柴达木盆地诺木洪贝壳堤水体演变的介形类证据  

Water Evolution of Nuomuhong Shell Ridge in Qaidam Basin:Evidence from Ostracods

作　　者：李玮[1] 屈海英 李莎[3] 周淑敏[1] 宋先腾 王晓楠 LI Wei;QU Haiying;LI Sha;ZHOU Shumin;SONG Xianteng;WANG Xiaonan(Department of Geological Engineering,Qinghai University,Xining,Qinghai 810016,China;Sichuan Ya’an Ecological and Environmental Monitoring Center,Ya'an,Sichuan 625000,China;Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing,Jiangsu 210008,China;Xining Comprehensive Investigation Center of Natural Resources,China Geological Survey,Qinghai 810000,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing,Beijing 100083,China)

机构地区：[1]青海大学地质工程系,青海西宁810016 [2]四川省雅安生态环境监测中心站,四川雅安625000 [3]中国科学院南京地质古生物研究所,江苏南京210008 [4]中国地质调查局西宁自然资源综合调查中心,青海西宁810000 [5]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《现代地质》2022年第1期14-26,共13页Geoscience

基　　金：青海省科技计划项目(2017-ZJ-955Q)。

摘　　要：柴达木盆地贝壳堤保存有大量大小混杂及两壳绞合的双壳类化石,是全球干旱区罕见的地貌景观,为青藏高原东北部中晚更新世的气候与环境演化提供了重要的区域地质记录。该记录在诺木洪西北约20 km出露,将其命名为诺木洪贝壳堤。目前诺木洪贝壳堤的沉积属性存在河湖之争,对该贝壳堤剖面开展系统的介形类分析,建立了8个生物组合带,除1带化石稀少无法鉴定外,2-8带自下而上依次为:Ilyocypris-Candona-Candoniella组合、Ilyocypris-Candona-Leucocythere-Candoniella-Eucypris inflata组合、Leucocythere-Ilyocypris组合、Ilyocypris-Leucocythere-Candoniella-Candona组合、Ilyocypris-Candoniella-Leucocythere组合、Ilyocypris bradyi-Ilyocypris echinata组合和Ilyocypris bradyi-Candoniella组合。根据8个生物组合带的属种特征和古生态指标综合分析贝壳堤水体的演化过程,认为诺木洪贝壳堤为河流相沉积。1-5带沉积期由于频繁的河流改道,贝壳堤剖面处经历牛轭湖-浅水河流多次转变,牛轭湖阶段水体较深不利于介形类生存,而浅水河流阶段介形类相对繁盛;6-8带沉积期水体维持极浅河流状态,介形类繁盛,后因持续干旱河道封闭,水体盐度升高而不利于介形类生存;最终盐壳析出,诺木洪贝壳堤沉积结束。As a rare and distinctive geomorphological feature in arid regions around the world,a shell ridge in the Qaidam Basin preserves many bivalve fossils of different sizes and articulated shells,which provides important record for the paleoclimate and paleoenvironmental evolution of the middle-late Pleistocene NE Tibetan Plateau.The Nuomuhong Shell Ridge is newly discovered as fluvial sediments,which is different from early studies of lacustrine deposits.Through systematic analyses,we established eight ostracod assemblages for the Shell Ridge.Though scarce ostracod fossils were found in Assemblage 1 and they were hardly identified,fossils in other assemblages were relatively abundant.We named Assemblage 2 to 8 as follows:Ilyocypris-Candona-Candoniella,Ilyocypris-Candona-Leucocythere-Candoniella-Eucypris inflate,Leucocythere-Ilyocypris,Ilyocypris-Leucocythere-Candoniella-Candona,Ilyocypris-Candoniella-Leucocythere,Ilyocypris bradyi-Ilyocypris echinata and Ilyocypris bradyi-Candoniella.We clarified water evolution of the Shell Ridge based on ostracod fossil characteristics and their paleoecology information.We identified the Nuomuhong Shell Ridge fluvial deposits that went through frequent river diversions within the Assemblage 1 to 5 occurrence,during which the shell ridge sedimentation fluctuated between oxbow lake and shallow river environments.The shallow river environment was favorable for the living of ostracods,whereas the deeper water of oxbow lake was detrimental to their survival.The shallow river condition continued through the time of Assemblage 6 to 8,during which ostracods thrived in warmer climate till the river enclosed and salinity increased,which hampered ostracod survival.Subsequently,salt crust was likely formed after persistent droughts and the deposition of Nuomuhong Shell Ridge ended.

关 键 词：柴达木盆地 诺木洪贝壳堤 介形类 河流沉积 

分 类 号：P532[天文地球—古生物学与地层学] Q911.6[天文地球—地质学]