Abstract The Wufeng-Longmaxi Formations (WF-LM Fms) in the Sichuan Basin are sets of graptolite-bearing shale strata containing high-frequency bentonite layers. In order to investigate the influence of volcanism on the organic matter (OM) accumulation in shales, detailed observations of several typical profiles and wells were performed. Also, analyses including total organic carbon (TOC) contents and mineral compositions were conducted on 126 shale and 5 bentonite core samples. Major and trace element analyses were conducted on the selected 25 shale and 5 bentonite samples in the WF-LM Fms of well Lu-A. Results show that WF and LM1-4 members are the bentonites concentrated sections, while LM5-6 are the bentonites relatively concentrated sections and no bentonite is found in LM7-9 members. The high potassium (K) content of bentonites have the typical characteristics of intermediate-acid calcium-alkaline volcanic rocks such as andesite and dacite, which probably originated from intraplate collision or volcanic arc structural backgrounds related to the collision belt of the Cathaysia Block to the Yangtze Block. Productivity indicators (P content, excess Si, P/Al, Cu/Al, and Ni/Al) in the WF and LM1-3 members are all significantly higher than those in the Lingxiang (LX) and LM4-5+ members. The higher biological productivity during the Ordovician-Silurian (O–S) transition was attributed to the massive and intensive volcanism. The fertilization by volcanic ash brought abundant biologically relevant nutrient elements (N, P, Si, Fe, and Al) into the ocean, thus triggering the phytoplankton bloom and enhancing primary biological productivity. All the redox condition indexes (MoEF, UEF, NiEF, VEF, Mo/TOC, Corg/P, and U/Th) positively correlate with TOC content. During the O–S transition, the intensive and massive volcanic eruptions triggered global cooling, sea-level changes, late Ordovician mass extinction, and primary productivity increases, thus promoting anoxic, and possibly intermittently euxinic bottom conditions. In addition, the deposited bentonite layers had a strong capacity for oxygen isolation. Volcanism should be considered when modeling the OM accumulation of the WF-LM shales.

中文翻译：

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川南五峰—龙马溪页岩有机质积累——来自火山作用的证据与洞察

摘要 四川盆地五峰组—龙马溪组（WF-LM Fms）是一组含笔石的页岩地层，含有高频膨润土层。为了研究火山作用对页岩中有机质（OM）积累的影响，对几个典型剖面和井进行了详细观察。此外，还对 126 个页岩和 5 个膨润土岩心样品进行了包括总有机碳 (TOC) 含量和矿物成分的分析。对 Lu-A 井 WF-LM Fms 中选定的 25 个页岩和 5 个膨润土样品进行了主量和微量元素分析。结果表明，WF和LM1-4段为膨润土集中段，LM5-6段为膨润土相对集中段，LM7-9段未发现膨润土。膨润土的高钾（K）含量具有安山岩、英安岩等中酸性钙碱性火​​山岩的典型特征，可能起源于华夏地块碰撞带相关的板内碰撞或火山弧构造背景。扬子街区。WF和LM1-3成员的生产率指标（P含量、过量Si、P/Al、Cu/Al和Ni/Al）均显着高于凌翔（LX）和LM4-5+成员。奥陶纪-志留纪（O-S）过渡期间较高的生物生产力归因于大规模和密集的火山活动。火山灰的施肥将丰富的生物相关营养元素（N、P、Si、Fe和Al）带入海洋，从而引发浮游植物大量繁殖并提高初级生物生产力。所有氧化还原条件指标（MoEF、UEF、NiEF、VEF、Mo/TOC、Corg/P 和 U/Th）与 TOC 含量呈正相关。在 O-S 过渡期间，强烈而大规模的火山喷发引发了全球变冷、海平面变化、晚奥陶世大灭绝和初级生产力的增加，从而促进了缺氧，可能是间歇性的富氧底部条件。此外，沉积的膨润土层具有很强的隔氧能力。在模拟 WF-LM 页岩的 OM 堆积时应考虑火山活动。密集而大规模的火山喷发引发了全球变冷、海平面变化、晚奥陶世大灭绝和初级生产力增加，从而促进了缺氧，并可能是间歇性的富氧底部条件。此外，沉积的膨润土层具有很强的隔氧能力。在模拟 WF-LM 页岩的 OM 堆积时应考虑火山活动。密集而大规模的火山喷发引发了全球变冷、海平面变化、晚奥陶世大灭绝和初级生产力增加，从而促进了缺氧，并可能是间歇性的富氧底部条件。此外，沉积的膨润土层具有很强的隔氧能力。在模拟 WF-LM 页岩的 OM 堆积时应考虑火山活动。