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Pressure effect on cathodoluminescence emission intensity recorded in metamorphosed detrital zircons of the Sanbagawa schists 压力对三八川片岩变质碎屑锆石阴极发光发射强度的影响
IF 1.5 4区 地球科学
Island Arc Pub Date : 2022-04-06 DOI: 10.1111/iar.12444
Yuta Tsuchiya, Kazumasa Aoki, Tetsu Kogiso, Yoshiki Seo, Shogo Aoki, Hirotsugu Nishido
{"title":"Pressure effect on cathodoluminescence emission intensity recorded in metamorphosed detrital zircons of the Sanbagawa schists","authors":"Yuta Tsuchiya,&nbsp;Kazumasa Aoki,&nbsp;Tetsu Kogiso,&nbsp;Yoshiki Seo,&nbsp;Shogo Aoki,&nbsp;Hirotsugu Nishido","doi":"10.1111/iar.12444","DOIUrl":"10.1111/iar.12444","url":null,"abstract":"<p>The cathodoluminescence (CL) emission and spectra analyses were conducted on detrital zircons in the Cretaceous Sanbagawa schists to describe changes in CL properties of zircons associated with metamorphism. In addition, high-pressure (HP) and high-temperature (HT) experiments were conducted on the non-metamorphosed Miocene Ashizuri igneous zircons, and the CL emission intensities obtained from them were compared with those of the Sanbagawa zircons. As a result, as compared to low-grade Sanbagawa zircons, the emission intensities of the high-grade Sanbagawa zircons reduced. The emission intensities produced from the HP-treated Ashizuri zircons, on the other hand, were twice as high as those generated from untreated zircons, but less than half of those generated from HT-treated zircons. Combining our results with previous studies on the temperature influence on zircon CL properties, it indicates that increasing metamorphic pressure decreases the increase in the CL emission intensity of metamorphosed detrital zircons resulting from the increasing temperature. The pressure effect on the emission intensity of zircon during metamorphism might be larger than the temperature effect.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42440920","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Santonian-Campanian dinoflagellate cyst biostratigraphy and paleoenvironment of the Krishna-Godavari Basin, India 印度Krishna‐Godavari盆地Santonian‐Campanian甲藻囊生物地层学和古环境
IF 1.5 4区 地球科学
Island Arc Pub Date : 2022-03-30 DOI: 10.1111/iar.12443
Ashish K. Mishra, Arun Deo Singh, Vandana Prasad
{"title":"Santonian-Campanian dinoflagellate cyst biostratigraphy and paleoenvironment of the Krishna-Godavari Basin, India","authors":"Ashish K. Mishra,&nbsp;Arun Deo Singh,&nbsp;Vandana Prasad","doi":"10.1111/iar.12443","DOIUrl":"10.1111/iar.12443","url":null,"abstract":"<p>The present study deals with the biostratigraphic framework of Late Cretaceous sediments of the subsurface Well (DNG) “A” (2085–1840 m depth) from the Raghavapuram/Chintalapalli Shale of the Krishna-Godavari Basin and analyzed the palynological assemblage. The recorded palynological assemblage is dominated by marker dinoflagellate cyst viz. <i>Areoligera coronata, Areoligera senonensis, Heterosphaeridium spinaconjunctum, Nelsoniella aceras, Nelsoniella semireticulata, Odontochitina porifera, Xenascus ceratioides</i>, and <i>Xenascus gochtii</i> species. The last occurrence (LO) of significant species of dinoflagellate cysts is considered for the biostratigraphic establishment. On the basis of dinoflagellate cyst biostratigraphy, the examined sequences correspond to the Santonian-Campanian age. The dominance of gonyaulacoid dinoflagellate cysts is interpreted in terms of sea-level fluctuation and other paleoenvironmental signals through this biostratigraphic establishment. The recorded dinoflagellate cysts indicate the outer neritic, cool depositional environment. The sea-level rise, recorded in our study is linked with the transgressive phase during the Late Cretaceous (Santonian-Campanian) period.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41451841","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Miocene Nautilus (Mollusca, Cephalopoda) from Taiwan, and a review of the Indo-Pacific fossil record of Nautilus 台湾中新世Nautilus(软体动物,头足目)及其在印度-太平洋的化石记录
IF 1.5 4区 地球科学
Island Arc Pub Date : 2022-03-16 DOI: 10.1111/iar.12442
James L. Goedert, Steffen Kiel, Cheng-Hsiu Tsai
{"title":"Miocene Nautilus (Mollusca, Cephalopoda) from Taiwan, and a review of the Indo-Pacific fossil record of Nautilus","authors":"James L. Goedert,&nbsp;Steffen Kiel,&nbsp;Cheng-Hsiu Tsai","doi":"10.1111/iar.12442","DOIUrl":"10.1111/iar.12442","url":null,"abstract":"<p>The fossil record of the cephalopod genus <i>Nautilus</i> has been obscured because a few influential taxonomists during the 20th Century decided that fossils similar to <i>Nautilus</i> were instead other genera. We now recognize fossils once classified as species of other genera as species of <i>Nautilus</i>. This includes fossils from Miocene rocks of Taiwan that were previously described as <i>Kummelonautilus taiwanum</i> but herein recognized instead as being the northernmost Neogene record of <i>Nautilus</i> in the Indo-Pacific region. The name is corrected to <i>Nautilus taiwanus</i>, and now known to occur in two formations in central Taiwan, the early Miocene Shihmentsun and early to middle Miocene Houdongkeng formations. Miocene fossils from Indonesia that were placed in other genera are now considered to represent <i>Nautilus</i> as they were originally assigned, in addition to several Miocene species from Australia, which provide the southernmost Neogene fossil record for the genus. Some of these Indo-Pacific fossils may represent the same species, but more specimens are needed to determine the amount of variability within these Neogene taxa.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12442","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43132303","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Variety of the drift pumice clasts from the 2021 Fukutoku-Oka-no-Ba eruption, Japan 2021年日本福冈火山喷发的浮石碎屑种类
IF 1.5 4区 地球科学
Island Arc Pub Date : 2022-02-09 DOI: 10.1111/iar.12441
Kenta Yoshida, Yoshihiko Tamura, Tomoki Sato, Takeshi Hanyu, Yoichi Usui, Qing Chang, Shigeaki Ono
{"title":"Variety of the drift pumice clasts from the 2021 Fukutoku-Oka-no-Ba eruption, Japan","authors":"Kenta Yoshida,&nbsp;Yoshihiko Tamura,&nbsp;Tomoki Sato,&nbsp;Takeshi Hanyu,&nbsp;Yoichi Usui,&nbsp;Qing Chang,&nbsp;Shigeaki Ono","doi":"10.1111/iar.12441","DOIUrl":"10.1111/iar.12441","url":null,"abstract":"<p>Pumice rafts that arrived at the Nansei Islands, Japan, provided a unique opportunity to investigate the Fukutoku-Oka-no-Ba (FOB) eruption of August 2021. Despite drifting for 2 months for ~1300 km, the drift pumice raft had a large volume and contained a variety of pumice clasts, some of which were deposited during a high tide in a typhoon, while others were washed up on a sandy beach. Most of the drift pumice clasts are gray in color, vesicular, and have a groundmass containing black enclaves. Rare black pumice and the main gray pumice components have similar trachytic compositions, with SiO<sub>2</sub> = 61–62 mass% and total alkalis = 8.6–10 mass% (on an anhydrous basis). Both pumice types contain clinopyroxene, plagioclase, and rare olivine phenocrysts. Thin-section observations show that the gray pumice has more elongated vesicles as compared with the black pumice that has spherical vesicles, even where the two types of pumice are in the same clast. The glass in the black pumice is transparent and brown in color, while that in the gray pumice is colorless. No micro or nano-crystals were observed during electron and optical microscopy. Raman spectra of the brown-colored glass exhibit a clear magnetite peak, suggesting magnetite nanolites cause the brown color. High-Mg olivine in the black pumice has an equilibrium temperature of c. 1200 °C and a rim diffusion profile indicative of re-equilibration with the surrounding melt over a period of hours to days. The textural relationships between the gray and black pumice suggest that the black pumice had become black and viscous before the two types of pumice mixed. Therefore, crystallization of magnetite nanolites and a corresponding increase in melt viscosity were important in the eruption preparation process, which then resulted in a large-scale Plinian eruption.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12441","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47720828","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 21
Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources 日本西南纪伊半岛中部中部构造线周围广泛热异常的识别:可能的热源
IF 1.5 4区 地球科学
Island Arc Pub Date : 2022-01-21 DOI: 10.1111/iar.12440
Ken Yamaoka, Simon R. Wallis
{"title":"Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources","authors":"Ken Yamaoka,&nbsp;Simon R. Wallis","doi":"10.1111/iar.12440","DOIUrl":"10.1111/iar.12440","url":null,"abstract":"<p>Application of Raman spectroscopy of carbonaceous material thermometry to samples of metasedimentary rock from the low-grade Sanbagawa belt in the central Kii peninsula reveals a progressive decrease in temperature from ~390 °C close to the northern boundary, a major continental shear zone—the median tectonic line (MTL)—to ~270 °C and ~7 km to the south and roughly constant temperature distribution thereafter. Within the Sanbagawa belt, the thermal structure is not significantly modified by slip-on fault boundaries between different geological units or folding. Meso- and microstructural observations combined with strain analysis using detrital grains in meta-mudstone indicate a similar deformation history throughout the area and no correlation between ductile strain and temperature gradients. These observations suggest the observed thermal structure was developed after the main stages of ductile deformation of the Sanbagawa belt were complete and are not due to localized preferential exhumation along with the MTL. The observations also require a heat source along with the MTL. Order of magnitude estimates suggest the influx of warm fluid along the MTL are viable causes of the observed thermal anomaly. Although shear heating would be another possible explanation, thermal calculations require anomalous fast slip rates along the MTL and much greater frictional strength than generally considered reasonable. For these reasons, fluid infiltration is our preferred model.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46322170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Geochemistry and Sr–Nd isotopes of the Late Mesozoic lamprophyres in the Chaohu area, eastern China: Petrogenesis and tectonic implications 中国东部巢湖地区晚中生代煌斑岩的地球化学和Sr-Nd同位素:岩石成因和构造意义
IF 1.5 4区 地球科学
Island Arc Pub Date : 2022-01-06 DOI: 10.1111/iar.12438
Mo Chen, Longming Li, Tianxiang Kan, Hang Liu, Xilin Zhao, Jiahao Li, Xu Han
{"title":"Geochemistry and Sr–Nd isotopes of the Late Mesozoic lamprophyres in the Chaohu area, eastern China: Petrogenesis and tectonic implications","authors":"Mo Chen,&nbsp;Longming Li,&nbsp;Tianxiang Kan,&nbsp;Hang Liu,&nbsp;Xilin Zhao,&nbsp;Jiahao Li,&nbsp;Xu Han","doi":"10.1111/iar.12438","DOIUrl":"10.1111/iar.12438","url":null,"abstract":"<p>Late Mesozoic lamprophyres are widespread in the Chaohu area of the Lower Yangtze region, eastern China. These mantle-derived rocks are of great significance for understanding the characteristics of mantle source and tectonic environment of eastern China during the Late Mesozoic. The lamprophyres from the Chaohu area can be divided into two types. The type-I lamprophyres have low SiO<sub>2</sub> (43.8–44.5 wt.%) and TiO<sub>2</sub> (1.06–1.14 wt.%), high MgO (13.5–17.5 wt.%) and high contents of compatible elements, and are enriched in LREE and LILE but depleted in HFSE. They have high initial <sup>87</sup>Sr/<sup>86</sup>Sr (0.70767–0.70904) and negative εNd (<i>t</i>) (−4.8 to −4.4). The type-II lamprophyres are characterized by low contents of SiO<sub>2</sub> (43.0–45.4 wt.%), high TiO<sub>2</sub> (1.74–2.55 wt.%), MgO (9.17–15.4 wt.%), and compatible elements. They are also enriched in LREE and LILE but depleted in HFSE. They show enriched Sr-Nd isotopic compositions with initial <sup>87</sup>Sr/<sup>86</sup>Sr values (0.70773–0.70886) and εNd (<i>t</i>) values (−8.6 to −7.8). The type-I lamprophyres show higher Mg<sup>#</sup> and MgO contents but significant lower TiO<sub>2</sub> than the type-II lamprophyres. In addition, the type-I lamprophyres have relatively similar initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios but higher εNd(<i>t</i>) values than the type-II lamprophyres. The difference of geochemical characteristics between the type-I and type-II lamprophyres may be caused by different degrees of partial melting of an amphibole-bearing garnet lherzolite mantle. The lithospheric mantle was metasomatised by the fluids caused by the rollback of the Paleo-Pacific plate subduction during the Late Cretaceous.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49442597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Changes in elements and magnetic properties of Sendai Bay sediments caused by the 2011 Tohoku-oki tsunami 2011年东北海啸引起仙台湾沉积物元素和磁性的变化
IF 1.5 4区 地球科学
Island Arc Pub Date : 2022-01-06 DOI: 10.1111/iar.12437
Hirokuni Abe, Noriko Kawamura, Naoto Ishikawa, Tetsu Kogiso
{"title":"Changes in elements and magnetic properties of Sendai Bay sediments caused by the 2011 Tohoku-oki tsunami","authors":"Hirokuni Abe,&nbsp;Noriko Kawamura,&nbsp;Naoto Ishikawa,&nbsp;Tetsu Kogiso","doi":"10.1111/iar.12437","DOIUrl":"10.1111/iar.12437","url":null,"abstract":"<p>Nearshore marine sediments deposited along island arcs can preserve evidence of past disaster events, such as tsunamis. Evidence of a tsunami that occurred off the Pacific coast of Tohoku, Japan, on March 11, 2011, was likely preserved in marine sediments. Using geochemical and rock magnetic analyses, this study aimed to investigate tsunami records preserved in marine sediments in Sendai Bay, located west of the epicenter of the 2011 Tohoku earthquake. We collected sediment samples at five stations (S-1, S-2, S-3, S-4, and S-5) in Sendai Bay from 2002 to 2014. We compared the samples collected before and after the tsunami. We established that the silt component increased, while that of fine sand decreased at stations S-3, S-4, and S-5 in the 2011 sediment sample. Notably, the concentrations of terrestrial and industrial metallic elements (Cu, Zn, and Pb) and total nitrogen, carbon, and sulfur amounts increased, while the magnetic susceptibility and isothermal remanent magnetization values decreased after the tsunami. We also found that Ti-poor magnetite increased in the 2011 samples, indicating tsunami-mediated changes. The study area experienced a large typhoon 6 months after the tsunami, leading to flooding. The elevation in the total organic carbon and total nitrogen ratio in the 2012 sample suggested that terrestrial organic matter was supplied by the flood.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44077625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Volume 30 Acknowledgements 第30卷致谢
IF 1.5 4区 地球科学
Island Arc Pub Date : 2021-12-07 DOI: 10.1111/iar.12433
{"title":"Volume 30 Acknowledgements","authors":"","doi":"10.1111/iar.12433","DOIUrl":"10.1111/iar.12433","url":null,"abstract":"","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2021-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47142164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
U–Pb dating of detrital zircon from Permian successions of the South Kitakami Belt, Northeast Japan: Clues to the paleogeography of the belt 日本北上南带二叠系碎屑锆石U-Pb定年:古地理线索
IF 1.5 4区 地球科学
Island Arc Pub Date : 2021-12-03 DOI: 10.1111/iar.12435
Yuxiao Li, Makoto Takeuchi
{"title":"U–Pb dating of detrital zircon from Permian successions of the South Kitakami Belt, Northeast Japan: Clues to the paleogeography of the belt","authors":"Yuxiao Li,&nbsp;Makoto Takeuchi","doi":"10.1111/iar.12435","DOIUrl":"10.1111/iar.12435","url":null,"abstract":"<p>The South Kitakami Belt in the northeast Japan is unique in presence of a thick Paleozoic–Mesozoic sedimentary rocks. The Permian sedimentary succession in the Maiya area of this belt is divided into the Nishikori, Tenjinnoki, and Toyoma formations, in ascending stratigraphic order. The Tenjinnoki Formation includes the Yamazaki Conglomerate Member containing granitic clasts. We performed U–Pb dating for detrital zircon of one sample of tuffaceous sandstone from the Nishikori Formation, six samples of sandstone from the Tenjinnoki and Toyoma formations, and five granitic clasts from the Yamazaki Conglomerate using laser ablation-inductively coupled plasma-mass spectrometry. Our dating results show that the tuffaceous sandstone sample has two age peaks at 287 and 301 Ma for the Nishikori Formation, three age peaks at 320–300, 290, and 270 Ma for the Tenjinnoki and Toyoma Formation, and ages of 311, 300, and 270 Ma from granitic clasts of the Yamazaki Conglomerate. In addition, older ages of 452–435 and 380 Ma were obtained from some zircon grains of the sandstone and granitic clasts. Our results suggest igneous activity in these periods. The South Kitakami Belt's origin with respect to continental blocks has been discussed in regard of the margin of North China Block or South China Block. Based on the stratigraphic ages and timing of igneous activity, we conclude that during the Permian the South Kitakami Belt was located at the margin of the South Central Asian Orogenic Belt, near the Solonker-Xra Moron-Changchun suture and the North China Block in East Asia.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2021-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41893812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 2
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 日本中部千叶剖面Byk‐E tephra床的沉积过程:定义全球边界层型剖面和千叶阶点的标志层
IF 1.5 4区 地球科学
Island Arc Pub Date : 2021-11-15 DOI: 10.1111/iar.12432
Yasufumi Satoguchi, Yoshihiro Takeshita, Hiroomi Nakazato, Yusuke Suganuma
{"title":"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","authors":"Yasufumi Satoguchi,&nbsp;Yoshihiro Takeshita,&nbsp;Hiroomi Nakazato,&nbsp;Yusuke Suganuma","doi":"10.1111/iar.12432","DOIUrl":"10.1111/iar.12432","url":null,"abstract":"<p>The global boundary stratotype section and point (GSSP) for the Chibanian Stage and Middle Pleistocene Subseries is present at the base of the Byk-E tephra bed in the Chiba section, located in the central Boso Peninsula, Japan. The Byk-E tephra bed, which erupted from the older Ontake Volcano, is a conspicuous marker bed in the Chiba section; therefore, it provides a clear local and regional marker for the GSSP. However, the sedimentological characteristics of the Byk-E tephra bed have not been well documented. Here, we provide a detailed description and an isopach map of the Byk-E tephra bed based on the lithofacies, grain-size compositions, and grain orientations in the Chiba section and other localities in the Boso Peninsula. The lithofacies and grain size compositions of the tephra bed show that the lower part of the bed show no evidence of flow-induced deposition. These results suggest that the Byk-E tephra bed is most likely deposited as fallout deposits under a weak bottom current that could not direct the heavy mineral grains. Therefore, the Byk-E tephra bed is not to erode the underlying bed during the deposition, indicating that there is no stratigraphic discontinuity. The isopach map drawn from the observed thickness of the fallout unit, show that the distribution of the Byk-E tephra extends more than 260 km but a limited azimuthal range.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2021-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45829644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
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