【摘要】：青藏高原上廣泛分布的風(fēng)成沉積物是很好的環(huán)境演變信息載體,記錄了亞洲季風(fēng)與西風(fēng)帶大氣環(huán)流演變信息,同時(shí)作為“冰源黃土”,還記錄了高原第四紀(jì)冰川進(jìn)退與粉塵堆積的相互關(guān)系。在青藏高原東北部的阿尼瑪卿山東面山坡海拔3500m~4500 m的地區(qū)形成了一個(gè)明顯的砂質(zhì)黃土覆蓋帶,本文選取河北鄉(xiāng)風(fēng)成黃土剖面(HB)作為研究對象,采集了29個(gè)OSL樣品,采用粗顆粒(63-90μm)石英SAR法對以上樣品進(jìn)行系統(tǒng)測年,構(gòu)建了HB剖面高分辨率年代學(xué)框架。在此年代學(xué)框架的基礎(chǔ)上,選取有效的環(huán)境代用指標(biāo)探討了該區(qū)環(huán)境演變特征,總結(jié)高原上已有的年代數(shù)據(jù)探討了沉積模式及其氣候響應(yīng)機(jī)制。從地層的沉積年代序列來看,HB剖面主要記錄了46.3±3.2~27.5±2.8 ka之間連續(xù)的環(huán)境變化信息,屬于末次冰期MIS 3階段。粒度變化可以很好地反映出該區(qū)域?qū)夂蜃兝涫录泻芎玫捻憫?yīng),揭示青藏高原黃土記錄對氣候快速變冷事件的響應(yīng)比暖事件的響應(yīng)更加敏感。磁化率對氣候的響應(yīng)存在階段性差異,對冷期的氣候快速變冷事件響應(yīng)不明顯,而對暖期里的快速變冷事件響應(yīng)較明顯,整體上表現(xiàn)出:暖期對應(yīng)高值、冷期對應(yīng)低值的分布規(guī)律。通過與黃土高原和青海湖地區(qū)黃土磁化率的對比,發(fā)現(xiàn)青藏高原高海拔區(qū)域的磁化率平均值最低,這可能與該區(qū)域海拔較高、成壤作用較弱有關(guān)。根據(jù)年代與深度的變化關(guān)系,可以將該區(qū)域的粉塵堆積速率分為2個(gè)階段:在46.3±3.2 ka~36.5±2.9 ka期間的粉塵堆積速率為24.8 cm/ka;在36.5±2.9 ka~27.5±2.8 ka之間粉塵堆積速率為27.5 cm/ka,指示出在中MIS 3階段氣候相對晚MIS 3階段較好一些。高密度年代結(jié)果同時(shí)還檢測到MIS 2階段LGM地層的缺失,整個(gè)青藏高原東北部黃土沉積也呈現(xiàn)類似情況,青藏高原上黃土的沉積在間冰階以堆積為主,而在冰階可能以侵蝕為主,這與黃土高原黃土的沉積模式明顯不同,呈現(xiàn)出一種反相位的關(guān)系,說明青藏高原北部是黃土高原的一個(gè)重要物源區(qū),尤其在LGM和MIS 4等冷冰階。
[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 鹵3.2N 27.5 鹵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 鹵3.2 ka~36.5 鹵2.9 ka and 27.5 cm/ka, of 36.5 鹵2.9 ka~27.5 鹵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.
【學(xué)位授予單位】：青海師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P532

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