白云石晶体结构和地球化学特征对沉积环境响应:以扬子地台晚埃迪卡拉纪灯影组白云岩为例  

Dolomite crystal structure and geochemical characteristics in response to depositional environment:An example of dolomite from the Late Ediacaran Dengying Formation of the Yangzi Plateau

作　　者：杨志波 季汉成[1,2] 鲍志东[1,2] 史燕青[1,2] 赵雅静 向鹏飞[1,2] YANG Zhibo;JI Hancheng;BAO Zhidong;SHI Yanqing;ZHAO Yajing;XIANG Pengfei(College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China;State Key Laboratory of Petroleum Resource and Prospecting,China University of Petroleum(Beijing),Beijing 102249,China)

机构地区：[1]中国石油大学(北京)地球科学学院,北京102249 [2]中国石油大学(北京)油气资源与探测国家重点实验室,北京102249

出　　处：《地学前缘》2024年第3期68-79,共12页Earth Science Frontiers

基　　金：国家重点研发计划项目(2017YFC0603104,2019YFB1504101);中国石油化工股份有限公司重点科技项目(JP21005)。

摘　　要：受沉积环境的影响,在白云石形成过程中,其晶体结构与地球化学记录着相应的环境信息。本文以扬子地台晚埃迪卡拉纪灯影组杨坝剖面为例,通过系统采样研究了白云石的晶体结构和地球化学特征,明晰了基于岩石学和地球化学特征的灯影组沉积环境演化,归纳出了白云石晶体结构、地球化学特征与形成环境的耦合关系。结果表明:(1)杨坝剖面灯影组主要发育叠层石、核形石、泡沫棉石及凝块石等4种微生物白云岩和少量的晶粒、颗粒及角砾白云岩,垂向发育多期的微生物白云岩叠置韵律层,主要为局限台地潮坪相颗粒滩相。(2)地球化学分析表明,灯影组沉积演化过程为:一段主要为干旱气候、较高盐度的较浅水体,发育泥、粉晶白云岩沉积;二段下部水体加深、潮湿、低盐度,微生物白云岩最为发育;二段中上部水体总体相对较浅,湿度降低,盐度略增高;四段时水体先加深后迅速变浅,湿度逐渐降低,盐度亦逐渐增大。(3)研究区白云石晶体结构特征突显出典型的高Mg/Ca环境下流体参与形成,在干旱、高盐度的环境下,a/c值负偏,潮湿、低盐度的环境会导致晶胞参数a/c值正偏。有序度分布表明,随有序度的增加,a/c值逐渐靠近理想白云石。该结果不仅阐明准同生白云石晶体结构与形成环境关联,还揭示元古宇灯影组古海水环境特征。The crystal structure and geochemistry of dolomite in the Yangba section of the Late Ediacaran Dengying Formation on the Yangtze Platform are investigated to understand how they reflect the sedimentary environment in the paper.The study involves systematic sampling to analyze the evolution of the sedimentary environment based on petrological and geochemical characteristics.The research aims to elucidate the relationship between the crystal structure of dolomite,its geochemical properties,and the formation environment.The findings indicate the following:(1)The Yangba section of the Dengying Formation predominantly contains various types of microbial dolomite,including stromatolites,oncoids,foam asbestos,thrombolites,as well as some grain,particle,and breccia dolomite.The vertical sequence shows rhythmic layers of multi-stage microbial dolomite,primarily in restricted platform tidal flat and grain beach facies.(2)Geochemical analysis reveals that the Dengying Formation underwent sedimentary evolution in a shallow water environment characterized by arid conditions and high salinity,resulting in the deposition of mud and powder crystal dolomite.The lower part of the second section experienced deepening water conditions with increased humidity and lower salinity,leading to the prevalence of microbial dolomite.The middle and upper parts of the second section had relatively shallower water,decreasing humidity,and slightly higher salinity.In the fourth period,the water fluctuated between deepening and quick shallowing,accompanied by decreasing humidity and increasing salinity.(3)The dolomite crystal structure in the study area indicates the involvement of Mg^(2+)-rich fluids.In arid,high salinity environments,there is a/c negative deviation,while in humid,low salinity conditions,there is a/c positive deviation.The order degree distribution suggests that a/c approaches ideal dolomite as the order degree increases.These results not only elucidate the connection between the crystal structure of contemporaneous dolomite and

关 键 词：晶体结构 地球化学特征 沉积环境 扬子地台 灯影组 

分 类 号：P588.245[天文地球—岩石学] P578.61[天文地球—地质学] P581P586