黄河源区河北（HB）黄土剖面高密度光释光年代学及其环境意义

发布时间：2018-08-26 11:38

【摘要】：青藏高原上广泛分布的风成沉积物是很好的环境演变信息载体,记录了亚洲季风与西风带大气环流演变信息,同时作为“冰源黄土”,还记录了高原第四纪冰川进退与粉尘堆积的相互关系。在青藏高原东北部的阿尼玛卿山东面山坡海拔3500m~4500 m的地区形成了一个明显的砂质黄土覆盖带,本文选取河北乡风成黄土剖面(HB)作为研究对象,采集了29个OSL样品,采用粗颗粒(63-90μm)石英SAR法对以上样品进行系统测年,构建了HB剖面高分辨率年代学框架。在此年代学框架的基础上,选取有效的环境代用指标探讨了该区环境演变特征,总结高原上已有的年代数据探讨了沉积模式及其气候响应机制。从地层的沉积年代序列来看,HB剖面主要记录了46.3±3.2~27.5±2.8 ka之间连续的环境变化信息,属于末次冰期MIS 3阶段。粒度变化可以很好地反映出该区域对气候变冷事件有很好的响应,揭示青藏高原黄土记录对气候快速变冷事件的响应比暖事件的响应更加敏感。磁化率对气候的响应存在阶段性差异,对冷期的气候快速变冷事件响应不明显,而对暖期里的快速变冷事件响应较明显,整体上表现出:暖期对应高值、冷期对应低值的分布规律。通过与黄土高原和青海湖地区黄土磁化率的对比,发现青藏高原高海拔区域的磁化率平均值最低,这可能与该区域海拔较高、成壤作用较弱有关。根据年代与深度的变化关系,可以将该区域的粉尘堆积速率分为2个阶段:在46.3±3.2 ka~36.5±2.9 ka期间的粉尘堆积速率为24.8 cm/ka;在36.5±2.9 ka~27.5±2.8 ka之间粉尘堆积速率为27.5 cm/ka,指示出在中MIS 3阶段气候相对晚MIS 3阶段较好一些。高密度年代结果同时还检测到MIS 2阶段LGM地层的缺失,整个青藏高原东北部黄土沉积也呈现类似情况,青藏高原上黄土的沉积在间冰阶以堆积为主,而在冰阶可能以侵蚀为主,这与黄土高原黄土的沉积模式明显不同,呈现出一种反相位的关系,说明青藏高原北部是黄土高原的一个重要物源区,尤其在LGM和MIS 4等冷冰阶。
[Abstract]:The eolian sediments widely distributed on the Qinghai-Xizang Plateau are a good information carrier for environmental evolution, recording the atmospheric circulation evolution information of the Asian monsoon and westerly zones and serving as "ice source loess". The relationship between the Quaternary glacier advance and retreat and dust accumulation in the plateau is also recorded. An obvious sandy loess cover zone was formed in the area of 3500m~4500 m on the eastern slope of Animaqing Mountain in the northeast of Qinghai-Xizang Plateau. In this paper, 29 samples of OSL were collected from the (HB) section of the Xiangfeng loess section in Hebei Province. The high resolution chronological framework of HB profile was constructed by using the quartz SAR method with coarse particles (63-90 渭 m). On the basis of this chronological framework, the characteristics of environmental evolution in this area are discussed by selecting effective environmental substitute indexes, and the sedimentary model and its climate response mechanism are discussed by summarizing the available chronological data on the plateau. According to the sedimentary chronological sequence of the strata, the HB section mainly records the continuous environmental change information between 46.3 卤3.2N 27.5 卤2.8 ka, which belongs to the MIS 3 stage of the last glacial epoch. The grain size change can well reflect that the region has a good response to the climate cooling events. It is revealed that the response of the loess records of the Qinghai-Xizang Plateau to the rapid cooling events is more sensitive than the response of the warm events. The response of magnetic susceptibility to climate is different at different stages, but the response to the rapid cooling event in cold period is not obvious, but the response to rapid cooling event in warm period is obvious, which shows that the warm period corresponds to high value on the whole. The cold period corresponds to the distribution law of low value. By comparing with the loess magnetic susceptibility in the Loess Plateau and Qinghai Lake region, it is found that the average value of the magnetic susceptibility in the high altitude area of the Qinghai-Tibet Plateau is the lowest, which may be related to the relatively high altitude and the weak role of the loessification in the Qinghai-Tibet Plateau. According to the relationship between age and depth, The dust accumulation rate in this area can be divided into two stages: the dust accumulation rate of 24.8 cm/ka; in the period of 46.3 卤3.2 ka~36.5 卤2.9 ka and 27.5 cm/ka, of 36.5 卤2.9 ka~27.5 卤2.8 ka indicates that the climate of the middle MIS 3 stage is better than that of the late MIS 3 stage. At the same time, the absence of LGM strata in the MIS _ 2 stage was detected, and the loess deposits in the northeastern Qinghai-Xizang Plateau were similar. The loess deposits on the Qinghai-Xizang Plateau were mainly deposited on the interglacial terrace, while the erosion was probably the main one in the ice terrace. This is obviously different from the sedimentary model of loess in the Loess Plateau, showing an inverse phase relationship, indicating that the northern Qinghai-Xizang Plateau is an important provenance of the Loess Plateau, especially in the cold ice terrace such as LGM and MIS _ 4.
【学位授予单位】：青海师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P532

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