早全新世浑善达克沙地古湖泊演化与环境变迁

发布时间：2018-07-23 14:11

【摘要】：目前,全球气候变暖问题得到了世界各地关注,而区域环境演变过程对全球变化水位响应非常敏感。浑善达克沙地位于中国内蒙古高原中东部的干旱和半干旱气候的过渡区,处于季风边缘区,生态环境十分脆弱。该地广泛存在着流动沙丘、半固定沙丘和固定沙丘等,同时在沙地腹地广泛分布着众多的湖泊,是湖泊演化的理想之地,成为沙地与湖泊演化过程的典型地区,也是两者彼此消长耦合关系的重要场所。试图探索季风边缘区过渡带的气候演化过程及湖泊面积变化对气候的响应,进而提高对季风边缘区环境演变的认识。本文结合野外考察与室内实验分析的方法,对该研究点剖面进行粒度指标分析和OSL年代测试,建立湖泊演化时间序列。利用湖泊数字高程模型(DEM)的方法,根据研究区存在的湖岸堤高程,反演浑善达克沙地早-中全新世的湖泊时空变化格局。本文得出的主要结论如下:1.通过系统的野外考察发现,在浑善达克沙地腹地哈嘎淖尔北部保存较好的高湖岸阶地,在剖面湖滨砂特征较为明显位置,自下向上采集样品,其中采样点高程最高达到1313 m,表明该地区存在古湖的地质地貌证据;1)按照阶地剖面采样点海拔高程来推测,古湖水位分别高出现代湖泊38 m、39 m、40 m、41 m、43 m等,其OSL年代测试结果分别为9.6±1、8.9±0.8、10.3±0.8、8.1±0.6、7.5±0.6 ka,表明早中全新世初期发育高湖面,揭示了气候湿润;2)通过结合湖滨沉积物的OSL年代测试结果与古湖岸地高程,表明在9.6~7.5 ka间,古湖水位逐渐上升,湖泊面积不断的扩大,气候环境湿润。其中7.5 ka时期为干湿气候的突变点,为古湖发育达到鼎盛时期。根据1313 m的古湖面,得出244 km2的湖泊面积,多出现在湖泊面积243 km2,该古湖向东延伸到巴音淖尔,向北扩张到乌日塔音淖尔,并向南部和西部扩展,形成较大的古湖。同时其周缘的沙地被古湖水淹没,造成沙地里的巨大湿地系统。表明当时气候相当湿润,生态环境极其优越;湖泊面积演化共有两个阶段,第一阶段是距今9.6~7.5 ka期间,该湖区内气候温暖湿润,湖水位连续的上涨,为湖泊水位的上升期;第二阶段是在7.5 ka~至今,气候逐渐变干旱,湖面萎缩、古湖出现解体,呈现出了哈嘎淖尔湖当今的规模。2.剖面粒度分析结果表明,风成沙和湖滨砂在粒径和表面形态存在明显的差异。风成沙粒径分布区间0~0.5 mm,颗粒表面形态特征有碟形坑、撞击坑、麻面结构等,主要特征为不光滑的麻面。而湖滨砂粒径取值范围0~4.2 mm,其表面形态则复杂多变,不仅存在水环境的贝壳状断口、平行解理面、磨光面,还有风成环境的碟形坑、麻面等特征。
[Abstract]:At present, the problem of global warming has been paid attention to all over the world, and the regional environmental evolution process is very sensitive to the response of global water level. Hunshandake sandy land is located in the transitional region of arid and semi-arid climate in the central and eastern part of Inner Mongolia Plateau in China. It is located in the edge of the monsoon and the ecological environment is very fragile. There are moving dunes, semi-fixed dunes and fixed dunes in this area. At the same time, many lakes are widely distributed in the hinterland of sandy land, which is the ideal place for lake evolution and becomes a typical area of sand land and lake evolution process. It is also an important place for the coupling between them. This paper attempts to explore the process of climate evolution in the transitional zone of the monsoon margin and the response of the lake area changes to the climate so as to improve the understanding of the environmental evolution of the monsoon marginal zone. In this paper, based on the methods of field investigation and laboratory experiment, the granularity index and OSL age of the section of the study point are analyzed, and the time series of lake evolution are established. By using the (DEM) method of the lake digital elevation model, the spatial and temporal variation patterns of lakes in the Hunshandake sandy land during the early and middle Holocene were inversed according to the levee height of the lake bank in the study area. The main conclusions of this paper are as follows: 1. Through the systematic field investigation, it is found that in the north of Haga Nur, the hinterland of Hunshandake sandy land, the high lakeshore terrace is well preserved, and the samples are collected from the bottom up in the obvious position of the lakeside sand characteristics in the profile. The height of the sampling site is up to 1313 m, indicating that there is a geological and geomorphological evidence of the ancient lake in this area. 1) according to the elevation of the sampling site in the terrace profile, the water level of the ancient lake is respectively higher than that of the modern lake, such as 38 m ~ 39 m ~ (39 m) ~ 40 m ~ (40) m ~ (41) m ~ (43 m) and so on. The OSL dating results were 9.6 卤18.9 卤0.810 卤0.810 卤0.810 卤0.8lb 8.1 卤0.6n 7.5 卤0.6 ka, respectively, indicating that high lake surface was developed in the early middle Holocene, indicating that the paleolake water level gradually increased between 9.67.5ka and 9.67.5ka by combining the OSL dating results of lakeshore sediments and the paleolake shore elevation, indicating that the high lake surface was developed in the early middle Holocene. The lake area continues to expand, the climate environment is moist. Among them, 7.5 ka period is a sudden point of dry and wet climate, which is the peak period of ancient lake development. According to the ancient lake area of 1313 m, the lake area of 244km2 is found mostly in the lake area of 244km2. The ancient lake extends eastward to Bayannur, extends northward to Uzhitanaoer, and extends to the south and west of the lake to form a larger ancient lake. At the same time, the surrounding sandy land was submerged by the ancient lake, resulting in a huge wetland system in the sandy land. The results show that the climate was very humid at that time and the ecological environment was extremely superior, and there were two stages in the lake area evolution. The first stage was the warm and humid climate and the continuous rise of the lake water level, which was the rising period of the lake water level. In the second stage, the climate gradually became dry, the lake surface shrank, and the ancient lake disintegrated, showing the present scale of Haga Nur Lake. The results of grain size analysis show that there are obvious differences in particle size and surface morphology between eolian sand and lakeside sand. The particle size distribution range of eolian sand is 0 ~ 0. 5 mm. The surface morphology of the particles is characterized by disc crater, impact crater, hemp surface structure and so on. The main features are not smooth hemp surface. On the other hand, the size of lakeside sand is in the range of 0 ~ 4.2 mm, and its surface morphology is complex and changeable. There are not only shell-like fracture surfaces in water environment, parallel cleavage surfaces, polished surfaces, but also dish pits and hemp surfaces in wind-formed environments.
【学位授予单位】：内蒙古师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.632

【参考文献】