Xujiahe fine-grained sediments (FGSs) are regarded not only as important shale gas targets but also as significant regional hydrocarbon source rocks. To analyze the provenance and depositional conditions of the Xujiahe FGSs, trace elements and rare-earth elements (REEs) from two wells in the western Sichuan Basin were investigated. The results indicate that the Xujiahe FGSs mainly originated from the upper continental crust (UCC), the source rocks gradually changed from mixed influence to relatively pure sedimentary rocks from the second member of Xujiahe Formation (Xu2 member) to the fourth member of Xujiahe Formation (Xu4 member), which was related to the uplift of Longmen Mountain. La–Th–Sc and Th–Co–Zr/10 diagrams indicate an active continental margin environment. The redox condition indices (V/Cr and Th/U) suggest that the Xujiahe FGSs were deposited in an oxic environment, while the paleoclimate indices suggest differences among the members. The Xu3 member shows a stable warm-humid climate, and the Xu2 and Xu4 members alternate between humid and arid climates. The combination of climate and tectonics is the key factor in the formation of the Xujiahe FGSs. The warm and humid climate result in high productivity in the basin, tectonic movement influence the substance supply and create a high sedimentary rate for the Xujiahe Formation; thus, the organic matter in the Xujiahe FGSs can still be effectively preserved even under oxidation conditions.

中文翻译：

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四川盆地西部须家河组上三叠统细粒沉积物微量和稀土元素特征及其物源沉积环境意义

须家河细粒沉积物（FGSs）不仅被视为重要的页岩气目标，也是重要的区域烃源岩。为分析须家河FGS的物源和沉积条件，对四川盆地西部2口井的微量元素和稀土元素（REEs）进行了调查。结果表明，须家河FGS主要起源于上陆壳（UCC），烃源岩从须家河组二段（须二段）到须家河组四段由混合影响逐渐转变为相对纯净的沉积岩（ Xu4 成员），这与龙门山的隆起有关。La-Th-Sc 和 Th-Co-Zr/10 图表示活跃的大陆边缘环境。氧化还原条件指数（V/Cr 和 Th/U）表明须家河 FGS 沉积在好氧环境中，而古气候指数表明成员之间存在差异。徐三段为稳定的暖湿气候，徐二段和徐四段为湿润和干旱气候交替。气候与构造的共同作用是形成须家河FGS的关键因素。温暖湿润的气候导致盆地生产力高，构造运动影响物质供给，为须家河组创造高沉积速率；因此，即使在氧化条件下，须家河 FGS 中的有机物仍然可以得到有效保存。而Xu2和Xu4成员在潮湿和干旱气候之间交替。气候与构造的共同作用是形成须家河FGS的关键因素。气候温暖湿润，盆地生产力高，构造运动影响物质供给，使须家河组沉积速率高；因此，即使在氧化条件下，须家河 FGS 中的有机物仍然可以得到有效保存。而Xu2和Xu4成员在潮湿和干旱气候之间交替。气候与构造的共同作用是形成须家河FGS的关键因素。温暖湿润的气候导致盆地生产力高，构造运动影响物质供给，为须家河组创造高沉积速率；因此，即使在氧化条件下，须家河 FGS 中的有机物仍然可以得到有效保存。