地学前缘 ›› 2023, Vol. 30 ›› Issue (3): 28-43.DOI: 10.13745/j.esf.sf.2022.5.32

• 寒武系页岩地质、地球化学特征 • 上一篇    下一篇

宜昌地区寒武系水井沱组(第二统第三阶)生物组合面貌及其地层分布

潘晓强(), 华洪*(), 代乔坤, 骆劲舟, 刘紫薇   

  1. 陕西省早期生命与环境重点实验室/西北大学 地质学系 大陆动力学国家重点实验室, 陕西 西安 710069
  • 收稿日期:2022-04-06 修回日期:2022-04-30 出版日期:2023-05-25 发布日期:2023-04-27
  • 通讯作者: *华 洪 (1966—),男,教授,博士生导师,主要从事前寒武纪古生物学与地层学的研究工作。 E-mail: huahong@nwu.edu.cn
  • 作者简介:潘晓强(1996—),男,硕士,早期生命与环境研究专业。E-mail: 1557233387@qq.com
  • 基金资助:
    国家自然科学基金项目(42172014);国家自然科学基金项目(41621003);国家自然科学基金项目(41890844);中国科学院先导专项项目(XDB26000000);国家重点研发项目(2017YFC0603101)

Fossil assemblages and their stratigraphic distribution in the Shuijingtuo Formation (Cambrian Series 2, Stage 3) in Yichang area, Hubei Province, China

PAN Xiaoqiang(), HUA Hong*(), DAI Qiaokun, LUO Jinzhou, LIU Ziwei   

  1. Shaanxi Key Laboratory of Early Life and Environments/State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China
  • Received:2022-04-06 Revised:2022-04-30 Online:2023-05-25 Published:2023-04-27

摘要:

近年来随着“鄂宜页1井”高产气井的突破,寒武系水井沱组(第2统第3阶)已成为中扬子区页岩气勘查开发新的主力层系。本文旨在前人研究的基础上,通过对水井沱组中主要生物类型、古生物组合面貌及其时空分布的简要总结,为鄂西地区的页岩气勘探提供对比借鉴。宜昌地区寒武纪地层发育完整,广泛出露于宜昌、秭归、长阳、兴山等地,古生物化石较为丰富,是开展寒武纪地层及古生物研究的经典地区之一。埃迪卡拉纪—寒武纪过渡时期的地质记录中保存了寒武纪大爆发和后生动物多样化事件的化石证据,从寒武系纽芬兰统到第二统,自下而上发现了岩家河生物群、水井沱生物群(包括清江生物群)、石牌生物群和京山布尔吉斯页岩型生物群等,它们化石类群多样,浮游生物和底栖生物丰富,而在长阳发现的清江生物群更是具有典型布尔吉斯页岩型动物群特异埋藏化石库的特点,出现了大量高保真度的软躯体类群,代表了远离海岸的较深水环境,为寒武纪大爆发研究打开了一个新的窗口。从岩性、生物类型以及构造运动来看,宜昌地区水井沱组发育一套以黑色页岩或钙质页岩夹碳质灰岩为主的黑色岩系,其中海绵化石在黑色岩系中呈现出较高的丰度和多样性,显示当时深水低氧的沉积环境。同时繁盛的微体生物表明当时海洋具备较高的初级生产力,为有机质的埋藏富集以及页岩气的形成奠定了良好的物质基础;加上黄陵背斜刚性基底的影响,并未引起储层变形和破坏。因此,宜昌地区水井沱组黑色岩系具有很高的勘探开发潜力。

关键词: 宜昌地区, 寒武系第二统第三阶, 水井沱组, 生物组合面貌

Abstract:

In recent years, with the breakthrough of well Eyiye 1, the Cambrian Shuijingtuo Formation (Series 2, Stage 3) has become a new target for shale gas exploration and development in the Middle Yangtze area. Based on previous studies, this paper presents a brief summary of the main fossil types and palaeobiological assemblages and their temporospatial distribution in the Shuijingtuo Formation to provide a reference for shale gas exploration in western Hubei. Well-preserved fossil assemblages occur abundantly in the Early Cambrian sedimentary succession in the Yichang, Zigui, Changyang and Xingshan areas, which provides an excellent geological record of the Cambrian explosion, with rapid metazoan diversification events spanning the Ediacaran-Cambrian transition, making this region an ideal place for studying Cambrian strata and paleontology. Many fossil Lagerstätten, namely the Yanjiahe biota, Shuijingtuo biota (including the Qingjiang biota), Shipai biota and Jingshan Burgess Shale-type biota, were recovered from the bottom part of the Cambrian Terreneuvian upward to Series 2. Among them, the Shuijingtuo biota is comparable with the Niutitang fauna in Guizhou and the Xihaoping biota in southern Shaanxi, and represented by fossils of more than 10 phyla, such as trilobites, radiolarians, brachiopods, bradoriids, hyoliths, archaeocyatha, monoplacophora, lobopodium, protoconodonts, sponges, gastropods, chancelloriids and possibly cnidarians, as well as some unidentified taxa and microflora. Whilst the Qingjiang biota found in Changyang is of typical Burgess Shale-type fossil Lagerstätten and distinguished by soft-bodied taxa, which opens up a new window on the Cambrian explosion in the deep water habitat far away from the coast. The Cambrian Shuijingtuo Formation in the Yichang area developed a black rock system with distinct lithology, palaeobiological assemblages and tectonic movement, which is dominated by black shale or calcareous shale mixed with carbon limestone and contains high abundance of diverse sponge fossils, indicating a deep-water, low-oxygen sedimentary environment at that time. Meanwhile, the flourishing of microbial organisms indicates the ocean at that time possessed high primary productivity that laid a good material foundation for the burial and enrichment of organic matter and formation of shale gas; and the hydrocarbon reservoir did not experience deformation and destruction owing to the Huangling anticline rigid substrate. Therefore, the black rock system of the Shuijingtuo Formation in the Yichang area has high exploration and development potential for shale gas.

Key words: Yichang area, Cambrian Series 2, Stage 3, Shuijingtuo Formation, fossil assemblages

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