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251.
J. N. Pattan Toshiyuki Masuzawa D. V. Borole G. Parthiban Pratima Jauhari Mineko Yamamoto 《Journal of Earth System Science》2005,114(1):63-74
A 2m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13‡03′S: 74‡44′E; water depth
5099m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements
(Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply.
The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ∼ 74 ka and Australasian microtektites
of ∼ 770 ka.
Low carbonate content (< 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon
content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water
environment during the past ∼ 1100ka. Our data suggest that during ∼ 1100 ka and ∼ 400 ka siliceous productivity was lower,
complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline.
However, during the last ∼ 400 ka, siliceous productivity increased with substantial reduction in the terrigenous sediment
supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher
prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their
burial to seafloor remained unaffected throughout the past ∼ 1100 ka. 相似文献
252.
253.
M. Akaogi H. Kojitani H. Yusa R. Yamamoto M. Kido K. Koyama 《Physics and Chemistry of Minerals》2005,32(8-9):603-613
Phase transitions in MgGeO3 and ZnGeO3 were examined up to 26 GPa and 2,073 K to determine ilmenite–perovskite transition boundaries. In both systems, the perovskite
phases were converted to lithium niobate structure on release of pressure. The ilmenite–perovskite boundaries have negative
slopes and are expressed as P(GPa)=38.4–0.0082T(K) and P(GPa)=27.4−0.0032T(K), respectively, for MgGeO3 and ZnGeO3. Enthalpies of SrGeO3 polymorphs were measured by high-temperature calorimetry. The enthalpies of SrGeO3 pseudowollasonite–walstromite and walstromite–perovskite transitions at 298 K were determined to be 6.0±8.6 and 48.9±5.8 kJ/mol,
respectively. The calculated transition boundaries of SrGeO3, using the measured enthalpy data, were consistent with the boundaries determined by previous high-pressure experiments.
Enthalpy of formation (ΔH
f°) of SrGeO3 perovskite from the constituent oxides at 298 K was determined to be −73.6±5.6 kJ/mol by calorimetric measurements. Thermodynamic
analysis of the ilmenite–perovskite transition boundaries in MgGeO3 and ZnGeO3 and the boundary of formation of SrSiO3 perovskite provided transition enthalpies that were used to estimate enthalpies of formation of the perovskites. The ΔH
f° of MgGeO3, ZnGeO3 and SrSiO3 perovskites from constituent oxides were 10.2±4.5, 33.8±7.2 and −3.0±2.2 kJ/mol, respectively. The present data on enthalpies
of formation of the above high-pressure perovskites were combined with published data for A2+B4+O3 perovskites stable at both atmospheric and high pressures to explore the relationship between ΔH
f° and ionic radii of eightfold coordinated A2+ (R
A) and sixfold coordinated B4+ (R
B) cations. The results show that enthalpy of formation of A2+B4+O3 perovskite increases with decreasing R
A and R
B. The relationship between the enthalpy of formation and tolerance factor (
R
o: O2− radius) is not straightforward; however, a linear relationship was found between the enthalpy of formation and the sum of
squares of deviations of A2+ and B4+ radii from ideal sizes in the perovskite structure. A diagram showing enthalpy of formation of perovskite as a function of
A2+ and B4+ radii indicates a systematic change with equienthalpy curves. These relationships of ΔH
f° with R
A and R
B can be used to estimate enthalpies of formation of perovskites, which have not yet been synthesized. 相似文献
254.
Hajime Obata Yoshiyuki Nozaki Yoshiyuki Yamamoto 《Geochimica et cosmochimica acta》2004,68(5):1035-1048
To carry out comparative geochemical investigation of refractory and reactive metals in different oceanic settings covering different θ-S characteristics, productivity, dissolved oxygen profiles, water and sediment discharge, etc., we have determined the vertical profiles of dissolved (<0.04 μm) Al, In and Ce, as well as 210Pb and 210Po in the eastern Indian Ocean (from 40°S in the Southern Ocean to 8°N in the Bay of Bengal) and the Southeast Asian Seas. In the Antarctic Circumpolar Region, the concentrations of these refractory metals are very low, presumably due to very low the atmospheric input and intensified scavenging. Resemblance in the vertical profiles of these metals is often seen in some other stations. However, there are also significant differences among their distributions, for example, in the magnitude of surface enrichment caused by the external input from eolian and fluvial-coastal sources. Comparison of Al distributions in surface waters with those of atmospherically derived 210Pb suggests the relative importance of eolian input over fluvial-coastal sources. Fluvial and coastal input appears to be insignificant for dissolved In, but may be important for Ce. The mean residence time of Al in the surface mixed layer was estimated to be ∼2 years which is similar to that of 210Pb.In the intermediate and deep waters, the concentrations of each element vary with depth and location. The range of variation is in the order of Al>Ce>In, depending upon particle reactivity. Although dissolved Al decreases along the water trajectory by particle scavenging, variations of dissolved In and Ce are relatively small which may be due to less scavenging for both elements. Compared with significantly high (>4 pM) dissolved Ce throughout the water column in the Bay of Bengal, dissolved Al concentration remains low, suggesting that it has higher affinity to particles and hence is scavenged by sinking particulate matter. This is consistent with the observation that the dissolved Al in the Antarctic Intermediate Water (AAIW) decreases from 4 to 6 nM in the 30°S Perth Basin to <0.7 nM in the 10°S West Australia Basin along its trajectory. Using the chlorofluorocarbons (CFCs) ventilation age of AAIW (Fine, 1993), the mean residence time of Al in the intermediate and deep waters in the eastern Indian Ocean is estimated to be <17 yr, approximately the same as that of 210Pb (10-15 yr). In the semiclosed basins of Southeast Asia, the distributions of Al, In and Ce are also very unique. In the South China Sea, there is a strong sediment source for dissolved In and Ce during the deepwater passage through the Luzon Strait. 相似文献
255.
Yalkun Yusuf Masashi Matsuoka Fumio Yamazaki 《Journal of the Indian Society of Remote Sensing》2001,29(1-2):17-22
In this paper, we present a method of earthquake damage detection by comparing the optical images with panchromatic bands for the Gujarat, India earthquake, which occurred on January 26, 2001. The data used in this study are optical remote sensing images taken by Landsat-7 satellite on January 8 and February 29, 2001, before and after the earthquake. We have investigated the pre and post-earthquake satellite images calculating the differences in the reflection intensity (digital number) of the two images. The estimated affected area has been subtracted on a pixel unit based on the obtained frequency distributions of the differences in the optical sensor values, which show significant changes in the reflectance due to the earthquake disaster. We have investigated the accuracy of our analysis result using a classification method for the training areas with aerial photographs taken after the earthquake. The two damage detection methods show a very similar result. 相似文献
256.
Kuroko and Hydrocarbon Deposits from Northern Honshu,Japan: A Possible Common Hydrothermal/Magmatic Origin? 总被引:1,自引:0,他引:1
Geoffrey P. Glasby Toshiro Yamanaka Junji Yamamoto Hiroshi Sato Kenji Notsu 《Resource Geology》2004,54(4):413-424
Abstract. Northern Honshu is the most important area for mineral and oil resources in Japan. Many kuroko deposits and oil and gas fields are distributed in two belts along the northeast Japan arc, the kuroko metal‐belt on the Pacific side and the oil‐belt on the Sea of Japan side. The kuroko deposits are located mainly in the Green Tuff strata which formed as a result of submarine vol‐canism during the late Miocene and Pliocene. Most of the source rocks of the oil and gas deposits formed at the same time as the kuroko deposits and some of them are located in reservoirs of hydrothermally‐altered volcanic rocks in the Green Tuff region. There is general agreement that the kuroko deposits formed as a result of submarine hydrothermal and magmatic activity whereas almost all petroleum geologists and geochemists consider that hydrocarbon deposits were generated independently of such activity. Since the discovery of hydrothermally‐generated petroleum in the Guaymas Basin, Gulf of California, however, it is clear that petroleum can be formed almost instantaneously in terrestrial and submarine hydrothermal areas. The paleo‐northeastern Sea of Japan is therefore considered to be a potential area for hydrothermal petroleum generation because thick organic‐rich sediments overlie an active submarine volcanic area. Several lines of geological and geochemical evidence suggest the possibility of hydrothermally‐enhanced maturation of organic matter and the contribution of magmatic activity to the formation of these deposits. Although most of the oil and gas in northern Honshu has been generated conventionally as a consequence of the high geothermal gradients there, it appears that some of the oil and gas fields may have formed as a result of extensive hydrothermal and magmatic activity during the late Miocene to Pliocene. Because of the much steeper angle of the faults in the vicinity of the Hokuroku basin than in the Akita basin, the magmatic contribution to the kuroko mineralization would have been far greater than to the oil and gas deposits of the Niigata and Akita basins. We therefore propose a strong relationship between metal and oil and gas generation in northern Honshu based on the structure and tectonics of the northern Honshu arc‐backarc system. 相似文献
257.
Tokujiro Takayama Masatoshi Nishi Hiroaki Yamamoto Yoshinori Sanada Shigemi Matsuda Takashi Uchida 《Resource Geology》2004,54(1):89-98
Abstract. The MITI Nankai Trough wells were drilled for exploration of methane-hydrate-bearing sediments in association with seismic inferred bottom simulating reflectors (BSRs). In this project, log data showed low velocity compressional-wave (P-wave) layers below methane-hydrate-bearing formations. Dipole shear sonic acoustic tools (DSI) could not acquire accurate compres-sional velocity in this zone, thus it was not possible to accurately correlate between logging, VSP and surface seismic profiles.
Small amount of gas was presumed to cause the problem in obtaining the low velocity P-wave data. VSP interval velocity data was used to assess the DSI inferred low-velocity layer, which showed lower values than the velocity of the drilling muds. Synthetic seismogram was created by VSP-compensated velocity to compare against corridor stack of VSP. As a result, the depths above and below the methane-hydrate-bearing interval were correlated with synthetic seismograms and reflectivity events on the VSP profiles. By using this correlation technique, distribution of methane-hydrate-bearing formations and free-gas-bearing formations can be determined. 相似文献
Small amount of gas was presumed to cause the problem in obtaining the low velocity P-wave data. VSP interval velocity data was used to assess the DSI inferred low-velocity layer, which showed lower values than the velocity of the drilling muds. Synthetic seismogram was created by VSP-compensated velocity to compare against corridor stack of VSP. As a result, the depths above and below the methane-hydrate-bearing interval were correlated with synthetic seismograms and reflectivity events on the VSP profiles. By using this correlation technique, distribution of methane-hydrate-bearing formations and free-gas-bearing formations can be determined. 相似文献
258.
Yukinori Tani Kota Kurihara Fumiko Nara Nobuyasu Itoh Mitsuyuki Soma Yuko Soma Atsushi Tanaka Minoru Yoneda Masashi Hirota Yasuyuki Shibata 《Organic Geochemistry》2002,33(12)
Photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of Lake Baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial/post-glacial transition. The sedimentation age of the core spans the last 24 14C ka. Chlorophyll a, its derivatives, carotenoids and total organic carbon (TOC) started to increase after 15 14C ka, and the onset of biogenic silica occurred at 10 14C ka. This indicated that the post-glacial growth of diatoms was preceded by that of other phytoplankton groups. In the record of the pigments and TOC, a temporary decrease was observed in the period 11.5–10.5 14C ka, corresponding to the Younger Dryas cold period. The similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of TOC suggested the important contribution of fecal pellets to sedimentary organic matter in the lake. 相似文献
259.
We describe an active right-lateral strike-slip fault zone along the southern margin of the Japan Sea, named the Southern Japan Sea Fault Zone (SJSFZ). Onshore segments of the fault zone are delineated on the basis of aerial photograph interpretations and field observations of tectonic geomorphic features, whereas the offshore parts are interpreted from single-/multichannel seismic data combined with borehole information. In an effort to evaluate late Quaternary activity along the fault zone, four active segments separated by uplifting structures are identified in this study. The east–northeast-trending SJSFZ constitutes paired arc-parallel strike-slip faults together with the Median Tectonic Line (MTL), both of which have been activated by oblique subduction of the Philippine Sea plate during the Quaternary. They act as the boundaries of three neotectonic stress domains around the eastern margin of the Eurasian plate: the near-trench Outer zone and NW–SE compressive Inner zone of southwest Japan arc, and the southern Japan Sea deformed under E–W compression from south to north. 相似文献
260.
Oishi ShujiDepartment of Environmental Science Technology Faculty of Engineering Shinshu University Wakasato Nagano - JapanYamamoto HirofumiDepartment of Chemistry Material Engineering Faculty of Engineering Shinshu University 《中国地质大学学报(英文版)》2002,13(1):35-39
Well-formed crystals of emerald, Be3AI2Si6O18:Cr, were easily grown from an Na2O-MoO3 flux by an isothermal technique. The crystal growth was conducted by heating a mixture of solute and flux at 1 100 ℃ for 24 h. The evaporation loss of flux depended on the amount of Na2O added to MoO3. Emerald crystals of lengths up to 2.1 mm and widths of 1. 4 mm were grown. The crystal sizes were dependent on the evaporation loss of the flux. The obtained crystals were transparent and exhibited the typical emerald-green color. The form of the emerald crystals was a twelve-sided prism bounded by well-developed faces. The aspect ratios were in the region of 1. 4 to 2. 3. The density was (2. 64±0.02) g/cm3. The IR absorption bands were in good agreement with the literature data. 相似文献