火山活动期断陷湖盆富有机质混积页岩形成条件:以松辽盆地南部梨树断陷沙河子组富有机质页岩为例

中国地质调查局实施部署的JLYY-1井在松辽盆地南部沙河子组钻遇51 m的富有机质混积页岩.经过取心观察和室内综合分析发现，这套51 m厚的页岩具有以下特征:第一，混积（来自盆内和盆外的硅质、钙质无机矿物物源以及不同类型的有机物源混合沉积）；第二，页岩中夹多套薄层凝灰岩或凝灰质泥/页岩；第三，页岩的纹层和页理极为发育，现场岩心浸水实验观察到大量气泡顺页理面涌出.基于JLYY-1井的元素测井资料，结合地球化学测试、扫描电镜成像、光学显微成像和Roqscan矿物成分成像测试结果，将其归纳为火山活动期断陷湖盆的富有机质混积页岩形成模式，并得出其形成条件如下:（1）多种有机物源的输入提高了页岩中有机质的丰度，也使Ⅰ型、Ⅱ型和Ⅲ型干酪根均有发育；（2）火山活动后期营养元素迁移造成藻类勃发；（3）干热气候条件下封闭咸水环境的碳酸盐岩化作用促进有机质生烃；（4）水体氧化分层形成了该段页岩的4类纹层:硅质、黏土质、钙质和黄铁矿纹层. 

Hybrid Sedimentary Conditions of Organic-Rich Shales in Faulted Lacustrine Basin during Volcanic Eruption Episode:A Case Study of Shahezi Formation (K1sh Fm.), Lishu Faulted Depression,South Songliao Basin

JLYY-1 well was drilled to explore the continental shale gas resources by the China Geological Survey of the Shahezi Formation in the south of Songliao basin, where 51 m hybrid sedimentary shale layer contributed to a high-yield shale gas breakthrough. Through coring observation and indoor comprehensive analysis, it is found that this set of 51 m shale has the following characteristics. First, hybrid sedimentary(carbonate minerals and siliceous minerals account for a high proportion, followed by volcanic materials). Second, shale is intercalated with multiple sets of thin-layer tuff or tuffaceous mud/shale. Thirdly, a large number of bubbles gushing along the foliation surface were observed in the field core immersion experiment. Based on the element logging data of well JLYY-1, combined with the test results of scanning electron microscope imaging, optical microscopic imaging, and Roqscan mineral composition imaging, it is summarized as the formation mode of organic-rich hybrid sedimentary shale in the faulted continental basin during volcanic activity periods, and the formation conditions are as follows. (1) The input of multiple organic sources improves the abundance of organic matter in shale contributing to the co-preservation of type Ⅰ, Ⅱ and type Ⅲ kerogens. (2) In the later stage of volcanic activity, the migration of nutrient elements leads to algae bloom in the intervening shales. (3) Carbonate diagenesis contributes to hydrocarbon generation in the hybrid sedimentary shales which are sedimented in a closed saltwater environment under dry and hot climates. (4) The oxidation stratification of the water body forms four types of laminae of shale in this section: siliceous, clayey, calcareous, and pyrite laminae.