上扬子台地北缘上奥陶统碳酸盐岩微相及古环境意义  

Microfacies and Paleoenvironmental Significance of Upper Ordovician Carbonate Rocks in Northern Margin of the Upper Yangtze Platform

作　　者：靳晓雨 曾敏 陈思[1] 杨雪清[2] 申婷 JIN Xiaoyu;ZENG Min;CHEN Si;YANG Xueqing;SHEN Ting(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,Sichuan,China;College of Earth Sciences,Yunnan University,Kunming 650500,Yunnan,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]云南大学地球科学学院,云南昆明650500

出　　处：《西北地质》2022年第4期158-174,共17页Northwestern Geology

基　　金：国家自然科学基金面上项目“班怒带两条主要蛇绿岩带之间成因联系:来自沉积记录的约束”(41872110);中国博士后基金“扬子地台宝塔组龟裂纹灰岩的微生物成因及古环境意义”(2018M633331)联合资助。

摘　　要：晚奥陶世桑比期晚期—凯迪期早期作为奥陶纪末生物大绝灭前的关键时期,其中蕴藏了一些与大灭绝有关的古海洋古环境信息。本研究通过对四川省南江县桥亭乡上奥陶统(桑比阶—凯迪阶)西乡组至宝塔组进行野外实测、取样、室内磨片,以及碳酸盐岩微相分析,共识别出8种微相:紫红色薄层状白云岩、灰色层状白云岩、灰黑色层状白云岩夹黑色页岩、无生物扰动层状白云岩、钙质石英砂岩、似球粒黏结灰岩、生物碎屑泥粒灰岩和生物碎屑粒泥灰岩。根据各微相特征并结合野外宏观特征综合分析,将南江桥亭剖面的沉积相划分为陆表海潮坪相组合、混积台地相组合及碳酸盐缓坡台地相组合。经研究表明,西乡组大部都为近岸浅水的潮坪相沉积,在顶部开始出现海侵趋势,随后在宝塔组快速转变为碳酸盐岩缓坡沉积,海平面明显上升与凯迪早期的全球性海侵相对应,并且全球性GICE事件可能与此次海侵有关。The Late Sandbian to the Early Katian of the Late Ordovician,as a key period before the end-Ordovician mass extinction event,records paleo-marine and paleo-environments information related to the mass extinction.Based on section measurement,sample collection and thin-section preparation and microfacies analysis,a total of eight carbonate microfacies are identified through system analysis in the Xixiang Formation to Pagoda Formation of the Upper Ordovician(Sandbian-Kadian stage)in Qiaoting section(Nanjiang,Sichuan),which are purplish-red thin laminated dolomite,gray laminated dolomite,gray-black laminated dolomite with black shale,laminated dolomite without bioturbation,calcisilicarenite,peloids bond limestone,bioclastic packstone,and bioclastic wackestone.According to the characteristics of each microfacies and combining with the field observation,we classify these samples into three sedimentary facies types,namely,epicontinental sea carbonate tidal flat,clastic-carbonatite diamictite,and carbonate ramp.The results indicate that most of the Xixiang Formation are tidal flat deposits with shallow water,which began to be transgressive at the top and then rapidly changed to carbonate ramp deposits in the Pagoda Formation.The obvious sea level rise corresponds to the global transgression in the early Katian period,and the global GICE event may be related to this transgression.

关 键 词：上奥陶统 碳酸盐岩微相 宝塔组 GICE 

分 类 号：P588.245[天文地球—岩石学]