晚第四纪青海湖水位变化与风沙地貌发育过程

Qinghai Lake, which is situated in the northeastern Qinghai-Tibetan Plateau, is selected as the study area in this project. The important geomorphology such as lake paleoembankment, lake terrace, and outcrops paleolacustrine sediment, which formed with variations of Qinghai lake level, will be accurately distinguished, orientated, measured, and dated using multiple methods. On the basis of these analyses, the paleoshoreline series and their spatial distribution will be recovered, and the history of Qinghai lake level variations during the late Quaternary will be reconstructed. Based on knowledge of modern aeolian geomorphology, the distribution, characteristics and formation age of paleo-aeolian sand will be studied in order to reconstruct the aeolian geomorphic process during the lake shrank periods. Combined with the temporal-spatial pattern of lake level variation and aeolian geomorphology evolution, this study will elucidate their relationship and discuss the possible forcing mechanism. Results of this study will provide evidence for further understanding of the Qinghai Lake evolution, especially of the formation and development of aeolian geomorphology around Qinghai Lake.

本项目选择位于青藏高原东北缘的青海湖为研究对象，通过对青海湖水位变化过程中形成的古湖岸堤、湖成阶地、高位湖相沉积等重要地貌体进行准确判别、定位、测量，并采用多种方法定年，重建青海湖主要的古湖岸线系列及其空间分布，恢复晚第四纪青海湖湖面升降历史；通过对现代风沙地貌和古风成砂的分布、特征及形成时代进行研究，重建湖泊水位退缩期的风沙地貌发育过程。综合分析青海湖水位变化与风沙地貌的发育过程和时空规律，揭示二者之间的关系及动力机制，为更好的认识青海湖的演变特别是湖周风沙地貌的形成发展提供证据。

青海湖盆地内的风成沉积物总量不大，但可谓青藏高原风成沉积物的缩影，主要分布于湖滨、河谷以及山麓地带，其中连片的沙地主要包括湖东沙地、甘子河沙地和鸟岛沙地。从风成沙丘的形成与分布特征看，气候和沙源是湖区风成沉积物形成发育首要的基本条件。国内外大量研究已经证实，我国和世界上许多沙漠的形成演化均与河流湖泊的演变密切相关。河流湖泊消退后裸露的大片河滩及湖滩，为沙漠的发展提供了空间以及重要的物质来源。本项目通过4年的研究，对湖区周边沙地以及青海湖水位变化过程中遗留的古湖岸堤、高位湖相沉积等进行了系统的调查，旨在探讨晚第四纪以来风沙地貌发育过程及其与湖泊水位变化的关系，并为湖区沙地治理提供科学依据。研究结果表明：（1）青海湖地区人工治理9~11年以上的沙丘土壤水分受植被影响较大，在现代气候环境背景下，相较于乌柳，沙棘可能更适于本区的植物固沙；区域大气降尘具有15~30μm和＜1μm两个主要组分。（2）全新世之前青海湖湖面曾经高于现代~40m，但全新世以来湖面高度始终低于~3206m。（3）青海湖盆地的风沙地貌过程和青海湖水位变化共同受控于气候条件变化。早中全新世气候温暖湿润，区内有云杉林分布，风沙活动相对较弱，湖泊水位相对较高；4ka以后随着气候转向干冷，云杉林消失，河湖逐渐萎缩，风沙活动增强。（4）晚第四纪以来青海湖湖滨沙地的风沙地貌过程与青海湖水位变化联系紧密，其余地势相对较高区域的风沙地貌过程与青海湖水位变化之间缺乏直接联系。