The nature of scattered and concretion pyrite in the Upper Abalak Formation of the Salym oil field (Western Siberia)     

A. Iu. Iurchenko  N. Takahata  K. Tanaka  Y. Sano  N. S. Balushkina  G. A. Kalmykov 《Moscow University Geology Bulletin》2016,71(6):466-471

Dispersed and concretionary pyrite in chert–clay–carbonate and carbonate rocks of the Abalak Formation (Salym oil field) have been studied. The study was conducted using Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), and high spatial resolution Secondary Ion Mass Spectrometry (Nano-SIMS). As a result, three morphological groups of pyrite have been distinguished: large cubic crystals, framboidal pyrite, and fine-crystal aggregates that replace organic remnants. The sulphur isotope ratio allows one to distinguish two genetic types of pyrite. The source of the sulphur for the first genetic group was H₂S produced by bacterial sulphate reduction, while the second group pyrite was formed with sulphur as a product of thermochemical sulphate reduction.  相似文献   

Displaced dolomites in radiolarian cherts of the Chichibu Belt on Shikoku Island,Southwest Japan     

Hiroyoshi Sano 《Sedimentary Geology》1984,37(3):203-223

The northern tract of the Chichibu Belt on Shikoku Island, Southwest Japan, in places contains dolomites of Late Carboniferous age displaced into radiolarian cherts. The sections here examined are along the Niyodo gorge, central Shikoku. The sequence begins with thinly interbedded dolomitized radiolarian cherts and dolomites with a small amount of dolomitized radiolarian claystone and calcisiltite beds. These rocks, 5–10 m thick, are succeeded by a thick section of bedded and massive dolomites, commonly 40–50 m thick, which have thin intercalations of radiolarian claystone in the upper part. This dolomite sequence is depositionally overlain by a sequence, up to 50 m thick, comprising thinly interbedded radiolarian cherts and claystones, which, in turn, contain lenticular bodies of dolomite.Thin-section examination reveals that most of dolomites of the area have an arenitic or lithic texture, and should be termed doloarenite and dololithite. This means that dolomites are detrital. All lines of evidence suggest that the dolomites were not formed in the same depositional site in which the radiolarian cherts were being accumulated, but formed instead as allochthonous bodies which were displaced into a deep oceanic basin of chert deposition.The following sequence of events is postulated: (1) deposition of shallow-water calcareous sediments in a subtidal area; (2) dolomitization in a very shallow-water to supratidal environment; (3) displacement of dolomitized sediments, possibly mainly as debris flows into a deep-water, truely pelagic realm, in which siliceous radiolarian sediments were accumulating; (4) continued accumulation of siliceous sediments after the major influx of dolomitized sediments; and (5) minor influxes of dolomitized sediments during the continuous accumulation of siliceous sediments.  相似文献   

Triassic mid-oceanic sedimentation in Panthalassa Ocean: Sambosan accretionary complex, Japan     

Tetsuji  Onoue  Hiroyoshi  Sano 《Island Arc》2007,16(1):173-190

Abstract   The Sambosan accretionary complex of southwest Japan was formed during the uppermost Jurassic to lowermost Cretaceous and consists of basaltic rocks, carbonates and siliceous rocks. The Sambosan oceanic rocks were grouped into four stratigraphic successions: (i) Middle Upper Triassic basaltic rock; (ii) Upper Triassic shallow-water limestone; (iii) limestone breccia; and (iv) Middle Middle Triassic to lower Upper Jurassic siliceous rock successions. The basaltic rocks have a geochemical affinity with oceanic island basalt of a normal hotspot origin. The shallow-water limestone, limestone breccia, and siliceous rock successions are interpreted to be sediments on the seamount-top, upper seamount-flank and surrounding ocean floor, respectively. Deposition of the radiolarian chert of the siliceous rock succession took place on the ocean floor in Late Anisian and continued until Middle Jurassic. Oceanic island basalt was erupted to form a seamount by an intraplate volcanism in Late Carnian. Late Triassic shallow-water carbonate sedimentation occurred at the top of this seamount. Accumulation of the radiolarian chert was temporally replaced by Late Carnian to Early Norian deep-water pelagic carbonate sedimentation. Biotic association and lithologic properties of the pelagic carbonates suggest that an enormous production and accumulation of calcareous planktonic biotas occurred in an open-ocean realm of the Panthalassa Ocean in Late Carnian through Early Norian. Upper Norian ribbon chert of the siliceous rock succession contains thin beds of limestone breccia displaced from the shallow-water buildup resting upon the seamount. The shallow-water limestone and siliceous rock successions are nearly coeval with one another and are laterally linked by displaced carbonates in the siliceous rock succession.  相似文献   

Short-term temperature and salinity variations in the Tsushima Strait in 2004: Behavior of the surface low-salinity water in the strait     

Kosuke Mori  Takeshi Matsuno  Tomoharu Senjyu  Naoki Hirose  In-Seong Han 《Journal of Oceanography》2009,65(3):301-310

Temporal variations in temperature and salinity observed in 2004 were investigated on a short time scale in the Tsushima Strait. The data were obtained by long-term in situ measurements at Mitsushima and Futaoi Island using an instrument equipped with a piston-type wiper to avoid biofouling. In addition, the temperature and salinity values of the surface layer obtained by a commercial ferryboat between Hakata and Busan were used to investigate their spatiotemporal variations. Temperature and salinity variations with a time scale of several days had a negative correlation in the summer. This evidence suggests that a warm and less saline water mass, which is considered to be mainly the Changjiang Diluted Water (CDW), flowed intermittently through the Tsushima Strait in summer. In late July 2004, a large low-salinity water mass was detected in the Tsushima Strait. At that time, the freshwater transport through the Tsushima Strait transiently reached about 12 × 10⁴ m³s⁻¹, which is estimated from observed acoustic Doppler current profiler (ADCP) data along a ferryboat line and inferred salinity profiles. This estimated value is more than double the maximum of the climatological monthly mean of the Changjiang discharge. Furthermore, salinity and surface current data obtained by high frequency ocean radar (HF radar) indicate that water properties at Mitsushima may occasionally represent part of the water flowing through the western channel via a countercurrent, although Mitsushima is geographically located in the eastern channel.  相似文献   

A multi-proxy reconstruction of spatial and temporal variations in Asian summer temperatures over the last millennium   总被引：1，自引：0，他引：1  

Feng?Shi  Quansheng?GeEmail author  Bao?Yang  Jianping?Li  Fengmei?Yang  Fredrik?Charpentier?Ljungqvist  Olga?Solomina  Takeshi?Nakatsuka  Ninglian?Wang  Sen?Zhao  Chenxi?Xu  Keyan?Fang  Masaki?Sano  Guoqiang?Chu  Zexin?Fan  Narayan?P.?Gaire  Muhammad?Usama?Zafar 《Climatic change》2015,131(4):663-676

To investigate climate variability in Asia during the last millennium, the spatial and temporal evolution of summer (June–July–August; JJA) temperature in eastern and south-central Asia is reconstructed using multi-proxy records and the regularized expectation maximization (RegEM) algorithm with truncated total least squares (TTLS), under a point-by-point regression (PPR) framework. The temperature index reconstructions show that the late 20th century was the warmest period in Asia over the past millennium. The temperature field reconstructions illustrate that temperatures in central, eastern, and southern China during the 11th and 13th centuries, and in western Asia during the 12th century, were significantly higher than those in other regions, and comparable to levels in the 20th century. Except for the most recent warming, all identified warm events showed distinct regional expressions and none were uniform over the entire reconstruction area. The main finding of the study is that spatial temperature patterns have, on centennial time-scales, varied greatly over the last millennium. Moreover, seven climate model simulations, from the Coupled Model Intercomparison Project Phase 5 (CMIP5), over the same region of Asia, are all consistent with the temperature index reconstruction at the 99 % confidence level. Only spatial temperature patterns extracted as the first empirical orthogonal function (EOF) from the GISS-E2-R and MPI-ESM-P model simulations are significant and consistent with the temperature field reconstruction over the past millennium in Asia at the 90 % confidence level. This indicates that both the reconstruction and the simulations depict the temporal climate variability well over the past millennium. However, the spatial simulation or reconstruction capability of climate variability over the past millennium could be still limited. For reconstruction, some grid points do not pass validation tests and reveal the need for more proxies with high temporal resolution, accurate dating, and sensitive temperature signals, especially in central Asia and before AD 1400.  相似文献   

Sr and Nd isotope compositions of atmospheric mineral dust at the summit of Mt. Sefuri, north Kyushu, southwest Japan: A marker of the dust provenance and seasonal variability     

Tomoharu Miyamoto  Reiko Hamamoto  Takeru Yanagi 《Geochimica et cosmochimica acta》2010,74(5):1471-1484

We analyzed Rb-Sr-Nd isotope ratios of mineral dust in total aerosol load collected with rainwater continuously from 1998 to 2006 at the summit of Mt. Sefuri, northern Kyushu, southwestern Japan. During this period, the total mass of the dust generally increased in late winter, peaked in early spring, and then decreased.⁸⁷Sr/⁸⁶Sr in atmospheric mineral dust varied from 0.7096 to 0.7180, and εNd(0)_CHUR from −19.9 to −3.5. During heavy deposition periods, the dust had high ⁸⁷Sr/⁸⁶Sr isotope ratios and low to middle εNd(0)_CHUR values, respectively. These compositions are comparable to those of sand and loess in arid areas of Northeast China, Takla Makan and Western Beijing. Such particles were transported by westerlies from those areas to northern Kyushu in winter and spring. In summer and autumn, the isotopic compositions of the dust varied greatly; however, during light deposition periods, the Sr isotope composition was low. In these seasons, the contributions to the dust from Japanese soils and volcanic ash, transported by southern winds, were relatively larger than in winter and spring because of decreased mineral dust particle transport from the continent. Nevertheless, fine sandy desert particles and loess in general accounted for most mineral dust deposition in northern Kyushu year-round, even in summer. Local soils derived from weathered granite and volcanic ash were minor components only.The net mass of water-insoluble inorganic matter in the collected mineral dust fluctuated from year-to-year; deposition on Mt. Sefuri was relatively large before 2001, decreased from 2002 to 2005, and increased greatly in spring 2006. These year-to-year differences probably reflected changes in the strength of the westerlies and in climate conditions in the arid source areas.  相似文献   

Synthesis of highly dense and fine-grained aggregates of mantle composites by vacuum sintering of nano-sized mineral powders     

Sanae Koizumi  Takehiko Hiraga  Chihiro Tachibana  Miki Tasaka  Tomonori Miyazaki  Tamio Kobayashi  Asako Takamasa  Naoki Ohashi  Satoru Sano 《Physics and Chemistry of Minerals》2010,37(8):505-518

Synthesized mineral powders with particle size of <100 nm are vacuum sintered to obtain highly dense and fine-grained polycrystalline mantle composites: single phase aggregates of forsterite (iron-free), olivine (iron containing), enstatite and diopside; two-phase composites of forsterite + spinel and forsterite + periclase; and, three-phase composites of forsterite + enstatite + diopside. Nano-sized powders of colloidal SiO₂ and highly dispersed Mg(OH)₂ with particle size of ≤50 nm are used as chemical sources for MgO and SiO₂, which are common components for all of the aggregates. These powders are mixed with powders of CaCO₃, MgAl₂O_4, and Fe(CO₂CH₃)₂ to introduce mineral phases of diopside, spinel, and olivine to the aggregates, respectively. To synthesize highly dense composites through pressureless sintering, we find that calcined powders should be composed of particles that have: (1) fully or partially reacted to the desired minerals, (2) a size of <100 nm and (3) less propensity to coalesce. Such calcined powders are cold isostatically pressed and then vacuum sintered. The temperature and duration of the sintering process are tuned to achieve a balance between high density and fine grain size. Highly dense (i.e., porosity ≤1 vol%) polycrystalline mantle mineral composites with grain size of 0.3–1.1 μm are successfully synthesized with this method.  相似文献   

Clinopyroxene REE Geochemistry of the Red Hills Peridotite, New Zealand: Interpretation of Magmatic Processes in the Upper Mantle and in the Moho Transition Zone   总被引：1，自引：0，他引：1  

Sano  Sakae; Kimura  Jun-Ichi 《Journal of Petrology》2007,48(1):113-139

The Red Hills peridotite in the Dun Mountain ophiolite of SouthIsland, New Zealand, is assumed to have been produced in a paleo-mid-oceanridge tectonic setting. The peridotite is composed mostly ofharzburgite and dunite, which represent residual mantle andthe Moho transition zone (MTZ), respectively. Dunite channelswithin harzburgite blocks of various scales represent the MTZcomponent. Plagioclase- and clinopyroxene-bearing dunites occursporadically within common dunites. These dunites representproducts of melt–wall-rock interaction. Chondrite-normalizedrare earth element (REE) patterns of MTZ clinopyroxenes showa wide compositional range. Clinopyroxenes in plagioclase dunitesare extremely depleted in light REE (LREE) ([Lu/La]_N >100),and are comparable with clinopyroxenes in abyssal peridotitesfrom normal mid-ocean ridges. Interstitial clinopyroxenes inthe common dunite have flatter patterns ([Lu/La]_N 2) comparablewith those for dunite in the Oman ophiolite. Clinopyroxenesin the lower part of the residual mantle harzburgites are evenmore strongly depleted in LREE ([Lu/La]_N = 100–1000) thanare mid-ocean ridge peridotites, and rival the most depletedabyssal clinopyroxenes reported from the Bouvet hotspot. Incontrast, those in the uppermost residual mantle harzburgiteand harzburgite blocks in the MTZ are less LREE depleted ([Lu/La]_N= 10–100), and are similar to those in plagioclase dunite.Clinopyroxenes in the clinopyroxene dunite in the MTZ are similarto those reported from mid-ocean ridge basalt (MORB) cumulates,and clinopyroxenes in the gabbroic rocks have compositions similarto those reported from MORB. Strong LREE and middle REE (MREE)depletion in clinopyroxenes in the harzburgite suggests thatthe harzburgites are residues of two-stage fractional melting,which operated initially in the garnet field, and subsequentlycontinued in the spinel lherzolite field. The early stage meltingproduced the depleted harzburgite. The later stage melting wasresponsible for the gabbroic rocks and dunite. Strongly LREE–MREE-depletedclinopyroxene in the lower harzburgite and HREE-enriched clinopyroxenein the upper harzburgite and plagioclase dunite were formedby later reactive melt migration occurring in the harzburgite. KEY WORDS: clinopyroxene REE geochemistry; Dun Mountain ophiolite; Moho transition zone; orogenic peridotite; Red Hills  相似文献   

Tree-ring reconstructed summer temperature anomalies for temperate East Asia since 800 C.E.     

Edward R. Cook  Paul J. Krusic  Kevin J. Anchukaitis  Brendan M. Buckley  Takeshi Nakatsuka  Masaki Sano 《Climate Dynamics》2013,41(11-12):2957-2972

We develop a summer temperature reconstruction for temperate East Asia based on a network of annual tree-ring chronologies covering the period 800–1989 C.E. The East Asia reconstruction is the regional average of 585 individual grid point summer temperature reconstructions produced using an ensemble version of point-by-point regression. Statistical calibration and validation tests indicate that the regional average possesses sufficient overall skill to allow it to be used to study the causes of temperature variability and change over the region. The reconstruction suggests a moderately warm early medieval epoch (ca. 850–1050 C.E.), followed by generally cooler ‘Little Ice Age’ conditions (ca. 1350–1880 C.E.) and 20th century warming up to the present time. Since 1990, average temperature has exceeded past warm epochs of comparable duration, but it is not statistically unprecedented. Superposed epoch analysis reveals a volcanic forcing signal in the East Asia summer temperature reconstruction, resulting in pulses of cooler summer conditions that may persist for several years. Substantial uncertainties remain, however, particularly at lower frequencies, thus requiring caution and scientific prudence in the interpretation of this record.  相似文献   

SHRIMP U–Pb zircon dating of quartz-bearing eclogite from the Sanbagawa Belt, south-west Japan: implications for metamorphic evolution of subducted protolith     

Kazuaki Okamoto  Hironao Shinjoe  Ikuo Katayama  Kentaro Terada  Yuji Sano  Simon Johnson 《地学学报》2004,16(2):81-89

In order to decipher the origin of eclogite in the high‐P/T Sanbagawa metamorphic belt, SHRIMP U–Pb ages of zircons from quartz‐bearing eclogite and associated quartz‐rich rock (metasandstone) were determined. One zircon core of the quartz‐rich rock yields an extremely old provenance age of 1899 ± 79 Ma, suggesting that the core is of detrital origin. Eight other core ages are in the 148–134 Ma range, and are older than the estimated age for trench sedimentation as indicated by the youngest radiolarian fossil age of 139–135 Ma from the Sanbagawa schists. Ages of metamorphic zircon rims (132–112 Ma) from the quartz‐rich rock are consistent with metamorphic zircon ages from the quartz‐bearing eclogite, indicating that eclogite facies metamorphism peaked at 120–110 Ma. These new data are consistent with both the Iratsu eclogite body and surrounding highest‐grade Sanbagawa schists undergoing coeval subduction‐zone metamorphism, and subsequent re‐equilibration under epidote amphibolite facies conditions during exhumation.  相似文献