Seasonal variations in river discharge and nutrient export to a Northeastern Pacific estuary   总被引：1，自引：0，他引：1  

A.C. Sigleo  W.E. Frick 《Estuarine, Coastal and Shelf Science》2007,73(3-4):368-378

Seasonal variations in dissolved nitrogen and silica loadings were related to seasonal variability in river discharge. Dissolved nutrient concentrations measured weekly at three stations in the Yaquina River, Oregon from 1999 through 2001, and then monthly in 2002 were used as the basis for developing a nutrient loading regression as part of a larger agency program for evaluating nutrient processes. Because realistic models of nutrient transport require dense data sets to capture both long and short term fluctuations in nutrient concentrations, data at one freshwater station also were collected hourly for the same years using an in-stream monitor.The effects of storm events on dissolved nutrient transport were examined during three storms, including one in a high rainfall-discharge year, and two in average years, one of which followed a drought year. During the drought year (WY2001), total dissolved nitrate input was considerably less than in wetter years. Dissolved nitrate concentrations, however, were unusually high in the first winter storm runoff after the drought. The freshwater dissolved nitrate nitrogen loads varied from 40,380 kg day⁻¹ during a high-flow storm event to 0.11 kg day⁻¹ during late summer, low flow conditions. Dissolved silica dynamics differed from those of nitrate because during storm events, silica concentrations in the Yaquina River decreased to near zero at the storm height, probably due to dilution by near surface or overland flow, and later recovered.During the time interval studied, over 94% of the dissolved nitrate and silica were transported from the watershed during the winter months of greater rainfall, indicating that seasonality and river flow are primary factors when considering nutrient loadings from this watershed system.  相似文献   

探地雷达(GPR)在海南岛东北部海岸带调查中的应用 ^*   总被引：2，自引：0，他引：2  

殷勇  朱大奎  I.P.Martini 《第四纪研究》2006,26(3):462-469

对海南岛东北部海岸带调查采用了探地雷达(GPR)研究海岸带沙体的结构、展布和沉积序列,取得了很好的效果。文章通过和有限的露头资料对比以及对反射波形态、结构的研究,确定了海滩脊、海岸沙丘的反射特征以及潜水面的位置。雷达图像显示五龙港古海滩脊由亚水平、不连续、高振幅和透镜状反射波组成;木兰头海岸沙丘已受到人类活动的扰动,短的、陡倾斜反射可能代表未受扰动的海岸风成沙的前积层。研究表明探地雷达是一种可靠、快速和经济的地球物理方法,在砂砾质海岸可产生高质量、高分辨率和连续的反射剖面,值得加以推广。  相似文献   

东帕米尔变质核杂岩构造的厘定     

刘振涛  王宏君  祁世军  赵树铭 《新疆地质》2003,21(1):85-91

卡拉库鲁木变质核杂岩是慕土塔格岩体的南缘部分，由长城系片麻岩以及燕山期花岗岩组成，其中长城系片麻岩为一套低角闪岩相的变质侵入岩，主要岩性为（石榴石）黑云二长片麻岩、（石榴石）黑云斜长片麻岩；根据变形程度，将其划分为内带、中带及外带，其中在内带见有燕山期花岗岩。剥离断层沿变质核杂岩边缘呈向南凸出的弧形展布。剥离断层上盘滑脱体由长城系赛图拉岩群高绿片岩－低角闪岩相的变质岩系构成。变质核杂岩构造的形成时代为早－中侏罗世。  相似文献   

Confirmation of an Early Cretaceous age for the Qihulin Formation in eastern Heilongjiang Province, China: constraints from a new discovery of radiolarians   总被引：1，自引：0，他引：1  

Gang Li  Qun Yang 《Cretaceous Research》2003,24(6):691-696

The coal-bearing, alternating marine and non-marine Longzhaogou Group in eastern Heilongjiang, northeastern China, has long been considered as Jurassic, or mainly Jurassic, in age. However, recent studies have demonstrated that the ammonites and dinoflagellate cysts are of Early Cretaceous age. This has now been confirmed by new radiolarian evidence. The radiolarian fauna recovered from the upper Qihulin Formation of the Longzhaogou Group consists of nine poorly preserved species referable to nine genera. Novixitus is a Cretaceous genus, and the specimens of Archaeodictyomitra sp. and Xitus sp. recovered resemble A. vulgaris Pessagno and X. spicularius (Aliev), respectively.  相似文献   

帕米尔北缘弧形推覆构造带东段的基本特征与现代地震活动   总被引：35，自引：10，他引：35       下载免费PDF全文

陈杰  曲国胜  胡军  冯先岳 《地震地质》1997,19(4):14

帕米尔北缘弧形推覆构造带东段由强烈活动的艾卡尔特弧形活动褶皱－逆断裂带与卡兹克阿尔特弧形活动褶皱－逆断裂带南、北两条巨型边缘弧形构造带及其间的推覆构造构成。每个弧形带分别由多个不同级别的、相对独立的次级弧形构造组成。每个弧形构造实际上就是一个独立的逆冲推覆席体，都有其各自独特的几何学、运动学、动力学特征，但同时又具有自相似性特征。独立地震破裂区或形变带与独立活动的弧形推覆构造可能具有一定的对应关系  相似文献   

Deep structure of the northeastern Japan arc and its implications for crustal deformation and shallow seismic activity   总被引：7，自引：1，他引：7  

Akira Hasegawa  Junichi Nakajima  Norihito Umino  Satoshi Miura 《Tectonophysics》2005,403(1-4):59-75

Seismic tomography studies in the northeastern Japan arc have revealed the existence of an inclined sheet-like seismic low-velocity and high-attenuation zone in the mantle wedge at depths shallower than about 150 km. This sheet-like low-velocity, high-attenuation zone is oriented sub-parallel to the subducted slab, and is considered to correspond to the upwelling flow portion of the subduction-induced convection. The low-velocity, high-attenuation zone reaches the Moho immediately beneath the volcanic front (or the Ou Backbone Range) running through the middle of the arc nearly parallel to the trench axis, which suggests that the volcanic front is formed by this hot upwelling flow. Aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the Backbone Range where they are expelled from solidified magma and migrate further upward. The existence of aqueous fluids may weaken the surrounding crustal rocks, resulting in local contractive deformation and uplift along the Backbone Range under the compressional stress field of the volcanic arc. A strain-rate distribution map generated from GPS data reveals a notable concentration of east–west contraction along the Backbone Range, consistent with this interpretation. Shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone. Based on these observations, a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern Japan arc.  相似文献   

Land degradation in the source region of the Yellow River, northeast Qinghai-Xizang Plateau: classification and evaluation   总被引：6，自引：0，他引：6  

Jianmin Feng  Tao Wang  Shanzhong Qi  Changwei Xie 《Environmental Geology》2005,47(4):459-466

Land degradation imposes a great threat to the world. It is not merely an environmental issue, but also a social and economic problem. Land desertification is among the main aspects of environment changes in the source region of the Yellow River. Previous studies focused on water resource utilization and soil erosion, but land degradation in the source region of the Yellow River even the whole Qinghai-Xizang Plateau received little attention. Based on the data obtained by field investigation and TM satellite images of 2000, this study provides the classification and evaluation information of the land degradation in the source region of the Yellow River. There are six types of land degradation in this region: water erosion in the northern mountains around the Gonghe Basin, sandy desertification in the Gonghe Basin and Upland Plain Area, aridization in the lower reaches, salinization in the Gonghe Basin, vegetation degradation in the intramontance basin and freezing and thawing erosion in the high mountains. The total degraded area is 34,429.6 km², making up 37.5% of the land in the study area. Finally, land degradation in the source region of the Yellow River was evaluated according to changes in the physical structure and chemical component of soils, land productivity, secondary soil salt and water conditions.  相似文献   

东北帕米尔中新世中下地壳物质的折返过程：公格尔西滑脱剪切带的构造变形与年代学证据     

蔡志慧  许志琴  曹汇  梁凤华 《地质学报》2016,90(11):2999-3010

公格尔西滑脱剪切带位于东北帕米尔公格尔片麻岩穹窿西缘。通过我们详细的野外观测、显微构造观察、石英电子背散射衍射(EBSD)测试以及锆石U-Pb测年,对公格尔西滑脱剪切带的几何学、运动学特征及其形成演化时限进行了研究。公格尔西滑脱剪切带糜棱岩中大量的石榴子石、矽线石和蓝晶石等表明其为高级变质产物。S/C组构、旋转碎斑及不对称褶皱等变形现象说明剪切带上盘向W或SW低角度剪切的运动特征。高级变质糜棱岩和浅色岩脉记录约20 Ma的206 U-238Pb锆石年龄,说明公格尔西滑脱剪切带初始形成于早中新世。结合前人研究成果,我们认为公格尔西滑脱剪切带曾是狭长的帕米尔中下地壳滑脱带的最北段。由于新生代印度亚洲大陆碰撞以后印度板块仍持续向N俯冲推进,帕米尔地壳由S向N开始增厚,进变质作用最初发生于南帕米尔,约20 Ma时到达北帕米尔。东北帕米尔中下地壳物质开始折返于中新世中期。而直到6~4 Ma,东北帕米尔公格尔地区开始快速隆起,此时公格尔新生代高级变质岩才快速折返。  相似文献   

新疆西准噶尔玛依勒山地区阔依塔斯杂岩体地球化学特征及锆石U-Pb年龄   总被引：1，自引：1，他引：0       下载免费PDF全文

靳松  荣桂林  张兆祎  李天刚  彭朝晖  吴立昂 《中国地质》2016,(1):99-110

新疆西准噶尔北部广泛发育中酸性侵入岩,其形成时代为晚石炭世—早二叠世,岩石类型为辉石闪长岩、石英闪长岩和花岗闪长岩。阔依塔斯杂岩体的形成年龄为(297±2)Ma,Si O2为52.40%~67.53%;高Al2O3,14.92%~17.85%;里特曼指数(δ)小于3.3,介于1.47~1.98;富钠贫钾,K2O/Na2O为0.15~0.49;铁高而镁低,Fe OT/Mg O为1.01~1.69。其稀土配分模式右倾,轻重稀土分馏明显,具有微弱铕正异常。地球化学和年代学特征表明:岩体形成于后碰撞演化的晚期阶段,这一时间早于东准噶尔后碰撞的时间(二叠纪末)。该杂岩体主体可能为幔源岩浆底侵镁铁质下地壳,导致发生部分熔融的产物。  相似文献   

江西象山地质公园丹霞地貌成景地层沉积环境分析     

刘鑫  陈留勤  李馨敏  李余亮 《现代地质》2018,32(2):260

随着旅游地学的兴起和地学科普的需求,红层与丹霞地貌正在吸引着越来越多的关注。赣东北贵溪市象山地质公园发育以赤壁丹崖为特色的丹霞地貌景观,成景地层为上白垩统圭峰群河口组以砾岩为主的红色碎屑岩,冲刷侵蚀界面、粒序层理和交错层理等沉积构造发育,这为沉积环境分析提供了良好的判断标志。对该套成景地层进行厘米级实测,另外选择2处砾岩露头进行砾石统计以获取碎屑颗粒粒径、岩性、磨圆度和风化程度等信息。在实测厚度为40余米的地层柱状图上,识别出7种岩相类型,即正粒序砾岩、逆粒序砾岩、无沉积构造砾岩、平行层理砾岩、交错层理砾岩、聚集状砾岩、砂岩。砾石以中砾(2~5 cm)为主,磨圆度低,风化程度中等,成分以凝灰岩为主(58%~665%),其次为石英、花岗岩、砂岩。砾石成分和砾向分析结果说明,盆地南部早白垩世凝灰岩提供了主要的碎屑物质。根据野外实测红层剖面和砾石统计分析,认为成景地层为冲积扇沉积体系的产物。河口组红层沉积时期,盆地边缘断层活跃,间歇性强降雨事件导致冲积扇朵叶上洪泛河流搬运的沉积物供应充足,最终在剖面上形成砾岩和砂岩频繁互层及其厚度横向不稳定的现象。在中国东南地区晚白垩世总体干燥的古气候背景下,河口组中河流作用主导的冲积扇沉积体系可能指示了古气候向湿润转变,降水增加,相对丰富的水系将粗碎屑搬运到盆地区发生沉积。  相似文献