青藏高原北部可可西里库赛湖年纹层微区分析及形成机理  

Micro-Area Analysis and Mechanism of Varves from Lake Kusai in the Hoh Xil Area,Northern Tibetan Plateau

作　　者：陈钰[1] 刘兴起[1,2,3] 何利[4] 叶莉[5] 陈惠芬[6] 李凯[2,3] 

机构地区：[1]首都师范大学资源环境与旅游学院,北京100048 [2]中国科学院南京地理与湖泊研究所,南京210008 [3]湖泊与环境国家重点实验室,南京210008 [4]北京师范大学地理学与遥感科学学院,北京100875 [5]北京师范大学基建处,北京100875 [6]国立台湾海洋大学应用地球科学研究所

出　　处：《地质学报》2016年第5期1006-1015,共10页Acta Geologica Sinica

基　　金：湖泊与环境国家重点实验室开放基金(编号2014SKL001);中国科学院战略性先导科技专项项目(编号XDA05080403)资助成果

摘　　要：湖泊年纹层是进行高分辨率古气候环境研究的重要载体之一,其形成机理的研究能够为高分辨率古气候环境信息的提取提供重要的依据。本文以青藏高原北部可可西里库赛湖沉积的年纹层为研究对象,通过纹层薄片显微镜观察,以及纹层的扫描电镜、X衍射和同步辐射X射线荧光等微区分析,对库赛湖沉积年纹层的形态、沉积和成分特征进行了研究,以探讨库赛湖年纹层形成过程和机理。结果表明:年纹层层偶由深浅相间的微层组成,深色层主要由灰褐色—黑褐色的粗颗粒物质组成,磨圆中等、分选性差,矿物以石英、长石、白云母、黏土矿物等为主,其中石英含量占73%左右,且具有明显的风力搬运特征;浅色层呈灰白色,矿物颗粒较细,除石英、长石、白云母、黏土外,还有自生的文石,同时浅色层中含有大量的枝角类碎片和半月形介形类生物壳体。研究认为,库赛湖冬季温度低、风力强劲,风的机械搬运作用使大量的陆源物质在冰面堆积,等到春季湖泊开封,冰面上粗颗粒物质沉积到湖底形成库赛湖年纹层的深色层(粗颗粒层);夏季温度升高,冰雪融化,降水增加,河流搬运的陆源粗颗粒物质由于重力作用先在湖泊边缘沉积,而黏土矿物等细颗粒物质则在湖泊中心沉积,同时夏季湖水温度升高,蒸发作用加强,生物活动增强,湖泊自身的生物、化学作用加强,从而形成以细碎屑矿物、生物残体、自生碳酸盐沉积为主的浅色层(细颗粒层)。因此,库赛湖的年纹层层偶是由冬季冰面风成物质形成的粗颗粒深色层(冰融化后,风成物质沉降至湖底堆积)和夏季沉积的细颗粒浅色层两者交替而形成的。The varved lake sediments are one of important archives for high-resolution paleoclimate and paleoenvironment studies,and studying their sedimentary mechanism could provide an important basis for high-resolution paleoclimatic and paleoenvironment reconstructions.In this paper,observation of petrographic thin sections under microscope,and micro-area analyses,such as scanning electron microscope,as well as X-ray diffraction analysis,and synchrotron radiation X-ray fluorescence analysis,are used to study morphology,deposition and mineral characteristics of varved Lake Kusai sediments in the Hoh Xil region of Northern Qinghai-Tibetan Plateau,and thus to investigate their sedimentary process and mechanism.The results show that Varved Kusai Lake sediments are very steadily and well rhythmically laminated with interaction of light and dark layer..The dark layers are made of grey brown or black brown coarse material with middle rounded and poor sorted grains,composed of quartz,feldspar,mica,and clay minerals,among which quartz accounts for about 73%.The features of the dark layers are quite similar to those of aeolian deposits.The light layers are made of gray and white thin material,composed of quartz,feldspar,muscovite,and clay minerals.The light layers contain authigene minerals such as aragonite.Meanwhile the light layers include many half-moon-shaped ostracod shells and cladocera remains.Thus,we suggest that dark layers are formed by coarse sand and silt that were deposited on lake ice by aeolian processes during winter when the temperature is low and the wind is strong.Upon ice thawing during summer,these sands and silts may be released and deposited into lake sediments to form dark layers（coarse particle layer）.We interpret the light layers（fine particle layer）to represent summer season accumulations,when thin materials are transported to the lake center by high discharge caused by snow melting and high precipitation.Authigene minerals such as aragonite deposited under the condition of high evaporation,and

关 键 词：青藏高原北部 可可西里 库赛湖 年纹层 微区分析 形成机理 

分 类 号：P532[天文地球—古生物学与地层学] P512.2[天文地球—地质学]