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1.
《Palaeoworld》2022,31(4):658-678
Conglomerates, exposed on either side of the Yarlung Tsangpo suture zone (YTSZ) in southern Tibet, have attracted wide attention in elucidating uplift and erosion histories of the Himalayan-Tibetan orogen. However, the provenance of these conglomerates remains controversial. Although radiolarian-bearing chert clasts within these conglomerates have received little focus, identification of the radiolarian assemblages they contain could shed light on the provenance of these sedimentary units. We present the first report of Upper Jurassic to Lower Cretaceous (upper Kimmeridgian–lower Barremian) radiolarian assemblages recovered from chert clasts within the Liuqu and Gangrinboche conglomerates in the Xigaze area. To extract radiolarian fossils from independent clasts in the conglomerates, a detailed and efficient experimental process is illustrated. The assemblages are well correlated to those in the YTSZ and Tethyan Himalaya, showing typical Tethyan characteristics. The lithology of chert clasts and ages of constituent radiolarian faunas suggest that the chert clasts in Liuqu and Gangrinboche conglomerates were derived from the Bainang terrane. This interpretation implies that Early Cretaceous accretionary complexes in the YTSZ had been exposed and eroded before deposited as clasts in the Cenozoic Liuqu and Gangrinboche conglomerates.  相似文献   

2.
In the Argolis, the Basal Sequence, constituting the eastern Pelagonian margin which bordered the Maliac-Vardar oceanic domain, includes shallow-water carbonates of Late Triassic-Early Jurassic, condensed pelagic limestones of Early-Middle Jurassic, radiolarian cherts of late Middle-Late Jurassic age and siliceous mudstones and sandstones rich in ophiolite fragments. Up-section, coarse breccias, including clasts of boninites derived from the ophiolite obducted onto the Pelagonian margin in Late Jurassic times crop out. Near Angelokastron a small quarry exposes pervasively sheared dark reddish-brown, radiolarian-bearing cherty shales with disrupted fragments of chert and chert nodules impregnated by ferro-manganese oxides. These shales occur in the footwall of a thrust bringing them into contact with the Pantokrator Limestone of the Basal Sequence. We collected more than 30 samples of the chert fragments and the shaly matrix. Thirteen nodules and one matrix sample yielded determinable radiolarians. Low to non-detectable concentrations of trace metals such as Co, Cr, Cu, Ni, Zn, and Pb indicate a hydrothermal origin of the ferro-manganese mineralization. The radiolarian taxa found indicate four age groups for the nodules that are embedded in the siliceous shale matrix that yielded a Middle Jurassic age (middle Bathonian). The first group includes a nodule of Late Triassic age (late Norian to Rhaetian); the second group nodules of Early Jurassic age (late early to late Pliensbachian and probably middle-late Toarcian); the third group nodules of early Middle Jurassic age (Aalenian–Bajocian); the last group finally includes nodules of late Middle Jurassic age (Bajocian–Bathonian). The presence of Upper Triassic to Middle Jurassic Mn-impregnated chert nodules in a Middle Jurassic matrix indicates a deep oceanic environment of deposition outside the Pelagonian realm (easternmost Adria Plate), which at that time was a shallow-water carbonate platform with a thin pelagic limestone cover. The chert nodules are with all certainty derived from the oceanic Maliac-Vardar domain and were, together with their host formation, tectonically emplaced onto the Pelagonian margin. We speculate that these nodules, more lithified than their matrix, were exhumed on the slope of an intra-oceanic accretionary wedge and were redeposited in the Middle Jurassic siliceous mudstones on the floor of the subducting Maliac-Vardar Ocean.  相似文献   

3.
This paper presents a newly found fauna of Ladinian (Middle Triassic) radiolarians from the Hong Hoi Formation of the Lampang Group, Sukhothai Zone, northern Thailand. The Ladinian age determined by the radiolarian fauna concords with the age previously determined by mollusks. The study section consists of intercalated sandstone and shale in the lower part and a thick conglomerate in the upper part. The radiolarian-bearing siliceous beds are intercalated within the lower unit. The lithic sandstone of the lower unit consists mainly of volcanic rock fragments, quartz, and feldspar, whereas the thickly bedded conglomerate of the upper unit is characterized by abundant gravel-sized clasts of volcanic rock and limestone. These lithic features of the study section suggest that during deposition the Hong Hoi Formation was located near a supply of volcanic materials. A forearc basin close to the Sukhothai Arc would be the most suitable environment for the deposition. The Ladinian age determined by the radiolarian fauna supports the occurrence of intensive volcanic activity within the Sukhothai Arc during the Middle Triassic.  相似文献   

4.
Radiolarians provide age constraints for many previously undated terranes in the New England Orogen (NEO), a tectonic collage developed along the eastern margin of Australia.Djungati terrane, the age range of which was previously unknown, contains two distinctive siliceous sedimentary lithofacies. The oldest is a thick sequence of red, ribbon-bedded cherts which probably accumulated in a deep ocean-floor setting far from land. Middle Silurian through Late Devonian radiolarians have been recovered from these cherts. Green tuffaceous cherts which contain a latest Devonian (Famennian) radiolarian fauna depositionally overlie the lower red ribbon-bedded chert sequence. These cherts are intercalated with volcaniclastic sediments and the fauna which they contain can be used to constrain the timing of accretion of older rocks into a subduction complex.Anaiwan terrane, which was also previously undated, contains thin ribbon-bedded cherts which are depositionally overlain by tuffaceous chert, siliceous siltstones and volcaniclastic sediments. Latest Devonian (?late Famennian) and Early Carboniferous radiolarians have been recovered from these cherts and tuffaceous siltstones.Radiolarians also occur in fine-grained siliceous sediments of the Yarrimie Formation, part of the Gamilaroi terrane. These radiolarians are of Late Devonian (Frasnian) affinity and their presence indicates that blocks of limestone, which contain Givetian conodonts and corals and were previously thought to indicate the age of the Yarrimie Formation, are allochthonous.  相似文献   

5.
The opening of the Paleo-Tethys are reconstructed, including the depositional setting and redox conditions, based on an analysis of radiolarian fossils and the geochemistry of a Devonian siliceous succession in the Chiang Dao area of northern Thailand. The succession is subdivided into the following five rock types (in ascending stratigraphic order): black shale (Lower Devonian), siliceous shale (Middle Devonian), tuffaceous chert and tuff (Middle/Upper Devonian), and chert (Upper Devonian). The succession was deposited in continental margin and pelagic environments between the Sibumasu Block and the Indochina-North China blocks. The concentrations of terrestrial-derived elements (Al2O3, TiO2, Rb, and Zr) suggest that the succession (except for the chert) was supplied with terrigenous material and volcanic ash from the adjacent continent, deposited within a SiO2-rich environment. Geochemical indicators of redox conditions (total organic carbon and the Th/U ratio) reveal a gradual change from anoxic to oxic oceanic conditions between the black shale and chert. Taking into account the interpreted depositional setting and redox conditions, the initial Paleo-Tethys developed as a small, closed anoxic-suboxic oceanic basin during the Early to Middle Devonian, located close to the continental margin. Black shale and siliceous shale were deposited in the basin at this time. Opening of the Paleo-Tethys started around the Middle and Upper Devonian boundary, marked by voluminous volcanic activity. The tuffaceous chert was deposited under oxic conditions, suggesting that ash and pumice within the chert were derived from a continental source. After the Late Devonian, the Paleo-Tethys developed as a deep, broad ocean in which pelagic chert was deposited.  相似文献   

6.
云南哀牢山缝合带由于长期未找到晚石炭世至二叠纪深海环境的化石及沉积地层记录,对哀牢山古特提斯盆地演化历史存在着不同认识。文中报道了采自云南墨江坝留地区上三叠统歪古村组底砾岩中的早石炭世和中二叠世放射虫化石,所有放射虫化石发现于4件燧石质砾石中,共计11属9种和7未定种及1属种未定放射虫。其中,3件砾石含有Albaillella deflandrei Gourmelon,Albaillella sinuosa Won and Seo等早石炭世放射虫化石组合,另1件砾石含有Pseudoalbaillella spp.,Quadricaulis scalae Caridroit and De Wever,Cauletella sp.和Ishigaum sp.等中二叠世放射虫化石组合。由此表明,哀牢山缝合带存在着早石炭世和中二叠世深海盆地沉积地层记录,哀牢山深海盆地应该在中二叠世之后封闭。该成果为探讨哀牢山古特提斯盆地演化提供了放射虫古生物学证据,进而说明哀牢山缝合带与金沙江缝合带一样,也存在石炭纪和二叠纪深水洋盆沉积地层记录,指示其演化历史是相同的。  相似文献   

7.
The Middle Jurassic Kcira-Dushi-Komani Mélange in the northwestern Mirdita Ophiolite Zone contains blocks of Triassic oceanic crust, radiolarites and open marine limestones. We describe the microfacies and present biostratigraphic data from radiolarite clasts and blocks and from basalt-radiolarite blocks with preserved autochthonous sedimentary cover. The radiolarians yield Middle to Late Triassic (Late Anisian to Late Norian) ages for the oceanic realm from which the ophiolite and radiolarite blocks and clasts derived. Together with limestone blocks, the provenance areas of the components in the Kcira-Dushi-Komani Mélange are determined as the distal shelf and the ocean floor of the Neotethys. In the course of ophiolite obduction, the components were transported by mass movements into newly formed trench-like basins in front of the westward propagating nappe stack. These basins were later incorporated in the nappe stack forming the typical features of a syntectonic mélange. Our radiolarian biostratigraphic data confirm Late Anisian formation of the Neotethys Ocean, parts of which became closed in the Middle Jurassic. The data clearly speak in favour of one Neotethys Ocean to the east, from which the Mirdita ophiolites derived as far-travelled nappes.  相似文献   

8.
Guadalupian–Lopingian sedimentary rocks are widely distributed in accretionary complexes in Japan, but the Guadalupian–Lopingian boundary (G–LB) is not well documented from these pelagic sediments. To identify the G–LB and to better correlate an extinction event that occurred around the Guadalupian–Lopingian boundary, we examined the conodont biostratigraphy from a Permian pelagic chert sequence in the Gujo-hachiman section, Gifu, southwest Japan. Age-diagnostic conodonts, including Clarkina postbitteri postbitteri, were found in this section. The biostratigraphic occurrences of these age-diagnostic conodonts can pinpoint the “G–L transitional zone” in the Gujo-hachiman section by comparison with well-studied sections from south China, including the GSSP section. The transitional zone was recognized by the first occurrence horizons of both Clarkina postbitteri hongshuiensis and C. p. postbitteri. The G–LB has been placed at or above the first occurrence horizon of the radiolarians Albaillella yamakitai or Albaillella cavitata in previous studies from China and Japan. We detected the first occurrence horizon of A. yamakitai below the base of the “G–L transitional zone,” in the Upper Capitanian. The conodont biostratigraphy is consistent with the radiolarian biostratigraphy in this section, which can be correlated to relevant sections in China.  相似文献   

9.
西藏南部放射虫微体古生物研究进展   总被引:6,自引:0,他引:6  
西藏南部的雅鲁藏布蛇绿岩带以及该带之南的沉积地层带(特提期沉积区,北喜马拉雅亚区)中广泛发育着大量含放射虫地层,放射虫研究在确定该区蛇绿岩的形成时代,解释造山带复杂的地层层序以及揭示印度板块与欧亚板块在古近纪碰撞老祖宗前的古海洋盆地的演化历史等方面发挥了重要作用。根据已发表的文献以及我们正在进行中的初步成果显示,藏南地区的含放射虫地层的时代分布之中三叠世(安尼期)至晚白垩(土仑期)。这些地层的岩性包括硅质岩,硅质泥岩,凝灰质细碎屑岩和泥晶灰岩等,尽管藏南的放射虫研究已取得一些成果,但系统的放射虫研究与地层研究仍然有待于进一步深入开展。  相似文献   

10.
The greatest mass extinction occurred at the end of the Permian. Most records of the mass extinction are not from pelagic sediments, but from shallow-marine and terrestrial sediments. Although several pelagic sections that span the end-Permian mass extinction have been found, these sections contain few index fossils and are often discontinuous because of small faults. We found the index fossils Albaillella cf. triangularis (Radiolaria) in siliceous claystone beds, Hindeodus parvus (Conodont) in the overlying black claystone beds, and Neospathodus cf. cristagalli and Ns. waageni (Conodont) in the subsequent siliceous claystone beds in Akkamori section-2 in northern Japan. These fossils suggest that this section ranges from the late Permian to the Early Triassic, including the early Induan and Olenekian stages. Furthermore, the lithological changes in the section, i.e., starting from bedded chert through siliceous claystone and black claystone to siliceous claystone, are concordant with those of well-known Permian–Triassic pelagic sequences in Japan. There is no gap between each lithofacie of the Akkamori section-2. Critical lithological continuity between Upper Permian siliceous claystone beds and uppermost Permian to lowermost Triassic black claystone beds of the Akkamori section-2 was recognized by observing hand-polished specimens and thin sections. Such paleontological and sedimentological evidence implies that the Akkamori section-2 is a continuous pelagic section that records the end-Permian mass extinction event. The carbonaceous black claystone beds have high total organic carbon (TOC) concentrations (1.06–3.31 wt.%), suggesting oceanic anoxia at least deep and probably stable primary productivity. A decrease in radiolarian abundance from 26–563 to 0.27–20 specimens/cm2 coincided with an increase in TOC content from 0.01–0.16 to 1.06–3.31 wt.% at the boundary of the siliceous claystone and the overlying black claystone beds near the top of the Permian, implying that radiolarian extinction occurred at the end of the Permian coinciding with oceanic anoxia. Although TOC contents decreased in the early Olenekian (Smithian), radiolarian abundance did not increase at that time, indicating that radiolarian recovery was delayed by > 1.5 m.y.  相似文献   

11.
Jurassic and Cretaceous radiolarian faunas were discovered in bedded chert of the Dinaric and Vardar tectonic zones of Bosnia and Herzegovina. Only Triassic radiolarians have previously been described in Bosnia and Herzegovina, while the finds of Bajocian, Bathonian-Callovian, Oxfordian-Kimmeridgian, Tithonian-Berriasian, and Campanian are new. Additional localities of Triassic and Jurassic radiolarians were investigated in Serbia. By correlation with radiolarians from the previous studies within Serbia, the Late Aalenian-Bajocian and Bathonian-Callovian Serbian radiolarian beds are newly dated. The first find of Cretaceous radiolarians in Serbia is reported. The oldest Mesozoic Radiolaria-bearing formations outcropping in the Western Belt of the Vardar Zone are dated Mid-Upper Triassic. The youngest radiolarians come from the Upper Cretaceous (Campanian) of the northern part of this belt of the Vardar Zone, where they co-occur with planktonic foraminifers. The distribution of 70 radiolarian samples within sections is shown. The taxonomic composition of 39 samples is analyzed. Radiolarian species extracted from 13 samples are described and figured. The list of 72 taxa and 3 plates of Jurassic radiolarians of Bosnia and Herzegovina, 3 plates of Triassic, 1 plate of Middle Jurassic, and 1 plate of Upper Cretaceous radiolarians of Serbia are presented.  相似文献   

12.
Varied west-transported and far-traveled Jurassic mélanges in southwestern Serbia represent a key to understand the geodynamic history and to solve paleogeographic questions and reconstructions in the Triassic–Jurassic passive and active margin arrangement of the Inner Dinarides. Of special interest are the carbonate-clastic radiolaritic mélange areas in the Zlatar Mountain below the Dinaridic Ophiolite nappe. The present study reports from a Middle Jurassic sedimentary mélange in the area of Vodena Poljana. Carbonate components and blocks of the mass-flow deposits consist exclusively of a reworked Middle/Late Anisian to Early Jurassic distal shelf succession. Ophiolite components from the Dinaridic Ophiolite nappe stack are missing in the spectrum. The underlying series of the Zlatar Mélange belong to Early/Middle Anisian shallow-water carbonates and to Late Anisian to Middle Jurassic deep-water sedimentary rocks of the Hallstatt facies zone. South of Vodena Poljana in the overlying ophiolitic mélange occur Late Triassic radiolaritic components from the sedimentary cover of the Late Triassic ocean floor, beside ophiolite clasts and limestone components from the continental slope. A comparison with preserved Hallstatt Limestone successions and Jurassic mélange complexes from the Eastern Alps, Western Carpathians, and Albanides strengthen the interpretation of a provenance of the Zlatar mélange from the distal passive margin facing the Neotethys Ocean to the east. An autochthonous Dinaridic Ocean west of the Drina-Ivanjica Unit cannot be confirmed.  相似文献   

13.
A diverse and well-preserved latest Permian radiolarian fauna was obtained from bedded siliceous rocks and siliceous mudstones of the Dongpan Section, southwest Guangxi, China. All encountered specimens of the order Spumellaria and a few specimens of the order Entactinaria were selected for the taxonomic study of this paper. Thirty-three species, 15 of which are new species, were identified. They belong to 15 genera, three of which (Paracopicyntra, Copiconulus, and Yujingella) are new. The most interesting result of our study is that eight typical Middle Triassic spumellarian genera (Paroertlispongus Kozur and Mostler, Tetrapaurinella Kozur and Mostler, Paurinella Kozur and Mostler, Lithelius Haeckel, Archaeospongoprunum Pessagno, Tamonella Dumitrica, Kozur and Mostler, Bistarkum Yeh, and Tetraspongodiscus Kozur and Mostler) were discovered in the upper Changhsingian strata studied herein. Therefore, the most important and characteristic spumellarian families of the Middle Triassic were already present in the Late Permian of South China.  相似文献   

14.
Within the Late Cretaceous mélange complex of the Izmir-Ankara suture zone in central Sakarya area, north-western Turkey, a megablock with radiolarian cherts associated with basaltic pillow lavas has been dated by radiolarians. The studied radiolarian assemblage and conodonts yielded an early Late Carnian age. This age is the oldest obtained from the chert blocks all along the suture belt and has important implications for the rifting/opening age of the Izmir-Ankara branch of the Tethys ocean in north-western Turkey. Based on this new data, it is concluded that during the Late Triassic the Izmir-Ankara seaway was connected to the other Tethyan oceanic branches and deep enough to provide chert sedimentation and exchange radiolarians with the main open oceans. It is further suggested that the long-lasting misinterpretation of a Liassic rifting/opening of the Izmir-Ankara ocean should be revised.  相似文献   

15.
During the Triassic, the Bayan Har Basin is a huge triangular basin surrounded by the North China Platform, South China Platform and Qingtang Terrane. It is filled by a Triassic turbidite sequence, the Bayan Har Group. For a long time, the series of Bayan Har Group in the eastern part of the basin were considered to be a Lower to Upper Triassic sequence, and in the western part, was attributed to the Upper Triassic. A well-preserved diversified radiolarian fauna was recovered from radiolarian chert and tuffite interbeds of the Bayan Har Group turbidites and adjacent stratigraphic units in the Hoh Xil area, northern Tibet. Sixty-seven species are identified and subdivided into two assemblages: late Anisian and early Carnian. Combined with the discovery of the Late Permian and Early Triassic turbidite in the Bayan Har Group in this area by Huang et al., it proves that all the Triassic is also present in the Bayan Har Group sequence in the western part. The evolution of the Bayan Har Basin may be traced back to the Late Permian. The massive sequence of the Bayan Har Group and its provenance indicate that the Kunlun and Qinling orogenic belts rapidly rise during the Middle-Late Triassic. The basin extended to the end of the Triassic, possibly locally to the Jurassic.  相似文献   

16.
Radiolarian cherts are locally intercalated, mostly as up to 45 m thick sequences of rhythmically bedded chert, in the Jurassic to Lower Tertiary Nicoya Ophiolite Complex of western and southern Costa Rica (Central America). Additionally, bedded chert is present in some Campanian and Paleocene/Eocene sedimentary series that overly the Nicoya Complex. The ophiolitic cherts may be thermally recrystallized to different grades due to post depositional basaltic magmatism. The radiolarian skeletons mainly consist of microquartz; complete dissolution of the skeletons, i.e. exclusive preservation of the fillings, is rare. The fillings are variable in composition: quartz, length-fast chalcedony, and quartz-pigment mixtures are dominant; opal-CT, clay minerals, chlorite, zeolites, baryte, manganese and iron oxides, epidote and calcite are subordinate. The non-siliceous minerals may locally replace the siliceous phases and/or intergrow with them. Thus, approximately 40 preservation types have been observed in the Costa Rican cherts. In combination with the different preservation grades, a large number of preservation variants is present. However, in the cherts of the Nicoya Complex quartz-rich preservation types are strongly dominant, whereas opal-CT, zeolites and calcite are more important in the cherts of the overlying sedimentary series. Types and grades of radiolarian preservation represent an important aid in the reconstruction of the postdepositional diagenetic and thermal history of the Costa Rican cherts.  相似文献   

17.
近30年来,巴基斯坦盐岭地区的Wargal组和Chhidru组以及在喜马拉雅地区相当地层的地质时代被许多学者视为中二叠世(瓜达鲁普世)。根据华南与盐岭地区瓜达鲁普统和乐平统的牙形类化石带对比,可以确定Amb组和Wargal组底部的时代为瓜达鲁普世晚期,瓜达鲁普统与乐平统的界线位于Wargal组下部,吴家坪阶与长兴阶的界线位于Chhidru组的下部,而二叠与三叠系的界线位于Mianwali组下部的Kathwai段之内。我国西藏南部色龙群及相当地层含有与巴基斯坦盐岭地区Kalabagh段和Chhidru组可对比的乐平世腕足动物群以及二叠系—三叠系界线附近连续的牙形类化石带,由此可以推定色龙群的时代应为乐平世。  相似文献   

18.
本研究系统描述了中国东北那丹哈达地体中三叠系顶部和侏罗系下部的放射虫动物群及其系统分类,包括5个放射虫生物群,建立了一个新属,10个新种,并报道了121个种级分类单元。通过与加拿大和日本的相关动物群进行比较研究,我们确定了所描述的放射虫生物群的年代归属分别为:晚三叠世诺利(Norian)晚期至瑞替(Rhaetian)早期,辛涅缪尔(Sinemurian)早、中期。  相似文献   

19.
在广西钦州地区小董镇大虫岭深海硅质岩剖面中,首次处理出了层序连续的牙形石化石,并由老至新划分了二个牙形石带,即Jinogondolella granti带和Clarkina dukouensis带。通过这二个牙形石带与斜坡相和盆地相碳酸盐岩硅质岩系中的牙形石带进行对比,划分了本剖面中乐平统生物地层底界。本文对深海硅质岩系中这一界线地层牙形石动物群特征进行了简要的描述。  相似文献   

20.
《Palaeoworld》2020,29(2):186-238
Nonmarine biostratigraphic/biochronologic schemes have been created for all or parts of the late Carboniferous–Middle Triassic using palynomorphs, megafossil plants, conchostracans, blattoid insects, tetrapod footprints and tetrapod body fossils, and these provide varied temporal resolution. Cross correlation of the nonmarine biochronologies to the Standard Global Chronostratigraphic Scale has been achieved in some parts of the late Carboniferous–Middle Triassic in locations where nonmarine and marine strata are intercalated, the nonmarine strata produce biochronologically significant fossils and the marine strata yield fusulinids, conodonts and/or ammonoids. Other cross correlations have been aided by magnetostratigraphy, chemostratigraphy and a growing database of radioisotopic ages. A synthetic nonmarine biochronology for the late Carboniferous–Middle Triassic based on all available nonmarine index fossils, integrated with the Standard Global Chronostratigraphic Scale, is presented here. The focus is on the nonmarine biostratigraphy/biochronology of blattoid insects, conchostracans, branchiosaurid amphibians, tetrapod footprints and tetrapod body fossils within the biochronological framework of land-vertebrate faunachrons. Correlation to the Standard Global Chronostratigraphic Scale presented here is divided into seven time intervals: Pennsylvanian, Carboniferous–Permian boundary, Cisuralian, Guadalupian, Lopingian, Permian–Triassic boundary and Early to Middle Triassic. The insects, conchostracans and branchiosaurs provide robust nonmarine correlations in the Pennsylvanian–Cisuralian, and the footprints and tetrapod body fossils provide robust correlations of varied precision within the entire Pennsylvanian–Middle Triassic. Radioisotopic ages are currently the strongest basis for cross correlation of the nonmarine biostratigraphy/biochronology to the Standard Global Chronostratigraphic Scale, particularly for the Pennsylvanian–Cisuralian. Chemostratigraphy and magnetostratigraphy thus far provide only limited links of nomarine and marine chronologies. Improvements in the nonmarine-marine correlations of late Paleozoic–Triassic Pangea require better alpha taxonomy and stratigraphic precision for the nonmarine fossil record integrated with more reliable radioisotopic ages and more extensive chemostratigraphic and magnetostratigraphic datasets.  相似文献   

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