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现代地质 ›› 2022, Vol. 36 ›› Issue (01): 14-26.DOI: 10.19657/j.geoscience.1000-8527.2021.025

• 海洋地质学 • 上一篇    下一篇

柴达木盆地诺木洪贝壳堤水体演变的介形类证据

李玮1(), 屈海英2, 李莎3, 周淑敏1, 宋先腾4, 王晓楠5   

  1. 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
  • 收稿日期:2020-10-16 修回日期:2020-12-11 出版日期:2022-02-10 发布日期:2022-03-08
  • 作者简介:李 玮,女,副教授,1989年出生,古生物学与地层学专业,主要从事微体古生物学教学与研究。Email: xiaoweiapple1212@163.com
  • 基金资助:
    青海省科技计划项目(2017-ZJ-955Q)

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

LI Wei1(), QU Haiying2, LI Sha3, ZHOU Shumin1, SONG Xianteng4, WANG Xiaonan5   

  1. 1. Department of Geological Engineering, Qinghai University, Xining, Qinghai 810016, China
    2. Sichuan Ya’an Ecological and Environmental Monitoring Center, Ya’an, Sichuan 625000, China
    3. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, Jiangsu 210008, China
    4. Xining Comprehensive Investigation Center of Natural Resources, China Geological Survey, Xining, Qinghai 810000, China
    5. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
  • Received:2020-10-16 Revised:2020-12-11 Online:2022-02-10 Published:2022-03-08

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:IlyocyprisCandonaCandoniella组合、IlyocyprisCandonaLeucocythereCandoniellaEucypris inflata组合、LeucocythereIlyocypris组合、IlyocyprisLeucocythereCandoniellaCandona组合、IlyocyprisCandoniellaLeucocythere组合、Ilyocypris bradyiIlyocypris echinata组合和Ilyocypris bradyiCandoniella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。

关键词: 柴达木盆地, 诺木洪贝壳堤, 介形类, 河流沉积

Abstract:

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.

Key words: Qaidam Basin, Nuomuhong Shell Ridge, ostracod, fluvial deposit

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