米仓山地区埃迪卡拉系灯影组核形石微组构及环境意义

The oncoid is of great significance for revealing the paleoenvironment and microbial evolution during the Ediacaran period-one of the most important transitional period -because of its abundant information. At present, the researches on the oncoid in the Tongying Formation of Ediacaran are mostly focused on the morphology and sedimentary environment, but are lack of genetic mechanisms and comprehensive evaluation of paleoenvironmental indicators. Based on the detailed exploration and comparison of 13 sections in the Tongying Formation of Ediacaran around Sichuan Basin, this paper chooses two typical sections in Nanjiang Yangba and Wangcang Shuanghui in Micang Mountain as the research objects. In combination with the multidisciplinary study and different methods of analysis and testing, the macro and microstuctures, microbial, in-situ micro-area geochemical parameters, vertical evolutionary sequence of the oncoids are studied. The fabric of oncoids is comprehensively analyzed, which is arranged from centimeter to nanometer scale, to establish suitable classification scheme and find out the temporal-spatial distribution rules. The microbial components and types are identified to explore the formation mechanism of oncoids. This paper also shows a deeply understanding of the enviroment information including ancient climate, water energy, salinity, water depth, composition and seawater fluctuation affected by chemical conditions to comprehensively evaluate the environment indicators and their coupling relationship. The following two mechanism problems, namely "how do the oncoids form" and "under what environmental conditions can oncoids form", are discussed in this paper to provide a critical method for revealing the paleoenvironment of the Tongying Formation in Ediacaran during the sedimentary period.

核形石以其蕴含的丰富信息对于揭示埃迪卡拉纪这一重大过渡期的古环境及微生物演化具有重要意义。目前国内对埃迪卡拉系灯影组核形石的研究多集中在形态和沉积环境方面，缺乏成因机制及古环境指标的综合评价。本次研究在四川盆地周缘13条埃迪卡拉系灯影组剖面详细勘查对比的基础上，选取米仓山地区南江杨坝和旺苍双汇2条典型剖面为研究对象，多学科与多种分析测试手段相结合，开展核形石的宏微观组构、微生物、原位微区地球化学测试、垂向演化序列等方面的研究。完成从cm-nm级核形石组构的全面解剖，建立适用的分类方案，探明其时空分布规律；鉴定微生物组分及类型，探索核形石的形成机制；深挖其蕴含的古气候、水体能量、盐度、水深、成分、海水化学条件波动等环境信息，综合评价各环境指标及其耦合关系。着力解决核形石是“如何形成的”和“在什么环境条件下形成的”两个机制性问题，以期为揭示埃迪卡拉纪灯影组沉积时期古环境提供重要途径。

项目选取米仓山地区南江杨坝和旺苍双汇2条典型剖面为研究对象，多学科与多种分析测试手段相结合，开展核形石的宏微观组构、微生物、原位微区地球化学测试、垂向演化序列等方面的研究；在cm-nm级核形石组构的全面解剖的基础上，建立核形石分类方案，分析核形石时空分布规律；鉴定微生物组分及类型，探索核形石的形成机制，挖掘核形石蕴含的古气候、水体能量、盐度、水深、成分、海水化学条件波动等环境信息，综合评价各环境指标及其耦合关系。.项目按照计划书设计，完成了研究剖面核形石发育段的精细描述及样品采集，完成了宏微观特征的系统描述，建立了核形石的分类方案，并对核形石垂向上粒度、形态、核心与核形石之间的耦合关系等进行了探索；应用扫描电镜识别出7种细菌类型，分析了其成分及形态特征；综合应用同位素、微量元素、阴极发光、扫描电镜等手段，对核形石的形成过程、形成环境、受控因素进行了分析，研究认为核形石形成于受物源影响的潮坪环境，整体上核形石发育不够完善，以薄皮核形石、弥散粒为主，代表着核形石发育的最初阶段，其粒度差异大、形态多变、垂向高频变化的特征反映了埃迪卡拉纪灯影期海水受限、水浅、频繁动荡、受物源影响明显的特征。项目的研究重点解决了核形石“如何形成的”和“在什么环境条件下形成的”等问题，为揭示埃迪卡拉纪灯影组沉积时期古环境提供了重要途径。