中-晚始新世东亚季风气候对渤海湾盆地济阳坳陷富有机质页岩发育的控制作用

The organic-rich shale in the upper fourth Member (Es4U) and lower third Member (Es3L) of the Eocene Shahejie Formation in Jiyang Depression in eastern China has become an important section of the exploration and development of lacustrine shale oil in eastern China. Many drill cores in Jiyang depression show that the organic-rich shale of the Es4U and Es3L is generally developed seasonal laminae, which has provide an ideal research vehicle for exploring the evolution of the East Asian monsoonal climate during this period. Extraction of East Asian monsoonal climate intensity from the shale deposition records, and identify the characteristics of the seasonal cycles, which is the key factor to further reveal the development mechanism of the organic-rich shale that controlled by East Asian monsoonal climate. In this project, the organic-rich shale from the Es4U and Es3L in Jiyang Depression was used as the research object. The macroscopic observation of the core and the microscopic analysis of the thin section and cathodoluminescence combining with qualitatively analysis of the mineral content and quantitatively analysis of isotope and elemental geochemistry, evolution characteristics of East Asian monsoonal climate intensity has been elucidated; coupling relationships between the East Asian monsoonal climate intensity, different laminae types and lithofacies have been clarified as well as the genetic mechanism of different shale lithofacies. Associating with different depositional processes of seasonal laminae in different shale lithofacies, cycle characteristics of the East Asian monsoon climate corresponding to different shalelithofacies depositions were elucidated, and a control model of East Asian monsoonal climate for the development mechanism of organic-rich shales in the Jiyang Depression was established, which in order to provide a certain scientific evidence and theoretical guidance for shale oil exploration.

济阳坳陷始新世沙四上-沙三下亚段富有机质页岩，是我国东部湖相页岩油勘探开发的重要层段。坳陷内多口页岩油钻井的连续取心，揭示该套页岩普遍发育了季节性纹层，为探索该时期东亚季风气候的演化提供了理想的研究载体。提取该套页岩记录中的东亚季风气候强度，查明其季节周期特征，是进一步揭示东亚季风气候控制富有机质页岩发育的关键。本项目以济阳坳陷沙四上-沙三下亚段富有机质页岩为研究对象，采用岩心宏观观察与薄片、阴极发光等微观分析相结合，矿物含量半定量分析与同位素和元素定量分析相结合的方法。在阐明东亚季风气候强度演化规律的基础上，确立季风气候强度、页岩纹层结构类型及页岩岩相类型三者之间的耦合关系，追溯不同页岩岩相的成因机制，并查明不同页岩岩相对应的东亚季风气候的周期特征。最终建立东亚季风气候对济阳坳陷富有机质页岩发育的控制模型，为该套页岩层系的页岩油勘探开发提供重要的理论基础。

中-晚始新世，渤海湾盆地广泛发育了一套具有季节性纹层的富有机质页岩，为该时期中国东部受东亚季风气候影响提供了直观的证据。东亚季风气候不仅可以促进水文循环，产生明显的季节性降雨，而且对湖相富有机质页岩的发育过程具有重要控制作用。通过对渤海湾盆地济阳坳陷中-上始新统沙四上-沙三下亚段富有机质页岩开展系统的岩石矿物学、沉积学以及地球化学分析，取得了以下认识：提出了碳酸盐（白云石含量小于10%）的氧同位素值对季风气候变化的指示意义，即碳酸盐的氧同位素值随东亚季风强度的增强而减小，随东亚季风强度的减弱而增大；阐明了中-晚始新世东亚季风气候的演化规律及其季节周期特征，认为印度-太平洋暖池（IPWP）的区域性增强，影响了东亚季风气候的稳定性，造成了湖水强烈蒸发，引起周期性的湖水高盐度，导致在沙四上亚段下部和沙四段与沙三段交界处形成了两期干旱事件；建立了东亚季风气候对富有机质页岩发育的控制模型，受东亚季风气候周期性变化的影响，湖盆经历了6个演化阶段（欠补偿型浅盐湖→补偿型浅湖→欠补偿型半深湖-深湖→欠补偿-补偿型半深湖-深湖→补偿型半深湖-深湖→欠补偿型浅湖-半深湖），在此过程中引起氧化还原交替、藻类间歇勃发、陆源间歇供给，进而控制了富有机质页岩岩相类型及成因模式；揭示了不同的湖盆演化阶段富有机质页岩中有机质的差异富集机理，在半深湖-深湖发育阶段，有机质的富集主要受控于氧化还原条件和古生产力，在浅湖发育阶段，有机质的富集主要受湖水的氧化还原条件控制。此外，过量输入的陆源碎屑（石英和粘土矿物总量>22%）对有机质具有明显的稀释作用，而适量的陆源碎屑供给（石英和粘土矿物总量<22%）对有机质的富集具有一定的促进作用。本项目为探究含油页岩非均质性的本质提供了重要的理论基础。