Differential timing of vertical-axis block rotations in the northern Ryukyu Arc: Paleomagnetic evidence from the Koshikijima Islands,Japan     

Satoshi Tonai  Yusuke Suganuma  Juichiro Ashi  Tetsumaru Itaya  Hisashi Oiwane  Shoichi Kiyokawa 《Tectonophysics》2011,497(1-4):71-84

Over 300 samples for paleomagnetic analysis and K–Ar dating were collected from 27 sites at NW–SE and NE–SW trending dike swarms (herein, NW dikes and NE dikes, respectively) in the Koshikijima Islands, northern Ryukyu Arc. The NW dikes are Middle Miocene in age and have directions (D = ? 37.7^°, I = 51.8^°, α₉₅ = 9.6^°, and κ = 40.8) that are deflected westward relative to the stable eastern Asian continent. Conversely, the NE dikes, of Late Miocene age, have directions (D = 16.1^°, I = 57.7^°, α₉₅ = 7.1^°, and κ = 41.9) that show no such deflection. These differences are interpreted as indicating that the Koshikijima Islands underwent approximately 40^° of counter-clockwise rotation during the Middle to Late Miocene. A synthesis of the paleomagnetic and structural data suggests a three-stage history of extensional deformation: (1) displacement upon normal faults (F₁ faults) without vertical-axis block rotation, (2) strike-slip reactivation of F₁ faults and oblique-normal displacement on NE–SW-trending faults (F₂ faults) with vertical-axis block rotation, and (3) oblique-normal displacement on F₂ faults without vertical-axis block rotation. Regional differences in the timing and amount of counter-clockwise vertical-axis block rotations indicate that the northern Ryukyu Arc rotated as several distinct rigid blocks.  相似文献   

Inter-laboratory comparison of oxygen isotope compositions from biogenic silica     

Bernhard Chapligin  Melanie J. Leng  Anne Alexandre  Akira Ijiri  Aldo Shemesh  Ulrike Herzschuh  Hanno Meyer  Yusuke Okazaki  Zachary D. Sharp  Corinne Sonzogni  Florence Sylvestre  Ruth Yam 《Geochimica et cosmochimica acta》2011,75(22):7242-7256

Several techniques have been introduced in the last decades for the dehydration and release of O₂ from biogenic silica (opal-A) for oxygen-isotope analysis. However, only one silica standard is universally available: a quartz standard (NBS28) distributed by the IAEA, Vienna. Hence, there is a need for biogenic silica working standards. This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the δ¹⁸O values of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of δ¹⁸O values (+23 to +43‰) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by scanning electron microscopy (SEM) were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a standard deviation (SD) for δ¹⁸O values between 0.3‰ and 0.9‰ (1σ). Based on the results, we propose four additional biogenic silica working standards (PS1772-8: 42.8‰; BFC: 29.0‰; MSG60: 37.0‰; G95-25-CL leaves: 36.6‰) for δ¹⁸O analyses, available on request through the relevant laboratories.  相似文献   

Distribution of ephyrae and polyps of jellyfish <Emphasis Type="Italic">Aurelia</Emphasis><Emphasis Type="Italic">aurita</Emphasis> (Linnaeus 1758) <Emphasis Type="Italic">sensu lato</Emphasis> in Mikawa Bay,Japan     

Masaya Toyokawa  Kaoru Aoki  Satoshi Yamada  Akira Yasuda  Yusuke Murata  Tomohiko Kikuchi 《Journal of Oceanography》2011,67(2):209-218

We surveyed the distribution of colonies of polyps of Aurelia aurita sensu lato (s.l.) in Mikawa Bay, Japan. First, we surveyed the distribution of ephyrae of A. aurita s.l. at 75 stations encompassing the whole of Mikawa Bay in early 2008. A total of 37 ephyrae were sampled mostly from fishing ports. Ephyrae were most abundant around the islands located near the mouth of the bay, and decreased from the western part to the eastern part of Mikawa Bay. Next, we selected five fishing ports in Mikawa Bay where ephyrae occurred and surveyed the underside of floating piers and underwater overhangs of wharfs. We found dense colonies of polyps of A. aurita s.l. under nearly all of the floating piers at the two islands located near the mouth of the bay. Fitting a logistic regression model to the dataset showed that the percentage coverage of Aurelia polyps was significantly greater at the two islands compared with the other locations. In addition, the coverage of Aurelia polyps was greater when the coverage of other fouling organisms was in the range of 65–90%, and the coverage of Aurelia polyps was lower on floating piers with a vinyl surface and on concrete wharfs. The combined distribution of polyp colonies of A. aurita s.l. in Ise Bay and Mikawa Bay suggested that A. aurita s.l. in the two bays probably forms a single population and shoals of medusae mainly originate from protected harbors along the mouth-part of the bays.  相似文献   

Dust influx reconstruction during the last 26,000 years inferred from a sedimentary leaf wax record from the Japan Sea     

Yusuke Yokoyama  Tatsuhiro Naruse  Nanako O. Ogawa  Ryuji Tada  Hiroshi Kitazato  Naohiko Ohkouchi 《Global and Planetary Change》2006,54(3-4):239-250

We obtained the high-resolution record of terrestrial biomarkers (C₂₉ and C₃₁ n-alkanes) for the last 26,000 years from Oki Ridge in the south Japan Sea that enabled us to discuss millennial scale climate changes. Our sampling resolution for the biomarker during the major deglaciation period (10–19.5 cal ka BP) is 300 years and for the elemental analyses (total organic carbon and total nitrogen) is as good as ca 200 years. The estimated mass accumulation rate of these molecules during the last glacial period is substantially higher than during the Holocene. They also exhibited two distinct peaks at 17.6 cal ka BP and 11.4 cal ka BP, which are coincident with Heinrich Event 1 and the latest stage of the Younger Dryas, respectively. The unique oceanographic setting of the Japan Sea tends to preferentially preserve organic material of aeolian origin. The nature of our biomarker record in fact suggests a strong aeolian signal, and hence their flux to the Japan Sea potentially reflects the climate conditions of the dust source regions and transport intensity. Our results are consistent with previously reported monsoon variations based on other proxies that is indicative of a strong linkage between North Atlantic climate and Asian monsoon intensity.  相似文献   

Growth patterns of the last ice age coral terraces at Huon Peninsula   总被引：1，自引：0，他引：1  

Tezer M. Esat  Yusuke Yokoyama   《Global and Planetary Change》2006,54(3-4):216-224

At Huon Peninsula, Papua New Guinea, prolific coral growth during the last-glacial was episodic and in response to a series of sea-level rises. The resultant step-like coral terraces are currently situated from 20 m up to 140 m above sea-level due to continuous tectonic uplift of the Peninsula. The sea-level rises were in response to periodic partial disintegration of Northern Hemisphere ice sheets associated with severe climate swings and occurred within decadal timescales. The relatively rapid 15 m to 35 m rise in sea-levels exposed new head-room for corals to colonize. The resulting terrace structures contain individual corals that do not appear to have grown sequentially in time and with elevation. Additionally, following the peak, sea level fell relatively slowly over several thousand years and corals grew and filled in the flanks of the terrace such that younger corals now occupy lower elevations. We have labeled these structures “pack-up” reefs. This is in contrast to coral terraces formed during major sea-level rises from glacial to interglacial or glacial to interstadial transitions where the rate of sea level rise is commensurate with coral growth rates and corals can keep up with sea-level rise by growing on top of each other in a time orderly sequence. Deriving sea-level information from pack-up terraces is difficult and is likely to be ambiguous. The periodic fluctuations in climate were associated with atmospheric radiocarbon swings that seem to have varied smoothly with time. The same corals that show a scatter in stratigraphic temporal ordering appear regularly distributed in time and with radiocarbon content attesting to the veracity of the age measurements and at the same time confirm the disordered distribution of corals in “pack-up” type reefs.  相似文献   

Energy Balance of Irrigated Intercropping Field in the Middle Reaches of Heihe River Basin     

WU Jinkui DING Yongjian WANG Genxu SHEN Yongping Yusuke YAMAZAKI Jumpei KUBOTA 《中国地理科学(英文版)》2006,16(3):243-248

1 Introduction Most of the solar radiation that ecosystem seizes is con- sumed on latent, sensible and soil heat flux. Among them, latent heat flux shares the biggest part (Gutierrez and Meizer, 1994; Ham et al., 1991; Rachidi et al., 1993). The radiation budget and the energy balance are crucial to water conversion and effective water utilization. Also, they are important parts of research of water-saving ag- riculture (Mo et al., 1997). At present, the researches on radiation budget and e…  相似文献   

Petrogenesis of ultramafic rocks and olivine-rich troctolites from the East Taiwan Ophiolite in the Lichi mélange     

Morishita  Tomoaki  Ghosh  Biswajit  Soda  Yusuke  Mizukami  Tomoyuki  Tani  Ken-ichiro  Ishizuka  Osamu  Tamura  Akihiro  Komaru  Chihiro  Aari  Shoji  Yang  Hsiao-Chin  Chen  Wen-Shan 《Mineralogy and Petrology》2018,112(4):521-534

Mineralogy and Petrology - We examine ultramafic and olivine-rich troctolite blocks of the East Taiwan Ophiolite (ETO) in the Lichi Mélange. Although ultramafic rocks are extensively...  相似文献   

Single planet formation regime in the high-ionization environment:Possible origin of hot Jupiters and super-Earths     

Yusuke Imaeda  Toshikazu Ebisuzaki 《地学前缘(英文版)》2018,9(4):1023-1031

We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 10~(-7.4)M_☉yr~(-1), only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes(tandem planet formation regime and dispersed planet formation regime), in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early.  相似文献   

Software Dedicated for the Curation of Geochemical Data Sets in Analytical Laboratories     

Yusuke Yachi  Hiroshi Kitagawa  Tak Kunihiro  Eizo Nakamura 《Geostandards and Geoanalytical Research》2014,38(1):95-102

Software designed for analytical laboratories to guarantee traceability and accessibility of rocks with their geochemical properties has been developed. The software documents the sample origin, current sample location and the location of any sample subsets (e.g., thin sections, solutions, etc.), and archives all associated geochemical data sets. The software can be installed on a personal computer so is available for use in any laboratory and allows curation before and after publication. The software will be of use in integrating and sharing geological reference materials within and among institutes. In this article, the system design and implementation are detailed. All source codes for the software are available at http://dream.misasa.okayama-u.ac.jp/ .  相似文献   

Depositional process of the Byk-E tephra bed in the Chiba section,central Japan: A marker bed defining the Global Boundary Stratotype Section and Point for the Chibanian Stage     

Yasufumi Satoguchi  Yoshihiro Takeshita  Hiroomi Nakazato  Yusuke Suganuma 《Island Arc》2021,30(1):e12432

  相似文献