五峰组—龙马溪组笔石带划分与沉积环境的意义——以重庆武隆接龙剖面为例

Graptolite biostratigraphy and sedimentary environment significance:a case study from the Wufeng Formation-Longmaxi Formation of Jielong Section in Wulong,Southeastern Chongqing

渝东南地区五峰组-龙马溪组地层发育典型的黑色笔石页岩。以重庆武隆地区接龙剖面为例,基于页岩中笔石形态、保存特征,结合地球化学数据测试分析,讨论研究区笔石发育特征与黑色页岩沉积环境变化的关系。结果表明:接龙剖面上奥陶统凯迪阶上部至志留系多维列统埃隆阶顶部(五峰组-龙马溪组)识别16属、19种笔石类型,划分10个连续发育的笔石带。凯迪阶主要发育WF2-WF3笔石带,笔石出现较少,呈星点状分布,笔石结构坚固,体质量大,为复杂的胞管,反映深水厌氧还原沉积环境。赫南特阶主要发育WF4-LM1笔石带,下部主要为雕笔石属、双笔石属。观音桥层为生屑灰岩,发育赫南特贝动物群,上部为黑色炭质硅质页岩,笔石丰富,有机质质量分数高,整体反映由深水陆棚相到闭塞浅海相再到深水陆棚相的沉积环境。鲁丹阶主要发育LM2-LM5笔石带,下部笔石大量发育,多为双列攀合型,丰度大,呈无序叠加分布于岩层表面,为静水强厌氧还原沉积环境。埃隆阶主要发育LM6-LM7笔石带,发育胞管多为半耙笔石属、耙笔石属,丰度降低,主要发育粉砂质泥页岩与泥质粉砂岩夹层,为浅水陆棚相的沉积环境。该结果为渝东南地区五峰组-龙马溪组页岩气勘探提供参考。

The typical black shale is grown in Wufeng Formation-Longmaxi Formation in southeastern of Chongqing.Taking Jielong Section of Wulong Area in Chongqing as an example,based on the shape and preservation characteristics of the graptolites in the shale,combined with the geochemical data analysis,we discussed the relationship between the development characteristics of the stone in the study area and the sedimentary environment of the black shale.The results show that Jielong Section identified a total of 16 genera and 19 types of graptolities stone,which are divided into 10 continuous developmental biological graptolite biozones from the upper part of the Upper Ordovician Kaidi Step to the top of the Silurian multi-dimensional system of the Silomian Order(Wufeng Formation-Longmaxi Formation).The Katian mainly develops the WF2-WF3 graptolite biozones,which has less pen stone content and is distributed in a star shape.The graptolites structure is solid and the body mass is large.It is a complex cell tube and reflects the sedimentary condition of deep water anaerobic reduction environment.The Hernantian mainly develops the WF4-LM1 graptolite biozones,and the lower part is mainly the genus of the genus stylus and the double genus.The Guanyinqiao Group developed clastic limestone,with Hirnantia Fauna,and the upper part is black carbonaceous siliceous shale.It is rich in graptolites and high in organic matter.It reflects the deposition from deep water shelf phase to occluded shallow sea phase,and to deep water shelf phase.The Rhuddanian Stage mainly develops the LM2-LM5 graptolite biozones,and the lower part is developed in a large number,mostly double-column climbing type,with abundance and disorderly superimposed distribution on the surface of the rock layer.It is a static water strong anaerobic reduction deposition environment.The LM6-LM7 graptolite biozones is mainly developed in the Aeronian,and the developmental cell tube is mostly agenus of the genus Penta,and the abundance is reduced.The main development is silty mud shale and argillaceous silt interlayer,and the sedimentary environment is shallow water and shelf shed sedimentary environment.The results provide reference for shale gas exploration of Wufeng Formation-Longmaxi Formation in Southeast Chongqing.