基于岩石薄片分析的介形类化石赋存状态及地质意义——以济阳坳陷始新统泥页岩为例  

Ostracod Fossil Occurrence in Thin Sections and Its Geological Significance:Case Study on Eocene Shale of Jiyang Depression

作　　者：张存霞 

机构地区：[1]中石化股份胜利油田分公司勘探开发研究院,山东东营257015

出　　处：《地质论评》2015年第6期1407-1416,共10页Geological Review

基　　金：国家重点基础研究发展计划973项目(编号2014CB239102)的成果

摘　　要：首次利用岩石薄片观察和统计介形类化石的赋存状态,对济阳坳陷页岩的沉积环境及层序进行了研究。根据介形类化石在层面上的分布特征,将化石分布形式分为均匀分布、零星分布、条带状分布三种,按其保存状况分为双瓣、单瓣、破碎及压扁变形四种类型,化石丰度分为丰富(>100瓣/4cm2)、中等(30~100瓣/4cm2)和稀少(<30瓣/4cm2)三种。介形类化石的赋存状态与古盐度、岩相、层序及页岩中碳酸盐含量密切相关。研究表明:1济阳坳陷古近系沙河街组四段纯下亚段(Es4cx)——古近系沙河街组三段下亚段(Es3x)沉积期水体环境经历了由咸变淡的过程,盐度变化与化石丰度变化一致;2碳酸盐含量处于50%~60%范围内,最有利于介形类化石的保存;3纹层状灰质泥岩相和纹层状泥质灰岩相化石丰度高,但纹层状构造形成时期沉积速率慢,沉积基底较坚实,不利于介形虫死亡后的埋藏和保存,因此化石多以破碎为主。4介形类化石的盛衰与地层层序关系密切,一个层序内化石丰度呈现为出现-繁盛-衰退三个阶段,分别对应于低位体系域、湖扩展体系域和高位体系域。该方法解决了常规分析中难以观察到的化石原始保存和分布状态的问题,实现化石信息获取的最大化。For the first time this paper studies the sedimentary environment and sequence stratigraphy of Jiyang depression by means of observation and statistics of ostracods occurrence in thin sections. According to the characteristics of ostracods distribution on the level,the distribution patterns of fossil are classified into uniform distribution,dispersed distribution and banded distribution. Based on the ostracods preservation condition,the fossil is classified into double valve,single valve,fracture and flattening deformation. The fossil abundance is sorted into rich( > 100 flap /4cm2),medium( 30 ~ 100 flap /4cm2) and rare( < 30 flap /4cm2). Ostracods occurrence is closely related to the palaeosalinity,lithofacies,sequence stratigraphy and carbonate content of shale. Research shows that: 1The watery environment of Es4cx—Es3xJiyang depression has undergone an evolution of water body from salty to fresh,where the salinity change is agreement with fossil abundance change. 2 The carbonate content in the range of 50% ~ 60% is most conducive to the preservation of ostracods fossil. 3 The fossil abundance of laminated tuffaceous shale facies and laminated argillaceous limestone facies are very high,however,the slow deposition rate during the period of laminated structure formation and firm deposition basement are not favorable to the burial and preservation of ostracods fossil,thus the majority of fossil presence is in form of fracture.4 The vicissitude of ostracods abundance has a close relationship with stratigraphic sequence. The ostracods abundance sequentially presents three stages: appearance — prosperity—recession,corresponding to the low stand system tract,lake expansion system tract and high stand system tract respectively. This method solving the problem that the primary preservation and the distribution patterns of fossil are difficult to observe using the routine analysis,is able to be used to maximize the fossil information acquisition.

关 键 词：泥页岩 薄片 介形类化石 赋存状态 古盐度 碳酸盐含量 岩相 层序地层 

分 类 号：Q915.2[天文地球—古生物学与地层学]