地学前缘 ›› 2023, Vol. 30 ›› Issue (6): 181-198.DOI: 10.13745/j.esf.sf.2023.2.11

• 深层-超深层海相层系烃源岩发育、生烃演化和油气地球化学特征及示踪 • 上一篇    下一篇

鄂西-黔东北地区早寒武世有机质富集机理对比研究

张力钰1,2(), 陈强路1,2, 黎茂稳2,3, 袁坤1,2, 马晓潇3, 席斌斌1,2, 岳勇4, 黄泰誉5   

  1. 1.中国石化石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126
    2.中国石化油气成藏重点实验室, 江苏 无锡 214126
    3.中国石化石油勘探开发研究院, 北京 102206
    4.中国地质调查局 武汉地质调查中心, 湖北 武汉 430223
    5.中国煤炭地质总局 勘查研究总院, 北京 100039
  • 收稿日期:2023-01-04 修回日期:2023-02-05 出版日期:2023-11-25 发布日期:2023-11-25
  • 作者简介:张力钰(1992—),女,博士,助理研究员,矿物学、岩石学、矿床学专业,主要研究方向为沉积学和沉积地球化学。E-mail: zhangliyu.syky@sinopec.com
  • 基金资助:
    国家自然科学基金企业创新发展联合基金项目“海相深层油气富集机理与关键工程技术基础研究(U19B6003);中国石油化工集团公司科技部项目“海相深层高温高压条件下烃类转化与保持机制(P19032)

Comparative study on the organic enrichment mechanisms between western Hubei and northeastern Guizhou during the Early Cambrian

ZHANG Liyu1,2(), CHEN Qianglu1,2, LI Maowen2,3, YUAN Kun1,2, MA Xiaoxiao3, XI Binbin1,2, YUE Yong4, HUANG Taiyu5   

  1. 1. Wuxi Research Institute of Petroleum Geology, Petroleum Exploration and Production Research Institute, SINOPEC, Wuxi 214126, China
    2. Key Laboratory of Petroleum Accumulation Mechanisms, SINOPEC, Wuxi 214126, China
    3. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 102206, China
    4. Wuhan Center of China Geological Survey, Wuhan 430223, China
    5. General Prospecting Institute, China National Administration of Coal Geology, Beijing 100039, China
  • Received:2023-01-04 Revised:2023-02-05 Online:2023-11-25 Published:2023-11-25

摘要:

寒武纪早期地球环境和生物面貌发生了巨大变化,中上扬子广泛发育的富有机质沉积是重要的烃源岩。了解这套烃源岩的形成与古地理背景、古气候和古海洋之间的耦合关系,明确不同沉积环境有机质富集机理的差异有助于我们认识环境与资源的内在联系,为资源潜力分析提供地质依据。本研究以鄂西-黔东北地区早寒武世沉积剖面为研究对象,通过岩石学、有机地球化学(岩石热解、干酪根碳同位素和总有机碳)和无机地球化学(主量、微量元素和全岩矿物X衍射)方法,识别了烃源岩特征,对比分析了内陆架盆地(或台盆相)和斜坡相有机质富集的主控因素。结果显示,研究区早寒武世有机质已高过成熟,干酪根类型以Ⅰ型为主。内陆架盆地/台盆相的鸭子口剖面Al含量,Ba、Cu、Zn和Ni等营养元素含量,以及黏土含量在有机质富集段无明显变化;Mo、U和V等氧化还原敏感元素和TOC含量在水井沱组下段较高,向上逐渐减小;Th/U值和V/(V+Ni)值分别均小于2和大于0.54,指示水井沱组下段持续缺氧。斜坡相ZK513井Al含量和黏土含量在有机质富集段无明显变化;Ba、Cu、Zn和Ni等营养元素,Mo、U和V等氧化还原敏感元素以及TOC含量的变化趋势耦合,在牛蹄塘组、九门冲组上段分别有明显和略微增大,表明初级生产力增大和水体缺氧硫化。Th/U值和V/(V+Ni)值显示牛蹄塘组缺氧硫化,九门冲组上段整体缺氧。结合古地理背景以及前人的研究认识,认为斜坡相的ZK513井有机质富集的主控因素是较高的生产力和有利保存条件,即上升洋流带来的营养元素促进了初级生产力,形成大量有机质并引发后续的细菌硫酸盐还原作用(BSR)和海水缺氧硫化;内陆架盆地/台盆相的鸭子口剖面初级生产力未明显增强,有机质富集主要受保存条件控制。

关键词: 早寒武世, 鄂西-黔东北地区, 有机质富集, 上升洋流, 缺氧硫化

Abstract:

Early Cambrian petroleum source rocks are widely distributed in the middle and upper Yangtze region. Understanding the coupling relationship between source-rock deposition and paleogeography/paleoclimate/paleo-ocean and the mechanistic differences in organic enrichment under different depositional environments is critical for understanding the intrinsic relationship between environment and resources, so as to provide a geological basis for resource potential analysis. In this study, Early Cambrian source rocks from outcrops in western Hubei and wells in northeastern Guizhou are characterized to reveal the main controlling factors of organic accumulation in intrashelf/interplatform basins and slope facies, using petrological, organic geochemical (rock pyrolysis, kerogen carbon isotope, total organic carbon) and inorganic geochemical (whole-rock major and trace elements, X-ray diffraction) methods. The Early Cambrian source rocks in the study area are mainly composed of type I kerogen. Along the Yazikou basin cross-section the Al contents, nutrient elements (Ba, Cu, Zn, Ni) and clay contents remain nearly constant in the organic rich interval. The redox sensitive elements (Mo, U, V) and TOC are higher in the lower Lower Cambrian Shuijingtuo Formation and show an upward decreasing trend. The Th/U (< 2) and V/(V+Ni) (> 0.54) ratio data suggest continuous anoxia in the lower Shuijingtuo Formation. In contrast, in well ZK513 slope facies, there is no obvious increase of Al and clay contents in the organic rich interval but co-variation and slight increase of nutrient elements, redox-sensitive elements and TOC in the Lower Cambrian Niutitang Formation and upper Lower Cambrian Jiumenchong Formation, indicating an increase of primary productivity and marine euxinia; such euxinic condition is further conform by the Th/U and V/(V+Ni) ratio data. Based on the paleogeographic features and previous researches, we propose that the main controlling factors of organic enrichment in well ZK513 (slope facies) are high productivity and favorable preservation conditions, where high nutrient elements brought by upwelling promote the primary productivity and lead to organic accumulation and subsequent bacterial sulfate reduction (BSR) and seawater uxinia. Whereas in the Yazikou section of the intrashelf/interplatform basins with no significant primary productivity enhancement, organic enrichment is mainly controlled by the preservation conditions.

Key words: the early Cambrian, western Hubei-Northeastern Guizhou area, organic matter enrichment, upwelling, uxinia

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