滇东北DD1井五峰组—龙马溪组地层界线划分及沉积环境演变  

Boundary definition ofWufeng Formation and Longmaxi Formation in well DD1 and sedimentary environment evolution of Northeastern Yunnan

作　　者：冯伟明[1,2] 李嵘 赵瞻[1,2] 余谦 杨瀚[3] 谢渊 叶定南[4] FENGWeiming;LI Rong;ZHAO Zhan;YU Qian;YANG Han;XIE Yuan;YE Dingnan(Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan China;Key Laboratory Sedimentary Basins Oil and Gas Resources,Ministry of Land and Resources,Chengdu 610081 Sichuan China;Chongqing Institute of Geology and Mineral Resources,Chongqing 400042 China;No.113 Geological party,Sichuan Bureau of Geological and Mineral Exploration and Development,Luzhou 646000,Sichuan China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]自然资源部沉积盆地与油气资源重点实验室,四川成都610081 [3]重庆地质矿产研究院,重庆400042 [4]四川省地质矿产勘查开发局一一三地质队,四川泸州646000

出　　处：《中国地质》2021年第1期297-308,共12页Geology in China

基　　金：国家科技重大专项“页岩气勘查评价技术试验与应用推广”(2016ZX05034-004);中国地质调查局地质调查二级项目“四川盆地下古生界海相页岩气基础地质调查”(DD20160176);“滇东北地区页岩气地质调查”(DD20190080)联合资助。

摘　　要：DD1井上奥陶统临湘组泥灰岩之上发育大套粉砂质泥岩,笔石化石缺乏,也未发现观音桥段含赫南特贝灰岩标志层,O-S界线通过生物地层和岩石地层方法难以确定。微量、稀土元素分析表明,粉砂质泥岩中部(1288.3 m)的Th、Sr、Y、Th/U以及Cen、Eun、δCe、δEu曲线均呈现尖锐的异常峰,该处ΣREE含量显著高于上下地层,REE分布曲线右倾斜率更大。将DD1井与扬子地区其他O-S界线剖面的元素地球化学特征进行对比分析,可判断DD1井存在五峰组观音桥段,该标志层的厚度也小于1 m。微量元素地球化学氧化-还原判别图还表明,五峰期—龙马溪期早期沉积水介质主要处于弱氧化环境,观音桥期氧化性达到最强;根据沉积学标志分析,O-S之交沉积相演变过程为:潮下→潮间→潮上→潮间,在观音桥期水体最浅,为潮上带沉积。Although the Upper Ordovician Linxiang Formation marl in DD1 well is covered with thick silty mudstone,there is a lack of graptolite fossil,and no Hirnantia limestone marker stratum of the Guanyinqiao Member.Therefore,it is difficult to determine the boundary between Ordovician System and Silurian System by biostratigraphic and petrostratigraphic methods.The analysis of trace elements and REE of silty mudstone in the well DD1 shows that Th,Sr,Y,Th/U,Cen,Eun,δCe andδEu curves at the middle part of silty mudstone(1288.3m)present sharp abnormal peaks with significantly higherΣREE content of silty mudstone(1288.3m)than its upper and lower silty mudstone and great right slope of the REE distribution curve.By comparing the elemental geochemistry characteristics of the well DD1 with other O-S boundary in the Yangtze Region,it can be concluded that there exists Guanyinqiao Member of Wufeng Formation in the well DD1,and the thickness of this marker layer is also less than 1 m.The geochemical redox discriminant graph shows that the sedimentary water medium mainly was in weak oxidation environment from the Wufeng period to the early Longmaxi period,and its oxidation was the strongest in the Guanyinqiao period.According to the analysis of sedimentary markers,the evolution process of the sedimentary facies at the O-S transition is as follows:subtidal→intertidal→supertidal→intertidal;in the Guanyinqiao period,the water was the shallowest,and there existed supertidal deposits.

关 键 词：五峰组 观音桥段 奥陶系—志留系界线 化学地层 滇东北 油气地质调查工程 

分 类 号：P534.42-43[天文地球—古生物学与地层学] P512.2[天文地球—地质学]