Abstract: Shale gas, as a key unconventional natural gas resource, plays a significant role in the global energy transition and energy supply security. The Cambrian Qiongzhusi Formation shales in Sichuan Basin are important targets for shale gas exploration owing to their substantial thickness and relatively high organic matter abundance. This study focuses on the Lower Cambrian Qiongzhusi Formation shales from Well Z203 in the Ziyang area of central Sichuan Basin. Core and thin-section observations, X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM) analyses, and geochemical analyses were integrated to systematically characterize the evolution of the sedimentary environment. Further, the organic matter enrichment mechanisms were investigated using organic geochemical indices. The results indicate that the Qiongzhusi Formation in Well Z203 was deposited in a terrigenous clastic shelf setting controlled by the Deyang-Anyue rift trough, with deep-water shelf deposits dominating throughout the succession. The lithology mainly comprises mudstone/shale, silty mudstone, and argillaceous siltstone. During deposition of the first submember of Member 1 of Qiongzhusi Formation, the climate was arid, terrigenous input was moderate and variable, and paleoproductivity remained at a moderate level. During deposition of the second submember of Member 2 of Qiongzhusi Formation, the climate shifted from semi-arid to semi-humid conditions, terrigenous input tended to stabilize, paleoproductivity increased, and trilobite fossils first appeared. During deposition of the Member 2 of Qiongzhusi Formation, continued infilling of the rift trough led to shallowing of the water depth. Meanwhile, the climate became more humid, the degree of water-column oxygenation increased, paleoproductivity further increased, and trilobite fossils were abundant. Overall, the depositional environment of Qiongzhusi Formation evolved from a deep-water, low-energy, mud-rich setting toward a shallow, higher-energy setting with increasing silt input, under the control of the rapid transgression to slow regression cycles. Total organic carbon (TOC) contents are mainly in the range of 0 to 3%, with relatively high organic-matter enrichment in the first, fifth and seventh intervals of Qiongzhusi Formation. The relationships between TOC contents, paleoproductivity and redox proxies suggest that organic-matter enrichment in the Qiongzhusi Formation shales of Well Z203 mainly occurred in shale intervals deposited during rapid transgression and was jointly controlled by moderate productivity supply and dysoxic to weakly reducing preservation conditions, presenting a pattern dominated by the characteristics of moderate productivity supply and dysoxic to weakly reducing preservation.

Key words: Qiongzhusi Formation, sedimentary environment evolution, organic matter enrichment, paleoproductivity, redox environment, Deyang-Anyue rift trough

摘要： 页岩气作为重要的非常规天然气资源，在全球能源结构转型和供应保障中占重要地位。四川盆地寒武系筇竹寺组沉积厚度大、有机质丰度较高，是页岩气勘探的重要目标。以川中资阳地区Z203井下寒武统筇竹寺组页岩为研究对象，基于岩心与岩石薄片观察、X射线衍射（XRD）分析、扫描电镜（SEM）分析和地球化学分析等手段，系统分析了筇竹寺组沉积环境的演化特征，并结合有机地球化学指标探讨了有机质的富集机制。研究结果表明，Z203井筇竹寺组沉积于受德阳—安岳裂陷槽控制的陆源碎屑陆棚环境，整体以深水陆棚沉积为主，岩性主要为泥页岩和粉砂质岩类。筇竹寺组一段（筇一段）1亚段沉积期的气候干旱，陆源输入中等且不稳定，古生产力处于中等水平；筇一段2亚段沉积期的气候由半干旱转为半湿润，陆源输入趋于稳定，古生产力增强，并开始出现三叶虫化石；筇竹寺组二段（筇二段）沉积期，受前期地层充填影响，裂陷槽内水深变浅，气候更加湿润，沉积水体的氧化程度增强，古生产力进一步提高，三叶虫化石大量发育。总体上，筇竹寺组的沉积环境表现为由深水、低能、富泥质沉积向相对浅水、高能、粉砂质沉积增强的演化趋势，并受快速海侵—缓慢海退旋回控制。筇竹寺组的总有机碳（TOC）含量主要分布在0～3%，其中，在筇竹寺组1小层、5小层和7小层中有机质相对富集。TOC含量与古生产力及氧化-还原指标的响应关系表明，Z203井筇竹寺组有机质的富集主要发生在快速海侵期页岩段，受中等生产力供给与贫氧—弱还原保存条件协同控制，表现为“中等生产力供给、贫氧—弱还原保存主控型”模式。

关键词: 筇竹寺组, 沉积环境演化, 有机质富集, 古生产力, 氧化-还原环境, 德阳—安岳裂陷槽