Geochemical Characteristics of Cherts from the Wufeng and Longmaxi Formations in the Wuxi Area, Sichuan Basin
QIU Zhen1,2, TAN Xin2,3, LU Bin1,2, SHI Zhen-sheng1,2, JIANG Zeng-guang2,3, ZHOU Jie1, CHEN Liu-qin3
1. National Energy Shale Gas Research & Development(Experiment) Center, Langfang Hebei 065007, China;
2. Research Institute of Petroleum Exploration & Development, Beijing 100083, China;
3. School of Earth Science, East China University of Technology, Nanchang 330013, China
Abstract：Cherts are widely deposited in the Wufeng and Longmaxi formations, which are key strata for exploring shale gas reservoir, in the Wuxi area, Sichuan Basin. Relative significant differences in terms of the genesis and forming environment are existed among cherts in different areas. In this study, 51 samples of bedded cherts from the Wufeng and Longmaxi formations of at the Tianba section in the Wuxi area were analyzed for major, trace elements and REE. Combining with the petrological and paleontological data, we have conducted detailed analogical study on the origin and depositional environment of cherts from the Wufeng and Longmaxi formations in this area. Results show that cherts of the Wufeng and Longmaixi formations in the Wuxi area were formed in the continental margin environment, which is far away from the hydrothermal activity center, with overall influence of terrestrial debris. Cherts of the Longmaxi Formation are more influenced than those of the Wufeng Formation by terrestrial debris. In addition, cherts of the Wufeng Formation are mainly composed of siliceous organisms, with local influence of hydrothermal activity, whereas cherts of the Longmaxi Formation are composed of both siliceous organisms and terrestrial debris.
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