The relative sea-level fluctuations play a vital role in the organic matter enrichment of black shales across the world. The Wufeng-Lower Longmaxi shales deposited during the Late Ordovician to Early Silurian stage are accompanied by the global transgression and regression, whereas the role of relative sea-level changes on organic matter accumulation has been rarely discussed. In this study, we integrated TOC content, X-ray diffraction (XRD) mineralogical composition, thin section and scanning electron microscope (SEM) images, elemental geochemical data, and petrographic features of pyrite framboids to investigate the varying paleoenvironmental conditions and the effect of relative sea-level changes on organic matter accumulation under a robust sequence stratigraphic framework.

Based on detailed petrographic observations and mineralogical analysis, six major lithofacies are identified in the Wufeng-Lower Longmaxi formations, including siliceous mudstone, clay-rich siliceous mudstone, siliceous-argillaceous mixed shale, silty mudstone, siltstone, and bentonite. TOC content is generally higher in the transgressive systems tracts (relative sea-level rise stage) than in the highstand systems tracts and falling stage systems tract (relative sea-level fall stage). Multiple geochemical proxies indicate contrasting paleoenvironmental changes between relative sea-level rise and fall stage. Relative sea-level rise resulted in elevated productivity, predominantly anoxic conditions, low detrital flux, and moderate water mass restriction, as indicated by high biogenic Si content, high Mo-EF (enrichment factor of element Mo), small-sized pyrite framboids, low Al content and moderate Mo/TOC ratio. On the contrary, relative sea-level fall generally resulted in decreased productivity, dysoxic conditions, increased detrital flux, and strongly restricted conditions. The correlations between TOC content and geochemical proxies suggest that organic matter accumulation was a combined effect of paleoproductivity, paleoredox conditions, detrital influx, and water mass restriction. The variation of these factors was strongly influenced by relative sea-level fluctuations related to Hirnantian glaciation and regional tectonic movements during the Late Ordovician-Early Silurian transitional stage.

相对的海平面波动在全球黑色页岩的有机质富集中起着至关重要的作用。奥陶纪晚期至志留纪早期阶段的五峰-下龙马溪组页岩伴有全球海侵和回归，而相对海平面变化对有机质积累的作用却鲜有讨论。在这项研究中，我们综合了TOC含量，X射线衍射（XRD）矿物学组成，薄片和扫描电子显微镜（SEM）图像，元素地球化学数据以及黄铁矿黄铁矿的岩石学特征，以研究变化的古环境条件以及对黄铁矿的影响。稳健层序地层学框架下有机物积累的相对海平面变化。

根据详细的岩相观测和矿物学分析，在五峰—下龙马溪组中确定了六个主要岩相，包括硅质泥岩，富含粘土的硅质泥岩，硅质泥质泥质混合页岩，粉质泥岩，粉砂岩和膨润土。海侵系统区域（相对海平面上升阶段）中的TOC含量通常高于海床系统区域和下降阶段系统区域（相对海平面下降阶段）中的TOC含量。多种地球化学指标表明，相对海平面上升和下降阶段之间的古环境变化是相反的。相对的海平面上升导致生产力提高，主要是缺氧条件，碎屑通量低，水质限制适中，如高生物硅含量，高Mo-EF（元素Mo富集因子），小型黄铁矿磁石，Al含量低，Mo / TOC比适中。相反，相对的海平面下降通常导致生产力下降，缺氧条件，碎屑通量增加以及条件受到严格限制。TOC含量与地球化学代理之间的相关性表明，有机质积累是古生产力，古氧化还原条件，碎屑涌入和水质限制的综合作用。这些因素的变化在很大程度上受与奥陶纪-志留纪晚期过渡期的赫南特冰川作用和区域构造运动有关的相对海平面波动的影响。碎屑通量增加，条件受到严格限制。TOC含量与地球化学代理之间的相关性表明，有机质积累是古生产力，古氧化还原条件，碎屑涌入和水质限制的综合作用。这些因素的变化在很大程度上受与奥陶纪-志留纪晚期过渡期的赫南特冰川作用和区域构造运动有关的相对海平面波动的影响。碎屑通量增加，条件受到严格限制。TOC含量与地球化学代理之间的相关性表明，有机质积累是古生产力，古氧化还原条件，碎屑涌入和水质限制的综合作用。这些因素的变化在很大程度上受与奥陶纪-志留纪晚期过渡期的赫南特冰川作用和区域构造运动有关的相对海平面波动的影响。