黄土高原南部第四纪不同时间尺度侵蚀环境演变及驱动机制

发布时间：2018-05-27 11:32

本文选题：黄土高原 + 侵蚀环境　；参考：《中国科学院研究生院(教育部水土保持与生态环境研究中心)》2016年博士论文

【摘要】：黄土高原土壤侵蚀是关系黄河中下游安全以及黄土高原区可持续发展的重要生态问题。过去学者们在黄土高原降雨侵蚀产沙过程、植被水土保持效应、土壤侵蚀时空分布特征等方面的研究都取得了丰硕的成果,对现代黄土高原土壤侵蚀问题的防治起到了积极关键的作用。但学术界对黄土高原土壤侵蚀问题的由来、地质历史时期的发展规律以及土壤侵蚀的驱动机制和影响因素,还存在许多争议,主要原因在于缺乏下游的地质沉积记录证据。本文通过科学钻探对黄土高原南部关中盆地卤阳湖区进行了岩芯采样分析,通过古地磁、光释光等定年手段,对卤阳湖1号钻岩芯400 m以上的沉积速率,2号钻50 m岩芯沉积速率,卤阳湖东滩的天骄湖人工剖面2.8 m沉积速率进行了计算,并通过碳酸盐、粒度、磁化率等气候环境代用指标对2号钻和天骄湖人工剖面进行了详细的气候环境变化分析,主要得出以下几项重要结果:(1)卤阳湖1号钻岩芯400 m(5.23 Ma)沉积速率计算结果表明,湖区沉积速率在2.58 Ma后有明显上升,与黄土古土壤剖面底界年龄一致。卤阳湖区5.23 Ma以来的沉积速率在4.18-3.58 Ma、2.5-1.7 Ma、1.07-0.78 Ma、0.78-0.12 Ma、0.12-0.09Ma、67-63 ka、13-9.8 ka,这7个时期有明显加快,其中后6个时期与青藏高原自青藏运动(2.58 Ma开始)以来的抬升活动具有明显的对应关系,说明黄土高原土壤侵蚀周期在长时间尺度上受控于青藏高原的构造隆升作用。第四纪以来卤阳湖区沉积速率以0.12 Ma为界可划分为前后两个阶段,2.58-0.12 Ma期间,卤阳湖沉积速率变化微弱增加,变化范围在3-10 cm/ka,0.12 Ma后,沉积速率明显加大,0.12-0.09Ma间的平均沉积速率是前段时间的近10倍,说明0.12 Ma左右是黄土高原土壤侵蚀环境演变的重要转折期。(2)卤阳湖2号钻50 m岩芯将近15万年的沉积序列表明,12万年前后构造强烈抬升的同时,也恰好对应黄土-古土壤S1阶段,属温湿气候期,该阶段在卤阳湖上游地区侵蚀面分布广泛,在下游三门峡地区则发生了黄河彻底贯通的重大环境事件。这些证据说明卤阳湖区在12万年前后的高沉积速率是构造强烈抬升、温湿气候环境以及三门峡的彻底贯通三种因素共同作用的结果。(3)卤阳湖东滩2.8 m的人工剖面研究结果表明近三万年来,卤阳湖区湖泊水位经历了低-高-低的变化过程,与该区末次冰盛期以来的干-湿-干的气候变化序列一致,表明卤阳湖区水位变化主要受控于东亚夏季风影响。全新世后期4.6 ka后的干旱气候造成了卤阳湖的大面积萎缩,为卤阳湖的快速消亡创造了条件。在此基础上,2 ka后围湖造田,捞硝晒盐等湖区周边人为活动的快速增加,是导致卤阳湖沉积速率快速上升,退化为盐碱滩,并逐渐消亡的原因。
[Abstract]:Soil erosion in the Loess Plateau is an important ecological problem related to the safety of the middle and lower reaches of the Yellow River and the sustainable development of the Loess Plateau. In the past, scholars have achieved fruitful results in the process of rainfall erosion and sediment yield, the effect of vegetation soil and water conservation, and the space-time distribution characteristics of soil erosion on the Loess Plateau. It plays an active and key role in the prevention and control of soil erosion in the Loess Plateau. However, there are still many controversies about the origin of soil erosion in the Loess Plateau, the law of development in geological history, the driving mechanism and influencing factors of soil erosion, mainly due to the lack of evidence of geological deposition records in the lower reaches of the Loess Plateau. In this paper, the core sampling and analysis of Hanyang Lake region of Guanzhong Basin in the southern Loess Plateau are carried out through scientific drilling, and the dating methods such as paleomagnetism and photoluminescence are used. The sedimentation rates of the cores above 400 m in Hanyang Lake 1, 50 m in drill 2 and 2.8 m in the artificial section of Tianjiao Lake on the Dongtan of Hanyang Lake are calculated, and the carbonate, granularity, granularity are calculated. In this paper, the climatic and environmental changes of the artificial sections of No. 2 drill and Tianjiao Lake are analyzed by using the climatic and environmental proxy indexes such as magnetic susceptibility. The main results are as follows: 1) the calculation results of the sedimentation rate of the core of Hanyang Lake 1 are as follows: the core of Huiyang Lake 1 is 400 m / m ~ (5.23) Ma), and the results are as follows: The sedimentary rate of the lake area increased obviously after 2.58 Ma, which is consistent with the age of the bottom boundary of the loess paleosol profile. The sedimentation rate since 5.23 Ma in Hanyang Lake area is 4.18-3.58 Ma ~ 2.5-1.7 Ma ~ 1.07-0.78 Ma ~ (0.7) -0.12 Ma ~ 0.12 Ma ~ 0.12-0.09 Ma ~ (67) ~ (63) ka ~ (- 9.8) ka, and the latter six periods are obviously related to the uplift activity of Qinghai-Xizang Plateau since the Qinghai-Xizang Plateau started at 2.58 Ma, and there is a significant correlation between the latter six periods and the uplift activity of Qinghai-Tibet Plateau since the Qinghai-Tibet Plateau started at 2.58 Ma. The results show that the soil erosion period in the Loess Plateau is controlled by the tectonic uplift of the Qinghai-Xizang Plateau on a long time scale. Since the Quaternary period, the sedimentary rate of the Hanyang Lake area has been divided into two stages (0.12 Ma, 2.58-0.12 Ma), and the variation of the deposition rate of the lake has increased slightly, ranging from 3-10 cm / kg to 0.12 Ma. The average deposition rate of 0.12-0.09 Ma is 10 times higher than that of the previous period. It shows that 0.12 Ma is an important turning point of soil erosion environment evolution on the Loess Plateau. It also corresponds to the loess paleosol S1 stage, which belongs to the climate period of temperature and humidity. It is widely distributed in the upper reaches of Hanyang Lake, and a major environmental event of the Yellow River is completely connected in the lower Sanmenxia area. These evidences indicate that the high deposition rate of the lake area around 120,000 years is a strong tectonic uplift. The result of the combined action of three factors, namely, temperature and wet climate environment and the thorough penetration of Sanmenxia, shows that the lake water level in Hanyang Lake area has undergone a process of low to high to low variation in the past 30, 000 years, according to the artificial section of 2. 8 m on the east beach of Hanyang Lake. It is consistent with the dry-wet-dry climate change sequence since the last ice peak in this area, which indicates that the water level change in the Hanyang Lake region is mainly controlled by the East Asian Summer Monsoon (East Asian Summer Monsoon). The arid climate after 4.6 ka in the late Holocene resulted in a large area shrinkage of Hanyang Lake, which created conditions for the rapid extinction of Hanyang Lake. On this basis, the rapid increase of anthropogenic activities around the lake area after 2 ka, such as reclaiming the lake and recovering salt, is the reason why the deposition rate of Hanyang Lake increases rapidly, which degenerates into saline-alkali beach and gradually dies away.
【学位授予单位】：中国科学院研究生院(教育部水土保持与生态环境研究中心)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S157.1

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