Organic-rich siliceous rocks in the upper Permian Dalong Formation (NW middle Yangtze): Provenance, paleoclimate and paleoenvironment
Organic-rich siliceous rocks in the upper Permian Dalong Formation (NW middle Yangtze): Provenance, paleoclimate and paleoenvironment
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DOI：
10.1016/j.marpetgeo.2020.104728
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发表时间：
2021
影响因子：
4.2
通讯作者：
Wei Wu;Weiqing Liu;Chuanlong Mou;Hua Liu;Yulei Qiao;Pan Jienan;Shuyuan Ning;Xiaoxiao Zhang;Jian-xin Yao;Jingdong Liu
中科院分区：
文献类型：
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作者：
Wei Wu;Weiqing Liu;Chuanlong Mou;Hua Liu;Yulei Qiao;Pan Jienan;Shuyuan Ning;Xiaoxiao Zhang;Jian-xin Yao;Jingdong Liu
中扬子地区上二叠统大隆组富有机质页岩是重要的页岩气勘探层位。然而，硅质物质的来源和有机质富集的机理至今仍存在争议。根据地球化学资料，研究了鄂西地区大隆组的物源、古气候、古环境、初级生产力和水文条件，探讨了有机质的富集机制。大隆组页岩可划分为富有机质和贫有机质两个单元，平均TOC含量分别为5.81wt%和0.45wt%。鄂西盆地在沉积过程中是一个强约束盆地，大隆组物源具有大陆边缘沉积背景，主要为长英质和基性混合物源。大隆组页岩中主要有陆源碎屑石英、生物石英和热液石英。基于U，V，Mo的浓度和V/（V + Ni）比值，富有机质页岩沉积在缺氧硫化条件下。与此相反，有机贫页岩沉积在氧化-亚氧化条件下。大隆组具有中-高的初级生产力，控制着盆地的氧化还原条件。贫有机质页岩初级生产力的下降可能与气候从温暖潮湿向炎热干燥的转变有关。沉积模式表明，大隆组富有机质硅质岩的形成受初级生产力的控制。晚二叠世干热气候导致的初级生产力下降是控制有机质富集和生物石英形成的主要因素。
The organic-rich shales of the upper Permian Dalong Formation in the middle Yangtze area are considered an important shale gas exploration horizon. However, the origin of siliceous matter and the mechanism of organic matter enrichment are still controversial. Based on geochemical data, we studied the provenance, paleoclimate, paleoenvironment, primary productivity and hydrological conditions of the Dalong Formation in western Hubei Province and discussed the mechanism of organic matter enrichment. The shales of the Dalong Formation can be divided into two units, organic-rich and organic-lean shales, with average TOC contents of 5.81 wt% and 0.45 wt%, respectively. The western Hubei Basin was a strongly restricted basin during deposition, and the provenance of the Dalong Formation had a continental margin sedimentary background, mainly from mixed felsic and basic sources. Terrigenous clastic quartz, biological quartz and hydrothermal quartz are recognized in the shales of the Dalong Formation. Based on U, V, and Mo concentrations and V/(V + Ni) ratios, the organic-rich shales were deposited in anoxic-sulfurized conditions. In contrast, the organic-lean shales were deposited under oxic-suboxic conditions. The Dalong Formation had moderate to high primary productivity and controls on the redox conditions in the basin. The decrease in primary productivity in organic-lean shales may be related to the transition from a warm and humid climate to a hot and dry climate. The sedimentary model shows that the formation of organic-rich siliceous rocks in the Dalong Formation was controlled by primary productivity. The decrease in primary productivity driven by the hot and dry climate in the latest Permian is the main factor controlling the enrichment of organic matter and the formation of bioquartz.