玛湖凹陷金龙53井鱼化石埋藏环境及成因分析

Analysis on the burial environment and genesis of fish fossils in Well Jinlong 53 of Mahu Depression

鱼化石中包含了大量古湖泊水文和沉积环境信息。以鱼化石埋藏学理论为指导,以金龙53井鱼化石为主要研究对象,通过对金龙53井第3回次岩心进行厘米级精细描述,结合岩石薄片分析和前人研究成果,分析了该井风城组二段鱼化石的埋藏环境和化石形成过程。研究认为,金龙53井鱼化石埋藏区为半深湖到深湖环境,火山喷发和蒸发作用造成碱湖水化学性质骤变和缺氧可能是鱼类群体死亡的重要原因;鱼类死亡之后被异重流搬运到半深湖或深湖区快速埋藏,或者垂直落入深水区逐渐埋藏;鱼化石的形成经历了鱼类生活阶段、死亡垂落阶段、埋藏保存阶段和石化成岩阶段等4个阶段。该研究对重建玛湖凹陷二叠纪岩相古地理、指导油气勘探具有重要的意义。

Fish fossils contain a lot of hydrological and sedimentary environment information of ancient lakes.Guided by the theory of fish fossil taphonomy and taking the fish fossils of Well Jinlong 53 as the main research object,the burial environment and fossilation process of fish fossils in the second member of Fengcheng Formation of Well Jinlong 53 were analyzed based on the fine description of the third core of the well at the centimeter level,the rock thin section analysis and previous research results.It is concluded that the fish fossils in Well Jinlong 53 are burial in semi-deep to deep lacustrine environment,and the water chemistry variation and the hypoxia in alkali lakes caused by volcaniceruption and evaporation may be important reasons for massive fish death.Some of the dead fish might have been transported by hyperpycnal flow to semi-deep lake or deep lake and been buried rapidly,while others might have fallen vertically into the deep water area and been buried gradually.The formation of fish fossils has experienced four stages including fish life stage,death and falling stage,burial preservation stage and lithificational diagenesis stage.The study is of great significance for Permian paleogeography reconstruction and oil and gas exploration in Mahu Depression.