| Citation: |
Xiang-ying Ge, Chuan-long Mou, Xin Men, Qian Hou, Bin-song Zheng, Wei Liang, 2025. Lithofacies palaeogeography, depositional model and shale gas potential evaluation in the O3-S1 Wufeng-Longmaxi Formation in the Sichuan Basin, China, China Geology, 8, 338-359. doi: 10.31035/cg20230015
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Lithofacies palaeogeography, depositional model and shale gas potential evaluation in the O3-S1 Wufeng-Longmaxi Formation in the Sichuan Basin, China
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Abstract
The black shales of Wufeng and Longmaxi Formation (Late Ordovician-Early Silurian period) in Sichuan Basin are the main strata for marine shale gas exploration, which have a yearly shale gas production of 228×108 m3 and cumulative shale gas production of 919×108 m3. According to the lithological and biological features, filling sequences, sedimentary structures and lab analysis, the authors divided the Wufeng /Guanyinqiao and Longmaxi Formations into shore, tidal flat, shoal, shallow water shelf and deep water shelf facies, and confirmed that a shallow water deposition between the two sets of shales. Although both Formations contain similar shales, their formation mechanisms differ. During the deposition of Wufeng shale, influenced by the Caledonian Movement, the Central Sichuan and Guizhou Uplifts led to the transformation of the Sichuan Basin into a back-bulge basin. Coinstantaneous volcanic activity provided significant nutrients, contributing to the deposition of Wufeng Formation black shales. In contrast, during the deposition of Longmaxi shale, collisions caused basement subsidence, melting glaciers raised sea levels, and renewed volcanic activity provided additional nutrients, leading to Longmaxi Formation black shale accumulation. Considering the basic sedimentary geology and shale gas characteristics, areas such as Suijiang-Leibo-Daguan, Luzhou-Zigong, Weirong-Yongchuan, and Nanchuan-Dingshan are identified as key prospects for future shale gas exploration in the Wufeng-Longmaxi Formations.
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References
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Xiang-ying Ge, Chuan-long Mou, Xin Men, Qian Hou, Bin-song Zheng, Wei Liang, 2025. Lithofacies palaeogeography, depositional model and shale gas potential evaluation in the O3-S1 Wufeng-Longmaxi Formation in the Sichuan Basin, China, China Geology, 8, 338-359. doi: 10.31035/cg20230015
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Figure 1.
Distribution of major faults and division of structural areas of Sichuan Basin, China.
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Figure 2.
Graptolite biozones of Upper Ordovician-Lower Silurian (after Chen X et al., 2015, 2017).
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Figure 3.
Lithostratigraphic units of Upper Ordovician-Lower Silurian in Sichuan Basin and adjacent areas.
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Figure 4.
Sedimentary sequence of tidal flat facies in Wufeng formation of Huanggexi section, Daguan county, Yunnan Province.
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Figure 5.
Sedimentary sequence of tidal flat facies in Guanyinqiao Formation. a‒Fenghuang section, Youyang county, Chongqing City; b‒Xiadian section, Dejiang county, Guizhou province.
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Figure 6.
Characteristic features of shore facies in Guanyinqiao Formation. a‒thick beded pebbly sandstone in Liangbai, Zhenba County; b‒mud gravel in the quartz sandstones in Fucheng section, Nanzhen County; c‒quartz siltstones in Fucheng section, Nanzhen County; d‒quartz sandstones in Liangbai section, Zhenba County; e‒boundary of Wufeng and Guanyinqiao Formations in Wuxing section, Zhenba County; f‒bottom erosion structure between the Wufeng and Guanyinqiao Formations in Shuanghui section, Wangcang County; g‒parallel bedding in sandstones of Guanyinqiao Formation in Wuxing section, Zhenba County; h‒bottom erosion structure at the bottom of Guanyinqiao Formation in Fucheng section, Nanzheng County.
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Figure 7.
Characteristic features of shoal facies in Guanyinqiao Formation. a‒oolitic limestone of Guanyinqiao Formation in Dongkala section, Fenggang County; b‒coral developed in the biological limestones of Guanyinqiao Formation in Zhongshu section, Renhuai County; c‒oolitic limestone of Guanyinqiao Formation in Yonghe section, Fenggang County; d‒boundary of Wufeng, Guanyinqiao and Longmaxi Formations in Yonghe section, Fenggang County; e‒ macroscopic character of the Guanyinqiao Formation in Zhongshu section, Renhuai County; f‒ corals of the Guanyinqiao Formation in Zhongshu section, Renhuai County.
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Figure 8.
Horizontal beddings developed in the carbonaceous silty mudstones of Wufeng formation in Xiadian section, Dejiang County, Guizhou Province.
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Figure 9.
Characteristic features of shallow water shelf facies in Guanyinqiao Formation. a‒bioclastic-containing mudstone of Guanyinqiao Formation in Huangcao section, Wulong County; b‒hirnantia brachiopods of bioclastic-containing mudstone in Huangcao section, Wulong County; c‒hirnantia brachiopods of bioclastic-containing argillaceous limestone in Liangcun section, Xishui County; d‒hirnantia brachiopods of bioclastic-containing argillaceous limestone in Dalianghui section, Wangcang County.
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Figure 10.
Characteristic features of shallow water shelf facies in Longmaxi Formation. a‒gray-green silty mudstone of Longmaxi Formation in Tuping section, Zhengan County; b‒small ripple lamination developed in the silty mudstones of Longmaxi Formation in Tuping section, Zhengan County; c‒gray-green shales of the upper part of Longmaxi Formation in Huangcao section, Wulong County; d‒graygreen silt-containing mudstone of Longmaxi Formation in Hanjiadian section, Tongzi County.
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Figure 11.
Characteristic features of deep water shelf facies in Wufeng and Longmaxi Formations. a‒d‒macro characteristics of the black carbonaceous and siliceous mudstones; Longmaxi Formation, a‒Huangcao section, Wulong County; b‒Qiliao section, Shizhu County; c‒Guanyinqiao section, Qijiang County; d‒ Jiaoye 1well; e‒h‒radiolaria developed in carbonaceous and siliceous mudstones; Wufeng Formation, e‒Huangcao section, Wulong County; f‒Huangyingxiang section, Wulong County; g‒Fucheng section, Nanzheng County; h‒Shuanghui section, Wangcang County.
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Figure 12.
Characteristic features of deep water shelf facies in Wufeng and Longmaxi Formations of Huadi 1well and Xindi 2well. a‒pyrite nodules developed in the black shales (Huadi 1well, Wufeng Formation); b‒graptolite developed in the black carbonaceous and siliceous mudstones (Huadi 1 well, Longmaxi Formation); c‒ bentonites developed in the black shales(Xindi 2well, Wufeng Formation); d‒pyrites developed in the black shales (Xindi 2well, Longmaxi Formation); e‒pyrite framboids developed in the black shales (Huadi 1well, Longmaxi Formation); f‒radiolaria developed in the black shales (Huadi 1well, Wufeng Formation).
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Figure 13.
Sedimentary correlation diagram of the north east-south west direction in Sichuan Basin and its adjacent areas (the palaeogeography map were modified from Ge XY, 2020).
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Figure 14.
Sedimentary correlation diagram of the nearly east-west direction in Sichuan basin and its adjacent areas (the palaeogeography map were modified from Ge XY, 2020).
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Figure 15.
Lithofacies paleogeography map of Wufeng formation in Sichuan Basin and its surrounding areas.
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Figure 16.
Lithofacies paleogeography map of Guanyinqiao Formation in Sichuan Basin and its surrounding areas.
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Figure 17.
Lithofacies paleogeography map of the organic rich shales from Longmaxi Formation in Sichuan Basin and its surrounding areas.
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Figure 18.
Lithofacies paleogeography map of the upper part of Longmaxi Formation in Sichuan Basin and its surrounding areas.
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Figure 19.
Depositional model of black shales of Wufeng and Longmaxi Formations in Sichuan Basin.