川北—鄂西上二叠统富有机岩沉积与地球化学特征【碳酸盐岩与富有机岩形成环境专辑】
- 收稿日期:
2023-06-17
- 网络出版日期:
2023-10-08
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】本文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的研究,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至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三角图均指示热液活动频繁出现。【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到较高初级生产力的控制。这些营养物质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。
Sedimentological and geochemical characteristics of organic-rich rocks in the Upper Permian in North Sichuan and West Hubei provinces
- Received Date:
2023-06-17
- Available Online:
2023-10-08
Abstract: [Objective] As the development of non-conventional petroleum theories, the organic matter accumulation mechanism has been becoming the hotspot. One of the most debated issues is the main controlling factors of organic matter enrichment. Previous studies were lack of the depositional process analyses, which is likely the reasons of the debate. [Methods] This study combines the sedimentological and geochemical methods to conduct detailed sequence stratigraphy, facies and elemental analyses, aiming to address the sedimentary organic matter accumulation mechanism. [Results] The Upper Permian Wuchiaping and Dalong formations in the northern Sichuan Basin and the West Hubei Basin are subdivided into First Wuchiaping Member, Second Wuchiaping Member, Third Wuchiaping Member, First Dalong Member and Second Dalong Member in an ascending order. The Upper Permian is subdivided into 5 third-order stratigraphy sequences SQ1 to SQ5. Based on the sequence stratigraphy analysis, the development history of the rifting basin in northern Sichuan Basin and the West Hubei Basin is subdivided into four stages: initial stage, rapid rifting, rifting climax, and shrinking stage. The initial stage mainly occurred during the deposition of SQ2, and consists of dark cherty limestones of slope facies. The rapid rifting stage mainly occurred during the SQ3, and consists of calcareous shales of deepwater shelf facies. The rifting climax stage mainly occurred during the SQ4, and consists of black bedded cherts of basin facies. The shrinking stage mainly occurred during the SQ5, and consists of medium-thin-bedded limestones. The sweet-spot interval develops mainly from the highstand system tract (HST) of SQ3 to the transgressive system tract (TST) of SQ5, during which the nutrient elements Fe, Cu, Ni, Zn, and redox-sensitive element 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. [Conclusion] The development of high primary productivity is earlier than the strong reducing conditions during the deposition of the sweet-spot interval, suggesting that the reducing conditions in the bottom water resulted from the high consuming of oxygen during the organic matter decomposition, and that the organic matter enrichment was mainly controlled by primary productivity. The nutrient material input was related to the hydrothermal activity and volcanism during the formation of rifting basins. The tectonic activity brought episodically a lot of nutrient elements to the rifting sea, enhancing the primary productivity level. Thus, the primary productivity level is the onset and basic conditions for the extraordinarily high organic matter accumulation in the sweet-spot interval, and the strong reducing conditions in bottom water was the key factor for organic matter preservation and burial.
韦恒叶, 胡谍, 邱振, 张璇, 刘雯, 孔维亮, Ahmed Mansour. 川北—鄂西上二叠统富有机岩沉积与地球化学特征【碳酸盐岩与富有机岩形成环境专辑】[J]. 沉积学报. doi: 10.14027/j.issn.1000-0550.2023.086
Sedimentological and geochemical characteristics of organic-rich rocks in the Upper Permian in North Sichuan and West Hubei provinces[J]. Acta Sedimentologica Sinica. doi: 10.14027/j.issn.1000-0550.2023.086
Citation: |
Sedimentological and geochemical characteristics of organic-rich rocks in the Upper Permian in North Sichuan and West Hubei provinces[J]. Acta Sedimentologica Sinica. doi: 10.14027/j.issn.1000-0550.2023.086
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