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91.
《Geological Journal》2018,53(5):1665-1684
New results of structural and lithostratigraphic investigations performed in the Urtier Valley, located south of Aosta Valley at the northern flank of the Gran Paradiso Massif, shed new light on the nappe stack architecture of the Western Alps. Two distinct Piemonte–Ligurian units were recognized in the area: (a) the blueschist facies Broillot unit, with a well‐preserved lithostratigraphic succession that includes ophiolites and their metasedimentary cover and (2) the eclogitic Bardonney unit with clasts and/or slices of ophiolites embedded in a carbonate/quarzitic and/or metabasic matrix. Three major deformation stages have been recognized (D1, D2, and D3). D1 phase occurred during the peak metamorphic conditions (i.e., eclogite or blueschist facies). D2 and D3 phases are related to multistage exhumation processes, from early stacking to late refolding of former nappe contacts. Despite the intensity of deformation and metamorphism, the original lithostratigraphic succession of the Broillot unit allowed us to use a lithostratigraphic approach to reconstruct the structures in the study area. For the first time, differences in the nappe stack exposed south and north of the Aosta Valley are reported. In fact, contrary to what is observed in the north, the eclogitic units exposed in the Urtier Valley lay above and not below the blueschist units. A new model for the tectonic evolution, which ranges from stages of subduction to large‐scale nappe refolding, is proposed. It is able to explain the difference in the architecture of the north and south of the Aosta Valley. 相似文献
92.
大湄公河次地区在地质构造上是西南三江构造带和华南加里东褶皱带的向南或南西的延伸。在理清了各构造单元的延伸趋势及其相互关系的基础上,对该区大地构造单元作了统一划分和对比。以印缅山脉结合带、澜沧江-文冬-劳勿结合带、金沙江-哀牢山-马江结合带作为主结合带,将该区划分为印澳板块、中缅马陆块、印支陆块和华南陆块4个一级单元。然后在亲冈瓦纳的中缅马陆块和亲华南型的印支陆块内再以次级结合带分别划分出4个二级构造单元:亲冈瓦纳型的西缅微陆块、腾冲-毛淡棉微陆块,保山-掸泰微陆块、临沧-景栋微陆块,亲华南型的景洪-帕府-东马来西亚微陆块、思茅-大叻微陆块、昆嵩微陆块和长山微陆块;华南陆块以越北斋江结合带为界分为扬子和华夏两微陆块。简要论述了各构造单元的基本地质特征,提出将可可西里-澜沧江-文冬-劳勿结合带作为南部冈瓦纳大陆和北部劳亚大陆的分界,指出昆嵩微陆块和长山微陆块是华夏微陆块的南西延伸,其西部的对应体可能是昌都微陆块。 相似文献
93.
为全面支撑山水林田湖草整体保护、系统修复和综合治理,中国地质调查局部署了\"生态地质调查工程\".该工程自2019年以来,以地球系统科学理论为指导,重点开展了我国北方林草湿分布区1:50万生态地质调查以及黄河源区、大凉山区等重点生态功能区1:5万生态地质调查,采用\"空-天-地\"一体化调查技术,获取了不同尺度森林、草原、湿地等生态类型分布与变化,成土母岩、水文地质要素、土壤、地形地貌等生态地质条件,以及荒漠化、湖泊萎缩等生态问题分布数据,分析了生态-地质之间相互制约影响关系,剖析了主要生态问题的成因机理,划分了生态地质单元,建立了生态地质图谱,提出了基于地球系统科学的国土空间生态保护修复对策建议,为我国北方地区生态保护与系统修复工作提供了基础数据与技术支撑. 相似文献
94.
伊宁地块不是一个之前一贯认为的\"均匀地块\"或\"均一地块\",而是以乌孙山-塔勒得近东西向区域性大断裂为界的南、北两大次级构造带（\"弧-盆\"体系）叠加拼贴增生而成,火山岩浆作用为这一新的构造单元划分与建立提供了佐证。南构造带由喀拉峻岛弧带和其北的阿腾套弧后盆地构成,主要发育于晚泥盆世-早石炭世早期,火山岩同位素年龄峰值为355~350Ma,17个年龄平均值为351Ma;北构造带由北而南可再细分出清水河-苏布台弧后盆地→阿吾拉勒叠加岛弧带→特克斯-新源弧前盆地,主要发育于早石炭世中-晚期,同位素年龄峰值集中于345~329Ma,18个火山岩年龄平均值为340Ma。这两个\"弧-盆\"体系以大哈拉军山组钙碱性火山岩为主体,共生早石炭世海相阿克沙克组弧前及弧后沉积岩组合。大哈拉军山组火山岩主体以岛弧火山岩为主,见有富Nb玄武岩、高镁安山岩等,共生埃达克岩和高分异Ⅰ型花岗岩等小岩体;在弧后还见有碱性火山岩、碱性球泡流纹岩,共生双峰式火山岩。不仅大哈拉军山组火山岩在各构造相中显著有别,而且共生的阿克沙克组在各构造相中差异极为显著。两大次级构造带具有独立的基底建造史,差异显著的盆地沉积史,独特的火山岩浆史和构造演化史。早晚石炭世之间的鄯善运动使南、北两个次级构造带叠加拼贴,构成统一的伊宁地块,晚石炭世进入统一的陆内构造发展演化阶段,发育以伊什基里克组碱性双峰式火山岩为代表的裂谷火山岩浆建造。 相似文献
95.
Martin A. Andresen Nick Malleson Wouter Steenbeek Michael Townsley Christophe Vandeviver 《International journal of geographical information science》2020,34(7):1306-1322
ABSTRACT The analysis of geographically referenced data, specifically point data, is predicated on the accurate geocoding of those data. Geocoding refers to the process in which geographically referenced data (addresses, for example) are placed on a map. This process may lead to issues with positional accuracy or the inability to geocode an address. In this paper, we conduct an international investigation into the impact of the (in)ability to geocode an address on the resulting spatial pattern. We use a variety of point data sets of crime events (varying numbers of events and types of crime), a variety of areal units of analysis (varying the number and size of areal units), from a variety of countries (varying underlying administrative systems), and a locally-based spatial point pattern test to find the levels of geocoding match rates to maintain the spatial patterns of the original data when addresses are missing at random. We find that the level of geocoding success depends on the number of points and the number of areal units under analysis, but generally show that the necessary levels of geocoding success are lower than found in previous research. This finding is consistent across different national contexts. 相似文献
96.
H. Rathjens K. Bieger I. Chaubey J. G. Arnold P. M. Allen R. Srinivasan D. D. Bosch M. Volk 《水文研究》2016,30(23):4367-4383
A spatially distributed representation of basin hydrology and transport processes in hydrologic models facilitates the identification of critical source areas and the placement of management and conservation measures. Floodplains are critical landscape features that differ from neighbouring uplands in terms of their hydrological processes and functions. Accordingly, an important step in watershed modelling is the representation of floodplain and upland areas within a watershed. The aim of this study is (1) to evaluate four floodplain–upland delineation methods that use readily available topographic data (topographic wetness index, slope position, uniform flood stage, and variable flood stage) with regard to their suitability for hydrological models and (2) to introduce an evaluation scheme for the delineated landscape units. The methods are tested in three U.S. watersheds ranging in size from 334 to 629 km2 with different climatic, hydrological, and geomorphological characteristics. Evaluation of the landscape delineation methods includes visual comparisons, error matrices (i.e. cross‐tabulations of delineated vs reference data), and geometric accuracy metrics. Reference data were obtained from the Soil Survey Geographic (SSURGO) database and Federal Emergency Management Agency (FEMA) flood maps. Results suggest that the slope position and the variable flood stage method work very well in all three watersheds. Overall percentages of floodplain and upland areas allocated correctly were obtained by comparing delineated and reference data. Values range from 83 to 93% for the slope position and from 80 to 95% for the variable flood stage method. Future studies will incorporate these two floodplain–upland delineation methods into the subwatershed‐based hydrologic model Soil and Water Assessment Tool (SWAT) to improve the representation of hydrological processes within floodplain and upland areas. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
97.
Seismic surveys with sub‐bottom profiler were carried out in the Manfredonia Gulf in the southern Adriatic Sea. Here, a buried surface was recognized on which three valleys, located about 80 km from the shelf edge, were deeply incised. Beneath this surface, a pre‐upper Würm seismic unit (PW) was identified. Above, two seismic units were recognized: the transgressive system tract (TST) and highstand system tract (g2). On the basis of regional correlation with onshore and offshore data, these units and their boundaries were dated and correlated with phases of the last glacial–interglacial cycle. The incised valley system was attributed to the Marine Isotopic Stage (MIS) 2. The TST and g2 units fill the valleys and were attributed to the post‐glacial sea‐level rise and highstand. The incised valleys are anomalous with respect to published models; despite having many characteristics that would have limited the fluvial incision (the lowstand shoreline that remained on the shelf, the low gradient of the shelf, the subsidence that affected the study area since MIS 5), the valleys appear to be deeply incised on the shelf, with valley flanks that can exceed 40 m in height. The model to explain the formation of the valleys comprises enhanced river discharge as the key factor in increasing river energy and promoting erosion across the low gradient shelf. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
98.
Matthew Q. Lucas Michael Stat Matthew C. Smith Ernesto Weil Nikolaos V. Schizas 《Marine Ecology》2016,37(5):1079-1087
This study investigated differences in Symbiodinium diversity in the scleractinian coral species Agaricia lamarcki between shallow (20–25 m) and mesophotic (50–70 m) depths in the Northern Caribbean. Corals were sampled in each of four shallow sites (20–25 m; n = 18) and three mesophotic sites (50–70 m; n = 18) from Mona Island (Puerto Rico) and the US Virgin Islands during a mesophotic exploratory cruise and from the La Parguera shelf edge, off Southwestern Puerto Rico. Symbiodinium diversity was assessed using internal transcribed spacer 2 sequences clustered into operational taxonomic units (OTUs). Clustering resulted in eight clade C OTUs and one clade D OTU. Of these, there were three common Symbiodinium OTUs consisting of C3 and D1a.N14 in shallow reefs and C11.N4 in mesophotic reefs. Statistical tests (permutational multivariate analysis of variance and analysis of similarity) showed significant differences between clade C Symbiodinium OTUs in A. lamarcki colonies located at shallow and mesophotic depths, indicating symbiont zonation. Symbiodinium diversity in A. lamarcki from the Northern Caribbean is comparable to previous reports in the Southern Caribbean for this species. This is the first report of the thermal tolerant species Symbiodinium trenchii (D1a) in A. lamarcki. 相似文献
99.
为合作开发周边国家矿产资源,在实地调研的基础上,结合前人资料的收集与整理,将缅甸的大地构造单元自西向东划分为5个Ⅰ级构造单元、10个Ⅱ级构造单元.具体是：①西克钦邦-若开邦结合带（E-N1）（Ⅰ）,进一步划分为钦邦-若开邦结合带（E-N1）（Ⅰ1）、西克钦邦结合带（E-N1）（Ⅰ2）;②西缅甸-苏门答腊弧盆系（E-N1）（Ⅱ）,进一步划分为蒙育瓦-勃生岛弧带（E-N1）（Ⅱ1）、瑞保-仰光弧后盆地（E-N1）（Ⅱ2）、密支那岛弧带（E-N1）（Ⅱ3）;③腾冲-马来半岛造山带（T3-K）（Ⅲ）,进一步划分为八莫陆缘弧（T3-K）（Ⅲ1）、毛淡棉陆缘弧（T3-K）（Ⅲ2）、德林依达地块（Pz2）（Ⅲ3）;④保山-掸邦陆块（€-T2）（Ⅳ）;⑤昌宁-孟连-清莱结合带（C-T2）（Ⅴ）.这10个构造单元以9条断裂为边界.自西向东为：那加山-若开山逆冲断裂（F1）、平梨铺-卑谬伸展断裂（F2）、实皆-勃固右行平移断裂（F3）、葡萄-格杜逆冲断裂（F4）、英昆-八莫伸展断裂（F5）、南坎-抹谷右行平移断裂（F6）、曼德勒-垒固左行平移断裂（F7）、锡当-三塔左行平移断裂（F8）、孟宾-清迈逆冲断裂（F9）. 相似文献
100.
Hydrogeological investigation of mud-mound springs developed over a weathered basalt aquifer on the Liverpool Plains,New South Wales,Australia 总被引：1，自引：0，他引：1
The growth and collapse of mud mounds at a site on the Liverpool Plains in northern New South Wales, Australia has been observed over a 12-year period. The mud mounds appeared in a flat field for the first time in living memory in 1989, but their prior existence in the early Holocene is indicated by archaeological data. The piezometric head in bores drilled through a 7-m bed of clayey silt and screened in weathered basalt at a depth of 8 m was more than 2 m above ground level. Clay has been carried in suspension by water seeping to the ground surface where it has accumulated and formed a mound. Approximately eight years after their initial appearance, the growth of the mounds stopped and within a further three years they had almost completely disappeared.Mechanisms for the growth and decay of the mounds are reviewed. The chemistry of the shallow bore water and the water seeping from the surface of the mounds was dominated by sodium bicarbonate with a 4 mEq/l increase between the weathered basalt and the surface of the mound. Inverse modelling (PHREEQC) is used to determine possible chemical reactions that can account for this increase.
Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10040-003-0278-0.
Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10040-003-0278-0.
Resumen Se ha observado durante 12 años el crecimiento y el colapso de montículos de lodo en un emplazamiento ubicado en las Llanuras de Liverpool, en el estado australiano de Nueva Gales del Sur. Según la memoria existente, los montículos de lodo aparecieron en un campo llano por vez primera en 1989, pero, por datos arqueológicos, se conoce de su existencia a comienzos del Holoceno. Los niveles piezométricos en sondeos perforados a través de 7 m de limos arcillosos y ranurados en el basalto meteorizado a 8 m son superiores en más de 2 m a la superficie del terreno. La arcilla es portada en suspensión por el agua que descarga hacia la superficie del terreno, donde se acumula y forma el montículo. Unos 8 años después de su aparición, el crecimiento de los montículos se detiene y éstos acaban prácticamente desapareciendo en otros 3 años.Se revisa los mecanismos que originan el crecimiento y desaparición de los montículos. La química de las aguas someras de los sondeos y del agua que se filtra desde la superficie de los montículos está dominada por bicarbonato sódico, con un incremento de 4 meq/L entre el basalto meteorizado y la superficie del montículo. Se utiliza la modelación inversa (PHREEQC) para determinar las reacciones químicas que pueden explicar dicho aumento.
Résumé La croissance et l'effondrement de monticules de vase situés dans les plaines de Liverpool, dans le nord des Nouvelles Galles du Sud, ont été observés pendant 12 ans. Les monticules de vase sont apparus en terrain plat pour la première fois de mémoire d'homme en 1989; mais leur existence antérieure dès le début de l'Holocène est attesté par des données archéologiques. Le niveau piézométrique dans des forages traversant 7 m de silt argileux et recouvrant un basalte altéré à 8 m était de plus de 2 m au-dessus de la surface du sol. L'argile a été apportée en suspension par l'eau suintant à la surface du sol où elle s'est accumulée pour former un monticule. Environ 8 ans après leur première apparition, la croissance des monticules s'est arrêtée et ils ont presque complètement disparu dans les 3 ans qui ont suivi.Les mécanismes de croissance et de régression de ces monticules sont passés en revue. La chimie de l'eau des forages à proximité de la surface et de l'eau filtrant à la surface des monticules était dominée par le bicarbonate de sodium, avec une augmentation de 4 meq/l entre le basalte altéré et la surface du monticule. Une modélisation inverse (PHREEQC) a été mise en uvre pour déterminer les réactions possibles pouvant rendre compte de cet accroissement.相似文献