青藏高原风成沉积和那陵格勒河流阶地释光年代学及环境意义

发布时间：2018-10-14 20:15

【摘要】：全球气候变化问题引起了国际社会的普遍关注。青藏高原的隆升对东亚季风系统的形成及演化具有深远影响。青藏高原是西风带、东亚季风、西伯利亚高压以及印度季风四大环流共同作用地带,而青藏高原上分布着的大量风成沉积和河流地貌对气候系统变化十分敏感,是青藏高原古气候环境变化研究的宝贵载体。本文围绕青藏高原西宁-拉萨一线风成沉积物和柴达木盆地那陵格勒河流阶地晚第四纪以来的形成、演化及气候环境意义等科学问题,采用光释光(Optically Stimulated Luminescence,OSL)测年手段并结合14C测年,综合运用地层学、地貌学和古环境代用指标,重建晚第四纪古气候和古环境演化历史。本文由两部分组成。第一部分:风成沉积可反映堆积时的温度、湿度、风场、植被等因素。本文对青藏高原风成沉积的采样贯穿西宁—拉萨全线,不限于前人研究较多的青海湖、柴达木盆地和共和盆地,自东北向西南方向进行,重点剖析了夏拉、兴海、玛沁、曲玛莱和雅鲁藏布江等28个风成沉积剖面,获取121个OSL样品和13个14C样品,进行磁化率、粒度环境指标测试,并结合前人研究资料,从而对青藏高原风成沉积有比较清楚的认识。主要研究结果如下:(1)风成沉积物的OSL和14C测年结果对比显示,全新世样品在误差范围内一致。(2)青藏高原地区自晚更新世以来发生风成沉积,并持续至今。(3)黄土堆积集中至少在82 ka开始堆积,集中在82~70 ka、35~26 ka和17 ka以来三个阶段,说明黄土堆积易在由暖期-冷期转换期间堆积,具有滞后性。(4)未发现MIS4、MIS2和LGM阶段的风成堆积,可能是干冷的气候条件下植被条件较差,以致粉尘无法沉降。(5)风成沉积代表的沉积环境历史和青藏高原冰芯及湖泊沉积物记录的环境历史对比良好,可以作为独立的气候代用指标。第二部分:那陵格勒河发源于昆仑山,流经冲积扇,最终注入以富锂著称的三湖区(东台吉乃尔湖、西台吉乃尔湖和一里坪)。前人对那陵格勒河河谷地貌演化的研究工作做的较少,即使有,也缺乏确切的年代测定,使得人们对于那陵格勒河的发育历史还不是很清楚,且未和三盐湖区联系起来。本文选择那陵格勒河上游河段的阶地进行研究,通过OSL测年方法,重建了那陵格勒河流演化历史及驱动因素,并进一步分析了其阶地形成与盐湖演化的关系。主要研究结果如下:(1)那陵格勒河上游4级阶地的形成年代分别为13.1±1.0 ka(T4),11.3±1.0 ka(T3),9.9±1.7 ka(T2)和7.5±0.5 ka(T1)。(2)依据阶地的形成年代和拔河高度等参数,得到了那陵格勒河的下切速率为0.84 mm/a。(3)根据阶地形成年代、下切速率、阶地沉积物特征,并与气候事件对比,那陵格勒河阶地很可能属于气候成因,目前尚未发现构造成因的证据。并进一步推断三湖区自早全新世以来有一次锂元素的富集期。
[Abstract]:The problem of global climate change has aroused the universal concern of the international community. The uplift of the Qinghai-Xizang Plateau has a profound influence on the formation and evolution of the East Asian monsoon system. The Qinghai-Xizang Plateau is a westerly zone, an East Asian monsoon, a Siberian high and an Indian monsoon. However, a large number of aeolian deposits and river landforms distributed on the Qinghai-Tibet Plateau are very sensitive to climate system changes. It is a valuable carrier of paleoclimate environment change in Qinghai-Xizang Plateau. This paper focuses on the formation, evolution and climate and environmental significance of the aeolian sediments along the Xining-Lhasa line of the Qinghai-Tibet Plateau and the formation, evolution and climatic and environmental significance of the Naling Gelle River Terrace in the Qaidam Basin since the late Quaternary. The late Quaternary paleoclimate and paleoenvironmental evolution history were reconstructed by means of (Optically Stimulated Luminescence,OSL dating and combined with 14C dating, using stratigraphy, geomorphology and paleoenvironmental indicators. This paper consists of two parts. Part I: eolian deposition can reflect temperature, humidity, wind field, vegetation and so on. The sampling of eolian deposits on the Qinghai-Xizang Plateau runs through Xining Lhasa, and is not limited to Qinghai Lake, Qaidam Basin and Gonghe Basin, which have been studied by predecessors, from northeast to southwest. The emphasis is on Xiara, Xinghai and Maqin. Twenty-eight aeolian sedimentary profiles, such as Qumalai and Yalu Zangbo River, were obtained from 121 OSL and 13 14C samples. The magnetic susceptibility and particle size environmental indexes were tested, and combined with previous research data, Thus there is a clear understanding of the eolian deposits in the Qinghai-Xizang Plateau. The main results are as follows: (1) the OSL and 14C dating results of the aeolian sediments show that the Holocene samples are consistent in the error range. (2) eolian deposits have occurred in the Qinghai-Tibet Plateau since the late Pleistocene. (3) the accumulation of loess began at least at 82 ka, and was concentrated in the three stages since 82 ~ 70 ka,35~26 ka and 17 ka, indicating that loess accumulation is easy to accumulate during the transition from warm to cold period. (4) there is no wind accumulation in the MIS4,MIS2 and LGM stages, which may be due to the poor vegetation conditions in dry and cold climates. As a result, dust can not be deposited. (5) the history of sedimentary environment represented by aeolian deposition is well compared with that of ice core and lake sediment of Qinghai-Xizang Plateau, and it can be used as an independent climate substitute index. The second part: the Naalingrad River originated in the Kunlun Mountains, flowing through alluvial fans, and finally injected into the three lakes (East Taiwan Ginel Lake, West Taijinar Lake and Yi Li Ping). The previous researches on the geomorphological evolution of the Naalingrad River valley are less, and even if there are, there is also a lack of precise dating, which makes people not very clear about the history of the development of the Nalingrad River, and has not been connected with the Sanyan Lake region. In this paper, the terraces of the upper reaches of the Naringrad River are selected for study, and the evolutionary history and driving factors of the river are reconstructed by the OSL dating method, and the relationship between the terrace formation and the evolution of salt lakes is further analyzed. The main results are as follows: (1) the age of formation of terrace of the upper reaches of Naalingrad is 13.1 卤1.0 ka (T4), 11.3 卤1.0 ka (T3), 9.9 卤1.7 ka (T2) and 7.5 卤0.5 ka (T1). (2) according to the terrace age and tug-of-war height. According to the age of terrace formation, the undercutting rate, the sediment characteristics of terrace, and comparing with climatic events, the undercut rate of Nalinggrad River is 0. 84 mm/a. (3), which is likely to belong to climatic origin. No evidence of tectonic origin has been found. It is further inferred that there is a Lithium enrichment period in Sanhu region since the early Holocene.
【学位授予单位】：中国科学院大学(中国科学院青海盐湖研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P532

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