火山灰沉积与页岩有机质富集关系探讨——以五峰组—龙马溪组含气页岩为例

现代火山活动喷发形成的火山灰沉降到海水中能够提高海洋表层生产力、促进浮游生物繁盛，有利于有机质形成与富集沉积。而地质历史时期火山灰（斑脱岩）沉积与有机质富集关系研究相对较少，且存在着争议。以我国华南地区奥陶纪-志留纪转折期五峰组-龙马溪组页岩为例，开展含火山灰页岩层段与正常沉积的页岩层段的TOC含量、古生产力、氧化还原条件等对比分析，以探讨两者之间关系。研究结果初步表明:火山灰对高生产力背景的海洋区域影响相对较弱，对其有机质富集的促进作用不明显，而沉积水体氧化还原条件（富氧-贫氧-缺氧变化）与有机质含量关系密切，是这一时期有机质富集的主控因素。由于火山活动对沉积环境影响是十分复杂的过程，未来需要利用地质、地球化学等多种测试手段，开展更高分辨率（如厘米级、毫米级尺度）综合对比研究，精细解剖火山活动对有机质形成及富集作用的影响。火山活动相关的沉积事件是非常规油气沉积学重要研究内容之一，厘定它与页岩有机质富集关系，对我国页岩油气等非常规油气勘探开发具有重要意义。

Discussion of the Relationship between Volcanic Ash Layers and Organic Enrichment of Black Shale: A case study of the Wufeng-Long-maxi gas shales in the Sichuan Basin

Previous studies have shown that the deposition of volcanic ash from modern volcanic activity into seawater can improve marine surface productivity,promote the flourishing of plankton,and facilitate the formation and enrichment of organic matter. However,there are few studies on the relationship between volcanic ash deposition and organic matter enrichment in geological history,which has always been controversial. A large number of volcanic ash layers developed in the gas shales of the Wufeng-Longmaxi Formation during the Ordovician-Silurian transition in South China,providing a typical strata system for this research. Total organic carbon(TOC) content,paleo-productivity, and redox conditions of the shale horizons, including volcanic ash layers and no volcanic ash layers, were comparatively analyzed. The results show that the volcanic ash deposition during the Ordovician-Silurian transition had a relatively weak effect on marine productivity and did not significantly promote the accumulation of organic matter. The redox condition has a close relationship with TOC content,suggesting it could be the main controlling factor. The influence of volcanic activity on the sedimentary environment is a very complicated process. Therefore,in the future, comprehensive studies with higher resolution(such as centimeter-scale and millimeter-scale) should be carried out by using geological,geochemical,and other testing methods to finely analyze the impact of volcanic activity on the formation and enrichment of organic matter. Sediments related to volcanic activity are one of the research targets of unconventional petroleum sedimentology,and the determination of the relationship between them and organic enrichment in shale would have an important role in the exploration and development of unconventional petroleum,such as shale oil and gas.