The Ordovician shale (Wufeng Formation) in the Upper Yangtze Platform is now considered a successful development interval, independent of the Longmaxi Formation. However, accumulation mechanisms of organic matter (OM) within the Wufeng shale are rarely discussed and remain highly controversial. Petrological and geochemical characteristics were analyzed on 25 Wufeng samples from well X1 located in the Upper Yangtze Platform, and their implications for the OM accumulation mechanisms are further discussed. The Wufeng Formation is divided into three intervals based on graptolite biozones (named WF2, WF3, and WF4). Geochemical redox proxies (Mo, U, V, Ni, Cr, Co) suggest that WF2 and WF4 were deposited in oxic–suboxic conditions, whereas WF3 was deposited in suboxic–anoxic with episodes of euxinic conditions. Geochemical productivity proxies (Ba, P, Si) indicate high paleoproductivity when WF2 and WF3 were deposited, which may have been controlled by upwelling as suggested by the high ratio of Cd/Mo. WF2 (averaged 1.42% TOC) is not as organic-rich because of poor preservation conditions and terrestrial dilution. High paleoproductivity and suitable preservation conditions were the controlling factors for the organic-rich WF3 interval (averaged 3.00% TOC). However, low paleoproductivity and poor preservation conditions caused low accumulation of OM in WF4 (averaged 0.82% TOC). OM accumulation within the Wufeng Formation reflects the interaction between the variations in redox conditions and paleoproductivity. The sedimentary environment during Wufeng deposition was mainly controlled by sea level, which, in turn, was controlled by global climate and global and regional tectonics.

中文翻译：

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华南上扬子地台晚奥陶世页岩地球化学特征及有机质富集

上扬子地台奥陶系页岩（五峰组）目前被认为是独立于龙马溪组的成功开发层段。然而，五峰页岩内有机质（OM）的富集机制很少被讨论，并且仍然存在很大争议。对上扬子地台 X1 井 25 个五峰样品进行了岩石学和地球化学特征分析，并进一步探讨了其对 OM 成藏机制的意义。五峰组按笔石生物带划分为三个层段（WF2、WF3、WF4）。地球化学氧化还原代理（Mo、U、V、Ni、Cr、Co）表明WF2和WF4沉积在有氧-缺氧条件下，而WF3沉积在低氧-缺氧条件下，并伴有常氧条件。地球化学生产力指标（Ba、P、Si）表明 WF2 和 WF3 沉积时古生产力较高，这可能是由高 Cd/Mo 比率表明的上升流控制的。由于保存条件差和陆地稀释，WF2（平均 TOC 为 1.42%）有机质并不丰富。高古生产力和适宜的保存条件是富含有机质的WF3层段（平均TOC为3.00%）的控制因素。然而，低古生产力和较差的保存条件导致WF4中OM积累量较低（平均0.82% TOC）。五峰组内有机质的积累反映了氧化还原条件的变化与古生产力之间的相互作用。五峰沉积时期的沉积环境主要受海平面控制，而海平面又受全球气候和全球区域构造的控制。