【作者】 王晨华；

【导师】 王乃昂；

【作者基本信息】 兰州大学 ， 自然地理学， 2006， 硕士

【摘要】 花海盆地位于河西走廊西端,平均海拔约1195—1250m,多年平均降水56mm,年蒸发量达3000mm以上,年均气温8℃,属于温带干旱气候。干燥多风,常年盛行西北风,每年有风日数不少于300天,全年日照时数达三千三百多小时。流域内河流的流量主要靠山区的冰雪融水来补给,河流径流量的变化与区域温度正相关。区域温度升高,河流的径流量增加,温度降低则径流量减小。花海湖泊是河流的尾闾湖,湖泊水量主要靠河流的入湖水量来补给,湖泊水位对气候的变化非常敏感。 通过对地球化学和粒度等指标的综合分析,得知花海湖泊在沉积过程中以氧化环境为主,基本不存在还原环境。花海盆地位于干旱区,蒸发量远大于降水量,流域淋溶作用较弱,沉积物中Fe、Mn、Y、V、Rb等元素主要随水流进入湖泊,其含量变化主要记录了这些地球化学元素入湖量的变化,也即反映了入湖水量的变化。由于入湖水量的变化依赖于河流流量的变化,而河流流量变化与区域温度正相关,因此元素入湖量实际上反映了区域温度变化,温度升高,入湖水量增加,沉积物中元素含量增多,湖泊水位也升高;温度降低则入湖水量减少,沉积物中元素含量降低,水位降低。 在以上地球化学综合分析的基础上,结合粒度、CaCO₃、TOC、C/N和TS等指标随深度的变化,重建了花海盆地近11000年来湖泊水量和区域气候演化历史。全新世花海盆地经历了早期入湖水量逐渐增多,温度逐渐升高和变湿的过程,中期湖泊水位较高而且变化较小、气候稳定,晚期入湖水量减少,水位降低,气候相对变冷、变干的三个阶段,其中包括: 10600—10200aBP期间,湖泊水量减少,湖泊处于硫酸盐阶段,气候干冷。 10200—9500aBP期间,入湖水量增多,湖水盐度降低,气候逐渐变暖。 9500—9000aBP期间,湖泊水量突然减少,沉积物中元素含量骤减,区域环境恶化,风沙活动强烈,气候干冷。 9000—3500aBP期间,对应于全新世大暖期,湖泊水位较高,气候比较稳定,。但9000—8600aBP波动明显,气候不稳定;约在8300aBP、6200aBP、4500aBP存在三次入湖水量减少,湖泊萎缩的变化过程;4000—3500aBP左右水位升高,存在一期高湖面,湖泊扩张。反映了大暖期气候的不稳定性。更多还原

【Abstract】 The Huahai Basin lies in west Hexi corridor of the northwest China, at an average altitude of 1195—1250m a.s.l. Being one of the aridest regions in China, Huahai Lake basin receives precipitation of only 56mm annually according to a 30-year meteorological records with annual mean temperature of 8℃, and annual mean evaporation adds up to 3000mm. It belongs to arid climate of Temperate Zone, dry and windy in the region and prevailing wind of NW. There are more than 300 days with wind and 3300 hours with sunlight in the region annual mean year. The region is sensitive to environment changes owing to its location at the boundary between the Inner Mongolia, Xinjiang arid and Tibetan Plateau. Therefore the sediments in such an enclosed basin can provide high-resolution archives for paleoclimate or paleoenvironmental changes since Holocene or last deglaciaton. But till now, there are still many questions unsolved and some aspects need to be improved.In the drainage basin, precipitation is very limited and the variation of river runoff depends on water of melting glacier of mountain distinctively. The runoff fluxes correlate with variations of temperature in drainage basin, and the same relation between temperature and melted glacier of mountain. In the terminal Huahai Lake of river, evaporation is many times to precipitation, and lake level fluxes reckon on runoff of river mainly. In the same time, we know that runoff correlates to temperature positively. So, in the drainage basin, if climate becomes warmer, melting glacier and runoff will increase respectively, and geochemical elements in the sediments will increase also, at the same time lake level also higher;on the contrary, lake level will fall. Consequently lake level fluxes register temperature variation of drainage basin in fact. We have analyzed geochemical and granularity indexes for climate and environment evolution, and found that geochemical elements Fe 、Mn et.al. redox-sensitive metals in sediments from Huahai Lake recorded oxic conditionsmainly and reducing conditions of sedimentary sequence existed seldom. Content of geochemical elements in sediments registered variations of runoff and temperature.The section which was analyzed in the dissertation is located in 40°26’05" N, 98 0 04’47" E? altitude of 1195m a.s.l. In order to retrieve the history of huahai drainage basin since 11000 aB.P., we have done much work in the drainage basin: spot investigation, profile sample collection, section strata analysis, geophysical analysis, geochemical analysis and dependable 14C dating. The main conclusions are as follows:During 10600—10200aBP, the mount of lake water decreased. Lake was in the phase of sulfate, and climate of area was dry.In 10200—9500aBP, lake level was higher, salinity of lake water was falling, and climate was becoming wanner gradually.9500—9000aBP, the mount of lake water cut down abruptly, activity of wind was violent, climate was dry and cold, and environment of drainage basin deteriorated.9000—3500aBP, it was in Holocene climate optimum, lake level was higher and more stable. But during 9000—8600aBP lake level fluctuated obviously, climate was unstable. About 8300aBP^ 6200aBP, 4500aBP, there were three times runoff reduced and lake shrunk events. During 4000—3500aBP, and the lakeshore age is 4000 aBP when altitude is 1225m a.s.l. which the lake level was highest, climate was wetness, and lake proportion was expanded.During 3500—290aBP, it was a cold stage. Lake level decreased and it was in the phase of sulfate again. But amount of water in the lake increased in 1600aBP and environment meliorated relatively.As to the whole basin, the Holocene climate and environment experienced three stages: the early cold relatively stage and transformation wet gradually, the mid wetter and warmer stage and the late cold stage.更多还原