Provenance and tectonic setting of the Lower Cambrian Niutitang formation shales in the Yangtze platform,South China: Implications for depositional setting of shales |
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| Institution: | 1. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, 100081, China;2. Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Natural Resources, Beijing, 100081, China;3. Key Lab of Shale Oil and Gas Geological Survey, Chinese Academy of Geological Sciences, Beijing, 100081, China;1. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (Beijing), Beijing, 100083, China;2. College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China;3. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum (Beijing), Beijing, 102249, China;4. College of Geosciences, China University of Petroleum (Beijing), Beijing, 102249, China;1. Área de Ciencias de la Tierra, Facultad de Ingeniería, Universidad Autónoma de San Luís de Potosí, Av. Dr. Manuel Nava No. 8, Zona Universitaria, San Luis Potosí, C.P., 78290, Mexico;2. Department of Energy Resources, University of Stavanger, 4036 Stavanger, Norway;3. Instituto de Geología, Universidad Autónoma de San Luis Potosí, Manuel Nava #5Zona Universitaria, San Luis Potosí, S.L.P., Mexico;4. Unidad Académica de Ciencias de la Tierra, Universidad Autónoma de Guerrero, Ex–Hacienda de San Juan Bautista, S/N, Taxco el Viejo, Guerrero, Mexico;5. Grupo de Geología Exógena y del Sedimentario, Valle de la Hiedra 113B, Fracc. Valle de Santiago, Soledad de Graciano Sánchez, San Luis Potosí, C.P. 78433, Mexico;1. Sinopec Petroleum Exploration and Production Research Institute, Beijing 100083, People''s Republic of China;2. School of Energy Resources, China University of Geosciences, Beijing 100083, People''s Republic of China;3. Energy and Geoscience Institute, University of Utah, Salt Lake City, UT 84108, United States;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;2. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;4. Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA;5. School of Earth and Space Exploration, Arizona State University, Tempe 85287, USA;6. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;7. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;2. Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China;3. State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Wuhan 430074, China;4. Department of Geology, University of Cincinnati, Cincinnati 45221-0013, USA;5. Department of Earth Sciences, University of California, Riverside, CA 92521, USA;6. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;7. School of Earth and Space Exploration, Arizona State University, Tempe 85287, USA |
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| Abstract: | Geochemical compositions of the Lower Cambrian Niutitang Formation shales in the southeastern Yangtze Platform margin were investigated for provenance, tectonic setting, and depositional environment. The shale samples are characterized by higher abundances of large ion lithophile elements (Cs, Ba, and Pb), lower abundances of high field strength elements (Cr, Sc, and Co) and transition elements (Th, Zr, Hf, Nb, and Ta) relative to average shale. North American shale composition (NASC) -normalized rare earth element (REE) patterns are observed, with negative Ce anomalies, negative Eu anomalies, and positive Y anomalies. The chemical index of alteration (CIA) varies from 68.67–74.93. Alkali and alkaline element contents and CIA values suggest that the source rocks have undergone moderate weathering. The index of compositional variability (ICV), Zr/Sc and Th/Sc ratios vary from 0.53 to 1.07, 5.31 to 8.18 and 0.52–1.02, respectively. ICV values and relationships between Zr/Sc and Th/Sc ratios indicate negligible sedimentary recycling. The Al2O3/TiO2 (14–26) and TiO2/Zr (56–77) ratios imply that the source rocks of the investigated shales had intermediate igneous compositions. However, Cr/V ratios and a La/Th–Hf discrimination diagram suggest that the intermediate compositional signal of the source rocks was derived from a mixture of 75% mafic and 25% felsic igneous rocks rather than intermediate igneous rocks. The major source was the Jiangnan continental island arc with bimodal igneous rocks, lying to the south of the study area, together with a contribution from granites and gneisses uplifted and eroded in the Yangtze Block. Discrimination of tectonic setting using major and trace elements indicates that the source rocks originated in a transitional setting from active continental to passive margin, consistent with the failed intracontinental rift model for the evolution of the South China plate. The Niutitang Formation shales were deposited in a rift basin setting under conditions of anoxic bottom water in a redox-stratified water column, with organic-rich shales prospective for shale-gas production being found in deep-water downslope and basin environments rather than the shallow-water shelf. |
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| Keywords: | Niutitang shale Weathering Provenance Tectonic setting Depositional setting |
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