Xiao Bin, Guo Dongxu, Zhao Zhongying, Xiong Shuzhen, Feng Mingfei, Zhao Zhonghai, Li Sheng
College of Mining, Liaoning Technical University, Fuxin 123000, China.
PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China.
ACS Omega. 2024 Jul 15;9(29):31488-31507. doi: 10.1021/acsomega.4c01129. eCollection 2024 Jul 23.
The tectonic background and sedimentary environment during the transition period from the Ordovician to Silurian have been widely studied by many scholars. This study focuses on the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in the Bajiaokou profile at the southern margin of the Qinling Orogenic Belt in southern China. In order to study the aggregation mechanism of organic matter, geochemical proxies were proposed, including redox proxies (V, V/Al, U, U/Al, Mo, and Mo/Al), paleoproductivity proxies (P, P/Ti, Ba, Ba/Al, and Si), paleoclimate proxies (CIA), and terrigenous flux proxies (Al, Zr, and Zr/Al). In addition, Al-Co[EF] × Mn[EF] is used to provide information on paleoenvironmental parameters such as watermass restriction conditions. The redox proxies show that the Wufeng-Longmaxi shale is mainly accumulated under oxic-dysoxic conditions. During the shale deposition period of Wufeng-Longmaxi formations, the marine surface primary productivity in the southern Qinling area is generally low to moderate. The paleoclimate proxies show that from the Late Ordovician to the Early Silurian the southern Qinling area generally had a warm and humid climate. The upwelling current is widely developed in the northern margin of the Sichuan Basin and the southern margin of the Qinling area. Although the upwelling current was highly developed during the deposition of the Wufeng Formation in the Bajiaokou profile, the concentrated accumulation of a large amount of volcanic ash resulted in the low primary productivity of the ocean. During the sedimentary period of the Longmaxi Formation in the Bajiaokou profile, the development of seasonal upwelling currents and a small amount of volcanic ash supply increased the primary productivity to moderate, which provided a good material basis for the enrichment of organic matter, but the high detritus flux and the water body condition of oxic-dysoxic resulted in the slight enrichment of organic matter.
奥陶纪至志留纪过渡时期的构造背景和沉积环境已被众多学者广泛研究。本研究聚焦于中国南方秦岭造山带南缘芭蕉口剖面的上奥陶统五峰组和下志留统龙马溪组。为研究有机质的聚集机制，提出了地球化学指标，包括氧化还原指标（V、V/Al、U、U/Al、Mo和Mo/Al）、古生产力指标（P、P/Ti、Ba、Ba/Al和Si）、古气候指标（CIA）和陆源通量指标（Al、Zr和Zr/Al）。此外，Al-Co[EF]×Mn[EF]用于提供诸如水体限制条件等古环境参数的信息。氧化还原指标表明，五峰-龙马溪页岩主要在有氧-缺氧条件下沉积。在五峰-龙马溪组页岩沉积期，秦岭南部地区海洋表层初级生产力总体较低至中等。古气候指标表明，从晚奥陶世到早志留世，秦岭南部地区总体气候温暖湿润。四川盆地北缘和秦岭地区南缘上升流广泛发育。虽然芭蕉口剖面五峰组沉积期间上升流高度发育，但大量火山灰的集中堆积导致海洋初级生产力较低。在芭蕉口剖面龙马溪组沉积期，季节性上升流的发育和少量火山灰供应使初级生产力提高到中等水平，为有机质富集提供了良好的物质基础，但高碎屑通量和有氧-缺氧水体条件导致有机质轻微富集。
