首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 689 毫秒
1.
Urmia Salt Lake(USL) is a hypersaline lake located at the NW corner of the Iran platform. The lake area is estimated to have been over 5000 km~2 at one point, but has now decreased to 1000 km~2 in the last two decades. It contains 4.6×10~9 tons of halite and other detrital and evaporative minerals such as calcite, aragonite, dolomite, quartz, feldspars, augite and sylvite. This study examined the mineralogy and geochemistry of bed sediments along the mid-east toward NE bank sediments collected from 1.5 meters depth and nearby augite placer. Due to the diverse lithology of the surrounding geology, bed sediments vary from felsic in the mid-east to mafic in the northeast. Weathering of tephrite and adakite rocks of the Islamic Island at the immediate boundary has produced a large volume of augite placer over a 40 km length, parallel to the shoreline. Based on the study result, weathering increases from south to north and the geochemistry of the sediments shows enrichment of Mg O, Ca O, Sr and Ba associated with Sr deployment in all samples. Rare earth elements(REE) patterns normalized to the upper continental crust(UCC) indicated LREEs enrichment compared to HREEs with an elevated anomaly of Eu, possibly due to surface absorbance of Mn and Fe minerals, associated with Sr elevation originating from adakites in the lake basin vicinity.  相似文献   

2.
Ancient subduction zones are characterized by metamorphic and orogenic belts. The Zagros Orogenic Belt comprises almost all sections of an ancient subduction zone along which Neo-Tethyan oceanic crust was subducted beneath central Iran. The Eslami Peninsula, as a part of the Zagros Orogenic Belt in Azerbaijan province, northwestern Iran, is situated between the Lake Urmia fore-arc basin and the Sahand Magmatic Arc. This region contains Eocene leucite dikes, trachyte, tephrite, phenolite, basanite and syenite. Volcanic features related to the Sahand are located in the eastern part of the Eslami Peninsula. In view of its relative age and composition, the Eslami Peninsula proposed as an outer arc of the Sahand Magmatic Arc that formed within the post-collisional setting of the central Iranian and Arabian plates. After subduction and contact of the two plates, a symmetric pop-up structure has been created by thrusting in the Zagros belt as a result of the collision processes. The injesction of dikes in the Eslami Peninsula is also a result of the continent_continent collision.  相似文献   

3.
正1 Introduction Lake Urmia in the northwestern corner of Iran is one of the largest permanent hypersaline lakes in the world and the largest lake in the Middle East(1,2,3).The lake was  相似文献   

4.
A late Pleistocene long pollen record from Lake Urmia, NW Iran   总被引：4，自引：0，他引：4  
A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.  相似文献   

5.
Lake Balkhash is the third largest inland lake in Central Asia after the Caspian Sea and the Aral Sea.The Ili River-Balkash Lake Basin resides in the southeastern part of the Republic of Kazakhstan and the western part of China's Ili Prefecture,which belongs to the arid and semi-arid region.In the middle to late 20thcentury,the Ili River-Balkash Lake Basin was affected by climate change and human activities,and the problems of water ecology and water resources became increasingly prominent,which became the focus of attention for China and Kazakhstan.In this study,the water level derived from radar altimeter data,the water surface area extracted from Landsat data,and the temperature and precipitation data in the basin were comprehensively utilised.Data analysis of the time course and correlation of hydrological,meteorological elements in the lake basin,water dynamic changes,and influencing factors of Lake Balkhash was studied.The results show that the cyclical change of regional climate is the main factor affecting the change of lake water,and human activities in the short term can regulate the change of water volume in Lake Balkhash.The research results in this paper can provide a scientific basis for the solution of water disputes in cross-border rivers between China and Kazakhstan.  相似文献   

6.
Between 10,500 and 9000 cal yr BP, δ18O values of benthic ostracodes within glaciolacustrine varves from Lake Superior range from − 18 to − 22‰ PDB. In contrast, coeval ostracode and bivalve records from the Lake Huron and Lake Michigan basins are characterized by extreme δ18O variations, ranging from values that reflect a source that is primarily glacial ( − 20‰ PDB) to much higher values characteristic of a regional meteoric source ( − 5‰ PDB). Re-evaluated age models for the Huron and Michigan records yield a more consistent δ18O stratigraphy. The striking feature of these records is a sharp drop in δ18O values between 9400 and 9000 cal yr BP. In the Huron basin, this low δ18O excursion was ascribed to the late Stanley lowstand, and in the Lake Michigan basin to Lake Agassiz flooding. Catastrophic flooding from Lake Agassiz is likely, but a second possibility is that the low δ18O excursion records the switching of overflow from the Lake Superior basin from an undocumented northern outlet back into the Great Lakes basin. Quantifying freshwater fluxes for this system remains difficult because the benthic ostracodes in the glaciolacustrine varves of Lake Superior and Lake Agassiz may not record the average δ18O value of surface water.  相似文献   

7.
山东东平湖的变迁与黄河改道的关系   总被引：7，自引：5，他引：2       下载免费PDF全文
根据历史文献以及巨野、梁山、戴庙钻孔剖面的分析与研究及对东平湖底沉积的调查,确定了大野泽、梁山泊、安山湖、东平湖的沉积记录,提出东平湖由大野泽、梁山泊、安山湖演化而来。通过对东平湖演化与黄河决口和改道关系的分析与对比,指出历史时期东平湖演化历程与黄河关系密切,经历了黄河决口注入和改道流经湖区,河水注入、湖面扩大,河徙水退、湖面萎缩。黄河第一次大改道期间注入和一次改道流经大野泽。黄河第二次大改道期间两次注入、其中一次改道流经大野泽,水面北侵形成梁山泊。黄河第三次大改道期间三次决口注入,两次改道流经梁山泊,湖面进一步扩大成“八百里梁山泊”,之后黄河仅数次决入,水源短缺,湖面萎缩。黄河第四次大改道期间未流入梁山泊,湖面进一步缩小。黄河第五次大改道期间曾两次注入梁山泊,湖面又扩大成为一片泽国,而后断绝黄河水源,被分成安山湖等北五湖,梁山泊岁久填淤,变湖为陆。黄河第六次大改道期间黄河水源断绝,北五湖水面北移,逐渐萎缩消失,仅安山湖经历一次黄河决入,并淤塞而成东平湖,黄河水断绝时湖底干涸,黄河大汛期曾倒灌入湖。  相似文献   

8.
Tufa domes and towers are common around the margins of Winnemucca Dry Lake, Nevada, USA, a desiccated sub‐basin of pluvial Lake Lahontan. A 2·5 m diameter concentrically‐layered tufa mound from the southern end of the playa was sampled along its growth axis to determine timing, rate and geochemical conditions of tufa growth. A radiocarbon‐based age model indicates an 8200‐year tufa depositional record that begins near the end of the Last Glacial Maximum (ca 23 400 cal yr bp ) and concludes at the end of the most recent Lahontan highstand (ca 15 200 cal yr bp ). Petrography, stable isotopes and major and minor elemental compositions are used to evaluate the rate and timing of tufa growth in the context of the depositional environment. The deposit built radially outward from a central nucleation point, with six decimetre‐scale layers defined by variations in texture. Two distinct tufa types are observed: the inner section is composed of two layers of thinolite pseudomorphs after ikaite, with the innermost layer comprised of very small pseudomorphs (<0·25 cm) and an outer layer composed of larger, ca 3 cm long pseudomorphs, followed by a transitional layer where thinolite pseudomorphs grade into calcite fans. The outer section consists of three distinct layers of thrombolitic micrite with a branching mesofabric. The textural change occurred as lake levels began to rise towards the most recent Lahontan highstand interval and probably was prompted by warming of lake waters caused by increased groundwater flux during highstand lake levels. The Mg/Ca and Sr/Ca variations suggest a warming trend in the tufa growth environment and may also reflect increasing growth rates of tufa associated with increased fluxes of groundwater. This systematic study of tufa deposition indicates the importance of the hydrology of the lacustrine tufa system for reconstructing palaeoenvironmental records, and particularly the interaction of ground and surface waters.  相似文献   

9.
大地热流对滇池环境的影响与滇池污染治理的新思路   总被引：5，自引：0，他引：5  
滇池经过长达7年、投资40多亿元的治理,在污染源头控制上已经取得了明显成绩,在一定程度上缓解了生态环境的进一步恶化。滇池水体水质至今没有好转的根本原因在于对滇池蓝藻爆发机理的认识没有考虑其所处的特殊地理环境。滇池水体富营养化之后,是由于较高的大地热流背景和四季如春的气候条件使蓝藻得以不停息地繁殖,致使滇池的水生生态系统完全瘫痪,水体完全失去自净能力。“抑制蓝藻的繁殖”和“清除水体中的营养物质”两大问题形成了滇池治理中一个难解的死结。解开死结的有效措施是从抚仙湖调清水给滇池换水,恢复草海,提高湖水自净能力,发展水生生态系统,抑制藻类繁殖。  相似文献   

10.
乌梁素海和岱海沉积磷形态分布的差异性研究   总被引：3，自引：0，他引：3  
湖泊沉积物中磷的含量及形态分布等地球化学信息可以用来反演湖泊流域的古环境及污染历史。本文以乌梁素海和岱海两个不同类型的湖泊为研究对象,对两个湖泊沉积柱芯中磷形态分布的差异性进行了研究。结果表明,乌梁素海和岱海沉积柱芯中沉积磷的主导形态均为ACa P、De P和 Or P,但乌梁素海表层沉积物和沉积柱芯中Al P和 ACa P的含量水平明显高于岱海,而Ex P、De P和 Or P的含量水平明显低于岱海。两个湖泊沉积磷形态分布的差异性能较好地揭示出湖泊流域的地理环境、化学风化程度以及湖泊富营养化类型的差异性,沉积柱芯中ACa P含量及其分布特征能很好的指示湖泊自身发展过程中的富营养化水平,而De P含量及其分布特征则能较好的揭示出整个湖泊流域的古环境古气候信息。  相似文献   

11.
Field investigations at Dugway Proving Ground in western Utah have produced new data on the chronology and human occupation of late Pleistocene and early Holocene lakes, rivers, and wetlands in the Lake Bonneville basin. We have classified paleo-river channels of these ages as “gravel channels” and “sand channels.” Gravel channels are straight to curved, digitate, and have abrupt bulbous ends. They are composed of fine gravel and coarse sand, and are topographically inverted (i.e., they stand higher than the surrounding mudflats). Sand channels are younger and sand filled, with well-developed meander-scroll morphology that is truncated by deflated mudflat surfaces. Gravel channels were formed by a river that originated as overflow from the Sevier basin along the Old River Bed during the late regressive phases of Lake Bonneville (after 12,500 and prior to 11,000 14C yr B.P.). Dated samples from sand channels and associated fluvial overbank and wetland deposits range in age from 11,000 to 8800 14C yr B.P., and are probably related to continued Sevier-basin overflow and to groundwater discharge. Paleoarchaic foragers occupied numerous sites on gravel-channel landforms and adjacent to sand channels in the extensive early Holocene wetland habitats. Reworking of tools and limited toolstone diversity is consistent with theoretical models suggesting Paleoarchaic foragers in the Old River Bed delta were less mobile than elsewhere in the Great Basin.  相似文献   

12.
The freshwater Lake Kinneret (Sea of Galilee) and the hypersaline Dead Sea are remnant lakes, evolved from ancient water bodies that filled the tectonic depressions along the Dead Sea Transform (DST) during the Neogene-Quartenary periods. We reconstructed the limnological history (level and composition) of Lake Kinneret during the past ∼40,000 years and compared it with the history of the contemporaneous Lake Lisan from the aspect of the regional and global climate history. The lake level reconstruction was achieved through a chronological and sedimentological investigation of exposed sedimentary sections in the Kinnarot basin trenches and cores drilled at the Ohalo II archeological site. Shoreline chronology was established by radiocarbon dating of organic remains and of Melanopsis shells.The major changes in Lake Kinneret level were synchronous with those of the southern Lake Lisan. Both lakes dropped significantly ∼42,000, ∼30,000, 23,800, and 13,000 yr ago and rose ∼39,000, 26,000, 5000, and 1600 yr ago. Between 26,000 and 24,000 yr ago, the lakes merged into a unified water body and lake level achieved its maximum stand of ∼170 m below mean sea level (m bsl). Nevertheless, the fresh and saline water properties of Lake Kinneret and Lake Lisan, respectively, have been preserved throughout the 40,000 years studied. Calcium carbonate was always deposited as calcite in Lake Kinneret and as aragonite in Lake Lisan-Dead Sea, indicating that the Dead Sea brine (which supports aragonite production) never reached or affected Lake Kinneret, even during the period of lake high stand and convergence. The synchronous level fluctuation of lakes Kinneret, Lisan, and the Holocene Dead Sea is consistent with the dominance of the Atlantic-Mediterranean rain system on the catchment of the basin and the regional hydrology. The major drops in Lake Kinneret-Lisan levels coincide with the timing of cold spells in the North Atlantic that caused a shut down of rains in the East Mediterranean and the lakes drainage area.  相似文献   

13.
长江中游湖泊沉积微结构特征与沉积环境   总被引：11，自引：3，他引：11  
在长江中游的洪湖、东湖、网湖和大九湖等四个地点取得湖沼沉积物的钻孔样品,用偏光显微镜下和电子显微镜观察微结构特征并以此解释三种湖相粘土的成因和沉积环境的变化。在长江沿岸湖泊中,0.4~ 0.5kaBP以来形成的浅色粘土的微结构类型主要有 :显微层理构造、颗粒的定向性、较大的微孔隙和颗粒粒径,面与面或边与边接触方式。物源主要来自河流带来的泥沙.当时河湖相通,河流入湖水沙量大。 1~ 2.5kaBP期间形成的青色粘土的典型微结构是 :凝胶结构、絮凝结构、细颗粒粒径和小孔隙、低球度和淡水中心冈硅藻。主要是有机质胶体与粘土胶体相互作用形成的。此期间,河流带入湖泊的泥沙少,江汉平原拥有一个开阔、稳定、浮游生物较多的淡水湖泊环境。 0.4~ 1kaBP期间形成的黑色粘土的主要微结构类型是 :凝胶结构、大的圆孔隙和植物纤维的生物框架结构、呈双峰分布的孔隙。它主要是由于维管束植物残体大量积累形成的。当时江汉平原湖泊湖水变浅,大量挺水植物生长,有些湖泊沼已经沼泽化了。鱼骨框架结构证明,在 2.9~ 4kaBP的全新世温暖期山间盆地大九湖出现大量鱼类,但并没有导致喜温鱼类向上游明显迁徙。  相似文献   

14.
Samples of surface deposits in the Lake Sugan catchment, as well as surface lake sediments, eolian materials occulted in the lake ice cover, and airborne dust were collected for grain-size analysis. The results show that the coarse fraction of the lake sediments could be transported by ambient winds and to a lesser extent by river flow in the study area. Sediment cores were retrieved from Lake Sugan in December 2000, and 210Pb and 137Cs dating and grain-size analyses were performed on these samples. 210Pb ages and the volume percentage of the fraction of lake sediments >63 μm were used to reconstruct the dust storm history from 1957 to 2000. Observational data for dust storm events collected at a local meteorological station largely agrees with the reconstructed trend for the past 44 years, suggesting that lake sediments can be employed to trace the dust storm history of the northern Qinghai–Tibetan Plateau.  相似文献   

15.
Shoreline geomorphology, shoreline stratigraphy, and radiocarbon dates of organic material incorporated in constructional beach ridges record large lakes during the late Pleistocene and late Holocene in the Pyramid Lake subbasin of Lake Lahontan, Nevada, USA. During the late Holocene, a transgression began at or after 3595 ± 35 14C yr B.P. and continued, perhaps in pulses, through 2635 ± 40 14C yr B.P., resulting in a lake as high as 1199 m. During the latest Pleistocene and overlapping with the earliest part of the Younger Dryas interval, a lake stood at approximately 1212 m at 10,820 ± 35 14C yr B.P. and a geomorphically and stratigraphically distinct suite of constructional shorelines associated with this lake can be traced to 1230 m. These two lake highstands correspond to periods of elevated regional wetness in the western Basin and Range that are not clearly represented in existing northern Sierra Nevada climate proxy records.  相似文献   

16.
Lake Balkhash is the third largest inland lake in Central Asia after the Caspian Sea and the Aral Sea. The Ili River-Balkash Lake Basin resides in the southeastern part of the Republic of Kazakhstan and the western part of China's Ili Prefecture, which belongs to the arid and semi-arid region. In the middle to late 20th century, the Ili River-Balkash Lake Basin was affected by climate change and human activities, and the problems of water ecology and water resources became increasingly prominent, which became the focus of attention for China and Kazakhstan. In this study, the water level derived from radar altimeter data, the water surface area extracted from Landsat data, and the temperature and precipitation data in the basin were comprehensively utilised. Data analysis of the time course and correlation of hydrological, meteorological elements in the lake basin, water dynamic changes, and influencing factors of Lake Balkhash was studied. The results show that the cyclical change of regional climate is the main factor affecting the change of lake water, and human activities in the short term can regulate the change of water volume in Lake Balkhash. The research results in this paper can provide a scientific basis for the solution of water disputes in cross-border rivers between China and Kazakhstan.  相似文献   

17.
散落核素7Be和137Cs在洱海和红枫湖沉积物中蓄积对比   总被引：9，自引：6，他引：9  
沉积物柱芯分别采自滇西地区的洱海和黔中地区的红枫(及百花)湖,散落核素7Be和137Cs在沉积物中的蓄积特征对比分析表明,7Be在洱海及红枫湖沉积物中的累计值分别为(237±73)Bq/m2和(783±44)Bq/m2;按校正到沉降年代的数值,1986年以前137Cs的累计值分别为(519±26)Bq/m2及(3704±56)Bq/m2.由模式计算获知,(1)7Be和137Cs在红枫湖沉积物中的蓄积以侵蚀影响为主;在洱海的蓄积受直接散落控制.(2)在洱海和红枫湖地区7Be大气散落累计值分别为(0.07±0.02)Bq/cm2及(0.08±0.01)Bq/cm2;1986年以前137Cs大气散落累计值分别为(0.11±0.01)Bq/cm2及(0.37±0.01)Bq/cm2,显示出滇西与黔中地区之间137Cs散落的地区差异.这一现象可能反映出青藏高原对滇西地区存在着全球性大气扩散污染物散落的屏蔽效应.  相似文献   

18.
In recent decades, there have been discussions and predictions regarding the impact of climate on floods, due to its socioeconomic and environmental consequences. For accurate prediction of future flood events and their impacts, it is crucial to have an improved understanding on past flood events. Lacustrine sediments have been used as a natural archive to study the past flood events. Here, we study the impact of 1954 flood event on the lacustrine environment of Bengas and Rupa Lake in central Nepal based on X-ray fluorescence spectrometry (XRF) element analysis, magnetic susceptibility (MS), total organic carbon (TOC) and the biomarker molecular compositions. Results showed that 1954 flood event had significant impacts on the two lakes in terms of detrital input, organic matter deposition and aquatic production. Before the flood event, both two studied lakes had relatively lower catchment erosion rate, lower organic matter deposition and aquatic production. During the flood event, catchment erosion and aquatic production increased in both lakes due to mass transport deposits and the increased nutrition loading attributed to flood event. Following the flood event, Begnas Lake showed the sharp increase in organic matter deposition, whereas in the Rupa Lake organic matter deposition showed minor changes. The difference in organic matter deposition in lakes during flooding event is likely due to detrital material brought and deposited by the flood activity. Overall our results suggest that lacustrine sediments are sensitive to the extreme event and would be an ideal archive for the reconstruction of flood events.  相似文献   

19.
To describe and analyse the role of sediments in the matter cycling in large shallow transboundary Lake Peipsi (L. Peipsi) in north-eastern Europe, detailed surface-sediment mapping was conducted. On the basis of grain size the surface sediments fall into three groups: coarse-grained sediments (prevailingly sands in the lake’s southern part), fine-grained sediments (mainly silts) and silty sands, both in the central deeper part within the 8-m depth contour. The groups of deposits have a distinct spatial distribution, determined mainly by the current system in the lake. The main source of bottom sediments is the erosion of the lake floor and shores, the role of the river input seems to be limited. Fine-grained organic-rich sediments are very cohesive, playing the main role in the circulation of various inorganic and organic pollutants like nutrients and xenobiotics. Due to the cohesive character of the sediments their physical and chemical properties are extremely diverse and if the near-bottom shear stress increases (extreme meteorological events, changes in the water level, etc.), the lake floor may be subjected to episodic erosion and resuspension, which may cause remobilisation of impurities in muddy sediments and their return to the food chain.  相似文献   

20.
乜贞  卜令忠  郑绵平 《地球学报》2010,31(1):95-101
锂对国民经济和国家安全具有重要意义, 是21世纪的能源金属。近10年, 中国主要从国外进口碳酸锂产品。中国是一个多盐湖的国家, 盐湖锂占锂资源工业总储量的85%。现代第四纪盐湖主要分布在我国西北的青海、西藏、新疆和内蒙古四省区, 具有很好的开发前景。经过多年科研后, 目前国内已经在西台吉乃尔和扎布耶两个盐湖建立了卤水提锂产业。本文对比研究了这两个盐湖资源状况和地理气候条件, 以及由此而决定的盐湖资源开发工艺流程, 探讨了其工艺优化方向。并指出这两个盐湖具有锂资源储量大, 品位高的优势, 但是受盐湖类型或地理气候条件限制, 工艺上有待改善。建议继续加强对盐湖开发技术优化和对盐湖提锂产业的扶持。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号