Characteristics and formation mechanism of siltstone-mudstone rhythmic sedimentary sections in the Lower Silurian Longmaxi Formation in the Changning area,South Sichuan Basin,southwest China  

作　　者：Gaoxiang WANG Lei CHEN Yang YANG Cui JING Man CHEN Xiucheng TAN Xin CHEN Di CAO Zibo WEI Minglong LI Dong HUANG 

机构地区：[1]School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China [2]PetroChina Southwest Oil&Gasfield Company,Chengdu 610051,China [3]Sichuan Changning Natural Gas Development Co.Ltd,Chengdu 610051,China [4]Shale Gas Evaluation and Exploitation Key Laboratory of Sichuan Province,Chengdu 610091,China [5]Technology Innovation Center of Shale Gas Exploration and Development in Complex Structural Areas(Ministry of Natural Resources),Chengdu 610091,China [6]Sichuan Keyuan Testing Center of Engineering Technology,Chengdu 610091,China

出　　处：《Frontiers of Earth Science》2021年第4期754-769,共16页地球科学前沿（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant No.41602147);Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(No.2020CX020000).

摘　　要：The Lower Member of the Longrnaxi Forma-tion is generally dominated by siliceous shale,but recently we found some siltstone-mudstone rhythm sections developed in the Lower Member of the Longmaxi Formation.The study of formation mechanism of siltstone-mudstone rhythmic sedimentary sections may provide new insights into the shale sedimentary environ-ment.Therefore,we studied the characteristics and formation mechanism of siltstone-mudstone rhythmic sedimentary sections in the Lower Member of the Long-maxi Formation in the Changning area based on core observation,thin section identification,major elements and trace elements analysis.The results show the following:1)Two siltstone-mudstone rhythmic sedimentary sections are characterized by frequent interbed between black or gray-black shale and light gray siltstone,abundant argillaceous laminas and silty laminas,with obvious lithological boundaries having developed.Horizontal laminas and rhythmic laminas are well-developed in the shale layer,while the wavy laminas are well-developed in the siltstone layer.2)The major compositional elements are SiO2,Al2O3 and CaO,followed by Fe_(2)O_(3),MgO,K_(2)O and Na_(2)O.3)Compared with the world average shale,these siltstone-mudstone rhythmic sedimentary sections are rich in Mo,U and Ba,but less in V,Co,Ni,Cu.Compared with the shale layer,the siltstone layer has lower contents of V,Co and Ni.4).The geochemical redox indices,Mo-U and CIA values suggest the formation of the siltstone-mudstone rhythmic sedimentary sections are related to influences from bottom currents in an oxic condition with a warm and humid paleoclimate.

关 键 词：shale Longmaxi Formation bottom current deposit Sichuan Basin 

分 类 号：P618.13[天文地球—矿床学]