Sedimentary facies and biofacies of the Torinosu Limestone in the Torinosu area,Kochi Prefecture,Japan     

Hiromichi Ohga  Bogus&#x;aw Ko&#x;odziej  Martin Nose  Dieter U. Schmid  Hideko Takayanagi  Yasufumi Iryu 《Island Arc》2013,22(2):150-169

The Torinosu Limestone represents carbonate platform deposits in a foreland basin, the sedimentary setting of which is highly different from those of well‐known Late Jurassic reefs in the western Tethys that developed on shelf areas of continental margins and intra‐Tethyan platforms. Sedimentological and paleontological analyses were conducted on a 55.5 m‐thick Upper Jurassic–Lower Cretaceous (Tithonian–Berriasian) carbonate sequence (Torinosu Limestone) at the Eastern Hitotsubuchi Quarry, Kochi Prefecture, Southwest Japan. The carbonate sequence is composed of two sections that are separated by a subaerial exposure surface. Two and three depositional units have been defined in the lower and upper sections, respectively, based on changes in lithology and the biotic composition of the carbonates; they are numbered from 1 to 5, in ascending order. Calcified demosponges (stromatoporoids and a chaetetid Chaetetopsis crinita) are abundant in three units (2, 3, and 5), in which microencrusters (mostly Lithocodium aggregatum and Bacinella irregularis) and microbialites are also common to abundant. Although most of them are para‐allochthonous, in‐situ branching stromatoporoids are found on and above the subaerial exposure surface (unit 3). Corals are less common, poorly diverse, and primarily represented by the family Microsolenidae. Siliciclastic grains occur in all units, but they are particularly common in units 1 and 4. The co‐occurrence of the Lithocodium–Bacinella association, which is typical of oligotrophic or moderately mesotrophic shallow‐water environments, with microsolenids, which are indicative of high nutrient levels and/or low‐light intensity due to high turbidity, suggests repeated changes in nutrient levels associated with terrigenous input. Based on lithology, biotic composition, and succession, we infer that sea‐level changes and related terrigenous input controlled the sedimentary environment of the studied carbonate sequence.  相似文献   

Direct evidence for nitrogen isotope discrimination during sedimentation and early diagenesis in Lake Kasumigaura, Japan     

Ayato Kohzu  Akio ImaiToshihiro Miyajima  Takehiko FukushimaKazuo Matsushige  Kazuhiro KomatsuNobuyuki Kawasaki  Shingo MiuraTakayuki Sato 《Organic Geochemistry》2011,42(2):173-183

Sediment core samples from the center of Lake Kasumigaura, Japan, were collected from 1979 to 2007 at intervals of 1 month to 5 yr. We evaluated the degree of modification in N isotope composition during sedimentation and diagenesis. We estimated the degree of isotope discrimination during diagenesis by comparing historical changes in N isotope composition of the surface sediment (top 2 cm) against the vertical profile of the isotope composition of sediment core samples (15 cm depth). The degree of ¹⁵N enrichment during sedimentation appeared to be significant under the preferential N decomposition that occurred in the periods with low C/N ratio values of suspended particulate organic matter. We documented ¹⁵N depletion in sediment deeper than approximately 3 cm during diagenesis. The contrasting directions of N isotope discrimination during sedimentation and diagenesis suggest changing mechanisms of isotopic shift across an oxidation-reduction boundary.  相似文献   

Complex vertical migration of larvae of the ghost shrimp, Nihonotrypaea harmandi, in inner shelf waters of western Kyushu,Japan     

Akio Tamaki  Sumit Mandal  Yoshihiro Agata  Ikumi Aoki  Toshikazu Suzuki  Hisao Kanehara  Takashi Aoshima  Yasushi Fukuda  Hideshi Tsukamoto  Tetsuo Yanagi 《Estuarine, Coastal and Shelf Science》2010

The position of meroplanktonic larvae in the water column with depth-dependent current velocities determines horizontal transport trajectories. For those larvae occurring in inner shelf waters, little is known about how combined diel and tidally-synchronized vertical migration patterns shift ontogenetically. The vertical migration of larvae of Nihonotrypaea harmandi (Decapoda: Thalassinidea: Callianassidae) was investigated in mesotidal, inner shelf waters of western Kyushu, Japan in July–August 2006. The larval sampling at seven depth layers down to 60 m was conducted every 3 h for 36 h in a 68.5-m deep area 10 km off a major coastal adult habitat. Within a 61–65-m deep area 5–7.5 km off the adult habitat, water temperature, salinity, chlorophyll a concentration, and photon flux density were measured, and water currents there were characterized from harmonic analysis of current meter data collected in 2008. The water column was stratified, with pycnocline, chlorophyll a concentration maximum, and 2% of photon flux density at 2 m, recorded at around 22–24 m. The stratified residual currents were detected in their north component, directed offshore and onshore in the upper and lower mixed layers, respectively. More than 87% of larvae occurred between 20 m and 60 m, producing a net onshore transport of approximately 1.3 km d⁻¹. At the sunset flooding tide, all zoeal-stage larvae ascended, which could further promote retention (1.4-km potential onshore transport in 3 h). The actual onshore transport of larvae was detected by observing their occurrence pattern in a shallow embayment area with the adult habitat for 24 h in October 1994. However, ontogenetic differences in the vertical migration pattern in inner shelf waters were also apparent, with the maximum mean positions of zoeae deepening with increasing stages. Zoeae I and II performed a reverse diel migration, with their minimum and maximum depths being reached around noon and midnight, respectively. Zoeae IV and V descended continuously. Zoeae III had behaviors that were intermediate to those of the earlier- and later-stage zoeae. Postlarvae underwent a normal diel migration (nocturnal ascent) regardless of tides, with the deepest position (below 60 m and/or on the bottom) during the day. These findings give a new perspective towards how complex vertical migration patterns in meroplanktonic larvae enable their retention in inner shelf waters before the final entry of postlarvae into their natal populations.  相似文献   

Fragmentation of star-forming clouds enriched with the first dust     

Raffaella Schneider  Kazuyuki Omukai  Akio K. Inoue  Andrea Ferrara 《Monthly notices of the Royal Astronomical Society》2006,369(3):1437-1444

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Attenuation law of normal disc galaxies with clumpy distributions of stars and dust     

Akio K. Inoue † 《Monthly notices of the Royal Astronomical Society》2005,359(1):171-182

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Amount of intergalactic dust: constraints from distant supernovae and the thermal history of the intergalactic medium     

Akio K. Inoue †  Hideyuki Kamaya 《Monthly notices of the Royal Astronomical Society》2004,350(2):729-744

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Sediment and carbon storages in the Yahagi River Delta during the Holocene,central Japan     

Kiyoshi Fujimoto  Kumiko Kawase  Shigehiro Ishizuka  Koji Shichi  Akio Ohira  Hiroshi Adachi 《Quaternary Science Reviews》2009,28(15-16):1472-1480

We estimated stored sediment and carbon during the Holocene for each layer of the Yahagi River Delta, central Japan and discussed the provenance of stored carbon. To estimate the bulk density and the carbon content of each layer, we collected two 30 m deep undisturbed cores. The volume of each layer was calculated using ArcView 3D analyst. Although the volume ratio of each layer to the total volume was calculated to be 9.5% for the top mud layer, 34.9% for the upper sand layer, 32.8% for the middle mud layer and 22.9% for the lower sand layer, the mass ratio of each layer to the total mass was calculated to be 8.5, 40.9, 25.2 and 25.4%, respectively, and the stored carbon ratio in each layer to the total stored carbon was 20.4, 4.7, 55.9 and 18.9%, respectively. These results suggest that the top mud and middle mud layers have a significant role as a place for carbon sequestration during postglacial time. Total stored carbon in the study area of only 92.1 km² was estimated at 26 Tg C, which is equivalent to 0.003% of atmospheric carbon. This suggests that deltas on the globe have accumulated a massive amount of carbon during the evolution. The inorganic carbon ratio to total carbon reached more than 45% around the boundary between the middle mud and lower sand layers. The increasing trend in the C_org/N_total ratio accompanied with a decrease in δ¹³C from the bottom to the top horizon in the middle mud layer indicates a gradual increase in terrestrial organic matter contribution. The relative proportion of terrestrially derived materials decreases with increasing distance seaward.  相似文献   

Flow behavior and microstructures of hydrous olivine aggregates at upper mantle pressures and temperatures     

Tomohiro?OhuchiEmail author  Takaaki?Kawazoe  Yuji?Higo  Akio?Suzuki 《Contributions to Mineralogy and Petrology》2017,172(8):65

Deformation experiments on olivine aggregates were performed under hydrous conditions using a deformation-DIA apparatus combined with synchrotron in situ X-ray observations at pressures of 1.5–9.8 GPa, temperatures of 1223–1800 K, and strain rates ranging from 0.8 × 10^?5 to 7.5 × 10^?5 s^?1. The pressure and strain rate dependencies of the plasticity of hydrous olivine may be described by an activation volume of 17 ± 6 cm³ mol^?1 and a stress exponent of 3.2 ± 0.6 at temperatures of 1323–1423 K. A comparison between previous data sets and our results at a normalized temperature and a strain rate showed that the creep strength of hydrous olivine deformed at 1323–1423 K is much weaker than that for the dislocation creep of water-saturated olivine and is similar to that for diffusional creep and dislocation-accommodated grain boundary sliding, while dislocation microstructures showing the [001] slip or the [001](100) slip system were developed. At temperatures of 1633–1800 K, a much stronger pressure effect on creep strength was observed for olivine with an activation volume of 27 ± 7 cm³ mol^?1 assuming a stress exponent of 3.5, water fugacity exponent of 1.2, and activation energy of 520 kJ mol^?1 (i.e., power-law dislocation creep of hydrous olivine). Because of the weak pressure dependence of the rheology of hydrous olivine at lower temperatures, water weakening of olivine could be effective in the deeper and colder part of Earth’s upper mantle.  相似文献   

Changes in climate classification and extreme climate indices from a high-resolution future projection in Korea   总被引：1，自引：0，他引：1  

Kyung-Sook Yun  Ki-Young Heo  Jung-Eun Chu  Kyung-Ja Ha  Eun-Jeong Lee  Yumi Choi  Akio Kitoh 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(3):213-226

We investigate the future changes in the climate zone and six extreme temperature indices in Korea, using the 20-km high-resolution atmospheric general circulation model (MRI-AGCM3.1S). The Trewartha and K?ppen climate classification schemes are applied, and four summer-based extreme temperature indices (i.e., summer days, tropical nights, growing degree days, and cooling degree days (CDD) and two winter-based indices (frost days and heating degree days (HDD) are analyzed. To represent significantly the change in threshold indices, the monthly mean bias is corrected in model. The model result reasonably captures the temporal and spatial distribution of the present-day extreme temperatures associated with topography. It was found that in the future climate, the area of the subtropical climate zone in Korea expands northward and increases by 21% under the Trewartha classification scheme and by 35% under the K?ppen classification scheme. The spatial change in extreme climate indices is significantly modulated by geographical characteristics in relation to land-ocean thermal inertia and topographical effects. The change is manifested more in coastal regions than in inland regions, except for that in summer days and HDD. Regions with higher indices in the present climate tend to reveal a larger increase in the future climate. The summer-based indices display an increasing trend, while the winter-based indices show a decreasing trend. The most significant increase is in tropical nights (+452%), whereas the most significant decrease is in HDD (?25%). As an important indicator of energy-saving applications, the changes in HDD and CDD are compared in terms of the frequency and intensity. The future changes in CDD reveal a higher frequency but a lower temperature than those in HDD. The more frequent changes in CDD may be due to a higher and less dispersed occurrence probability of extreme temperatures during the warm season. The greater increase in extreme temperature events during the summer season remains an important implication of projecting future changes in extreme climate events.  相似文献   

Slab decarbonation and CO₂ recycling in the Southwestern Colombian volcanic arc     

Maria I. Marín-Cerón  Takuya Moriguti  Akio Makishima  Eizo Nakamura 《Geochimica et cosmochimica acta》2010,74(3):1104-1121

The contribution of subducted carbonate sediments to the genesis of the Southwestern Colombian arc magmas was investigated using a comprehensive petrography and geochemical analysis, including determination of major and trace element contents and Sr, Nd, Hf and Pb isotope compositions. These data have been used to constrain the depth of decarbonation in the subducted slab, indicating that the decarbonation process continues into the sub-arc region, and ultimately becomes negligible in the rear arc. We propose on the basis of multi-isotope approach and mass balance calculations, that the most important mechanism to induce the slab decarbonation is the infiltration of chemically reactive aqueous fluids from the altered oceanic crust, which decreasingly metasomatize the mantle wedge, triggering the formation of isotopically different primary magmas from the volcanic front (VF) with relatively high ¹⁷⁶Hf/¹⁷⁷Hf, high ⁸⁷Sr/⁸⁶Sr, negative values of εNd and lower Pb isotopes compared to the rear arc (RA).The presence of more aqueous fluids at the volcanic front may increase the degree of decarbonation into carbonate-bearing lithologies. Moreover, with increasing pressure and temperature in the subduction system, the decrease in dehydration of the slab, leads to cessation of fluid-induced decarbonation reactions at the rear arc. This development allows the remaining carbonate materials to be recycled into the deep mantle.  相似文献