广西南丹石炭系黄龙组下段碳酸盐岩地球化学特征及其古沉积环境意义  

Geochemical characteristics and environmental significance of the lower part of the Huanglong Formation in Nandan,Guangxi

作　　者：韩怡颖 刘希军[1,2,3] 王葆华[1,2] 时毓[1,2] 李政林[1] 刘潇 邓发亮[1] HAN Yiying;LIU Xijun;WANG Baohua;SHI Yu;LI Zhenglin;LIU Xiao;DENG Faliang(Guangxi Key Laboratory of Exploration for Hidden Metallic Ore Deposits,Guilin University of Technology,Guilin 541006,Guangxi,China;Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources Co-built By the Guangxi Province and MOE,Guilin University of Technology,Guilin 541006,Guangxi,China;Guangxi Science Innovation Base for Formation and Exploration of Strategic Critical Mineral Resources,Guilin University of Technology,Guilin 541006,Guangxi,China)

机构地区：[1]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541006 [2]桂林理工大学有色金属矿产勘查与资源高效利用省部共建协同创新中心,广西桂林541006 [3]桂林理工大学广西战略性关键矿场资源成矿与勘查科技创新基地,广西桂林541006

出　　处：《地球化学》2023年第5期637-648,共12页Geochimica

基　　金：国家自然科学基金项目(92055208);广西自然科学基金杰出青年科学基金项目(2019GXNSFFA245005);广西科技创新基地建设类项目(ZY21195031);广西八桂学者项目(2018-有色金属成矿理论与勘查技术);广西研究生教育创新计划项目(YCBZ2021093)联合资助。

摘　　要：广西南丹大厂石炭系黄龙组碳酸盐岩对探讨右江盆地石炭系古沉积环境和古海水氧化还原特征具有重要的意义。本文对研究区碳酸盐岩样品进行全岩地球化学分析,结果显示:碳酸盐岩的Mn/Sr值均小于3,表明样品能够反映原始海相化学性质;SiO_(2)、Al_(2)O_(3)和TiO_(2)等陆源元素的平均含量低,Zr、Th的含量较低且与ΣREE相关性不明显、Y/Ho值变化大但Nd含量相对稳定,说明样品受到陆源碎屑影响有限;碳酸盐岩的Ce异常,揭示了样品形成于次氧化环境,δEu接近于现代海水值,反映样品基本不受热液活动影响。根据古水深、古气候、古盐度等特征元素指标综合判别,研究区黄龙组下段沉积期为离岸距离相对较近的浅水沉积环境,总共经历了2次相对较大的海侵和海退旋回,但海水总体呈下降趋势,整体上属温暖潮湿的气候。这也进一步反映了石炭纪右江盆地为海相沉积环境。Carboniferous Huanglong Formation carbonate rocks in Nandan Dachang,Guangxi,are of great significance for revealing the Carboniferous paleosedimentary environment and seawater redox conditions in the Youjiang Basin.In this study,we present the whole-rock major and trace elements of these carbonate rocks.The Mn/Sr values of these carbonate rocks were all less than 3,indicating that the original marine chemical properties of the carbonate rocks were preserved.The average amounts of the terrestrial elements SiO_(2),Al_(2)O_(3),and TiO_(2) in these carbonate rocks was low.In addition,the Zr and Th levels of these carbonate rocks were low.Both Zr and Th did not show clear correlation withΣREE.Moreover,the Y/Ho ratios of these carbonate rocks showed a wide range of variation,but their Nd levels are relatively stable.All these major and trace element characteristics of the carbonate rocks suggest that their sedimentary environment was relatively stable,with low involvement of terrigenous clastics.TheδCe values of carbonate rocks suggest they were formed in a sub-oxidation environment.TheδEu values of carbonate rocks were akin to those of current seawater and not affected by hydrothermal activity.The water depth,paleoclimate,paleosalinity,and other characteristic element indices of these carbonate rocks indicate that their sedimentary environment was an offshore platform.This offshore platform experienced two relatively large transgressive cycles,which resulted in an oscillating decline in sea level,and the sedimentary environment was generally warm and humid.Our conclusion further reflects that the Youjiang Basin was a marine sedimentary environment during the Carboniferous Period.

关 键 词：广西南丹 石炭系 碳酸盐岩 地球化学 古环境 

分 类 号：P597[天文地球—地球化学]