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川南地区五峰组—龙马溪组沉积环境演化及其对页岩发育的控制
韩豫1,2,操应长1,2,梁超1,2,吴伟3,朱逸青3,武瑾4,赵梓龙2,唐晴2
(1.中国石油大学(华东)深层油气重点实验室,山东青岛 266580;2.中国石油大学(华东)地球科学与技术学院,山东青岛 266580;3.中国石油西南油气田公司页岩气研究院,四川成都 610051;4.中国石油勘探开发研究院,北京 100083)
摘要:
基于岩心观察、薄片观察、电镜观察、XRF元素扫描以及全岩X-衍射、ICP-MS元素分析、总有机碳含量测试等手段,对川南地区五峰组—龙马溪组页岩岩相类型及其沉积环境演化进行分析,并探讨沉积环境高频演化对岩相的控制作用。将川南地区五峰组—龙马溪组页岩划分为富有机质层状生物硅质页岩、富有机质纹层状(长英质-钙质)粉砂页岩、富有机质(钙质)粉砂页岩、富有机质纹层状钙质页岩、中有机质纹层状(长英质-钙质)粉砂页岩、中有机质块状黏土质页岩6种岩相类型。在岩相识别基础上借助特征元素比值Sr/Ba、U/Th、V/Cr、V/Ni、Ni/Co、Sr/Cu及Mo、Cu、Sr含量变化进行古沉积环境恢复,划分出7个演化阶段。结果表明:五峰组沉积早期气候温暖潮湿、水体较为氧化、盐度较低;五峰组沉积中期水体还原性增强、古生产力提高;五峰组晚期气候干冷,水体较为氧化,经历了赫南特冰期;龙马溪组自下而上古气候经历了暖湿—相对干热—暖湿—相对干热的演化,同时古水体也经历了还原—相对氧化—还原—相对氧化的演化。沉积环境高频演化对页岩岩相发育以及有机质富集具有明显的控制作用,不同岩相有机质含量与海洋古生产力和水体还原性均呈现良好的正相关性,其中在古生产力较高、水体还原性较强的阶段沉积的富有机质层状生物硅质页岩和富有机质纹层状(长英质-钙质)粉砂页岩有机质最为富集,且石英含量最高,是页岩气勘探开发的优势岩相。
关键词:  页岩岩相  纹层  沉积环境演化  有机质富集  五峰组—龙马溪组
DOI:10.3969/j.issn.1673-5005.2024.02.002
分类号::P 586
文献标识码:A
基金项目:国家自然科学基金项目(42172165,41902134);中央高校基本科研业务费专项(22CX06001A);泰山学者计划(TSQN201812030)
Sedimentary environment evolution of Wufeng Formation-Longmaxi Formation and its control on shale deposition in the southern Sichuan Basin
HAN Yu1,2, CAO Yingchang1,2, LIANG Chao1,2, WU Wei3, ZHU Yiqing3, WU Jin4, ZHAO Zilong2, TANG Qing2
(1.Key Laboratory of Deep Oil and Gas in China University of Petroleum(East China), Qingdao 266580, China;2.School of Geosciences in China University of Petroleum(East China), Qingdao 266580, China;3.Shale Gas Research Institute, PetroChina Southwest Oil & Gasfield Company, Chengdu 610051, China;4.PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China)
Abstract:
Based on core observation, thin section analysis, electron microscope examination, XRF scanning, whole rock X-ray diffraction, ICP-MS analysis, and total organic carbon content measurement, we analyzed the shale facies types and sedimentary environment evolution of Wufeng-Longmaxi Formation in southern Sichuan area, and discussed the controlling effect of high-frequency sedimentary environment evolution on lithofacies. The Wufeng-Longmaxi shale in southern Sichuan area can be divided into six lithofacies types:organic-rich layered biosiliceous shale, organic-rich laminated (felsic-calcareous) silty shale, organic-rich (calcareous) silty shale, organic-rich laminated calcareous shale, medium-organic laminated (felsic-calcareous) silty shale, and medium-organic massive mudstone. The paleo-sedimentary environment is reconstructed utilizing characteristic element ratios Sr/Ba, U/Th, V/Cr, V/Ni, Ni/Co, Sr/Cu, as well as the content of Mo, Cu, Sr, and seven evolutionary stages are delineated:the lower Wufeng Formation deposited under warm,humid conditions, with relatively oxidized,low salinity water; the upper Wufeng Formation witnessed increased water reduction and enhanced paleoproductivity. The top of the Wufeng Formation experienced mass extinction during the Hirnantian glaciation, characterizedby arid and cold paleoclimate. From bottom to top, the paleoclimates of Longmaxi Formation experienced the evolution of "warm/wet"-"relatively arid/hot"-"warm/wet"-"relatively arid/hot" and the ancient water body also experienced the evolution from reduction to relative oxidation. The sedimentary environment significantly influences shale lithofacies and organic matter enrichment. The content of organic matter in different lithofacies is positively correlated with marine paleoproductivity and water reducibility. Organic-rich layered biosiliceous shale and organic-rich laminated (felsic-calcareous) silty shale, deposited during stages of high paleoproductivity and strong water reduction, display abundant organic matter and high quartz content, making them favorable targets for shale gas exploration and development. This study provides a theoretical foundation for further exploration and development of shale gas and the investigation of fine-grained sedimentary rocks.
Key words:  shale lithofacies  laminae  sedimentary environment evolution  organic matter accumulation  Wufeng Formation-Longmaxi Formation 中国石油大学学报(自然科学版) 2024年4月第48卷 第2期 韩 豫,等:川南地区五峰组—龙马溪组沉积环境演化及其对页岩发育的控制
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