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Geoscience ›› 2019, Vol. 33 ›› Issue (03): 615-628.DOI: 10.19657/j.geoscience.1000-8527.2019.001

• Structural Geology and Stratigraphy • Previous Articles     Next Articles

Geochemical Characteristics and Paleoclimatic Implications of the Upper Permian and Middle-Lower Triassic Strata in Southern Ordos Basin

TAN Cong1(), YUAN Xuanjun1(), YU Bingsong2, LIU Ce1, LI Wen3, Cui Jingwei1   

  1. 1. PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China
    2. School of Earth Sciences and Resources,China University of Geosciences, Beijing 100083, China
    3. Exploration and Development Research Institute of Huabei Oilfield Company, Renqiu,Hebei 062550, China
  • Received:2018-05-14 Revised:2019-01-24 Online:2019-06-23 Published:2019-06-24
  • Contact: YUAN Xuanjun

Abstract:

To explore the paleoclimate evolution of the terrestrial Permian-Triassic system, mudstone samples were collected from the Permian Shiqianfeng Formation (P3s) and the Triassic Liujiagou (T1l), Heshanggou (T1h) and Zhifang (T2z) formations in the Shichuanhe section of Tongchuan (Shaanxi Province) in the southern Ordos Basin. The samples were analyzed for their mineralogy, petrology, and geochemistry. The paleosalinity, paleoredox and paleoclimate evolution were studied by the major-trace elements, total organic carbon (TOC), and carbon and oxygen isotopes. It is shown that the geochemical and carbon-oxygen isotope compositions near the P/T boundary had changed greatly. Fluctuation of climatic and environmental chemical indicators reflects the paleo-climatic/-environmental changes in the Ordos Basin from the Late Permian to the Middle-Late Triassic. It is shown that the Shiqianfeng Formation was deposited in a fluvial-deltaic environment that was relatively reduced, and that the paleoclimate was relatively warm and humid. The purplish-red clastic rock of the Lower Triassic Liujiagou and Heshanggou formations were deposited in shallow water, hot and arid fluvial-deltaic environment under strongly oxidizing conditions.During the deposition of the Middle-Triassic Zhifang Formation, the water level rose and chemical transfer was enhanced, and the depositional environment may have been semi-arid/-humid and reducing. Carbon isotope evidence shows that the P/T boundary in the terrestrial Ordos basin has significant negative δ13CPDB features, which are comparable with the global marine P/T boundary. This indicates that major geological events such as abrupt climate changes and mass extinctions were also recorded in the North China continental P/T boundary, consistent with the marine stratigraphic record.

Key words: Ordos Basin, Permian-Triassic boundary, carbon and oxygen isotope, paleoclimate, paleoenvironment

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