present.  相似文献   

2.
Reexamination of radiolarians from the Naiba and Bykovo formations of the Naiba reference section (West Sakhalin Mountains) is carried out. Distinguished in the section are the Cromyomma (?) nodosa-Amphipyndax sp. A (terminal early Cenomanian), Cuboctostylus kasinzovae-C. sakhalinensis (Middle Cenomanian), Cuboctostylus trifurcatus-Cassideus yoloensis (terminal middle-late Cenomanian), and Spongodiscus concentricus-Multastrum robustum (late Turonian to early Coniacian probably) assemblages. According to results of comparative analysis for North Pacific regions, concurrent radiolarian assemblages from the Naiba section and California contain up to 40% of species in common, whereas taxonomic similarity with assemblages from Japan is insignifican in contrast.  相似文献   

3.
First biogeographic maps are proposed for the late Eocene-Oligocene of the North Pacific. The maps are compiled based on distribution of 120 molluscan species studied in 30 reference sections of the region. The analyzed Machigar (Sakhalin), Rategin, Amanina-Gakh (western Kamchatka), Asagai-Momidziyama (Japan) type assemblages and their age analogues are well known and described long ago. Over 50 schematic biogeographic maps illustrate distribution areas of different taxa in the late Eocene, early Oligocene, and late Oligocene epochs. Some of them characterize distribution areas of individual species, while the others depict habitat areas of typical (Machigar and Rategin) assemblages or certain genera different in terms of their thermotropism. Analysis of the maps resulted in recognition of the Japan-Kamchatka and Kamchatka-North American paleoprovinces, and indications of general gradual seawater temperature decrease during the Oligocene are defined. The attention is paid to the commenced diversification of North Pacific biota that leads to formation of boreal communities and also to different-rank the amphipacific dusjunctions.  相似文献   

4.
《International Geology Review》2012,54(11):1321-1325
Velocity-density relationships in the south of Sakhalin, Primor'ye, Chukotka, Kamchatka, and the south of the Greater Kuril island arc are based on Neogene - lower Paleozoic rock samples from the part of the crust accessible to drilling. The calculated densities differ in regions with a different type of development of the crust. A comparison of the possible nature of the stresses in the crust of such regions during post-Cretaceous time suggests a similiar pattern of evolution of the crust of Japan and the south of the Kuril arc. The increased densities in the lower part of the crust in Sakhalin and Japan could evidently serve as a source of energy for the completion of future folding of this region.

The disproportion of changes in the velocities of the P and S waves with change in pressure on the rock samples suggest the possibility of discriminating the predominant directions (horizontal or vertical) of past tectonic stresses. A study of the changes in velocities of the P and S waves in the tectonically weakened regions of the crust may provide information on the present stress state of the earth. —Author.  相似文献   

5.
A spore-pollen assemblage was established for the first time in the sediments of the Malokuril??skaya Formation (Khromova Bay, Shikotan Island, Lesser Kuril Range, Kuril island arc system). This find enabled dating of the sediments of the uppermost part of the Malokuril??skaya Formation, which, based on this data, are referred to the Maastrichtian-Danian boundary. The assemblage of radiolarian species was identified for the entire section of the Malokuril??skaya Formation. In sediments of the lower part of the section, members of the Inoceramus group were described. These findings add new information to the paleontological characteristics of the Malokuril??skaya Formation. Moreover, our work allowed detailed correlation of the palynological assemblage studied with coeval palynological assemblages of adjacent areas. The similarity of Cretaceous-Paleogene sections of the Ust-Palanskaya (West Kamchatka), Uchir (Sakhalin Island) and Malokuril??skaya Formations, the Upper Cretaceous basement and the Cenozoic cover of the underwater Vityaz Ridge support the shared history of the development of the entire transition zone from the marginal Sea of Okhotsk to the Pacific at the Maastrichtian-Danian boundary.  相似文献   

6.
Recently, representatives of the genus Cuboctostylus Bragina (order Entactinaria) were included in the Upper Cretaceous radiolarian regional stratigraphic scale of Sakhalin. The Late Cretaceous species Hexacromyum pergamenti Bragina (order Spumellaria) has morphological similarity to representatives of the genus Cuboctostylus. Peculiar features of H. pergamenti internal structure are considered. Collections of Upper Cretaceous radiolarians from southern Cyprus, Serbia, northern Turkey, Crimean Mountains, East European Platform, northwestern Kamchatka, eastern slope of the Sredinnyi Range in Kamchatka, and Shikotan Island (Lesser Kurile Range) were used for the analysis of the taxonomic composition of Late Cretaceous representatives of the genera Cuboctostylus Bragina and Hexacromyum Haeckel as well as their stratigraphic and paleobiogeographic distribution. It is established that Cuboctostylus is distributed from tropical to south boreal realms. This genus is shown to exist through almost the entire Late Cretaceous: from the middle Cenomanian to initial Maastrichtian. Hexacromyum Haeckel populated both the south boreal realm and marginal areas of the Tethys Ocean in the Late Cretaceous. The new data presented may be used for distant interregional correlations. Cuboctostylus stellatus sp. nov. and several other Cuboctostylus taxa identified in open nomenclature are described; some morphological features of Hexacromyum pergamenti are specified.  相似文献   

7.
The seismic anisotropy of the mantle is studied based on the data of S and ScS waves from earthquakes occurred in the mantle transition zone over the period of 2007–2013 and recorded by seismic stations in the continental margin of Asia, on Sakhalin Island, and in the southern part of the Kamchatka Peninsula. The measurements of the azimuths of polarization of the fast S and ScS waves in the continental margin of Asia show that they are predominantly oriented in the E–SE directions. Based on the distribution of the shear wave splitting parameters, the symmetry of the medium can be described in terms of a transversely isotropic model with a horizontal symmetry axis and may correspond to horizontal flow in the upper mantle beneath the Amur Plate. The fast azimuths of polarization of ScS wave, which were determined to be of N–NE directions in the northern area of Sakhalin Island and in the continental part of Asia, may correspond to an inclined flow under the conditions of oblique subduction and complex geometry of the downgoing Pacific Plate. In the south of the Kamchatka Peninsula, the S- and ScS-wave azimuths of polarization from the M 8.4 Sea of Okhotsk earthquake are determined to be oriented along the direction of the Pacific Plate motion. The fast-S-wave azimuths of polarization from the aftershocks of the Sea of Okhotsk earthquake and from other large events of 2008–2009 are determined to be nearly parallel to the motion trend of the Pacific Plate, but orthogonal to it for the events of 2008–2009. On the basis of the distribution of azimuths of polarization of the fast S waves, the symmetry of the medium can be described in terms of a transversely isotropic model with the symmetry axis inclined orthogonally to the plane of downgoing plate and oriented westward orthogonally to the trench strike.  相似文献   

8.
Data on spores, pollen, and dinoflagellate cysts studied in composite section of Oligocene-Miocene deposits in southern part of West Siberia are presented. Eleven biostratigraphic units distinguished in the section are ranked as palynozones and beds with palynological assemblages. Palynological data substantiate age of deposits and specify ranges and boundaries of palynozones. Based on dinocyst assemblages first studied in sediments of the Zhuravka and Abrosimovo horizons (upper Oligocene, lower Miocene), the Pseudokomewuia Beds are included into local stratigraphic scheme. According to results of comparative analysis, similar and distinctive features of Oligocene-Miocene dinocyst assemblages from West Siberia, China and North America are elucidated. Based on palynological data, the local stratigraphic scheme of higher resolution is suggested for subdivision of Oligocene and Miocene deposits in southern part of West Siberia (Baraba and Kulunda lithofacies regions).  相似文献   

9.
Vegetation and climate during the last glacial maximum in Japan   总被引：1，自引：0，他引：1  
The Japanese Archipelago was almost entirely covered by coniferous forests during the last glacial maximum. Northern Hokkaido was distinguished by coniferous parkland and tundra vegetation, while southern Hokkaido and northernmost Honshu were covered by northern boreal coniferous forests consisting mainly of Picea jezoensis, Picea glehnii, Abies sachalinensis, and Larix gmelinii; Tsuga was missing from the forest. More diverse boreal forests including species from Sakhalin and northern Japan grew together in northeastern Honshu. Central Honshu and the mountains of southwestern Japan supported subalpine coniferous forests which are now mainly restricted in distribution to the central mountains. Temperate coniferous forests (Picea polita, Abies firma, and Tsuga sieboldii) existed principally in the modern mid-temperate and evergreen laurel-oak forest regions. Haploxylon pine and tree birch were also abundant in the boreal and cool-temperate zones, as was Diploxylon in the southern temperate zone. Significant populations of Fagus were found along the Pacific coasts of Kyushu and Shikoku, but they were too small to be defined as a beech forest zone. Quercetum mixtum (Quercus, Ulmus, and Tilia) was more common in the coastal lowlands of southwestern Japan than those of northeastern Honshu; it was completely eliminated from Hokkaido. The reduced mean August temperature inferred from the floral assemblages showed a latitudinal gradient 20,000 yr ago; it was 8–9°C in northern Hokkaido, 7.7–8.7°C in northernmost Honshu, 7.2–8.4°C in the central mountains, 6.5°C in the Chugoku District, and 5–6°C in Kyushu. The probable annual precipitation ranged from 1050 to 1300 mm along coasts in southwestern Japan during the culmination of the last glaciation.  相似文献   

10.
The most complete characterization of Dictyochophyceae (silicoflagellate) assemblages from sediments of the Kronotskii Bay, Eastern Kamchatka, which are typical of the Corbisema hexacantha (Middle Eocene) and Naviculopsis foliacea (terminal middle-initial Late Eocene) zones in the tropical/subtropical zonation by Bukry (1981), is considered for the first time. In total, 43 silicoflagellate species of 8 genera are identified. The prevalence of species of the genera Corbisema and Dictyocha in the assemblages suggest warm, close to subtropical conditions in a sea basin that existed in the Eastern Kamchatka region during the Middle-Late Eocene.  相似文献   

11.
More than 65 potentially active volcanoes on the Kamchatka Peninsula and the Kurile Islands pose a substantial threat to aircraft on the Northern Pacific (NOPAC), Russian Trans-East (RTE), and Pacific Organized Track System (PACOTS) air routes. The Kamchatka Volcanic Eruption Response Team (KVERT) monitors and reports on volcanic hazards to aviation for Kamchatka and the north Kuriles. KVERT scientists utilize real-time seismic data, daily satellite views of the region, real-time video, and pilot and field reports of activity to track and alert the aviation industry of hazardous activity. Most Kurile Island volcanoes are monitored by the Sakhalin Volcanic Eruption Response Team (SVERT) based in Yuzhno-Sakhalinsk. SVERT uses daily moderate resolution imaging spectroradiometer (MODIS) satellite images to look for volcanic activity along this 1,250-km chain of islands. Neither operation is staffed 24 h per day. In addition, the vast majority of Russian volcanoes are not monitored seismically in real-time. Other challenges include multiple time-zones and language differences that hamper communication among volcanologists and meteorologists in the US, Japan, and Russia who share the responsibility to issue official warnings. Rapid, consistent verification of explosive eruptions and determination of cloud heights remain significant technical challenges. Despite these difficulties, in more than a decade of frequent eruptive activity in Kamchatka and the northern Kuriles, no damaging encounters with volcanic ash from Russian eruptions have been recorded.  相似文献   

12.
The biotic turnover in the Pliensbachian-Toarcian transition and changes in assemblages of bivalves, ostracodes, foraminifers, dinocysts, spores, and pollen are described. Only five of 24 bivalve genera and two of four ostracode genera cross the Pliensbachian-Toarcian boundary so that composition of genera and families to be entirely renewed at the base of the Harpoceras falciferum Zone. In the interval of three ammonite zones, diversity of foraminifers is reducing from 27 genera in the Amaltheus margaritatus Zone (upper Pliensbachian) to 17 and then to 15 genera in the Tiltoniceras antiquum (lower Toarcian) and Harpoceras falciferum zones, respectively. Single dinocysts of the Pliensbachian are replaced by their abundant specimens at the base of the Toarcian, and substantial changes in composition of palynological assemblages are simultaneously established. Factors responsible for “mass extinctions” of marine invertebrates are suggested to be the paleogeographic reorganization, anoxic events, eustatic sea-level changes, and climatic fluctuations. The biotic turnover in the Arctic region is interrelated mainly with thermal changes, which caused the southward displacements of taxa distribution areas during a rapid cooling and their gradual return to former habitat areas in the period of warming, rather than with extinction events.  相似文献   

13.
Detailed seismic zoning of Sakhalin based on seismological, tectonic, geomorphological, hydrogeological, and other data is discussed. It is shown that strong crustal earthquakes occurred at the boundary between the Eurasian and Okhotsk plates and their recurrence in Central Sakhalin is equal to the duration of the tectonic cycle (75 years). This boundary in North Sakhalin is marked by the Upper-Piltun fault, which was the epicenter of the 1995 Neftegorsk earthquake with an intensity of 9. The analysis of paleosoils in the fault zone showed that such events repeat with an interval of 400 years. The development of large oil and gas reservoirs on the Sakhalin shelf will be accompanied by intensification of the seismicity, which can reach a magnitude of M = 6.0–6.5 in the Lunskoye field.  相似文献   

14.
The Upper Cretaceous Toyajo Formation is distributed around the Mt. Toyajo in the Aridagawa area, Wakayama, southwestern Japan. The formation is subdivided into three newly defined members, the Nakaibara Siltstone Member, Hasegawa Muddy Sandstone Member, and Buyo Sandstone Member, in ascending order. Close field observation elucidated the detailed biostratigraphy of the Toyajo Formation, and high-precision biostratigraphic correlation was made with the Yezo Group in Hokkaido (northern Japan) and Sakhalin and the Izumi Group in southwestern Japan.The Toyajo Formation contains diversified lower Campanian to upper Campanian heteromorph ammonoid assemblages, including Eubostrychoceras and Scaphites. Discovery of the heteromorph fauna demonstrates that scaphitid ammonoids survived until Campanian time in the northwestern Pacific region. Although Eubostrychoceras elongatum has been known in the northeastern Pacific region, the occurrence of this species in the northwestern Pacific region has been uncertain before. The rich occurrence of E. elongatum in the Aridagawa area indicates that this species was distributed widely in the northern Pacific realm.The Toyajo Formation is similar to the Izumi Group in various geologic features, and may indicate that the Toyajo Formation was deposited in a strike-slip basin along the Chichibu Belt formed by the movement along the Kurosegawa Tectonic Zone in the latest Cretaceous, like the Izumi Group, along the Median Tectonic Line.  相似文献   

15.
Diatom assemblages from the marine Paleogene of Western Kamchatka (the Kovachina, Viventek, and Kuluven formations) are studied. The shallow-water neritic assemblage from the Kovachina Formation of the Pyatibratskii Cape section is tentatively attributed to the middle Eocene, as it is lacking zonal index species. A high abundance and great taxonomic diversity are characteristic of diatoms from the upper part of the Viventek Formation in the Kovran River section. The zonal index species Cavitatus rectus identified here among the diatoms suggests that the respective assemblage is macerated from the synonymous diatom zone of the middle Oligocene (29.6?28.2 Ma). According to its taxonomic composition and structure, this assemblage is indicative of transgression environments and the presumable influence of the middle Oligocene climatic optimum. The Rocella gelida (upper part) and Thalassiosira praefraga diatom zones of the Oligocene-Miocene transition are established in the Kuluven Formation sediments of the Mt. Uvuch section in Kovachina Bay.  相似文献   

16.
In this study we utilize marine shell samples from two levels of historically uplifted sessile mollusk assemblages and raised wave-cut benches to evaluate the marine reservoir correction (ΔR) for the Pacific coast of central Japan. Elevation measurements of the uplifted marine shells indicate that the lower assemblage emerged during the 1923 Taisho Kanto earthquake (M7.9), whereas uplift of the upper assemblage is most likely but less confidently ascribed to the 1703 Genroku Kanto earthquake (M8.2). Radiocarbon dating of carefully selected samples from the upper and lower assemblages yielded very similar ΔR values of 82 ± 33 and 77 ± 32 yr, respectively. We regard the former ΔR value as a representative and more reliable value given the uncertainty in correlation of the upper assemblage with the 1703 earthquake. This result is consistent with previously reported ΔR values for the Pacific coast of south-central Japan and areas around the Sea of Japan that are influenced by warm ocean currents. Radiocarbon dating of coseismically uplifted shells can aid in estimating marine reservoir ages in the tectonically active Japan Islands.  相似文献   

17.
Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.  相似文献   

18.
The biofacies analysis of benthic foraminifers in sediments of the Sea of Okhotsk paleobasin revealed the presence of typical abyssal species in their Oligocene-Miocene assemblages that are missing in the Pliocene and Pleistocene section. The development of the abyssal fauna in the Sea of Okhotsk was determined by its relatively large depths (>2000 m) and intense water exchange with the Pacific Ocean. The Sakhalin folding phase at the Neogene-Quaternary transition resulted in the uplifting of the Japan-Kurile cordillera and separation of deep basins of the Japan and Okhotsk seas from the ocean, which was responsible for the formation of unfavorable conditions for migration and existence of the Pacific abyssal fauna. The taxonomic similarity and general tendencies in the development of the Neogene benthic foraminifers common for the Japan and Okhotsk seas imply the lack of narrow and shallow thresholds between these basins similar to the present-day Nevel’skoi, La Pérouse, and Sangar straits. Such bottom topography stimulated the intense northward water flow, which determined the similarity between the benthic foraminiferal assemblages of the Japanese and Okhotsk paleobasins.  相似文献   

19.
The results of studying dinocysts in the Upper Cretaceous-Lower Paleogene succession of the Kaliningrad region are considered. Distinguished in the succession are seven biostratigraphic units in the rank of the Palaeohystrichophora infusorioides, Chatangiella vnigrii, Cerodinium diebelii, Alisocysta margarita, Deflandrea oebisfeldensis, Areosphaeridium diktyoplokum, and Rhombodinium perforatum beds and one Charlesdowniea clathrata angulosa Zone. The Lyubavas Formation has not been distinguished on the west of the Sambian Peninsula. Ages of the Sambia, Alka, and Prussian formations are verified.  相似文献   

20.
This paper reports the results of the first comprehensive petrological study of mafic enclaves widespread in the products of recent (2006–2012) eruptions of Bezymianny Volcano, Kamchatka. Four types of mafic enclaves were distinguished on the basis of the composition and morphology of minerals, P–T conditions of formation of mineral assemblages, and structural and textural characteristics of the rocks. Disequilibrium assemblages of mafic enclaves indicate a complex structure of the magmatic plumbing system of the volcano, including a shallow chamber with andesite–basaltic andesite magmas and a deep reservoir filled in part with plagioclase–hornblende cumulates and fed by basic magmas with mantle harzburgite xenoliths. The mafic enclaves were formed at different levels of the magmatic plumbing system of the volcano and correspond to different degrees of mixing of interacting magmas. The most abundant enclaves were formed during magma ascent from the deep reservoir (960–1040°C, 5–9 kbar) into the shallow andesitic chamber (940–980°C). Enclaves of plagioclase–hornblende cumulates from the basic magmas feeding the deep reservoir (T > 1090°C and P > 9 kbar) are much less common.  相似文献   

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