【作者】 王小群；

【导师】 王兰生；

【作者基本信息】 成都理工大学 ， 地质工程， 2009， 博士

【摘要】 岷江上游古堰塞湖湖相沉积物保存有敏感反映古气候变化的重要信息。其中叠溪古堰塞湖湖相沉积物厚度达200余米,并在其中保留了以湖相沉积物为基座的六级阶地,测年显示其形成于距今2万年前左右,消亡时间起始于1万年前左右,在时代上即是末次冰盛期结束,经历增温期到新仙女木干冷期的阶段。无论从沉积物规模和沉积物记载的时间信息、环境地质信息都应当是相当丰富的,为研究该区域2万年以来的气候环境变化规律提供了非常丰富而宝贵的资料。本文主要对岷江上游叠溪古堰塞湖进行了深入研究,主要研究了古堰塞湖的分布特征、沉积物的沉积构造特征、沉积物中的环境信息指标(如:粒度测试分析、孢粉测试分析、碳氧同位素测试分析等)、堰塞湖的形成时间和消亡时间的测试等。根据这些测试与研究结果结合岷江上游一系列古堰塞湖的特征,对叠溪地区2万年以来的古环境古气候进行了分析,得到了该区域古气候古环境的演化规律。通过本次研究主要得到以下主要成果:(1)从古堰塞湖的岩相特征、空间展布特征以及物质成分结构特征等多个方面论证了叠溪团结村古老沉积物属于堰塞湖湖相沉积物,它不同于黄土沉积物、冰川湖沉积物、封闭湖泊沉积物。通过对古堰塞湖沉积物精细的颗分实验分析(共64个测试样),发现沉积物粒径范围多在(0,0.075mm)之间,属粉粒和粘粒范畴;沉积物纹层厚度在2～5cm之间;堰塞湖相沉积物纹层深色代表春夏雨水充足季节沉积,浅色代表秋冬旱季沉积;堰塞湖沉积物粗颗粒颜色较深,细颗粒颜色较浅,这种纹层特征正好与冰川湖相纹层特征相反。通过对古堰塞湖沉积物剖面系统的颗粒分析实验(共33个测试样),发现在整个沉积物纵剖面上从底到顶,颗粒总体有变细的趋势,中间存在粗细变化的波动现象。(2)综合各环境代用指标粒度(共33个测试样)、碳氧同位素(共20个测试样)、孢粉(共33个测试样)的研究成果,将整个团结村沉积物纵剖面划分为7个沉积环境时段:第①期段(22～20.8ka.BP):高程范围2130～2141m,该期段植被环境为森林草原类型,气候为冷干转为暖湿的过程;第②期段(20.8～17.7ka.BP):高程范围2141～2177m,该期段植被环境为草原森林类型,气候为暖湿转为冷干的过程;第③期段(17.7～16.4ka.BP):高程范围2177～2197m,该期段植被环境为混交林草原类型,气候为冷干转为暖湿的过程;第④期段(16.4～13.4ka.BP):高程范围2197～2224m,该期段植被环境为常绿针叶林类型,气候为暖湿转为较暖半干的过程;第⑤期段(13.4～11.9ka.BP):高程范围2224～2281m,该期段植被环境为针叶林及部分混交林类型,气候为较暖轻湿转为凉干的过程;第⑥期段(11.9～10.3ka.BP):高程范围2281～2299m,该期段植被环境为针叶林及部分混交林类型,气候为凉干转为冷湿的过程;第⑦期段(10.3～10ka.BP):高程范围2299～2310m,该期段植被环境为针、阔叶混交林植被类型,气候为冷湿转为暖干的过程。这些信息指示了在岷江叠溪地区,在10kaBP～22kaBP期间经历了大约7次环境的变迁。(3)叠溪古堰塞湖沉积物中保留下来了以湖相沉积物为基座的六级阶地,这六级阶地的存在表明了叠溪古堰塞湖曾经发生过六次溃决和相应的沉积过程,根据对阶地沉积物的年代测试和孢粉测试资料分析,对叠溪地区10kaBP以来的古气候古环境初步得到以下规律:1)叠溪古堰塞湖自10kaBP来开始溃决,并分为约6次溃决后消失,每一次溃决都有可能源于地质环境的改变;2)10～8.4kaBP间,气候由暖干转为暖偏凉轻湿;3)8.4～5.5kaBP间,气候由温暖偏凉轻微湿润转为温暖半干旱。(4)通过对青藏高原东部边缘相邻地区古气候古环境对比研究发现:叠溪地区与相邻的若尔盖地区在相同的时间段里气候环境特点存在差别,但在在2万年左右这些地区气候总体上一致表现出寒冷干燥;在1万年左右这些地区气候总体上一致表现出温暖湿润。这说明在青藏高原东部边缘,在这两个时间段上,区域气候一致,应该是大环境大气候的影响起主导作用。更多还原

【Abstract】 The important information with ancient climatic evolution of sensitive reflection was kept in the ancient dammed lake sediments in the upstream of Minjiang River. Among them the ancient dammed lake lacustrine sediments thickness is up to more than 200 meters, and it has kept the six terraces which have taken the lacustrine sediments as base. The 14C dating showed that it was formed in about 2 million years ago and disappeared in about 1 million years ago, that is, in the era of the last period of the end of the ice, going through periods of warming to Younger Dryas cold period of the stage. Regardless of the scale and sediment from the sediment record of the time information, geological environmental information should be very rich,for the study of the changes of climate and environment to provide a very valuable information in the region since 2 million years.The Diexi ancient dammed lakes of upstream Minjiang River has been in-depth study in this paper which include distributed characteristic of ancient dammed lakes, Structural Characteristics of sediment deposition, sediment indicators of environmental information, and the 14C dating of forming and disappearing of the dammed lake, etc. Based on these test results with the combination of a series of ancient dammed lakes characteristic in the upstream of Minjiang River, the paleoenvironment and palaeoclimatic evolution of Diexi region were analyzed since 20,000 years. Through this study the following main results:(1) The Diexi ancient dammed lake lithofacies characteristics, characteristics of spatial distribution, as well as structural characteristics of the material composition of many aspects, such as proof of the Diexi ancient sediments are lacustrine sediments, which is different from the loess sediments, glacial lake sediments, and closed lake sediments. Through particle analysis experiment of the lacustrine sediments(64 test samples), these sediment grain’s diameters are many in (0, 0.075mm), belong to the powder and clay grain; Sediment laminae thickness is between 2-5cm; The dark laminae of the ancient dammed lake sediment line layer represents the sufficient rainwater in spring and summer to deposit, dry deposition of light-colored representative of autumn and winter; The ancient dammed lake sediment thick particle color of sediment is relatively dark, detailed particle color is relatively shallow.(2) Based on the result of granularity analysis(33 test samples), carbon oxygen isotope analysis(20 test samples), and spore’s powder analysis(33 test samples), the whole Tuanjie village sediment profile is divided into 7 environment time intervals: The first stage (22 ~ 20.8 ka BP) : elevation range:2141~ 2130m, it is to be forest grassland vegetation types, the climate environment is from frigidity dry turn into warm wet process in the period; The second stage (20.8～17.7ka.BP):elevation range:2141～2177m, it is to be grassland forest vegetation types, the climate environment is from warm wet turn into frigidity dry process in the period; The third stage (17.7～16.4ka.BP):elevation range:2177～2197m, it is to be mingled forest grasslands vegetation types, the climate environment is from frigidity dry turn into warm wet process in the period; The fourth stage (16.4～13.4ka.BP):elevation range:2197～2224m, it is to be evergreen needle leaf forest vegetation types, the climate environment is from warm wet turn into warm semi-dry process in the period; The fifth stage (13.4～11.9ka.BP):elevation range:2224～2281m, it is to be needle leaf forest and mingled forest vegetation types, the climate environment is from warmer lilted wet turn into cold dry process in the period; The sixth stage (11.9～10.3ka.BP):elevation range:2281～2299m, it is to be needle leaf forest and part mingled forest vegetation types, the climate environment is from cold dry turn into frigidity wet process in the period; The seventh stage (10.3～10ka.BP):elevation range:2299～2310m, it is to be needle-broad leaf mingled forest vegetation types, the climate environment is from frigidity wet turn into warm dry process in the period. The information has pointed out that has gone through changes of the environment about 7 times during 10kaBP-22kaBP in the Diexi area.(3) The Diexi ancient dammed lake preserved in lacustrine sediments of the base 6 for the terrace, which the existence of six terrace shows the ancient dammed lake outburst had occurred in six of the corresponding deposition process. According to the dating and palynological test data, get the following laws to the palaeoclimate and ancient environment in this area since in 10kaBP: 1) The Diexi ancient dammed lake begins to burst since 10ka.BP, disappear after being divided into about 6 times burst , every time after all possible efforts from climate change; 2) Among the 10-8.4kaBP, the climate environment is from warm dry turn into warm-cold little wet process in the period; 3) Among the 8.4～5.5kaBP, the climate environment is from warm-cold little wet turn into warm semi-dry process in the period.(4) Through comparing the ancient environment and palaeoclimate of adjacent area of edge of the east of Qinghai-Tibet Plateau with discovering: Diexi region and adjacent Ruoergai area in the same period of time characterized by the existence of differences in climate and environment, but demonstrated unanimously generally in these regional climate in 2 million years it is frigidity and dry; These regional climate demonstrated unanimously generally that warm and wet in 10,000 years. These evidences prove on the edge of the east of Qinghai-Tibet Plateau, has these two time intervals, the regional climate is identical, the influence that it should be the great environmental macroclimate plays a leading role.更多还原