In geological history, volcanism is closely related to the deposition of many black shales. However, the specific mechanism between volcanism and the deposition of black shales is still unclear. The black shales developed in the Chang 7 Member of the Yanchang Formation in the Ordos Basin are considered the most important hydrocarbon source rocks in Central China. The shales are deposited by frequent volcanic activities and preserved by extremely rich volcanic ash layers, making them an excellent example when investigating the influence of volcanism on the deposition of black shales. In this paper, petrographic, mineralogical, and geochemical analyses of three typical tuff and black shale segments of the Chang 7 Member were carried out. The productivity indicators [total organic carbon (TOC), P/Al, Ni/Al, and Cu/Al], redox indicators (V/Al, Mo/Al, U/Al and U/Th), and clastic influx indicators (Ti/Al and ƩREE) of the shales basically increased together in the longitudinal direction, and a relatively good positive correlation existed between P/Al, Ni/Al, Cu/Al, V/Al, Mo/Al, U/Al, U/Th, Ti/Al, ƩREE, and TOC. This finding indicated that the development of the Chang 7 black shales is the result of a combination of high primary productivity, anoxic conditions, and increased clastic influx. Considering that increased clastic influx may dilute organic matter, many phosphate nodules represented high productivity above the volcanic ash layers, and anoxic conditions are likely to be the result of a large amount of organic matter degradation indicated by the covariations of TOC versus P/Al and TOC versus Ba/Al. Therefore, the Chang 7 black shales in this study may be mainly controlled by the increased primary productivity. In addition, compared with the Weathering Index of Parker of background shales (not the contact clip or tuff layer), that of the black shales was significantly reduced after tuff deposition. On the contrary, the clastic influx indicators, redox indicators, productivity indicators of black shales significantly increased. This finding suggested that a series of environmental effects, such as enhanced weathering of terrestrial sources, increased clastic influx, anoxic water, and productivity bloom, was likely caused by volcanic activity. Considering that hydrothermal activity at the same time as volcanism may not cause productivity bloom, the nutrients (P/Al and Fe/Al) of the Chang 7 tuffs were significantly depleted, and the total sulfur content of black shales was much higher than that in ordinary freshwater sedimentation. Therefore, this paper reviewed and proposed the volcanism hypothesis model of the Chang 7 black shales. Volcanism generates large amounts of SO₂ and volcanic ash. SO₂ forms large areas of acid rain and accelerates terrigenous weathering with an increase in the lake land-based sources of debris and nutrient supply, while volcanic ash is decomposed and releases nutrients. These phenomena lead to biological productivity bloom and massive accumulation of organic matter, which in turn results in lake water anoxia and the eventual formation of black shales.

在地质历史上，火山作用与许多黑色页岩的沉积密切相关。然而，火山作用与黑色页岩沉积之间的具体机制尚不清楚。鄂尔多斯盆地延长组长7段发育的黑色页岩被认为是华中地区最重要的烃源岩。这些页岩是由频繁的火山活动沉积而成，并被极其丰富的火山灰层保存下来，是研究火山作用对黑色页岩沉积影响的一个很好的例子。本文对长7段三个典型凝灰岩和黑色页岩段进行了岩石学、矿物学和地球化学分析。生产率指标 [总有机碳 (TOC)、P/Al、Ni/Al 和 Cu/Al]、氧化还原指标（V/Al、Mo/Al、U/Al 和 U/Th)，页岩碎屑流入指标 (Ti/Al 和ƩREE) 在纵向上基本一起增加，P/Al、Ni/Al、Cu/Al 之间存在较好的正相关关系、V/Al、Mo/Al、U/Al、U/Th、Ti/Al、ƩREE 和 TOC。这一发现表明，长 7 黑色页岩的发育是初级生产力高、缺氧条件和碎屑流入增加共同作用的结果。考虑到碎屑流入的增加可能会稀释有机质，许多磷酸盐结核在火山灰层以上表现出高生产力，缺氧条件很可能是有机质大量降解的结果，TOC 与 P/Al 和TOC 与 Ba/Al。所以，本研究中长 7 黑色页岩可能主要受初级生产力增加控制。此外，与背景页岩（不是接触夹或凝灰岩层）的Parker风化指数相比，黑色页岩在凝灰岩沉积后风化指数显着降低。反之，黑色页岩碎屑涌流指标、氧化还原指标、产能指标明显上升。这一发现表明，一系列环境影响，如陆地源的风化作用增强、碎屑流入增加、缺氧水和生产力爆发，很可能是由火山活动引起的。考虑到与火山活动同时发生的热液活动可能不会引起生产力的爆发，长7凝灰岩的养分（P/Al和Fe/Al）显着耗竭，黑色页岩的总硫含量远高于普通淡水沉积。为此，本文综述并提出了长7黑色页岩火山作用假说模型。火山活动产生大量 SO₂、火山灰。SO ₂形成大面积酸雨，加速陆源风化，增加湖底垃圾和养分供给，而火山灰分解释放养分。这些现象导致生物生产力爆发和有机物质的大量积累，进而导致湖水缺氧并最终形成黑色页岩。