湖北南漳—远安地区下三叠统嘉陵江组纹层状细粒碳酸盐岩特征及成因研究  

Characteristics and origins of fine-grained carbonate laminates of the Lower Triassic Jialingjiang Formation,in Nanzhang—Yuan’an area,Hubei province

作　　者：陈亚婕 沈越峰 张聪 刘俊[1] CHEN Yajie;SHEN Yuefeng;ZHANG Cong;LIU Jun(School of Resources and Environmental Engineering,Hefei University of Technology,Hefei,230009;Oil&Gas Survey Center,China Geological Survey,Beijing,100083)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]中国地质调查局油气资源调查中心,北京100083

出　　处：《地质论评》2025年第2期372-391,共20页Geological Review

基　　金：国家自然科学基金资助项目(编号:41902104,42172026,41772003,42302177);安徽省自然科学基金资助项目(编号:1908085DQ152);自然资源部地层与古生物重点实验室开放课题基金资助项目(编号:KLSP1903);第二次青藏高原综合科学考察项目(编号:2019QZKK0708)的成果。

摘　　要：湖北南漳—远安地区下三叠统嘉陵江组三段顶部发育一套典型纹层状细粒碳酸盐岩。笔者等通过野外工作,结合岩石学及地球化学分析,总结了该套纹层状细粒碳酸盐岩的基本特征,探讨了其形成机制及沉积环境。该套纹层状细粒碳酸盐岩由亮色纹层与暗色纹层交替平行堆叠而成,纹层单元(成对出现的亮色纹层与暗色纹层)平均厚度0.22~0.62 mm,亮色纹层的主要成分为微亮晶方解石,基本不含有机质;暗色纹层则是以黏土矿物、泥晶方解石以及有机质为主,并发现了大量胞外聚合物以及莓状黄铁矿。激光剥蚀电感耦合等离子体质谱仪面扫实验结果表明Sr元素浓度整体较高,其浓度范围在200×10^(-6)~460×10^(-6);而Ba元素浓度在亮色纹层中较低但在暗色纹层中较高,总体小于80×10^(-6)。较高的Sr/Ba值表明了纹层状细粒碳酸盐岩整体沉积于高盐环境中。通过对嘉陵江组沉积速率的计算推测出该纹层的形成由季节性周期变化控制。基于纹层状细粒碳酸盐岩的宏微观特征,认为亮色纹层形成于秋—冬季,主要成因机理是化学沉淀;而暗色纹层形成于春—夏季,成因机理包括底栖微生物席对沉积物的捕捉,微生物的生物矿化作用和有机矿化作用产生的微泥晶碳酸钙即自生泥晶以及悬浮在水体中的微生物与黏土矿物的相互吸附沉降。综合这一系列沉积特征以及主微量元素地球化学特征,推测该套纹层状细粒碳酸盐岩整体沉积于凝滞、还原、高盐的潮坪低洼环境中。Objectives:The fine-grained carbonate rocks with typical characteristics and well-preserved laminations occurred at the Third Member of the Lower Triassic Jialingjiang Formation,Nanzhang—Yuan’an area.This study aims to summarize the characteristics of fine-grained carbonate laminates,and elucidate the formation mechanisms and the depositional environments of the fine-grained carbonate laminates.Methods:In this study,field observation in combination with petrographic analysis under normal light,fluorescent,and scanning electronic microscopes,as well as geochemical analysis(LA-ICP-MS mapping)were conducted to solve these problems.Results:The laminae are composed of an alternating stacking of dark laminae and light laminae,with an average thickness ranging from 0.22~0.62 mm.There are abundant organic matter,extracellular polymeric substance(EPS),automicrites,and framboidal pyrites as well as clay minerals preserved within the dark laminae,while light laminae are rich in microcrystalline-sparitic calcite crystals with a few dolomitic crystals but rare clay minerals.LA-ICP-MS mapping analysis indicates different contents of some major and trace elements within different laminae.Conclusions:The study elucidates the formation mechanisms and depositional environment of the fine-grained carbonate laminates.The formation of the dark laminae is attributed to organic matter and clay mineral adsorption,biomineralization and organomineralization of microbes.While the light laminae may precipitate in a supersaturated calcium carbonate environment.These all indicate that those fine-grained carbonate laminates deposited in a stagnant,reduced,and hypersaline tidal flat pond environment.

关 键 词：泥晶—微晶碳酸盐岩 潮坪 微生物席 生物矿化作用 有机矿化作用 

分 类 号：P61[天文地球—矿床学]