The Ordovician–Silurian transition was a critical period in geological history, during which profound changes in climatic, biotic, and oceanic conditions occurred. To explore the provenance, palaeoclimate, and palaeoredox conditions in the Sichuan Basin during the Late Ordovician–early Silurian interval, we conducted mineralogical, geochemical, and isotopic analyses of three formations (Wufeng, Guanyinqiao and Longmaxi formations) in the Xindi No. 2 well. The ternary and bivariate diagrams indicate that the provenance is mainly felsic igneous rocks and originated mainly from a collisional setting, presumably due to an active continental margin. The chemical index of alteration (CIA) values in the lower Wufeng and Longmaxi formations are relatively high (67.48–73.57), indicating a warm and humid climate. In contrast, the CIA values declined rapidly (58.30–64.66) during the late Katian to early Hirnantian, which had a fluctuating cold and dry climate and was interrupted by a transient warm and humid climate. The palaeoredox indices (Mo concentrations and Mo_auth/U_auth, U/Th, V/Cr, Ni/Co, and V/V + Ni values) during the Late Ordovician–early Silurian indicate two cycles of water column euxinia. The first cycle occurred during Wufeng Formation deposition, with bottom waters evolving from oxic-suboxic to suboxic-anoxic. Most samples show relatively low redox-sensitive trace element concentrations during the Guanyinqiao Formation, pointing to oxic-suboxic conditions. The second cycle, during the late Hirnantian, transitioned from oxic to euxinic water conditions. Our δ¹³C_org data are comparable to previously reported records and exhibit a strong correlation between the Hirnantian isotopic carbon excursion (HICE), climate change, and redox conditions. We suggest that the variations in the δ¹³C values are related to two elements: (1) increased photosynthetic activity under oxic water conditions, and (2) increased carbonate weathering exposed by the glacio-eustatic sea- level. In addition, the high δ¹³C_org values might indicate a more shelf-proximal setting during Xindi No. 2 well deposition. The δ¹³C_org isotopic data effectively constrain the timing of the Late Ordovician mass extinction (LOME) and the evolution of the temporal changes in the climatic and ocean redox conditions, suggesting an apparent stratigraphic coincidence between climate and redox fluctuations and two-phase extinctions, which implies a strong causal relationship. The LOME was systematically driven by the combination of cooler glacial temperatures, glacio-eustatic sea-level fluctuations, and anoxic water conditions that caused the two pulses of extinction in the Yangtze shelf sea.

奥陶纪-志留纪过渡是地质史上的一个关键时期，在此期间气候、生物和海洋条件发生了深刻的变化。为探究四川盆地晚奥陶世—早志留世期物源、古气候和古氧化还原条件，对新地2井三层（五峰组、观音桥组和龙马溪组）进行了矿物学、地球化学和同位素分析。 . 三元和双变量图表明，物源主要是长英质火成岩，主要起源于碰撞环境，可能是由于活跃的大陆边缘。五峰组和龙马溪组下部化学蚀变指数（CIA）值较高（67.48～73.57），表明气候温暖湿润。相比之下，CIA 值在 Katian 晚期到 Hirnantian 早期迅速下降（58.30-64.66），其气候寒冷干燥，并被短暂的温暖潮湿气候打断。古氧化还原指数（Mo 浓度和 Mo_auth /U _auth , U/Th, V/Cr, Ni/Co, and V/V + Ni values) 晚奥陶世-早志留世表明水柱euxinia的两个旋回。第一个旋回发生在五峰组沉积期，底水由好氧-低氧向低氧-缺氧演化。大多数样品在观音桥组期间显示出相对较低的氧化还原敏感微量元素浓度，表明有氧-亚氧条件。第二个周期，在赫尔南阶晚期，从好氧水条件过渡到等渗水条件。我们的 δ ¹³ C _org数据与之前报告的记录相当，并且在 Hirnantian 同位素碳偏移 (HICE)、气候变化和氧化还原条件之间表现出很强的相关性。我们建议 δ 的变化¹³ C 值与两个因素有关：(1) 在含氧水条件下光合活性增加，以及 (2) 冰川海平面暴露的碳酸盐风化作用增加。此外，高δ ¹³ C _org值可能表明在新地2 号井沉积过程中更靠近陆架的环境。δ ¹³ C_组织同位素数据有效地限制了晚奥陶世大灭绝（LOME）的时间以及气候和海洋氧化还原条件的时间变化的演变，表明气候和氧化还原波动与两相灭绝之间明显的地层重合，这意味着强烈的因果关系。LOME 是由较冷的冰川温度、冰川海平面波动和缺氧水条件共同驱动的，这些条件导致了长江陆架海的两次灭绝脉冲。