鄂西宜昌地区寒武系水井沱组页岩生物成因硅特征及其对页岩气富集的影响  

Biogenic silica of the Lower Cambrian Shuijingtuo Formation in Yichang,western Hubei Province-features and influence on shale gas accumulation

作　　者：张瑜[1] 黄德将 张六六 万传辉 罗欢 邵德勇 孟康 闫建萍 张同伟 ZHANG Yu;HUANG Dejiang;ZHANG Liuliu;WAN Chuanhui;LUO Huan;SHAO Deyong;MENG Kang;YAN Jianping;ZHANG Tongwei(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China;Hubei/Central South Institute of Metallurgical Geology,Yichang 443003,China;School of Earth Sciences,Lanzhou University,Lanzhou 730000,China;Eighth Geological Brigade of Hubei Gelolgical Bureau,Xiangyang 441000,China;Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin TX 78713,USA)

机构地区：[1]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 [2]湖北冶金地质研究所(中南冶金地质研究所),湖北宜昌443003 [3]兰州大学地质科学与矿产资源学院,甘肃兰州730000 [4]湖北省地质局第八地质大队,湖北襄阳441000 [5]Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX 78713,USA

出　　处：《地学前缘》2023年第3期83-100,共18页Earth Science Frontiers

基　　金：国家自然科学基金重点项目(41730421)。

摘　　要：通过对鄂西宜昌地区寒武系岩家河组—水井沱组页岩进行高分辨率样品采集,利用总有机碳(TOC)含量、主量元素分析、氦孔隙度等定量分析和透反射光显微镜、阴极发光显微镜等定性分析相结合的方法,研究了水井沱组黑色岩系生物成因硅的纵向变化特征及其与页岩气富集的关系。结果表明:寒武系底部岩家河组和水井沱组上部贫有机质层段过剩硅含量低,未见明显生物碎屑痕迹,几乎不含或含少量自生成因石英,而水井沱组富有机质层段存在较多生物成因硅,具有明显的分段性(一段、二段)且硅质来源明显不同。富有机质层段底部(一段)过剩硅含量高,为4.44%~24.97%,平均值为16.76%,受钙质夹层的影响波动较大,生物成因硅占比高,受陆源碎屑影响小。生物碎屑类型主要为硅质海绵骨针,还有少量絮状硅质聚集体,骨针腔体和硅质聚集体粒间孔中可见有机质。而富有机质层段中上部(二段)过剩硅含量相对一段明显降低,为7.13%~20.47%,平均值为13.66%,受陆源碎屑影响更大。生物碎屑类型主要为放射虫、纺锤状硅质聚集体和海绵骨针,可见有机质与这些生物成因硅和陆源碎屑共生在一起。在整个富有机质层段,TOC含量与总硅含量无明显关系但与过剩硅呈明显正相关性,且镜下发现似藻类孢囊中块状有机质内杂乱分布大量微晶石英,早期成岩作用阶段形成的生物成因硅不仅因为与藻类等的共生关系确保了较高生产力,同时因其在适宜的沉积环境下自身较强的硬度形成支撑格架为有机质提供了赋存空间,揭示了宜昌地区水井沱组富有机质层段生物成因硅的发育有利于有机质的富集。一段TOC含量明显高于二段但孔隙度略低,这可能与生物成因硅在这两段的差异相对应,生物成因硅与陆源碎屑一定比例共生形成的刚性格架可能对孔隙的发育和保存起保护和支撑作用。宜昌地区�Shale samples from the lower Cambrian Yanjiahe-Shuijingtuo formations in Yichang,western Hubei were collected by high-resolution sampling method to investigate the vertical variation of biogenic silica and its significance for shale gas enrichment,by combining quantitative analyses of total organic carbon(TOC),major elements and helium porosity with qualitative microscopic observation using transmission and cathodoluminescence microscope.According to the results,the excess silicon content is low in the organic-poor Lower Cambrian Yanjiahe upper Shuijingtuo formations containing no visible trace of bioclastic debries and very little or barely no authigenic quartz.While the organic-rich layer of the Shuijingtuo formation has larger quantity of biogenic silicon and is divided into members 1 and 2 as the silicon sources are obviously different.The bottom part(member 1)has high excess silicon content ranging between 4.44%24.97%(average 16.76%),with significant fluctuation under the influence of calcareous intercalation;while biogenic silicon,mainly siliceous sponge spicules and a few flocculent siliceous aggregates,accounts for a high proportion with little influence from terrigenous clasts;and organic matter could be seen in the spicule cavity and interparticle pores of siliceous aggregates.In contrast,the middle-upper part(member 2),influenced by both biogenic silicon and terrigenous clasts,has significantly lower excess silicon content ranging between 7.13%20.47%(average 13.66%),with radiolarian,fusiform siliceous aggregates and sponge spicules as the main bioclastic types and mixed with organic matter.TOC is positively correlated with excess silicon in the organic-rich strata,and large numbers of fine granular chalcedony are observed under microscope in lumps of organic matter developed in an algal cyst-like structure,which reflects that the development of high hardness crystalline biogenic silicon,transformed from opal in the organic-rich layer is conducive to the enrichment of organic matter.Compared to member 2

关 键 词：鄂西地区 寒武系 页岩气 水井沱组 生物成因石英 孔隙 

分 类 号：P595[天文地球—地球化学] P588.22[天文地球—地质学]