川北—鄂西上二叠统富有机岩沉积与地球化学特征  

Sedimentological and Geochemical Characteristics of Late Permian Organic-Rich Rocks in North Sichuan and West Hubei Provinces

作　　者：韦恒叶 胡谍 邱振[3] 张璇 刘雯[3] 孔维亮 Mansour Ahmed WEI HengYe;HU Die;QIU Zhen;ZHANG Xuan;LIU Wen;KONG WeiLiang;Mansour Ahmed(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;Qiangtang Institute of Sedimentary Basin,Southwest Petroleum University,Chengdu 610500,China;PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China)

机构地区：[1]西南石油大学地球科学与技术学院,成都610500 [2]西南石油大学羌塘盆地研究院,成都610500 [3]中国石油天然气股份有限公司勘探开发研究院,北京100083

出　　处：《沉积学报》2024年第3期774-798,I0001,共26页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(42272118);四川省自然科学基金项目(2023NSFSC0279)。

摘　　要：【目的】随着非常规油气理论的发展,沉积有机质富集机理再次成为热点研究,其中有机质富集主控因素成为争论的焦点。以往的研究对沉积过程的分析较少,这可能是存在争论的原因之一。【方法】结合沉积学与地球化学研究方法,在分析层序地层学和沉积环境的基础上,详细开展元素地球化学研究,讨论富有机岩沉积有机质富集机理。【结果】四川盆地北部和鄂西盆地上二叠统吴家坪组自下而上分为吴一段、吴二段和吴三段,大隆组自下而上分为大一段和大二段。吴家坪组至大隆组自下而上总共分为五个三级层序SQ1~SQ5。由层序地层学分析将广利海槽和鄂西海槽的发展分为四个阶段,分别为初始、快速发展、高潮稳定和萎缩阶段。初始阶段主要发育SQ2时期斜坡相暗色硅质灰岩,快速发展阶段主要发育SQ3时期陆棚相钙质页岩,高潮稳定阶段主要发育SQ4时期盆地相黑色硅质岩,萎缩阶段主要发育SQ5时期斜坡相石灰岩。含异常高有机质的甜点段主要形成于SQ3高位域至SQ5海侵域沉积期,在该时期Fe、Cu、Ni和Zn营养元素周期性富集,Mo、V、Fe/Al和S等氧化还原敏感元素均表现为较高的水平,热液强度参数Al/(Al+Fe+Mn)和Al-Fe-Mn三角图均指示频繁的热液活动特征。【结论】在甜点段,高营养元素含量和初级生产力水平的出现早于强还原条件,说明沉积水体的氧化还原条件主要受控于沉积有机质沉降埋藏过程中对氧的消耗,有机质的富集主要受较高初级生产力的控制。营养物质P、Si、Fe、Zn的供应主要与裂陷槽形成过程中深部热液活动和周围火山活动有关,这些构造活动周期性带来大量营养物质提高了初级生产力水平。因此海洋表层高的初级生产力水平是甜点段异常高有机质富集的启动和基础条件,而海洋底部水体较强的还原环境是有机质埋藏和保存的关键因素。[Objective]The current focus of non-conventional petroleum theories is the accumulation mechanism of organic matter.One of the most commonly debated issues regards the main influences on organic matter enrichment previous studies lack analysis of the depositional process,which is the likely reason for the debate.[Methods]This study combines sedimentological and geochemical methods to conduct detailed sequence stratigraphy,and facies and elemental analyses,aiming to address the accumulation mechanism of sedimentary organic matter.[Results]The Late Permian Wuchiaping Formation and Dalong Formation in the northern Sichuan Basin and the West Hubei Basin are subdivided in ascending order into the First,Second and Third members of the Wuchiaping Formation,and the First and Second members of the Dalong Formation.The Late Permian is subdivided into five third-order stratigraphy sequences,SQ1 to SQ5.Analysis of the sequence stratigraphy revealed the four-stage developmental history of the rift basin in the northern Sichuan Basin and the West Hubei Basin:the initial stage followed by rapid rifting,rifting climax and a shrinking stage.The initial stage mainly coincided with the deposition of SQ2,and consists of dark cherty limestones of slope facies.The rapid rifting stage mainly occurred during SQ3,and comprises calcareous shales of deepwater shelf facies.The rifting climax stage mainly took place during SQ4,consisting of black bedded cherts of basin facies.The shrinking stage mainly occurred during SQ5,and consists of medium-or thin-bedded limestones.The sweet-spot interval developed mainly between the highstand system tract(HST)of SQ3 and the transgressive system tract(TST)of SQ5,during which the nutrient elements Fe,Cu,Ni,Zn and redox-sensitive elements Mo,V,Fe/Al and S were highly enriched.This sweet-spot interval is also associated with highly active hydrothermal activity indicated by Al/(Al+Fe+Mn)ratios<0.6 and the Al-Fe-Mn diagram.[Conclusions]The development of high primary productivity occurred prior to the strong

关 键 词：富有机岩 甜点段 吴家坪组 大隆组 层序地层 元素地球化学 四川盆地 鄂西盆地 

分 类 号：P512.2[天文地球—地质学]