Island Arc最新文献

{"title":"Geochronology and geochemistry of early Palaeozoic ultramafic rocks along Jiangshan-Shaoxing Fault and their tectonic significance","authors":"Cunzhi Wang,&nbsp;Zhizhong Huang,&nbsp;Qingbo Zhu,&nbsp;Guangfu Xing,&nbsp;Guodong Jin,&nbsp;Pingli Chu","doi":"10.1111/iar.12493","DOIUrl":"10.1111/iar.12493","url":null,"abstract":"<p>The origins of early Paleozoic orogen in South China have two different models: subduction model and intra-continental model. Here we report two new identification of ~440 Ma arc-related ultramafic intrusions in Tingzifan (TZF) and Fomuting (FMT) along Jiangshan-Shaoxing fault (JSF) in South China, respectively. The Silurian ultramafic intrusions are composed of olivine pyroxenite, the SiO₂, MgO and TiO₂ contents of olivine pyroxenites are 39.67–41.25 wt%, 28.98–31.38 wt% and 0.23–0.51 wt%, respectively. The geochemical compositions of the olivines, clinopyroxenes and hornblendes suggest an arc-related environment for these intrusions. As for the whole-rock trace elements, the ultramafic intrusions contain low total rare earth element (REE) contents (27.59–34.26 μg/g) and high field strength elements (HFSEs), such as Nb, Zr, Hf, Ti, and are systematically enriched in large ion lithophile elements and light rare earth elements (LREEs). Trace element compositions share most features of Alaskan-type ultramafic-mafic intrusions. Isotopically, the TZF and FMT ultramafic intrusions are characterized by negative Zircons <i>ε</i>_Hf(<i>t</i>) values (0.38–7.54). Combined with their whole-rock and mineral chemistry as well as zircon Hf isotope, we suggest that the Alaskan-type TZF and FMT pyroxenite were formed at the root of the continental arc by underplating and fractional crystallization of mafic magma which derived from subduction metasomatized mantle source. Thus, we proposed that the early Paleozoic ultramafic–mafic along Jiangshan-Shaoxing fault were most likely related to early Paleozoic subduction of the Paleo-South China Ocean between Cathaysia and Yangtze blocks, arguing that the origins of early Paleozoic orogen in the South China Block is a typical subduction-accretionary collisional-type orogenic belt rather than an intraplate belt.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43950624","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}

{"title":"U–Pb and fission-track dating of Miocene hydrocarbon source rocks in the Akita Basin, Northeast Japan, and implications for the timing of paleoceanographic changes in the sea of Japan","authors":"Takeshi Nakajima,&nbsp;Hideki Iwano,&nbsp;Tohru Danhara,&nbsp;Takafumi Hirata,&nbsp;Kenta Asahina,&nbsp;Koji U. Takahashi,&nbsp;Yasuaki Hanamura","doi":"10.1111/iar.12490","DOIUrl":"10.1111/iar.12490","url":null,"abstract":"<p>Middle to Late Miocene organic-rich siliceous mudstones (Onnagawa Formation) in the Akita Basin, Northeast Japan have been an important target for both paleoceanographic studies and hydrocarbon exploration in Japan. However, the reliable age of their formation has remained poorly constrained. Here, we report new zircon U–Pb and fission-track ages of the Onnagawa Formation from a previously well-studied outcrop route in the Yashima area, central Akita Basin. The thin tuff bed in the lower Onnagawa Formation was dated at around 11.6 Ma, whereas thin tuff beds in the upper Onnagawa Formation was dated at 10.4–9.6 Ma. The new age model constrains the base of the succession as older than 15.6–13.8 Ma and the top of the succession as 8.7–8.2 Ma. The results suggest that the lowest part of the succession was deposited before the Onnagawa Stage. The new age model indicates a rapid deposition in the lower Onnagawa Stage. The new age model also clarifies a temporary decrease in the sedimentation rate during 10.9–9.4 Ma, which coincided with a hiatus or slow deposition reported from other areas along the Sea of Japan coast. The new age model also revises the timing of paleoceanographic changes, of the best hydrocarbon source horizon, and of hydrothermal activity responsible for seafloor chemoautotrophic communities in the Akita Basin. This revised timing reveals that the onset of paleoceanographic changes from oxidizing to anoxic bottom environments favorable for hydrocarbon source rock formation was closely related to the tectonic uplift of the Northeast Japan Arc at ~12 Ma, whereas the timing of hydrothermal activity was related to the following extensional tectonics at ~9 Ma. The results of this study thus shed light on hitherto unclarified relationships between tectonics, volcanism, and paleoceanographic changes in the Sea of Japan.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12490","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47961450","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}

{"title":"Late Cretaceous tectono-magmatism of southeast China: Evidence from Qushandao Granite in the eastern Zhejiang province","authors":"Pingli Chu,&nbsp;Lang Bao,&nbsp;Zheng Duan,&nbsp;Minggang Yu,&nbsp;Yanhui Zhu","doi":"10.1111/iar.12494","DOIUrl":"10.1111/iar.12494","url":null,"abstract":"<p>The Qushandao Granite, mainly composed of alkali-feldspar granite, is situated in the eastern Zhejiang province of coastal southeast China. In this paper, we present whole-rock geochemistry, zircon U–Pb geochronology, and Hf isotopes to constrain the age, magma sources, and geodynamic setting of the Qushandao Granite. LA-ICP-MS zircon U–Pb dating results revealed that the Qushandao Granite was emplaced in the Late Cretaceous (101–98 Ma). Geochemically, the Qushandao Granite exhibits relatively high silica and alkali contents, metaluminous to weakly peraluminous (A/CNK = 0.98–1.02), and low abundances of phosphorus, titanium, magnesium, and calcium. It is also characterized by enrichment in Rb, K, Th, and depletion in Nb, Ta, P, Ti, and Sr with moderately to weakly negative europium anomalies (Eu/Eu* = 0.71–0.87). Furthermore, the Qushandao Granite displays lower FeO^T/MgO, 10⁴ × Ga/Al, and Zr + Nb + Ce + Y values relative to typical A-type granites. Therefore, we classify the Qushandao Granite as calc-alkaline I-type granite based on a synthesis of geological and geochemical characteristics. The Qushandao Granite shows variable zircon Hf isotopic compositions (<i>ε</i>_Hf(t) = −7.6 to +2.3) and <i>T</i>_DM2 model ages of 1.40–0.83 Ga with a mean value of 1.17 Ga. We argue that the Qushandao Granite was most likely generated by mixing of mantle-derived mafic magma and crust-derived felsic magma in the lower crust, and that it was formed during post-collisional extension in the Late Cretaceous, related to the gradually increasing subduction angle of the Paleo-Pacific plate.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41585972","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}

{"title":"Oxygen isotopes of the Japanese stalagmites as global and local paleoclimate proxies","authors":"Akihiro Kano,&nbsp;Hirokazu Kato,&nbsp;Akira Murata","doi":"10.1111/iar.12491","DOIUrl":"10.1111/iar.12491","url":null,"abstract":"<p>Stalagmite oxygen isotopes (δ¹⁸O) have been used to reconstruct terrestrial paleoclimates during the late Pleistocene and Holocene. However, the interpretation of the δ¹⁸O is not straightforward when determining the factor controlling δ¹⁸O; temperature or water δ¹⁸O. In addition, the water δ¹⁸O changes with rainfall intensity (amount effect), rainfall seasonality, and some other factors. Here, we first review the hydrochemical processes and behaviors of the oxygen isotopes and the other proxies in a cave system, which are fundamental for interpretating the paleoclimatic signals. We then introduce the oxygen isotope records of Japanese caves. Some of the Japanese stalagmites demonstrated a δ¹⁸O profile that represented a similar pattern to the Chinese stalagmite records, but had relatively small δ¹⁸O amplitudes, which can be explained mainly by temperature changes rather than the amount effect. This demands a reversal of the relationship between climate and rainwater δ¹⁸O across the Japanese Islands. Using δ¹⁸O data for rainwater samples from four sites in Japan (in Niigata, Fukuoka, Gifu and Mie Prefectures), we presents the results of model calculations to verify how the rainfall intensity and the seasonality relate with the δ¹⁸O of rainwater. A significant correlation coefficient was observed in Niigata, where the rainfall δ¹⁸O decreases with an increase in the annual amount of rainfall, and with a decrease in the winter rainfall. Similar trends were observed in Fukuoka, whereas while the results of Gifu and Mie exhibited no significant trends. Temperature change was would be the main factor controlling the stalagmite δ¹⁸O at the latter two sites. For a better understanding of the stalagmite δ¹⁸O records, the measurement of fluid inclusions and carbonate clumped isotopes can be used to evaluate the effect of temperature on the stalagmite δ¹⁸O, as well as to reconstruct the water δ¹⁸O. We predict that the ¹⁷O excess in stalagmites reconstructs the seasonal shift in the vapor sources.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12491","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45161567","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}

{"title":"Records of Nanhua island arc activity between the north and south Wuyi terranes in the Cathaysia Block","authors":"Huan Liu,&nbsp;Xilin Zhao,&nbsp;Jian Jiang,&nbsp;Jinguo Zhang","doi":"10.1111/iar.12492","DOIUrl":"10.1111/iar.12492","url":null,"abstract":"<p>The characteristics and pre-Devonian tectonic evolution between the North and South Wuyi terranes are important for understanding the tectonic framework and aggregation of the micro-terrenes in the Cathaysia Block, as well as the evolution of the South China Block. This paper provides systematic studies on the petrologic features, zircon U–Pb geochronology and geochemical characteristics of the low-grade meta-volcanic and metasedimentary rocks between the North and South Wuyi terranes, and proposes an alternative model for their tectonic evolution. Geochronological data show that the metasedimentary rocks have detrital zircon U–Pb ages ranging from 583 to 3284 Ma with a record of the Nanhua period (764–722 Ma). The meta-volcanic rocks have centralized ages ranging from 720 to 760 Ma and yield weighted average ages of 746–733 Ma. Geochemical studies of the meta-volcanic rocks show similar characteristics to island arc magmatic rocks, with relatively high SiO₂, K₂O and Al₂O₃, low TFeO and MgO contents, and enrichment of Rb, Ba, Th, Pb and Hf elements, and depletion in Ti, Nb, Sr and Ta. These features indicate that the North and South Wuyi terranes may have collided at about 746–733 Ma and eventually pieced together at 583 Ma, with the protoliths of the meta-volcanic rocks and the metasedimentary rocks formed in the same tectonic setting of an island arc during Nanhua island arc magmatism related to the collision. The occurrence of Nanhua island arc activity between the North and South Wuyi terranes suggests that multi-micro-terranes and multi-stage collisions may be major characteristics of the tectonic evolution process in the Cathaysia Block.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41493635","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}

{"title":"A trip into molten sulfur","authors":"Hikaru Sawada,&nbsp;Chong Chen,&nbsp;Hisanori Iwamoto,&nbsp;Ken Takai","doi":"10.1111/iar.12489","DOIUrl":"10.1111/iar.12489","url":null,"abstract":"<p>Lakes of molten sulfur are features sometimes found in seafloor hydrothermal vent systems. Daikoku of the northern Mariana Arc is notable for being home to one of such features inside its summit caldera, the “Sulfur Cauldron” discovered in 2006. A number of oceanographic research cruises since then have revealed significant volcanic activities on Daikoku Seamount, including an eruption event in 2014 leading to the formation of a new basin-like crater. How this event impacted the sulfur lake on Daikoku Seamount remained unclear. Here, we revisited Daikoku Seamount with a remotely operated vehicle to show that the new crater is currently home to a much larger molten sulfur lake than the Sulfur Cauldron, which we name the “Rengoku” sulfur lake. Our samples provided new insights on the structure of submarine sulfur lakes, and contribute to the time-series observation of volcanic and hydrothermal activities on Daikoku Seamount.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45963603","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}

{"title":"Age, geochemistry, mineralization, and tectonic significance of felsic-intermediate dikes in Shuangqishan Au deposit, Cathaysia block, South China","authors":"Feipeng Fan,&nbsp;Fan Xiao,&nbsp;Yan Zhou,&nbsp;Shizhong Chen","doi":"10.1111/iar.12482","DOIUrl":"10.1111/iar.12482","url":null,"abstract":"<p>The Shuangqishan Au deposit (&gt;15 t) is located in the Dehua-Youxi-Yongtai goldfield of the southeastern Cathaysia Block, South China. There are three stages of granites in the Shuangqishan Au deposit, the pre-mineralization granite porphyry formed in the Middle Jurassic (~166.0 ± 0.8 Ma), the metallogenic granite porphyry and monzonite porphyry formed in the late stage of the Late Jurassic (153–151 Ma), the post-mineralization granites (granite porphyry, the masanophyre, the dioritic porphyrite) formed in the Early Cretaceous (129.0–120.0 Ma). All rocks are characterized by high-K calc-alkaline and shoshonities series, the per-mineralization granites are enriched in Rb, Th, K, Zr, and Hf, depleted in Ba, P, and Ti, significant negative Eu anomaly and distinctly tetrad effect with highly fractionated I-type granitoids characteristics. The metallogenic granites and the post-mineralization granite porphyry are enriched in K, Rb, Th, Ce, Zr, Hf, and Y, enriched in LREE, strongly depleted in Sr, Ba Ta, P, Ti, have moderate negative Eu anomalies with I-type granites characteristics. However, the post-mineralization dioritic porphyrite displays strong depletions Sr, Ta, P, and Ti whereas Rb, Th, Ce, and Sm are enriched, enriched in LREE with weakly negative Eu anomalies. The metallogenic granite porphyry is significantly enriched in Au, As, Sb, W, Mo, and Bi, especially enriched in Au. The Lu-Hf isotopic data indicate that the magma source comes from the partial melting of the Paleoproterozoic crust, the minor part from the mantle in the Early Cretaceous. Therefore, we propose that the granitoids formed in the subducted plate environment from the Middle Jurassic to the Early Cretaceous, the Late Jurassic I-type granites (~153–146 Ma), The Shuangqishan Au deposit was formed in the stage from compression to extension, the Early Cretaceous granites (~129–114 Ma) mainly formed in the extensional environment and destroyed gold ore bodies.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43141702","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}

{"title":"Apatite U–Pb dating of dinosaur teeth from the Upper Cretaceous Nemegt Formation in the Gobi Desert, Mongolia: Contribution to depositional age constraints","authors":"Myu Tanabe,&nbsp;Kazumasa Aoki,&nbsp;Kentaro Chiba,&nbsp;Mototaka Saneyoshi,&nbsp;Shota Kodaira,&nbsp;Hirotsugu Nishido,&nbsp;Buuvei Mainbayar,&nbsp;Khishigjav Tsogtbaatar,&nbsp;Shinobu Ishigaki","doi":"10.1111/iar.12488","DOIUrl":"10.1111/iar.12488","url":null,"abstract":"<p>The Nemegt Formation in the Gobi Desert, Mongolia, hosts abundant dinosaur and other vertebrate remains, the ages of which are uncertain due to a lack of radioactive dating. In order to more strictly constrain the depositional age of Nemegt Formation, we conducted U–Pb isotope, trace elements, and Y-screening analyses using laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS) on apatites of five <i>Tarbosaurus bataar</i> teeth collected from the middle Nemegt Formation. As a result, the age of 66.7 ± 2.5 Ma was obtained from one of the samples which is suggested to be least affected by secondary alteration of the U distribution, and this can be interpreted as a lower limit for fossilization of the tooth samples. Combined with the previously suggested relative age of the Nemegt Formation based on faunal occurrences, our data supports the deposition of the middle–upper Nemegt Formation during the Maastrichtian stage. Given that the depositional age of the Nemegt Formation has not been examined by isotope dating directly using fossils and minerals from the formation, this study is the first to report that the depositional ages of the vertebrate-bearing strata in the Gobi can be discussed by fossil apatite U–Pb dating in combination with the Y-screening method.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44992700","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}

{"title":"Chronological and geochemical characteristics of metavolcanic rocks in the Nanping-Ninghua tectonic belt: Constraints on the formation of the Cathaysia block","authors":"Huicheng Wen,&nbsp;Xilin Zhao,&nbsp;Guocan Wang,&nbsp;Huan Liu,&nbsp;Mincheng Xu,&nbsp;Yang Jiang","doi":"10.1111/iar.12486","DOIUrl":"10.1111/iar.12486","url":null,"abstract":"<p>The tectonic properties of the Nanping-Ninghua tectonic belt (NNTB) play a crucial role in understanding the tectonic evolution of the Wuyi orogenic belt, which is related to the Neoproterozoic-Paleozoic tectonic evolution of the Cathaysian Block. In this study, We present comprehensive petrological, geochronological, and geochemical data on the metavolcanic rocks from the Louqian Formation in Changting, Fujian Province. Our results show that volcanism in Changting occurred between 740.4 and 723.5 Ma, based on zircon U–Pb data for the metavolcanic rocks. The metavolcanic rocks have SiO₂ contents ranging from 68.22 to 71.56 wt %, high Al₂O₃ and Na₂O + K₂O contents (13.30–15.19 wt % and 7.56–8.25 wt %, respectively), and low CaO, MgO, and FeO_T contents (0.09–1.25 wt %, 0.72–0.96 wt %, and 1.57–3.16 wt %, respectively). These samples are enriched in large-ion lithophile elements (LILEs) such as Ba and Rb, and depleted in high-field-strength elements (HFSEs) including Nb, Ta, and Ti, with significant negative Eu anomalies, indicating an affinity for arc igneous rocks. Based on previous geological studies, we suggest that the NNTB formed in an active continental margin environment during the Nanhua Period. The subduction of oceanic crust led to the formation of the volcanic belt along the Nanping-Ninghua continental margin, which was active until 696 Ma. During the Neoproterozoic, the North and South Wuyi terranes did not merge to form a single Wuyi terrane, and the Cathaysia Block was composed of several terranes.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42196339","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}

{"title":"Elevated sedimentation of clastic matter in pelagic Panthalassa during the early Olenekian","authors":"Shun Muto,&nbsp;Satoshi Takahashi,&nbsp;Satoshi Yamakita","doi":"10.1111/iar.12485","DOIUrl":"10.1111/iar.12485","url":null,"abstract":"<p>The end-Permian mass extinction is thought to have greatly altered biogeochemical cycles. The absence of chert and dominance of claystone in low-latitude pelagic deep-sea sedimentary sequences of Early Triassic Panthalassa (the deep-sea chert gap) has been believed to record radiolarian die-off and consequent decline in biogenic silica production. However, recent studies showed that the upper portion of the deep-sea chert gap has sedimentation rates higher than bedded chert, meaning that increased clastic inputs, rather than decreased biogenic silica inputs, resulted in the anomalous lithology. In this study, we focus on the Akkamori-2 section, which preserves a rare sedimentary sequence spanning a large part of the lower portion of the claystone of the deep-sea chert gap. We obtained conodont fossils that allow correlation with sections in South China that have numerous dated tuffs. By projecting the dates of the tuffs to our measured sections, we show that sedimentation rates of the lower portion of the deep-sea chert gap is also higher than bedded chert. Hence, most of the deep-sea chert gap was formed under increased clastic inputs, which likely records disturbance in the terrestrial landscape, probably aridification and/or increased seasonality in arid areas, that lead to elevated dust flux to the pelagic ocean. On the other hand, the idea that the deep-sea chert gap records lingering effects of the mass extinction event on radiolarians cannot explain the high sedimentation rates of the deep-sea chert gap. This previously favored scenario needs to be reconsidered, taking into account the burial efficiency of biogenic silica in the Early Triassic ocean, and also effects of increased clay deposition on preservation of radiolarians.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"32 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42477966","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}