Hydrochemical characteristics and salinity of groundwater in the Ejina Basin, Northwestern China   总被引：8，自引：0，他引：8  

X. Wen  Y. Wu  J. Su  Y. Zhang  F. Liu 《Environmental Geology》2005,48(6):665-675

A hydrochemical investigation was conducted in the Ejina Basin to identify the hydrochemical characteristics and the salinity of groundwater. The results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area. The ionic ration plot and saturation index (SI) calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area. Most of the stable isotope δ¹⁸O and δD compositions in the groundwater is a meteoric water feature, indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation. Based on radioactive isotope tritium (³H) analysis, the groundwater ages were approximately estimated in different aquifers. The groundwater age ranges from less than 5 years, between 5 years and 50 years, and more than 50 years. Within 1 km of the river water influence zone, the groundwater recharges from recent Heihe river water and the groundwater age is about less than 5 years in shallow aquifer. From 1 km to 10 km of the river water influence zone, the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer. The groundwater age is more than 50 years in deep confined aquifer.  相似文献   

Late Quaternary lake evolution in the Gaxun Nur basin,central Gobi Desert,China, based on quartz OSL and K‐feldspar pIRIR dating of paleoshorelines     

《第四纪科学杂志》2017,32(3):347-361

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Age of Gimli beach of Lake Agassiz based on new OSL dating     

James T. Teller  Lewis A. Owen 《第四纪科学杂志》2021,36(1):56-65

Gimli beach in Manitoba is one of the lowest elevation beaches in the southern Lake Agassiz basin, and is a distinct ridge composed of bedded sand and gravel that rises above the lake plain and extends for more than 40 km. Ten new optically stimulated luminescence (OSL) ages from Gimli beach yield ages mostly ranging from 9.7 ± 0.7 to 10.5 ± 0.8 ka (average 10.3 ± 0.5 ka), which is older by 0.6 to >1.0 ka than age estimates of previous researchers. Two of our new OSL ages are notably older than the others, dating to ~11.3 ± 0.8 and 13.9 ± 1.0 ka, which we attribute to poorly bleached sands. We ascribe an age of about 10 ka to Gimli beach, which is several centuries before overflow from Lake Agassiz and its vast drainage basin shifted from the western Great Lakes to glacial Lake Ojibway and the St. Lawrence Valley.  相似文献   

A preliminary estimate of how stream water age is influenced by changing runoff sources in the Nagqu river water shed,Qinghai-Tibet Plateau     

Yuheng Yang  Baisha Weng  Denghua Yan  Xiaoyan Gong  Yanyu Dai  Yongzhen Niu 《水文研究》2021,35(10):e14380

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Zircon U–Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications     

Q. Liu  Y.‐B. Wu  H. Wang  S. Gao  Z.‐W. Qin  X.‐C. Liu  S.‐H. Yang  H.‐J. Gong 《Journal of Metamorphic Geology》2014,32(2):177-193

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra‐high‐P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.  相似文献   

Sedimentary evidence and luminescence and ESR dating of Early Pleistocene high lake levels of Megalake Tengger,northwestern China     

Fan Yuxin  Li Zhenjun  Yang Guangliang  Yi Shuangwen  Zhang Qingsong  Liu Wenhao  Mou Xuesong 《第四纪科学杂志》2020,35(8):994-1006

The timing of high lake-level stands during the Late Pleistocene in western China remains controversial. Here we report new results from Megalake Tengger based on a study of palaeo-shorelines and a drill core from Baijian Lake in the northwestern Tengger Desert. Multiple dating methods, based on luminescence signals (quartz optically stimulated luminescence, K-feldspar post infrared-infrared stimulated luminescence) and electron spin resonance signals of quartz, were used to date beach sands from palaeo-shoreline profiles at altitudes of ~1310 m (+20 m above lake level), ~1320 m (+30 m) and ~1350 m (+60 m), and from the top 20 m of sandy sediments from the drill core obtained from the modern beach of Baijian Lake. The dating results show that high lake-level stands associated with the previously reported Megalake Tengger (~1310–1320 m) occurred during the late Early to Middle Pleistocene, which is much earlier than previously reported. In addition, no geomorphological evidence of shorelines and sedimentary evidence from the drill core profile were found to support the previously reported Late Pleistocene lake levels. Our results indicate that the exact age of the previously reported ‘high lake level event’ in a large part of northwestern China during the Late Pleistocene needs to be re-evaluated.  相似文献   

Sentinel-2卫星落叶松林龄信息反演   总被引：1，自引：0，他引：1  

唐少飞  田庆久  徐凯健  徐念旭  岳继博 《遥感学报》2020,24(12):1511-1524

林龄结构信息能够有效反映区域森林群落不同生长阶段的固碳能力，对于评估森林生态系统的健康状况具有重要意义。本研究以中国温带典型优势树种落叶松林为研究对象，分别选择其芽萌动期、展叶期和落叶期时段的Sentinel-2影像，采用多元线性回归（MLR）、随机森林（RF）、支持向量机回归（SVR）、前馈反向传播神经网络（BP）以及多元自适应回归样条（MARS）等5种方法依次构建落叶松林龄反演模型。通过相关性分析首先确定最佳遥感反演物候期，并在此基础上根据相关性差异筛选出5个最优特征变量用于模型反演，分别为冠层含水量（CWC），归一化水体指数（NDWI），叶面积指数（LAI），光合有效辐射吸收率（FAPAR）和植被覆盖度（FVC）。研究结果表明，展叶期为落叶松林最佳遥感反演物候期。除植被衰减指数（PSRI）以及落叶期的NDVI、RVI外，落叶松林龄与各指标之间均呈负相关关系，其中与冠层含水量（CWC）的相关性最高，pearson相关系数达到-0.74（p<0.01）。此外，不同模型反演结果表明，随机森林模型（RF）为最佳落叶松林龄估测模型，其平均决定系数R²和平均均方根误差RMSE分别为0.89和2.91 a；多元线性回归模型（MLR）的林龄估测结果最差，其平均决定系数R²和平均均方根误差RMSE仅为0.57和5.69 a，非线性模型能更好的解释林龄与建模变量之间的关系。  相似文献   

Last interglacial vegetation and climate history from the Portuguese coast          下载免费PDF全文

T. A. MINCKLEY  J. A. HAWS  M. M. BENEDETTI  S. C. BREWER  S. L. FORMAN 《第四纪科学杂志》2015,30(1):59-69

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Luminescence chronology of late Quaternary moraines and Last Glacial Maximum equilibrium‐line altitude reconstruction from Parlung Zangbo Valley,south‐eastern Tibetan Plateau          下载免费PDF全文

RENRONG CHEN  SHANGZHE ZHOU  ZHONGPING LAI  XIANJIAO OU  RONG CHEN  YINGBIN DENG 《第四纪科学杂志》2014,29(6):597-604

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Linking tracers,water age and conceptual models to identify dominant runoff processes in a sparsely monitored humid tropical catchment          下载免费PDF全文

Christian Birkel  Chris Soulsby 《水文研究》2016,30(24):4477-4493

Assessing catchment runoff response remains a key research frontier because of limitations in current observational techniques to fully characterize water source areas and transit times in diverse geographical environments. Here, we report a study that combines empirical data with modelling to identify dominant runoff processes in a sparsely monitored humid tropical catchment. The analysis integrated isotope tracers into conceptual rainfall–runoff models of varying complexity (from 5 to 11 calibrated parameters) that are able to simulate discharge and tracer concentrations and track the evolving age of stream water exiting the catchment. The model structures can be seen as competing hypotheses of catchment functioning and were simultaneously calibrated against uncertain streamflow gaugings and a 2‐year daily isotope rainfall–runoff record. Comparison of the models was facilitated using global parameter sensitivity analysis and the resulting effect on calibration. We show that a variety of tested model structures reproduced water and tracer dynamics in stream, but the simpler models failed to adequately reproduce both. The resulting water age distributions of the tested models varied significantly with little similarity between the stream water age and stored water age distributions. The sensitivity analysis revealed that only some of the more complex models (from eight parameters) could be better constrained to infer more plausible water age distributions and catchment storage estimates. These models indicated that the age of water stored in the catchment is generally older compared with the age of water fluxes, with evapotranspiration age being younger compared with streamflow. However, the water age distributions followed a similar temporal behaviour dominated by climatic seasonality. Stream water ages increased during the dry season (greater than 1 year) and decreased with increased streamflow (a few weeks old) during the wet season. We further show that the ratios of the streamwater age to stored water age distribution and the water age distribution of actual evapotranspiration to the stored water age distribution from constrained models could potentially serve as useful hydrological indicators of catchment functioning. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献