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华南南华纪南沱冰期海洋环境的沉积地球化学记录——来自黔东部南华系南沱组白云岩碳氧同位素和微量元素的证据
投稿时间:2019-07-24  修订日期:2019-12-11  点此下载全文
引用本文:沈洪娟,顾尚义,赵思凡,吴忠银,冯永.2020.华南南华纪南沱冰期海洋环境的沉积地球化学记录——来自黔东部南华系南沱组白云岩碳氧同位素和微量元素的证据[J].地质论评,(1):214-228,[DOI]:.
SHEN Hongjuan,GU Shangyi,ZHAO Sifan,WU Zhongyin,FENG Yong.2020.The sedimentary geochemical records of ocean environment during the Nantuo (Marinoan) glaciation in South China ——Carbon and oxygen isotopes and trace element compositions of dolostone in Nantuo Formation, Nanhuan System, in eastern Guizhou[J].Geological Review,(1):214-228.
DOI:10.16509/j.georeview.2020.01.016
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作者单位E-mail
沈洪娟 贵州大学资源与环境工程学院贵阳550025 Email:shenhongjuan615@163.com 
顾尚义 1) 贵州大学资源与环境工程学院贵阳550025 2) 贵州大学地质资源与环境教育部重点实验室贵阳550025 Email:gushangyi@126.com 
赵思凡 贵州大学资源与环境工程学院贵阳550025  
吴忠银 贵州大学资源与环境工程学院贵阳550025  
冯永 贵州大学资源与环境工程学院贵阳550025  
基金项目:注:本文为国家自然科学基金资助项目(编号:41663005,41762001)的成果
中文摘要:新元古代“雪球地球”事件代表地球经历的极端气候条件,对其后的大气和海洋氧化、生物地球化学循环和真核生物的演化都产生了深远的影响。然而同冰期化学沉积岩的缺乏,严重制约了对冰期海洋环境的了解。笔者等在贵州松桃地区一钻孔岩芯南华系南沱组中采集到一套同冰期白云岩,为南沱冰期海洋环境研究提供了理想材料。岩芯中白云岩层位于南沱组下部,夹持于两套杂砾岩、粉砂质泥岩组合中间,厚度1.61 m。偏光显微镜和扫描电镜观察表明岩性为微晶白云岩。采用Delta V Advantage稳定同位素质谱仪分析白云岩的碳、氧同位素,测定结果为:δ18OV PDB在-16.97‰~-8.37‰之间,δ13CV PDB在-9.68‰~-8.42‰之间,与冰期前后碳同位素组成对比,δ13CV PDB具显著低负值特征。电感耦合等离子体质谱仪(ICP MS)微量元素分析结果表明:白云岩样品中铁、锰含量很高,铁含量的平均值约为92867×10-6,锰含量的平均值约为10644×10-6;Mn/Sr值较大,平均值约为26.89。综合碳、氧同位素的相关性及微量元素特征分析表明,南沱组同冰期白云岩碳同位素组成代表了原始的沉积记录。研究结果表明:① 南沱组白云岩的出现反映了南沱冰期海洋中存在着开放的水体,这些开放水体为此时真核生物提供了重要的栖息场所。② 南沱冰期海洋处于富铁缺氧的环境,白云岩中碳同位素低负值主要是甲烷厌氧氧化的结果。③ 同位素质量平衡计算表明,冰期海洋中较高比例的有机质埋藏和极其有限的大气-海洋气体交换导致了大气中氧浓度的升高。
中文关键词:南华系南沱组  南华纪南沱冰期  白云岩  碳同位素  甲烷厌氧氧化  大气氧
 
The sedimentary geochemical records of ocean environment during the Nantuo (Marinoan) glaciation in South China ——Carbon and oxygen isotopes and trace element compositions of dolostone in Nantuo Formation, Nanhuan System, in eastern Guizhou
NameInstitution
SHEN HongjuanCollege of Resource and Environmental Engineering, Guizhou University, Guiyang, 550025
GU Shangyi1) College of Resource and Environmental Engineering, Guizhou University, Guiyang, 550025; 2) Key Laboratory of Karst Georesources and Environment, Guizhou University, Guiyang, 550025
ZHAO SifanCollege of Resource and Environmental Engineering, Guizhou University, Guiyang, 550025
WU ZhongyinCollege of Resource and Environmental Engineering, Guizhou University, Guiyang, 550025
FENG YongCollege of Resource and Environmental Engineering, Guizhou University, Guiyang, 550025
Abstract:Objectives: The Neoproterozoic Snowball Earth events represent the extreme climate change in the Earth’s history and exert a fundamental impact on subsequent atmospheric and oceanic oxygenation, elemental biogeochemical cycling, and eukaryotes diversification in the Ediacaran Era. However, the apparent lack of primary marine precipitates limited the understanding of the syn glacial ocean chemistry during the Snowball Earth. A bed of syn glacial dolostone in the Nantuo Formation, Nanhuan Sestem, of a drill core in Guizhou Province, south China, provided the ideal materials for research of ocean chemistry during the Nantuo (Marinoan) Glaciation.Methods: Observation of dolostone lithology was conducted by polarized light microscope and scanning electron microscope; The stable carbon and oxygen isotopic compositions of the dolostone samples were analyzed by Delta V Advantage stable isotope mass spectrometer in Guizhou University; trace elements of the samples were analyzed by inductively coupled plasma mass spectrometry (ICP MS).Results: The results show that the values of δ18OV PDB and δ13CV PDB of the samples are ranged from -16.97‰ to -8.37‰, and from -9.68‰ to -8.42‰, respectively. Compared with the carbon isotopic compositions of carbonate rocks before and after the Nantuo (Marinoan) Glaciation, δ13CV PDB values of the dolostone samples in the Nantuo Formation have significantly low negative values. The results of trace element analyses by ICP MS show that the contents of iron and manganese in the dolostone samples are very high with the average of iron,manganese, and strontium content 92867×10-6, 10644×10-6, and 470×10-6, respectively. The average Mn/Sr in the dolostone samples is 26.89. Based on the correlation of carbon and oxygen isotopes and the characteristics of trace elements, it is suggested that the carbon isotopic composition of dolostone in the Nantuo Formation represents the original sedimentary record.Conclusions: ① The finding of the dolostone bed in the Nantuo Formation indicates that open waters existed during the Nantuo (Marinoan) Glaciation in south China and the open water provided the oases for eukaryotes. ② Marine chemistry was dominated by anoxic and ferruginous conditions during the Nantuo (Marinoan) Glaciation, and negative carbon isotope excursion during the period was mainly ascribed to the anaerobic oxidation of methane (AOM) by iron and/or manganese oxides under the anoxic and ferruginous conditions. ③ Based on the simple isotope mass balance calculation, it is suggested that high fraction of buried organic matters and limited gas exchange between air and ocean—gas contribute to the rise of atmospheric oxygen level during the Nantuo (Marinoan) Glaciation.
keywords:Nantuo Formation, Nanhuan System  Nantuo (Marinoan) Glaciation  dolostone  carbon isotopes  anaerobic oxidation of methane  atmosphere oxygennation
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