摘要：

苏北盆地高邮—金湖凹陷古近系阜宁组二段(阜二段)不仅是主力烃源岩层,而且发育成分复杂的细粒混积岩,现已成为陆相湖盆非常规油气勘探重点层段。细粒混积岩沉积环境研究对于其形成过程、岩相特征及甜点区段预测均有重要作用。基于全岩X衍射、黏土X衍射、微量元素和TOC分析成果恢复确认阜二段整体处于非硫化缺氧水体环境; 5个特殊岩性层段依次表现为:“山字形层段”沉积时期气候整体干旱,“四尖峰—七尖峰层段”沉积时期气候变得相对湿润,“王八盖层段”沉积时期气候相对湿润且稳定,“泥脖子层段”沉积时期气候较其他层段明显湿润; “山字形至王八盖层段”沉积时期湖平面整体较低、波动强烈、逐渐上升,“泥脖子层段”沉积时期发生了大规模湖侵; 阜二段水体咸化,古盐度均大于10‰,垂向可分2段: “山字形—四尖峰层段”形成于咸水至超咸水环境,“七尖峰—王八盖—泥脖子层段”形成于半咸水至咸水环境。受古气候控制的半咸水环境是形成细粒混积岩的基本环境要素,进而建立了早期偏干旱和晚期偏湿润气候的混积模式。

关键词: 细粒混积岩, 沉积环境, 混合沉积模式, 阜宁组二段, 古近系, 高邮—金湖凹陷

Abstract:

The Member 2 of the Paleogene Funing Formation in the Gaoyou and Jinhu sags of the Subei Basin is not only the primary hydrocarbon source rocks, but also develops complex fine-grained mixed rocks. It has now become a key target for unconventional oil-gas exploration in continental lacustrine basins. Research on sedimentary environments of these facies plays a crucial role in both understanding their depositional processes and lithofacies characteristics,and predicting sweet spot intervals. Based on integrated analyses including whole-rock X-ray diffraction(XRD)analysis,X-ray clay mineral diffraction analysis,trace element geochemistry,and total organic carbon(TOC)content,this study reveals that the Member 2 of the Funing Formation was deposited in a non-sulfidic,anoxic water environment. The climate was generally arid and unstable during deposition of the “Shanzixing Unit”. The “Four-Seven Peaks Units” depositional period witnessed a more humid and still unstable climate. The climate during deposition of the “Wangbagai Unit” exhibited relative humidity and stability. In contrast,the “Nibozi Unit” depositional period experienced significantly more humid climatic conditions compared to other units. During the deposition of the “Shanzixing-Wangbagai units”,the lake level remained generally low but gradually rising with strong fluctuations. The “Nibozi Unit” depositional period experienced a major lacustrine transgression event. The Member 2 of the Funing Formation was deposited under saline water,with palaeosalinity consistently exceeding 10‰,which can be vertically subdivided into two intervals: the “Shanzixing-Four Peaks Units” formed in saline to hypersaline environments,and the “Seven Peaks-Wangbagai-Nibozi Units” developed in brackish to saline environments. This study proposes that the brackish water environment controlled by palaeoclimate constitutes the fundamental prerequisite for fine-grained mixed facies,thereby establishing mixed sedimentary models dominated by arid conditions in the early stage and humid conditions in the late stage.

Key words: fine mixed rocks, sedimentary environment, mixed sedimentation model, Member 2 of Funing Formation, Paleogene, Gaoyou and Jinhu sags

中图分类号: 

• P588.2