上扬子西南缘下志留统细粒沉积岩有机质富集机理研究——以盐津牛寨剖面为例

利用化学元素行为特征的差异性，以总有机碳（TOC）、主量元素和微量元素的含量或比值判别四川盆地西南缘盐津牛寨剖面下志留统龙马溪组细粒沉积岩形成时的初级生产力、氧化还原条件、陆源供应的输入和盆地水体滞留程度等环境特征，并对比川南沉降中心（长宁剖面）和南川非沉降中心（南川剖面）龙马溪组的古环境参数，综合探讨了早志留世上扬子海滞留海盆细粒沉积岩有机质富集的差异性。结果表明，盐津牛寨地区下志留统细粒沉积岩以黑色—灰黑色碳质页岩、页岩和泥岩为主，富有机质主要集中在龙马溪组下段，TOC平均含量为2.73%；Ba_bio显示盆地西南缘龙马溪组早期具有较高的生产力；Ni/Co、V/（V+Ni），U/Th和V/Cr揭示龙马溪组从底部缺氧环境逐步过渡到顶部的氧化环境；TiO₂、Al₂O₃、Zr表明龙马溪组下段陆源碎屑供应量明显增加；Mo/TOC值和U-Mo协变模式图均说明四川盆地西南缘在早志留世水体呈中等滞留环境。与长宁剖面和南川剖面对比分析，发现盆地西南缘TOC与氧化还原条件呈现显著的正向相关关系；与盆地水体的滞留程度呈现微弱的正向相关关系；与陆源碎屑物质的注入和初级生产力无明显相关性，表明缺氧还原的沉积环境是影响该地区龙马溪组黑色页岩有机质富集的主要因素。

Mechanism of organic matter enrichment of fine-grained sedimentary rocks in the Southwest margin of Upper Yangtze: A case study of the Niuzhai section,Yanjin

Based on the differences in the behavioral characteristics of chemical elements， the content or ratio of TOC， major elements and trace elements was used to discriminate the formation of fine-grained sedimentary rocks of the Early Silurian Longmaxi Formation in Niuzhai section of Yanjin， at the southwestern margin of the Sichuan Basin. Paleoproductivity， redox conditions， input of terrestrial supply and the degree of basin water retention， and other environmental characteristics are compared. Paleoenvironmental parameters of the Longmaxi Formation in the South Sichuan Subsidence Center （Changning section） and Nanchuan Underwater Uplift Area （Nanchuan section） are compared. Differences in organic matter enrichment of fine-grained sedimentary rocks in the stranded basin of the Yangtze Sea in the Early Silurian. The results show that the Early Silurian fine-grained sedimentary rocks in the Niuzhai area of Yanjin are mainly black carbonaceous shales， gray shales and black mudstones， and the organic-rich materials are mainly concentrated in the lower section of the Longmaxi Formation， with an average TOC content of 2.73%. Ba_bio shows that the Longmaxi Formation in this area had higher productivity in the early stage. Ni/Co， V/（V+Ni）， U/Th， and V/Cr ratios revealed that the Longmaxi Formation gradually transitioned from a hypoxic environment at the bottom to an oxidizing environment at the top； TiO₂， Al₂O₃ and Zr indicate that the supply of terrigenous debris in the lower segment of the Longmaxi Formation increased significantly； the Mo/TOC value and the U-Mo covariance model map indicate that the southwestern margin of the Sichuan Basin was in a moderately stagnant environment during the Early Silurian. Compared with the Changning and Nanchuan profiles， it is found that TOC in the southwestern margin of the basin has a significant positive correlation with redox conditions； it has a weak positive correlation with the retention of the basin water body； it has a weak positive correlation with the injection of terrigenous debris and primary productivity There is no obvious correlation， indicating that the anoxic reduction sedimentary environment is the main factor affecting the organic matter enrichment of the black shale of the Longmaxi Formation in this area.