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1.
Deformed marine terraces provide excellent measures of Quaternary tectonism along 400 km of the Pacific coast of Baja California between Ensenada and Punta Blanca. The nature and magnitude of deformation are well expressed by the present elevation of the marine limit, of Upper Pliocene or Lower Pleistocene age, which has been upwarped to 345m, 357m, and at least 195m in three separate localities, while occurring at lower levels elsewhere. Multiple terraces are found below this marine limit where appreciable uplift has occurred. Where relative subsidence has prevailed, fewer broader terraces or thick alluvial and eolian deposits occur. Terraces are further dislocated by NW-SE strike-slip faulting and by normal faults that trend NE-SW across the coast. Folding and faulting are less significant on the younger terraces than on the older features, and negligible for the Sangamonian terrace, except close to major faults. Crustal movements revealed by these terraces, and by similar features in southern California, Baja California Sur, and around the Gulf of California, are interpreted in terms of plate tectonics. Over the past 5 million years, the Peninsular Ranges have been carried northwestwards away from mainland Mexico, at an average rate of 6cm/yr, on the dis located limb of a spreading sea floor associated with the East Pacific Rise now found beneath the Gulf of California. The Pacific coast of the Peninsular Ranges comprises several discrete crustal slivers which, on the evidence of the marine terraces, have been warped and dislocated in response to tec tonic forces associated with rafting and subsequent crowding against transverse structures to the north. Uplift rates range as high as 1.0m/1000 yrs locally but are generally less, and are much less than rates found in the Transverse Ranges farther north. As in the latter province, basins typified by net sub sidence during Quaternary time are also found.  相似文献   

2.
海面变化研究是具重要理论和实践意义的地学研究领域。全球性气候变化、海面升降和环境变迁的预测等研究,引起国际学术界和各国政府部门高度重视,成为国际地圈- 生物圈计划(IGBP) 的重要研究课题。利用GIS软件Arc/Info 建立中国第四纪海面变化信息系统,对中国第四纪海面变化进行动态模拟、趋势预测和应用分析,并利用计算机屏幕、图形终端、笔式绘图仪、静电绘图仪和打印机对中国第四纪海岸古环境进行再造和演示。  相似文献   

3.
选取位于珠江口万顷沙ZK316-2钻孔进行孢粉、硅藻和岩性等分析,重建了珠江口晚更新世以来的海侵海退旋回和古环境特征。孢粉和硅藻分析表明:晚更新世期间该区域主要经历了一次大的海侵海退,期间有2次小的海平面波动。晚更新世地层海相特征明显,孢粉组合指示了温暖湿润的气候环境,其植被以南亚热带常绿林为主,孢粉组合以青冈属、蕈树属、金缕梅科等亚热带种属为主,期间出现的海桑属推测为滨海相沉积,指示了当时海平面的位置。晚更新世的海相沉积尽管14C测年结果为老于30 ka左右,但经过区域孢粉组合、硅藻特征、海平面高度等因素的综合对比分析后认为:下部海相层的年代更可能属于MIS 5期,而期间2次短暂的低海面记录可能与5b和5d海平面波动有关。钻孔上部13.9 m以上为全新世2 232 cal. a B.P.以来的沉积,孢粉分析表明植被仍以亚热带常绿林为主,但人类干扰因素的禾本科、松属、芒箕和火灾记录(炭屑)大量增加,指示了沿海人类活动增强和大规模农业的发展,这与全新世晚期海平面下降和三角洲的快速加积作用基本同步进行。  相似文献   

4.
Quaternary sea‐level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw‐rate variability over 103 to 105 year time scales. Here we present 11 mean throw rates for the Tepetate–Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca. 0.22 mm year?1 during the late Holocene, ca. 0.03 mm year?1 during the last glacial and at least 0.07 mm year?1 during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea‐level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land‐surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.  相似文献   

5.
选择位于福建平潭岛北部芦洋埔海积平原的PT01钻孔,岩芯长度28.3 m,采用加速器碳同位素(AMS 14C)和光释光(OSL)测年建立地层年代框架,认为晚更新世富含有孔虫等海相生物化石的地层应归属于MIS 5高海面期,即MIS 5e的潮下带滨海相沉积。结合岩性特征、古生物化石、沉积物色度、粒度分析及其参数等指标,进行了沉积单元的划分,重建了MIS 6末期以来的沉积相变化过程,揭示出MIS 5期间的多次海平面波动变化,即MIS 5高海面期沉积环境仍存在滨海、潮坪、潟湖、风成砂等沉积相之间的转换,并可能存在短暂的陆相或风化过程。而该区整个末次冰期的沉积缺失或较薄,上部全新世沉积也不发育,厚度仅为3.79 m,以沼泽相―风成砂相为主。  相似文献   

6.
Exceptional exposure of the forearc region of NW Peru offers insight into evolving convergent margins. The sedimentary fill of the Talara basin spans the Cretaceous to the Eocene for an overall thickness of 9000 m and records within its stratigraphy the complicated history of plate interactions, subduction tectonics, terrane accretion, and Andean orogeny. By the early Tertiary, extensional tectonism was forming a complex horst and graben system that partitioned the basin into a series of localized depocentres. Eocene strata record temporal transitions from deltaic and fluvial to deep‐water depositional environments as a response to abrupt, tectonically controlled relative sea‐level changes across those depocentres. Stratigraphic and provenance data suggest a direct relationship between sedimentary packaging and regional tectonics, marked by changes in source terranes at major unconformities. A sharp shift is recognized at the onset of deepwater (bathyal) sedimentation of the Talara Formation, whose sediments reflect an increased influx of mafic material to the basin, likely related to the arc region. Although the modern topography of the Amotape Mountains partially isolates the Talara basin from the Lancones basin and the Andean Cordillera to the east, provenance data suggest that the Amotape Mountains were not always an obstacle for Cordilleran sediment dispersal. The mountain belt intermittently isolated the Talara basin from Andean‐related sediment throughout the early Tertiary, allowing arc‐related sediment to reach the basin only during periods of subsidence in the forearc region, probably related to plate rearrangement and/or seamounts colliding with the trench. Intraplate coupling and/or partial locking of subduction plates could be among the major causes behind shifts from contraction to extension (and enhanced subduction erosion) in the forearc region. Eventually, collisional tectonic and terrane accretion along the Ecuadorian margin forced a major late‐Eocene change in sediment dispersal.  相似文献   

7.
The Eocene–Miocene carbonate deposition in the Gulf of Papua (GoP) corresponds to the carbonate evolution phase of this continental margin mixed depositional system. Global sea‐level (eustatic) fluctuations appear to have been the most important factor influencing the mixed depositional system development during its carbonate phase. Development of the major carbonate system in the Gulf was initiated during the Eocene. Subsequent to an early Oligocene hiatus, the carbonate system expanded its surface area, vertically aggraded, then systematically backstepped, and finally partially drowned during the late Oligocene–early part of the early Miocene. During the late early Miocene–early middle Miocene, the carbonate system continued its vertical growth in most platform areas, where it was able to keep up with sea‐level rise. At the early middle/late middle Miocene (Langhian/Serravallian) boundary, carbonate deposition shifted downward during a long‐term sea‐level regression, exposing most of the early middle Miocene platform tops. Following this downward shift, active carbonate production became restricted during the late middle Miocene to only the northeastern part of the study area, and carbonate accumulation was characterized by four systematically prograding units. At the very beginning of the late Miocene, the platform tops were re‐flooded. The carbonate system was partially drowned, systematically backstepped, and locally aggraded during part of the late Miocene, the early Pliocene, and the Quaternary. The overall organization of the carbonate sequence geometries, observed in the GoP, display a clear pattern, often referred to as the Oligocene–Neogene stratigraphic signature. This pattern is identical to contemporaneous sedimentary patterns observed in pure carbonate systems such as in the Maldives and in the Bahamas, and also in some siliciclastic systems. Because this pattern is observed in several globally distributed locations, the recognition of the Oligocene–Neogene stratigraphic signature in the GoP demonstrates that the depositional evolution during the late Oligocene–Miocene and the early Pliocene must have been dominantly controlled by eustatic fluctuations.  相似文献   

8.
长江河口地区第四纪古地理古环境变迁   总被引:21,自引:4,他引:17  
陈中原  杨文达 《地理学报》1991,46(4):436-448
通过对钻孔样品的粒度、层理揭片、矿物、微体古生物、孢粉、地球化学元素及古地磁等项目的实验室分析,着重探讨长江河口地区第四纪古地理、古环境变迁特征和长江三角洲的发育过程。  相似文献   

9.
The Murzuq Basin is one of the most petroliferous basins of North Africa. Its remote eastern flank has been largely ignored since early reconnaissance work in the 1950s and 1960s. This article presents new stratigraphic and sedimentological data on the Neoproterozoic through Devonian succession from the Mourizidie and Dor el Gussa regions. The Neoproterozoic to Cambrian Mourizidie and Hasawnah formations in the eastern part of the Mourizidie region dip to the east and north‐east, resting directly on late Precambrian metasediments and granitoids. These strata record the initial progradation of sand‐dominated braidplain systems upon peneplained Precambrian basement. Rhyolite clasts in the Hasawnah Formation may record tectonically driven uplift and unroofing in the southern Tibesti Massif or tectonomagmatic rejuvenation to the south of this massif. In the western part of the Mourizidie region, Late Ordovician through Silurian strata (Mamuniyat and Tanezzuft–Akakus formations) directly overlie late Precambrian metasediments and granitoids, and dip at a low angle towards the west into the Murzuq Basin. Elsewhere at the eastern Murzuq Basin flank, in Dor el Gussa, Late Ordovician glaciogenic sediments rest with angular unconformity upon shallow marine sandstones of Cambrian–Ordovician age. This angular unconformity may also occur in the Mourizidie region and indicates widespread tectonism, either as a result of a Middle–Late Ordovician orogenic event, far‐field tectonism related to the opening of the Rheic Ocean along the northern margin of Gondwana or alternatively crustal depression associated with the growth of Late Ordovician ice sheets. Unconformity development was also probably associated with glacial incision. Following ice sheet retreat, isostatic rebound during deglaciation resulted in uplift of tens to hundreds of metres, locally removing all Cambrian and Ordovician formations. Rising sea levels in the Silurian led to deposition of the Tanezzuft Formation on Precambrian basement in the northwestern Mourizidie region.  相似文献   

10.
在回顾南海北部海岸和陆架地层证据的基础上,梳理了珠江三角洲晚第四纪演变历史。结果显示:1)本区晚第四纪地层拥有2套海相沉积,上(新)海相层是当前间冰期(或10.5 ka B.P.以来)高海平面期间形成的沉积物,而下(老)海相层最可能是末次间冰期(126―120 ka B.P.)高海平面阶段留下的沉积物;2)老海相层顶面埋深在三角洲盆地内至少比现今海平面低10~15 m,在珠江口一带则低于20 m,这说明珠江三角洲盆地存在构造沉降,因为2次间冰期的海平面高度是相近的;3)在新生代欧亚板块大陆向东南伸展的构造格局下,南海北部陆架和海岸带经历长期连续的沉降,而长期平均沉降率在0.12 mm/a左右,明显低于GPS测出的现代沉降率;4)在这种板块运动基础上,晚第四纪断裂活动增强了三角洲盆地的沉降,为2次海侵提供了可容沉积空间。  相似文献   

11.
The Deccan basalts in central western India are believed to occupy large onshore–offshore area. Using geophysical and geological observations, onshore sub-surface structural information has been widely reported. On the contrary, information about offshore structural variations has been inadequate due to scarcity of marine geophysical data and lack of onshore–offshore lithological correlations. Till date, merely a few geophysical studies are reported that gauge about the offshore extent of Deccan Traps and the Mesozoic sediments (pre-Deccan). To fill this gap in knowledge, in this article, we present new geophysical evidences to demonstrate offshore continuation of the Deccan volcanics and the Mesozoic sediments. The offshore multi-channel seismic and onshore–offshore lithological correlations presented here confirm that the Mesozoic sedimentary column in this region is overlain by 0.2–1.2-km-thick basaltic cover. Two separate phases of Mesozoic sedimentation, having very distinctive physical and lithological characteristics, are observed between overlying basaltic rocks and underlying Precambrian basement. Using onshore–offshore seismic and borehole data this study provides new insight into the extent of the Deccan basalts and the sub-basalt structures. This study brings out a much clearer picture than that was hitherto available about the offshore continuation of the Deccan Traps and the Mesozoic sediments of Kachchh. Further, its implications in identifying long-term storage of anthropogenic CO2 within sub-basalt targets are discussed. The carbon sequestration potential has been explored through the geological assessment in terms of the thickness of the strata as well as lithology.  相似文献   

12.
Huangshan(Yellowmountain)islocatedinsouthernpoofthelowerreaChesoftheYangtZemyer,30'31'Nand118"if'E.ItShigheStLotUSFlowerPeakis1864mabovesealevel.ItisoneofthetencelebretedscenicSPOtSinChinaandwasincludedintheWorldNaturalandCultulalHeritageListbyU'NESCOin1990.OneofthemajorreasonsforincludingitinthelistisbecauseofHuangshan'simPOrtantvalueforgeologicalacgeomorphicscienceicresearches.Inthe~es,Lee(1936)proPOsedthe"confinnatoryevidenceofPleistoceneglacinhonfromtheHuangshan"l'l.Inthesi…  相似文献   

13.
This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid‐Jurassic age carbonate succession of the Southern Provence Sub‐basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second‐order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge‐shaped geometries) reflects a strong tectonic control. The sub‐basin was structured by extensional faults (oriented approximately 070–090/250–270). Sea‐level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub‐basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid‐Pliensbachian); (3) global climato‐eustatic sea‐level fall (latest Pliensbachian) and global climato‐eustatic sea‐level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea‐level fall linked to tectonic uplift related to the ‘Mid‐Cimmerian phase’ (mid‐Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).  相似文献   

14.
This study describes shoreline migration paths for late Quaternary sediments on the inner Barents Sea shelf between Kola and the Pechora Sea. The depositional geometries provide an example of stratigraphical architecture in a glacially influenced basin prone to isostatic movements as well as rapid and high-amplitude changes in eustatic sea level. The depositional geometries reflect asymmetrical relative sea level changes characterised by marine inundation upon deglaciation and prolonged forced regressions. Thus, all deposition occurs during the falling stage and lowstand systems tracts. The transgressive and highstand systems tracts are lacking and the maximum landward position of the shoreline is coinciding with the basal surface of forced regression. Shoreline migration is dominated by downward and seaward trajectories, but aggradation occurs on the falling limb of the relative sea level curve due to superimposed eustatic cycles of lower hierarchical order. Fluvial aggradation behind the shoreline takes place during the lowstand systems tract, but is also linked to high sediment supply and may also respond to superimposed lower order sea level fluctuations. Lateral variations in isostatic load due to asynchronous ice advances lead to regional variations in shoreline trajectories. Significant differences in sea level history exist across former ice margins leading to time-transgressive and laterally discontinuous stratigraphical surfaces. Sequence boundaries are not only diachronous along the depositional profile, but also laterally, and basal surfaces of forced regression are strongly diachronous across former ice margins. Absolute age control allows for estimates of the time differences along significant stratigraphical surfaces.  相似文献   

15.
Abstract We present here the initial results of a high-resolution (sparker) reflection seismic survey in Northern Lake Tanganyika, East African Rift system. We have combined these results with data from earlier multichannel reflection seismic and 5-kHz echosounding surveys. The combination of the three complementary seismic investigation methods has allowed us to propose a new scenario for the late Aliocene to Recent sedimentary evolution of the North Tanganyika Basin. Seismic sequences and regional tectonic information permit us to deduce the palaeotopography at the end of each stratigraphic sequence. The basin history comprises six phases interpreted to be responses to variations in regional tectonism and/or climate. Using the reflection seismic-radiocarbon method (RSRM), the minimum ages for the start of each phase (above each sequence boundary) are estimated to be: ?7.4 Ma, ? 1.1 Ma, ?393–363 ka, ?295–262 ka, ? 193–169 ka, ?40–35 ka. Corresponding lowstand lake elevations below present lake level for the last five phases are estimated to have been: ?650–700 m, ?350 m, ?350 m, ?250 m and ? 160 m, respectively. The latest phase from ?40–35 ka until the present can be subdivided into three subphases separated by two lowstand periods, dated at ?23 ka and ? 18 ka. From the late Miocene until the mid Pleistocene, large-scale patterns of sedimentation within the basin were primarily controlled by tectonism. In contrast, from the mid Pleistocene to the present, sedimentation in Lake Tanganyika seems to have responded dramatically to climatic changes as suggested by repeated patterns of lake level fluctuations. During this period, the basin infill history is characterized by the recurrent association of three types of deposits: ‘basin fill’ accumulations; lens-shaped ‘deep lacustrine fans’; and ‘sheet drape’ deposits. The successive low-lake-level fluctuations decreased in intensity with time as a consequence of rapid sedimentary filling under conditions of declining tectonic subsidence. The climate signal has thus been more pronounced in recent sedimentary phases as tectonic effects have waned.  相似文献   

16.
Tertiary and Quaternary deposits outcrop in the coastal cliff of Balanusviken at Sarsbukta in Vest-Spitsbergen. The Tertiary deposits appear by their foraminifera to belong to the Middle to Upper Oligocene. The Quaternary deposits consist of an upper part of Late Pleistocene to Holocene age, and a lower part which had previously been considered Middle Weichselian of age. Its foraminiferal assemblages suggest a higher age (Late Saalian, Eemian?). This lower part of the Quaternary deposits is related to a series of raised beaches with an upper limit at SO m above present day sea level. They were probably formed during the Eemian, and have not been distorted by later glaciation. The present study is based on sediment samples collected from the coastal cliff of Balanusviken, and particularly from that of Balanuspynten, Sarsbukta, Spitsbergen, during the summer expedition of Norsk Polarinstitutt in 19Sø.  相似文献   

17.
Swath bathymetry, single‐channel seismic profiling, gravity and box coring, 210Pb down‐core radiochemical analyses and sequence stratigraphic analysis in the Gulf of Alkyonides yielded new data on the evolution of the easternmost part of the Gulf of Corinth. Three fault segments, the South Strava, West Alkyonides and East Alkyonides faults, dipping 45, 30 and 45°, respectively, northwards, form the southern tectonic boundary of the Alkyonides Basin. Two 45° southwards dipping segments, the Domvrena and Germeno Faults, form the northern tectonic margin. The Alkyonides Basin architecture is the result of a complex interaction between fault dynamics and the effects of changes in climate and sea/lake level. Chrono‐stratigraphic interpretation of the seismic stratigraphy through correlation of the successive seismic packages with lowstands and highstands of the Late Quaternary indicates that the evolution of the basin started 0.40–0.45 Ma BP and can be divided in two stages. Subsidence of the basin floor during the early stage was uniform across the basin and the mean sedimentation rate was 1.0 m kyear?1. Vertical slip acceleration on the southern tectonic margin since 0.13 Ma BP resulted in the present asymmetric character of the basin. Subsidence concentrated close to the southern margin and sedimentation rate increased to 1.4 m kyear?1 in the newly formed depocentre of the basin. Actual (last 100 year) sedimentation rates were calculated to >2 mm year?1, but are significantly influenced by the presence of episodic gravity flow deposits. Total vertical displacement of 1.1 km is estimated between the subsiding Alkyonides Basin floor and the uplifting Megara Basin since the onset of basin subsidence at a mean rate of 2.4–2.75 m kyear?1, recorded on the East Alkyonides Fault. Gravity coring in the Strava Graben and in the lower northern margin of Alkyonides Basin proved the presence of whitish to olive grey laminated mud below thin marine sediments. Aragonite crystals and absence of the marine coccolithophora Emiliania huxleyi indicate sedimentation in lacustrine environment during the last lowstand glacial interval.  相似文献   

18.
The segment of the Interandean Depression of Ecuador between Ambato and Quito is characterized by an uppermost Pliocene–Quaternary basin, which is located between two N-S trending reverse basement faults: the Victoria Fault to the west, and the Pisayambo Fault to the east. The clear evidence of E-W shortening for the early Pleistocene (between 1.85 and 1.21 Ma) favours a compressional basin interpretation. The morphology (river deviations, landslides, folded and flexure structures) demonstrates continuous shortening during the late Quaternary. The late Pliocene-Quaternary shortening reached 3400 ± 600 m with a rate of 1.4 ± 0.3 mm yr−1. The E-W shortening is kinematically consistent with the current right-lateral reverse motion along the NE-SW trending Pallatanga Fault. The Quito-Ambato zone appears to act as a N-S restraining bend in a system of large right-lateral strike-slip faults. The compressive deformation which affects the Interandean Depression during the Pliocene is apparently coeval to the beginning subduction of very young oceanic lithosphere north of the Gulf of Guayaquil. The relatively buoyant new crust may have significantly increased the mechanical coupling in the subduction zone from Pliocene to Present.  相似文献   

19.
ABSTRACT

To answer the question “what has changed the surface temperatures of water bodies around Iran under climate change conditions,” Moderate Resolution Imaging Spectroradiometer (MODIS) sea surface temperature (SST) data with 9.2-km spatial resolution and monthly time step were evaluated. A significant increasing trend was obtained using Pearson’s correlation coefficient and Mann-Kendall trend test on data from the Caspian Sea (June) and the Southern Gulfs (September). High correlations of 0.69 and 0.97 between remotely sensed data and ERA-Interim reanalysis data were also obtained for June and September, respectively. To assess the impact of some climatic parameters on SST variability in those two months, zonal and meridional wind at 10 m, wind speed at 10 m, air temperature at 2 m, and mean sea level pressure were evaluated. High correlations between meridional wind and the Southern Gulf SST, and meridional wind and Caspian SST were ?0.86 and 0.75, respectively. Moreover, the results showed an important role of air temperature (0.96) and sea level pressure (?0.77) in the rising temperature trends of the Southern Gulfs. Wind speed was also detected in both regions as a booster of the trend.  相似文献   

20.
中国海陆过渡带——岸海洋环境特征与变化研究   总被引:7,自引:2,他引:5  
王颖  季小梅 《地理科学》2011,(2):129-135
海岸海洋是陆地与海洋过渡的地带,位居亚洲与太平洋之交的中国海岸类型丰富,河海交互作用与人类活动影响使海岸海洋环境与作用过程独具特色.河流的贯通作用,使得全球变化与人类活动对河流流域的作用,亦在海岸海洋地区表现出来,并对海洋环境形成显著的影响.历史与现实实例表明,在海岸海洋的开发利用中需重视研究海陆交互过渡带环境特征,尽...  相似文献   

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