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91.
Hideki Wada Toshihiro Tomita Kazuhiro Matsuura Keisuke Tuchi Masahiro Ito Toshiro Morikiyo 《Contributions to Mineralogy and Petrology》1994,118(3):217-228
This study is an attempt to correlate the graphitization process of carbonaceous matter during metamorphism with metamorphic grade. Graphitization can be parameterized using crystal structure and chemical and isotopic compositions. The extent of graphitization could be characterized mainly by temperature, duration of metamorphism and rock composition. We compared the graphitization trends for two metamorphic terrains, a contact aureole of the Kasuga area and a regional metamorphic terrain of high-temperature/low pressure type of the Ryoke metamorphic terrain in Northern Kiso area, Central Japan, and for two different lithologies (carbonate and pelite), using X-ray diffractogram, DTA-TG analysis, and chemical and stable isotope analyses. During contact metamorphism, graphitization and carbon isotopic exchange reactions proceeded simultaneously in pelitic and carbonate rocks. The decreases in basal spacing d(002) of the carbonaceous matter in carbonate rocks is greatly accelerated at temperatures higher than about 400° C. Furthermore, carbon isotopic ratios of graphite in carbonate rocks also change to 13C-enriched values implying exchange with carbonates. The beginning of this enrichment of 13C in the carbonaceous matter coincides with an abrupt increase of the graphitization processes. Carbon isotopic shifting up to 5 in pelites could be observed as metamorphic temperature increased probably by about 400° C. Carbonaceous matter in pelitic rocks is sometimes a mixture of poorly crystallized organic matter and well-crystallized graphite detritus. DTA-TG analysis is an effective tool for the distinction of detrital graphitic material. Two sources for the original carbon isotopic composition of carbonaceous matter in pelites in the Kasuga contact aureole can be distinguished, about-28 and-24 regardless of the presence of detrital graphite, and were mainly controlled by depositional environment of the sediments. Graphitization in limestones and pelitic rocks in regional metamorphism proceeds further than in a contact aureole. In the low-temperature range, the differences in extent of graphitization between the two metamorphic regions is large. However, at temperatures higher than 600° C, the extent of graphitization in both regions is indistinguishable. The degree of graphitization is different in limestones and pelitic rocks from the Ryoke metamorphic terrain. We demonstrate that the graphitization involves a progressive re-construction process of the crystal structure. The sequence of the first appearance of crystal inter planar spacing correlates with the metamorphic grade and indicates the crystal growth of three-dimensional structured graphite. 相似文献
92.
We investigated the biogenic components (biogenic opal, calcium carbonate, and organic carbon) of the marine sediments in core TY99PC18 recovered from the southeastern part of the Ulleung Basin, East Sea (Japan Sea). Our results indicate that primary productivity by diatoms increased after the last glaciation (15,000 14C years b.p.) probably because of the onset of vertical mixing of seawater and nutrient supply from the deep water. Between 5,000 and 10,000 14C years b.p. a shift in the dominant primary producer, i.e. from diatoms to coccolithophores, coincides with decreased productivity, which could be related to the influx of warm, low-nutrient waters at that time. During the late Holocene (after 5,000 14C years b.p.) the productivity of diatoms increased once more probably due to renewed ventilation and vertical mixing. 相似文献
93.
Ba and Ti in a sediment core (10 m long) from the Okhotsk Sea, covering the last 120 kyrs, were measured. The authigenic Ba
(Baex) contents were calculated and compared with the opal. The correlation coefficient between Baex and opal was quite small (r = 0.34), but it greatly grew larger (r = 0.90), if the Baex contents were multiplied by a simple function increasing with depth, except for two intervals. This may be due to the gradual
change in the sedimentation environment during the glacial ages. One of the exceptional interval is found at 60–170 cm in
depth, corresponding to 10–17 calendar kyr ago, the last termination period of glacial ages, where the Baex began to increase prior to opal. Since the calcium carbonate contents similarly increased prior to the opal increase, the
Baex may be also related to calcareous organisms besides siliceous ones. The other is the last interglacial period around 120
kyr ago when the opal contents were high, but those of the Baex were not increased. This can be explained, if the Baex was reduced to sulfide and dissolved away in a strongly anoxic environment during the biologically productive period. During
the glacial ages, the mass accumulation rate (MAR) of lithogenic Ti was about twice the amount of that during the interglacial
ages. For opal, however, the contrast between the glacial and interglacial ages was more remarkable in its MAR than in its
concentration in sediments, due to the larger variation in the bulk sedimentation rates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
94.
Biological community and sediment fatty acids associated with the deep-sea whale skeleton at the Torishima Seamount 总被引:1,自引:0,他引:1
A whale skeleton was discovered on the flat-topped summit of the Torishima Seamount, 4037 m deep, northwest Pacific Ocean, during a dive by the submersibleShinkai 6500 in 1992. The skeleton was encrusted with mytilid mussels and harbored benthic animals such as galatheid crabs, echinoderms, sea anemones, and unidentifiable tube worms. The whale skeleton was revisited in 1993. Sediment samples were collected to outline the chemical-microbial distribution in the sediment associated with the skeleton. In the sediment, there was a gradient of sulfide concentration with the peak of 20 n moles per gram sediment just beneath a bone. Corresponding gradients were observed in thiosulfate-oxidizing enzyme activity, bacterial colony counts and fatty acid amounts. Direct analysis of the sediment fatty acid composition suggested the occurrence of methane-oxidizing bacteria and sulfur-reducing bacteria in close association with the whale skeleton. These observations imply that the methane and sulfides were formed during the saprogenic process and utilized for the chemosynthetic bacterial production to feed the whale skeleton-animal community. 相似文献
95.
96.
Deyu Qian Nong Zhang Hideki Shimada Cheng Wang Takashi Sasaoka Nianchao Zhang 《Arabian Journal of Geosciences》2016,9(1):82
Goaf-side entry driving in underground coal mines could greatly improve coal recovery rates. However, it becomes more difficult to maintain stability, especially in deep coal mines. Pillar width plays a pivotal role in the stability of goaf-side entry driving. To obtain a reasonable and appropriate narrow pillar width, theoretical calculations of the widths of mining-damaged zone and limit equilibrium zone in the pillar are derived according to limit equilibrium theory. Based on the stability issues of goaf-side entry driving in the first island longwall coal face (LCF) at a depth of 800 m below the surface in Guqiao Coal Mine in China, a numerical model is established by FLAC software to analyze the stability of the surrounding rock of goaf-side entry driving during excavation, using various coal pillar widths and support schemes. The results obtained from theoretical calculations, numerical simulation, and engineering practice indicate that an 8-m-wide coal pillar is relatively reasonable, appropriate, and feasible. Field measurements show that deformations of the surrounding rock could be efficiently controlled 31 days after the support schemes were implemented in goaf-side entry driving with an 8-m-wide narrow pillar along the adjacent goaf side with a compaction duration of 10 months. The mining influence range of the overlying LCF on the stability of goaf-side entry driving is found to be the area from 50 m ahead of the LCF to 70 m behind the LCF as it passes over the measurement point. 相似文献
97.
Futoshi Nanayama Jun Tajika Toru Yamasaki Hiroshi Kurita Hideki Iwano Tohru Danhara Takafumi Hirata 《Island Arc》2021,30(1):e12403
Greenstone bodies emplaced upon or into clastic sediments crop out ubiquitously in the Hidaka belt (early Paleogene accretionary and collisional complexes exposed in the central part of northern Hokkaido, NE Japan), but the timing and setting of their emplacement has remained poorly constrained. Here, we report new zircon U–Pb ages for the sedimentary complexes surrounding these greenstones. The Hidaka Supergroup in the northern Hidaka belt is divided into four zones from west to east: zones S, U, and R, which contain in situ greenstones; and zone Y, which does not. Detrital zircons in zones S, U, and R have early Eocene U–Pb ages (55–47 Ma) and these strata are intruded by early Eocene granites (46–45 Ma), indicating that they were deposited between 55 and 46 Ma. Therefore, in situ greenstones in the northern Hidaka belt can only be explained by the subduction of the Izanagi–Pacific Ridge during 55–47 Ma. In contrast, the deposition of zone Y (the Yubetsu Group, younging to the west) began by 73–71 Ma, indicating that the accretionary prism in front of the paleo-Kuril arc formed at the same time as that in the Idonnappu zone and grew continuously until 48 Ma. The plutonic rocks that intruded the Hidaka belt are roughly divided into three stages: (1) early Eocene granites intruded the northern Hidaka belt at 46–45 Ma, during subduction of the Izanagi–Pacific Ridge; (2) the upper sequence of the Hidaka metamorphic zone was metamorphosed by magmatism at 40–37 Ma associated with the collision of the paleo-Kuril arc and NE Asia; and (3) younger granites intruded the entire Hidaka belt at 20–17 Ma in association with asthenospheric upwelling caused by back-arc expansion. 相似文献
98.
99.
Nguyen Tai Tue Tran Dang Quy Hideki Hamaoka Mai Trong Nhuan Koji Omori 《Estuaries and Coasts》2012,35(4):1060-1068
The spatio-temporal variations in stable isotope signatures (??13C and ??15N) and C/N ratios of particulate organic matter (POM), and physicochemical parameters in a creek water column were examined in an estuarine mangrove ecosystem of Xuan Thuy National Park, Vietnam. The objective was to examine the factors influencing creek water properties, and the sources and exchange of POM in this important mangrove ecosystem. The diel and seasonal variations in water temperature, flow velocity, pH, dissolved oxygen, and salinity demonstrated that tidal level, season, and biological factors affected the creek water properties. Mangroves had relatively low ??15N and very low ??13C values, with respective average values of 1.5?±?0.9?? and ?28.1?±?1.4??. The low mangrove leaf ??15N indicated minor anthropogenic nitrogen loading to the mangrove forests. A significant positive correlation between POM?C??13C and salinity along the axis of Ba Lat Estuary, Red River, indicated that marine phytoplankton (??13C value, ?21.4?±?0.5??) was the predominant source of POM at the estuary mouth. Based on the co-variation of ??13C and C/N ratios, marine phytoplankton and mangrove detritus were predominant in POM of major creeks and small creeks, respectively. During the diurnal tidal cycle, the dynamics of POM were affected by sources of organic matter, tidal energy, and seasonal factors. The contribution of mangrove detritus to POM reached a maximum at the low tide and was enhanced during the rainy season, whereas marine phytoplankton contribution was highest at high tide. 相似文献
100.
Qing Yu Jinrong Ma Hideki Shimada Takashi Sasaoka 《Geotechnical and Geological Engineering》2014,32(4):821-827
In order to find the relationship between the shaft lining stability and the coal extraction operation, a 3D numerical model of strata layers and shaft lining was established for simulating the influence of coal extraction operation on shaft lining. Certain factors including mining depth, safety pillar width, mining width and mining height were taken as the influence factors in the simulation. The results indicated that the coal extraction could lead to the initiation of the failure in the aquifer and rock layers. As the mining depth increases, the shear strain increment in aquifer becomes small. In this case, the distance between mining panel and aquifer should be larger than 220 m and the safety pillar width should not <70 m. The maximum principal stress in aquifer had a little relation to mining operations. The mining panel width should not exceed 50 m without any support. 相似文献