The discovery of terrigenous siliciclastic rocks and its significance of the Lower Permian Qixia Formation in northern Sichuan Basin
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1.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu;2.Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications,MNR Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu;3.Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications, MNR & Institute of Sedimentary Geology, Chengdu University of Technology,;4.Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications, MNR & Institute of Sedimentary Geology, Chengdu University of Technology;5.Exploration and Development Research Institute, PetroChina Southwest Oil & Gasfield Company;6.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology

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    Abstract:

    Terrigenous siliciclastic deposits have been found in the Lower Permian Qixia Formation marine carbonate strata at the Shuanghui section, Wangcang County, northern Sichuan Basin. The provenance and depositional environment of the terrigenous siliciclastic rocks are analyzed through field section observation, sedimentology, petrology and zircon U-Pb chronology methods. On this basis, the paleogeographic pattern of the study area are reconstructed. The results show that the siliciclastic rocks has typical coastal-tidal flat depositional characteristics, which reflects that the study area experienced a transient sea level drop and exposure in the Early Qixia Stage. The morphologies of detrital zircons in sandstone indicate that they have experienced long distance transport or recycle deposition, and the U-Pb ages of zircons are mainly concentrated in the four age ranges of 2600–2400 Ma, 1800–1200 Ma, 1000–700 Ma and 500?400 Ma. Compared with the Zircon U-Pb age spectrums of the Permian, Devonian, Silurian and Precambrian strata and intrusive rocks around the Yangtze block, and integrated regional tectono-sedimentary evolution, we propose that the Siluran-Devonian strata is the possible source of the Permian siliciclastic rocks. The zircon age frequency spectrum of the Qixia Formation siliciclastic rocks is very similar to those of Liangshan Formation, which indicates that the Liangshan Formation is probably the direct material source of the siliciclastic rocks. The occurrence of siliciclastic rocks indicates that there existed short-lived island or old land in the local area of the northern Upper Yangtze, which provided a favorable depositional environment and source supply for the formation of siliciclastic rocks. Based on the sedimentary characteristics and provenance analysis of the siliciclastic rocks, a multi-stage Early Permian paleogeographic evolution model in the northern Sichuan Basin is established. The discovery of the terrigenous siliciclastic rocks of the Qixia Formation is of great significance for the deep understanding of the Early Permian paleogeographic pattern, tectono-sedimentary evolution and hydrocarbon exploration in the northern Upper Yangtze region.

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History
  • Received:November 14,2023
  • Revised:January 06,2024
  • Adopted:February 04,2024
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