【作者】 杨梅；

【导师】 张成君；

【作者基本信息】 兰州大学 ， 地球化学， 2018， 硕士

【摘要】 新生代以来青藏高原的隆升对周边环境产生一系列的影响,形成了特征的东亚季风系统,造成了中国西部地区的干旱环境。自上新世晚期青藏高原隆升使柴达木盆地更加干旱,湖泊干涸、盐湖化,甚至成为干盐湖。盆地内部湖盆沉降中心大幅度自西向东迁移至三湖坳陷地区,自新近纪以来湖盆沉积了巨厚的新生代沉积物。对盆地内湖泊沉积物中古环境信息的提取,可以很好地反演出古生态环境、古气候的演变过程,了解青藏高原隆升的过程和特征,以及盆地内生态环境未来的发展趋势,并且也对全球过去环境演变机理的研究有重要意义。湖泊沉积物中有机质生物标志化合物对有机质来源、植被类型以及在指示古气候和古环境溯源方面有重要意义。本文主要用气相色谱—质谱仪来检测样品,对三湖地区达布逊湖气钾1井深度在2141 m⁴077 m范围内30个湖泊样品的生物标志化合物正构烷烃,类异戊二烯烷烃以及碳酸盐特征进行分析,并综合前人在孢粉、古地层、古植被等方面的研究,取得以下重要认识:（1）正构烷烃和类异戊二烯烷烃、甾类、萜类指标分析表明,样品具有明显的奇碳优势,主峰以C₃₁为主,显示了草本植物输入来源,Pr/Ph比值较低,说明整个剖面沉积物形成于还原环境,表明该段时期内有湖泊存在。（2）气钾1井样品从4000m至上共记录了下油砂山组（N₂¹）、上油砂山组（N₂²）、狮子沟组（N₂³）和七个泉组(Q₁₊₂)的演化历程,从2253 m处出现分界,反映出湖泊的由湿到干、从深到浅的演化过程。同时,水体从上油砂山组（N₂²）以来,在干冷环境水体盐度逐渐增加,限制了水生植物的生长,湖泊沉积物中有机质以挺水植物为主。（3）对生物标志化合物正构烷烃指标CPI、ACL、Paq、C₂₇/C₃₁、ΣC^-₂₁/ΣC⁺₂₂和Pr/Ph综合对比分析得出,达布逊湖地区上新世早期湖泊较为发育,水体深,水生植物发育;之后气候逐渐干冷,湖泊水体变浅,挺水植物和陆生植物贡献增加,以草原环境为特征,森林极不发育。指示了柴达木盆地从上新世以来气候逐渐干冷,降雨减少。更多还原

【Abstract】 Since the Cenozoic era,the uplift of the Tibetan Plateau has had a series of effects on the surrounding environment,forming a characteristic East Asian monsoon system,which has caused the arid environment in western China.The rapid uplift of the Tibet Plateau since the late Pliocene has increased the elevation of the plateau,the climate has become colder and drier,and the environment of ancient lakes has rapidly evolved.The Qaidam Basin is more arid,with lakes dried up,salt lakes,and even become dry lakes.The inner basin subsidence center of the basin migrated from west to east to the area of the Sanhu depression,and the basin has deposited a great thickness of Cenozoic sediments.The extraction of paleoenvironmental information from lake sediments in the basin can reflect the evolutionary process of the ancient ecological environment and paleoclimate,understand the process and characteristics of the uplift of the Tibetan Plateau,and the future development trend of the ecological environment within the basin.It is of great significance to study the global past environmental evolution mechanism.Since the Neogene in the Sanhu area of eastern Qaidam Basin,lake basins have deposited very thick lake sediments.The biomarker compounds of organic matter in lake sediments are of great important to the source of organic matter,vegetation types,and to the traceability of ancient climate and paleoenvironment.In this paper,we use gas chromatography-mass spectrometry to detect the samples of the normal biomarker alkanes for 30 lake samples within the depth of 2141 m⁴077 m in the Qijia-1well of the Dabson Lake in the Sanhu area.CPI,ACL,Paq,C₂₇/C₃₁,ΣC^-₂₁/ΣC⁺₂₂,isoprenoids and carbonates were analyzed,and the previous studies on sporopollen,paleostratigraphy,and paleo-vegetation were combined to obtain the following important understandings:（1）By analyzing the indexes of n-alkanes and isoprenoid alkanes,terpenoids,terpenoids,CPI,ACL,Paq,C₂₇/C₃₁,ΣC^-₂₁/ΣC⁺₂₂,and Pr/Ph,the results show thatQaidam basin neogene is given priority to with lake facies,organic matter is mainly from the aquatic plants,and less terrestrial herbs.（2）The depth of 4000 m from the Qijia-1 well was recorded from bottom to top in the Xiayoushashan Formation（N₂¹）,Shangyoushashan Formation（N₂²）,Shizigou Formation（N₂³）,and Qigequan Formation(Q₁₊₂).The evolutionary process reflects the evolution of the lake from wet to dry and from deep to shallow.At the same time,the water salinity gradually increased in the dry and cold environment since the Shangyoushashan Formation（N₂²）,limiting the growth of aquatic plants.（3）The comprehensive analysis of biomarkers shows that the early Pliocene lake in the Dabson lake area of Qaidam basin is relatively developed,with deep water and aquatic plants.Afterwards,the climate became dry and cold,the lake water became shallow,and the water plants and terrestrial plants increased their contribution to the organic matter in the lake sediments,characterized by grassland environment,and the forest was extremely underdeveloped.It indicates that the climate of Qaidam basin has cooled gradually since the Pliocene,and the rainfall has decreased,which is consistent with the global cooling background.更多还原