Sedimentation rates and heavy metal pollution of sediments in the Seto Inland Sea     

Akira Hoshika  Takayuki Shiozawa 《Journal of Oceanography》1984,40(5):334-342

In the Hiuchi-Nada area of the Seto Inland Sea, Japan, sedimentation rates were determined with the Pb-210 technique, and heavy metals in sediments were also analyzed. Sediments were collected in twelve short sediment cores and a long sediment core, using 1-m and 6-m gravity corers.The sedimentation rates vary from 0.14 to 0.31 g cm^–2yr^–1. The highest sedimentation rate was observed in the central part of the area, while lower sedimentation rates were observed in the eastern part.In Hiuchi-Nada, a remarkable increase in copper and zinc contents is noticeable as early as the 1800's. Over the past 240 years a copper smelter at the south-western side of this area has been causing serious pollution of the sediment. Now, anthropogenic copper and zinc loads into the sediment are 123 and 376 ton yr^–1 compared to natural copper and zinc loads of 82 and 401 ton yr^–1, respectively. The highest level of copper and zinc pollution was observed in the 1960's, when the relative enrichments above background values (copper; 19 and zinc; 93 mg kg^–1) were 5.5 and 2.8, respectively.  相似文献   

A single asteroidal source for extraterrestrial Ordovician chromite grains from Sweden and China: High-precision oxygen three-isotope SIMS analysis     

Philipp R. Heck  Takayuki Ushikubo  Noriko T. Kita  John W. Valley 《Geochimica et cosmochimica acta》2010,74(2):497-347

We examined oxygen three-isotope ratios of 48 extraterrestrial chromite (EC) grains extracted from mid-Ordovician sediments from two different locations in Sweden, and one location in south-central China. The ages of the sediments (∼470 Ma) coincide with the breakup event of the L chondrite parent asteroid. Elemental compositions of the chromite grains are generally consistent with their origin from L or LL chondrite parent bodies. The average Δ¹⁷O (‰-deviation from the terrestrial mass-fractionation line, measured in situ from 15 μm spots by secondary ion mass spectrometry; SIMS) of EC grains extracted from fossil meteorites from Thorsberg and Brunflo are 1.17 ± 0.09‰ (2σ) and 1.25 ± 0.16‰, respectively, and those of fossil micrometeorites from Thorsberg and Puxi River are 1.10 ± 0.09‰, and 1.11 ± 0.12‰, respectively. Within uncertainty these values are all the same and consistent with the L chondrite group average Δ¹⁷O = 1.07 ± 0.18‰, but also with the LL chondrite group average Δ¹⁷O = 1.26 ± 0.24‰ (Clayton et al., 1991). We conclude that the studied EC grains from correlated sediments from Sweden and China are related, and most likely originated in the same event, the L chondrite parent body breakup. We also analyzed chromites of modern H, L and LL chondrites and show that their Δ¹⁷O values coincide with averages of Δ¹⁷O of bulk analyses of H, L and LL chondrites. This study demonstrates that in situ oxygen isotope data measured by SIMS are accurate and precise if carefully standardized, and can be used to classify individual extraterrestrial chromite grains found in sediments.  相似文献   

36Cl, 26Al,and O isotopes in an Allende type B2 CAI: Implications for multiple secondary alteration events in the early solar system     

Takayuki Ushikubo  Yunbin Guan  Hajime Hiyagon  Naoji Sugiura  Laurie A. Leshin 《Meteoritics & planetary science》2007,42(7-8):1267-1279

Abstract— We measured ³⁶Cl‐³⁶S and ²⁶Al‐²⁶Mg systematics and O isotopes of secondary phases in a moderately altered type B2 CAI (CAI#2) from the Allende CV3 chondrite. CAI#2 has two distinct alteration domains: the anorthite‐grossular (An‐Grs) domain that mostly consists of anorthite and grossular, and the Na‐rich domain that mostly consists of sodalite, anorthite, and Fe‐bearing phases. Large ³⁶S excesses (up to ～400‰) corresponding to an initial ³⁶Cl/³⁵Cl ratio of (1.4 ± 0.3) × 10^?6 were observed in sodalite of the Na‐rich domain, but no resolvable 26Mg excesses were observed in anorthite and sodalite of the Na‐rich domain (the initial ²⁶Al/²⁷Al ratio < 4.4 × 10^?7). If we assume that the ³⁶Cl‐³⁶S and the ²⁶Al‐²⁶Mg systematics were closed simultaneously, the ³⁶Cl/³⁵Cl ratio would have to be on the order of ～10^?2 when CAIs were formed. In contrast to sodalite in Na‐rich domain, significant ²⁶Mg excesses (up to ～35‰) corresponding to an initial ²⁶Al/²⁷Al ratio of (1.2 ± 0.2) × 10^?5 were identified in anorthite of the An‐Grs domain. The ²⁶Al‐²⁶Mg systematics of secondary phases in CAI#2 suggest that CAIs experienced multiple alteration events. Some of the alteration processes occurred while ³⁶Cl (half‐life is 0.3 Myr) and ²⁶Al (half‐life is 0.72 Myr) were still alive, whereas others took place much later. Assuming that ²⁶Al was homogeneously distributed in the solar nebula, our study implies that alteration of CAIs occurred as early as within 1.5 Myr of CAI formation and as late as 5.7 Myr after.  相似文献   

Phototrophic activity and redox condition in Lake Hamana, Japan, indicated by sedimentary photosynthetic pigments and molybdenum over the last ∼250 years   总被引：1，自引：0，他引：1  

Nobuyasu Itoh  Yukinori Tani  Takayuki Nagatani  Mitsuyuki Soma 《Journal of Paleolimnology》2003,29(4):403-422

We analyzed photosynthetic pigments, total organic carbon (TOC), biogenic silica, and Mo, a redox-sensitive element, in ²¹⁰Pb-dated sediment cores to reconstruct the historical changes in primary productivity and anoxia in the central basin of Lake Hamana, a brackish lake in Shizuoka Prefecture, Japan, over the last 250 years. The algal photosynthetic pigments we analyzed included chlorophyll a (and its derivatives), chlorophyll b (and its derivatives), and carotenoids such as -carotene, lutein, zeaxanthin, diatoxanthin, fucoxanthin, alloxanthin, and -carotene. Marker pigments for phototrophic sulfur bacteria were also recorded, including okenone and bacteriopheophytin a, originating from Chromatium (a genus of purple sulfur bacteria), and isorenieratene and bacteriochlorophylls e ₁, e ₂ and e ₃ (and corresponding bacteriopheophytins) from brown Chlorobium (a brown-colored group of green sulfur bacteria). The occurrence of these pigments throughout the length of all cores indicates that the anoxia in Lake Hamana has existed over at least the last 250 years. The indicators related to primary productivity – TOC and pigments of aerobic and anaerobic phototrophs – and an indicator of anoxia, Mo, increased after 1860, indicating that productivity had increased in both the oxic and anoxic (sulfidic) zones. The depth profiles of the indicators in the sediment cores showed that among phototrophic sulfur bacteria, Chromatium preferentially increased relative to brown Chlorobium when the lake productivity was high, and hence high anoxia existed in the lake. This can be explained by a shallowing of the oxic/anoxic boundary zone due to changes in temporal and/or spatial extents of seasonal anoxia, which made the light intensity in the upper anoxic zone high enough for Chromatium to grow. The upper Chromatium layer may absorb the wavelengths of light that favor the growth of brown Chlorobium in the water column, resulting in a relative decrease in brown Chlorobium. During the 1950s, the trends among the indicators changed significantly. This change is attributed to the construction of training walls, built to direct tidal currents into the lake, on the Imagire-guchi Channel, the sole inlet of seawater to the lake, during 1954–1956, and the resultant increases of seawater intrusion and lake salinity. A decrease in okenone and bacteriopheophytin a, or in okenone/isorenieratene ratio, after 1960 accompanying a decrease in Mo, is attributed to a deepening of the anoxic zone, where the light intensity became too low for growth of Chromatium, more light-demanding than the brown Chlorobium. A decrease of zeaxanthin (cyanobacteria) after 1960 relative to lutein (green algae) and diatoxanthin (diatoms and dinoflagellates) indicated a change in algal assemblage, presumably due to the increased salinity. Principal component analysis with a data set of total algal carotenoids, okenone, isorenieratene, and Mo also suggested that a major change occurred around the 1950s.  相似文献   

Effects of deposit feeder Stichopus japonicus on algal bloom and organic matter contents of bottom sediments of the enclosed sea   总被引：4，自引：0，他引：4  

Michio K  Kengo K  Yasunori K  Hitoshi M  Takayuki Y  Hideaki Y  Hiroshi S 《Marine pollution bulletin》2003,47(1-6):118-125

Algae growing in an enclosed sea may inhibit eutrophication because they absorb nutrients in the water. However, dead algae often cause anaerobic conditions in the water just above and on sediment after they are deposited on the bottom. We found that Stichopus japonicus inhibited the anaerobic processes coupling water sulfite production in sediment. The present study investigates whether S. japonicus inhibits algal flourish and influences sediment properties such as organic matter contents. Aquarium experiments were carried out at Komatsushima port in Tokushima Prefecture, western Japan. The aquaria used in the experiments were supplied with water directly from the adjacent sea (6 L/min), laid with sand of 10 cm depths, and lighted at 12 h intervals. Six aquaria each containing a sea cucumber from Komatsushima port and six aquaria without any were used in the experiments. Water temperature ranged between 9 and 15 degrees C during December 2000 and April 2001. Salinity ranged between 32 per thousand and 34 per thousand. Algae began to cover the bottom of the aquaria without S. japonicus after 2 weeks, whereas no growth was evident in the aquaria containing sea cucumbers. Chlorophyll a concentration in the surface sediment of the aquaria with S. japonicus (6.1+/-3.6 microg/g, mean S.D.+/-standard deviation) was significantly lower than that without it (60+/-17 microg/g, U-test, p<0.05). Phaeophytin concentration in the surface sediment of the aquaria with S. japonicus (0.9+/-0.09 microg/g) was also significantly lower than that without it (4.5+/-1.0 microg/g, U-test, p<0.05). TOC concentration in the surface sediment of the aquaria with S. japonicus (2.6+/-1.3 microg/g) was slightly lower than that without it (4.0+/-1.2 microg/g). These results showed that algal biomass and organic matter concentration of the bottom were decreased in the presence of S. japonicus. Therefore, S. japonicus inhibits algal bloom and decrease the contents of organic matter deposited on the bottom of enclosed sea areas.  相似文献   

Fractal size and spatial distributions of fault zones: An investigation into the seismic Chelungpu Fault, Taiwan     

Kenshiro  Otsuki  Takayuki  Uduki  Nobuaki  Monzawa  Hidemi  Tanaka 《Island Arc》2005,14(1):12-21

Abstract   The fractality of fault zones of thickness T for the 248-m-long core from a borehole penetrating the northern segment of the seismic Chelungpu Fault, Taiwan, was analyzed. The frequency curve of T shows that the fractal dimension is normal when T is smaller than a characteristic thickness T _c, and it becomes abnormally large when T exceeds T _c. The fractal dimensions of size and spatial distributions of T increase as the mean distribution density of T increases, which is inconsistent with the evolution laws for ordinary brittle faults. This discrepancy implies that the thickening rate of T when T is more than T _c is not constant, but a decreasing function of fault displacement. The slow thickening rate is related to the elastohydrodynamic lubrication which was effective on the fault when T exceeds T _c. This slip instability mechanism can explain the large, fast and smooth slip on the northern segment of the Chelungpu Fault during the 1999 Chi-Chi earthquake.  相似文献   

Clayey injection veins and pseudotachylyte from two boreholes penetrating the Chelungpu Fault, Taiwan: Their implications for the contrastive seismic slip behaviors during the 1999 Chi-Chi earthquake   总被引：3，自引：0，他引：3  

Kenshiro  Otsuki  Takayuki  Uduki  Nobuaki  Monzawa  Hidemi  Tanaka 《Island Arc》2005,14(1):22-36

Abstract   The seismic slip that occurred during the 1999 Chi-Chi earthquake in Taiwan showed contrastive behaviors in different regions along the Chelungpu Fault: A large and smooth slip occurred in the north, while a relatively small slip associated with high-frequency seismic wave radiation occurred in the south. The core samples from shallow boreholes at northern (Fengyuan) and southern (Nantou) sites penetrating the seismic Chelungpu Fault were analyzed. The fault zones at the northern site are characterized by soft clayey material associated with clayey injection veins. This suggests that the fault zones were pressurized during ancient seismic slip events, and hence the elastohydrodynamic lubrication occurred effectively. In contrast, the fault rock from the southern site is old pseudotachylyte that has been shattered by repeated ancient seismic slip events. Statistical analysis of many pseudotachylyte fragments reveals that the degree of frictional melting tended to be low. In this case, the seismic slip is restrained by the mechanical barrier of a highly viscous melt layer. These contrastive fault rocks were produced by repeated ancient seismic slip events, but the two corresponding mechanisms of friction are likely to have also occurred during the 1999 Chi-Chi earthquake, thus causing the contrastive slip behaviors in the north and south.  相似文献   

Petrographic features of a high-temperature granite just newly solidified magma at the Kakkonda geothermal field, Japan     

Munetake Sasaki  Koichiro Fujimoto  Takayuki Sawaki  Hitoshi Tsukamoto  Osamu Kato  Ryo Komatsu  Nobuo Doi  Masakatsu Sasada 《Journal of Volcanology and Geothermal Research》2003,121(3-4):247-269

A 3729-m-deep geothermal research well, WD-1a, provides us with a unique opportunity to study initial petrographic features of a high-temperature granite just after solidification of magma. The well succeeded in collecting three spot-cores of the Kakkonda Granite that is a pluton emplaced at a shallow depth and regarded as a heat source of the active Kakkonda geothermal system. The core samples were collected at the present formation temperatures of 370, 410 and over 500°C. These samples are granodiorite to tonalite consisting mainly of plagioclase, quartz, hornblende, biotite and K-feldspar. A sample collected at a formation temperature of over 500°C possesses the following remarkable petrographic features compared to the other two samples. Interstitial spaces are not completely sealed. K-feldspar exhibits no perthite by the exsolution of albite lamella. Quartz includes glassy melt inclusions without devitrification. Hornblende is less intensively altered to actinolite, and biotite is not altered. This study directly confirmed that perthite in K-feldspar is a recrystallization texture formed at 410–500°C based on a comparison of the in situ temperatures of the samples. Chemical compositions of minerals were analyzed to compare temperatures determined from geothermometers in several publications to the in situ temperatures of the samples.  相似文献   

Multifractal analysis of spatial distribution of microearthquakes in the Kanto region   总被引：5，自引：0，他引：5  

Takayuki Hirata  Masajiro Imoto 《Geophysical Journal International》1991,107(1):155-162

b
The spatial distribution of earthquakes is a fractal, which is characterized by a fractal dimension. However, if a spatial distribution has a heterogeneous fractal structure, a single value of fractal dimension [e.g. D_o (capacity dimension) or D ₂ (correlation dimension)] is not enough to characterize it. From a multifractal viewpoint, we analysed the spatial distribution of microearthquakes in the Kanto region by using a local density function. Generalized dimensions, D_q , of the spatial distribution were calculated from the slopes of generalized correlation integrals, C_q(r) versus distance r , on a log-log plot, examining the self-similarity of the spatial distribution of microearthquakes. Self-similar structures are held well at scales from 1.26 to 12.6 km. Our results suggest that the spatial distribution of microearthquakes in the Kanto region is not a homogeneous fractal structure but a heterogeneous one with generalized dimensions D₂ = 2.2 ≤ D ₃≤…≤ D _∞= 1.7. The value of D _∞, the lower limit of fractal dimension, is the fractal dimension of the most intensive clustering in the heterogeneous fractal set. The fractal dimension of the most intensive clustering of microearthquakes in the Kanto region is 1.7.  相似文献   

Constraining atmospheric oxygen and seawater sulfate concentrations during Paleoproterozoic glaciation: In situ sulfur three-isotope microanalysis of pyrite from the Turee Creek Group, Western Australia     

Kenneth H. Williford  Martin J. Van Kranendonk  Takayuki Ushikubo  John W. Valley 《Geochimica et cosmochimica acta》2011,75(19):5686-5705

Previous efforts to constrain the timing of Paleoproterozoic atmospheric oxygenation have documented the disappearance of large, mass-independent sulfur isotope fractionation and an increase in mass-dependent sulfur isotope fractionation associated with multiple glaciations. At least one of these glacial events is preserved in diamictites of the ∼2.4 Ga Meteorite Bore Member of the Kungarra Formation, Turee Creek Group, Western Australia. Outcrop exposures of this unit show the transition from the Boolgeeda Iron Formation of the upper Hamersley Group into clastic, glaciomarine sedimentary rocks of the Turee Creek Group. Here we report in situ multiple sulfur isotope and elemental abundance measurements of sedimentary pyrite at high spatial resolution, as well as the occurrence of detrital pyrite in the Meteorite Bore Member. The 15.3‰ range of Δ³³S in one sample containing detrital pyrite (−3.6‰ to 11.7‰) is larger than previously reported worldwide, and there is evidence for mass-independent sulfur isotope fractionation in authigenic pyrite throughout the section (Δ³³S from −0.8‰ to 1.0‰). The 90‰ range in δ³⁴S observed (−45.5‰ to 46.4‰) strongly suggests microbial sulfate reduction under non-sulfate limiting conditions, indicating significant oxidative weathering of sulfides on the continents. Multiple generations of pyrite are preserved, typically represented by primary cores with low δ³⁴S (<−20‰) overgrown by euhedral rims with higher δ³⁴S (4-7‰) and enrichments in As, Ni, and Co. The preservation of extremely sharp sulfur isotope gradients (30‰/<4 μm) implies limited sulfur diffusion and provides time and temperature constraints on the metamorphic history of the Meteorite Bore Member. Together, these results suggest that the Meteorite Bore Member was deposited during the final stages of the “Great Oxidation Event,” when pO₂ first became sufficiently high to permit pervasive oxidative weathering of continental sulfides, yet remained low enough to permit the production and preservation of mass-independent sulfur isotope fractionation.  相似文献