鄂西咸丰地区五峰组—龙马溪组火山凝灰岩发育特征及其对页岩有机质富集的影响^*

Development characteristics of volcanic tuff of the Wufeng-Longmaxi Formations in Xianfeng area of western Hubei and its influence on enrichment of organic matter in shale

摘要

鄂西咸丰地区五峰组—龙马溪组富有机质泥页岩中含多层火山凝灰岩,但前人对火山活动与海相页岩有机质富集的内在关联缺乏系统的研究。依托咸丰地区鄂咸页1井岩心及露头资料对五峰组—龙马溪组富有机质泥页岩及火山凝灰岩系统采样,开展岩矿鉴定、微量元素、稀土元素及有机碳含量(TOC)测试,阐明了五峰组—龙马溪组火山凝灰岩分布特征、源岩成分、构造背景及成因机制,探讨了该沉积时期火山活动及其对页岩有机质富集的影响。结果表明,五峰组—龙马溪组可分为火山凝灰岩密集段、次密集段和不发育段,火山凝灰岩原始岩浆性质以中性安山岩为主,火山灰来源于扬子北缘与古秦岭洋的碰撞闭合形成岛弧的火山喷发事件。火山灰是晚奥陶世—早志留世陆源碎屑补给不足的中扬子滞留海盆重要的物质来源,一方面为海洋微生物生长提供了丰富的营养元素,提高了海洋古生产力;另一方面火山作用促使海洋形成缺氧环境,利于有机质的埋藏与保存。研究成果可为鄂西地区五峰组—龙马溪组页岩气进一步勘探提供基础地质资料。

Abstract

The organic-rich shale of Wufeng Formation and Longmaxi Formation in Xianfeng area of western Hubei Province contains multilayer volcanic tuff,but the internal relationship between volcanic activity and organic matter enrichment in marine shels has not been systematically studied. Based on the core and outcrop data of Well XY 1 in Xianfeng area,the organic-rich mud shale and volcanic tuff of Wufeng-Longmaxi Formations were systematically sampled,rock and ore identification,trace element,rare earth element and organic carbon content(TOC)tests were carried out,and the distribution characteristics,source rock composition,tectonic setting and genetic mechanism of volcanic tuff of Wufeng-Longmaxi Formations were expounded. The volcanic activity in this sedimentary period and its influence on the enrichment of organic matter in shale are discussed. The results show that the Wufeng-Longmaxi Formations can be divided into dense,sub-dense and undeveloped tuff segments. The primary magmatic properties of the tuff were mainly neutral andesite,and the volcanic ash originates from the volcanic eruption event of the island arc formed by the collision between the northern margin of the Yangtze and the ancient Qinling Ocean. Volcanic ash was an important material source in the Middle Yangtze Retention Basin where terrigenous detritus supply was insufficient in Late Ordovician and Early Silurian. On one hand,volcanic ash provided abundant nutrients for the growth of marine microorganisms and improved the marine palaeoproductivity. On the other hand,volcanism promoted the formation of anoxic environment in the ocean,which was conducive to the burial and preservation of organic matter. The results can provide basic geological data for further exploration of shale gas in the Wufeng-Longmaxi Formations in western Hubei Province.

关键词

鄂西地区 / 五峰组—龙马溪组 / 火山凝灰岩 / 物源 / 有机质富集

Key words

western Hubei Province / Wufeng-Longmaxi Formations / volcanic tuff / provenance / organic matter enrichment

基金资助

*湖北省地质局“鄂西地区中浅层页岩气资源潜力调查评价”项目(编号: KCDZ2024-34)和古生物与地质环境演化湖北省重点实验室开放研究基金项目(编号: PEL-202005)联合资助