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Paleoenvironment and Organic Matter Accumulation of the Upper Ordovician-Lower Silurian, in Upper Yangtze Region, South China: Constraints from Multiple Geochemical Proxies

Author

Listed:
  • Zisang Huang

    (School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China
    State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China)

  • Xingzhi Wang

    (School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China
    State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China)

  • Xiyan Yang

    (School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China)

  • Rukai Zhu

    (Research Institute of Petroleum Exploration&Development, PetroChina, Beijing 100083, China)

  • Jingwei Cui

    (Research Institute of Petroleum Exploration&Development, PetroChina, Beijing 100083, China)

  • Wenrui Shi

    (College of Geophysics and Petroleum Resources, Yangtze University, Wuhan 430100, China)

  • Yiqing Zhu

    (Shale Gas Research Institute, PetroChina Southwest Oil&Gas Field Company, Chengdu 610051, China)

Abstract

The origin of the organic-rich shale in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation is complex and controversial. This paper reports the geochemical data of Wufeng-Longmaxi Formations in the Upper Yangtze region to restore the paleoenvironment and explore the accumulation mechanism of organic matter. The total organic carbon (TOC) content of the Wufeng Formation was relatively high, with an average of 2.86%. The Lower Longmaxi Formation showed the highest TOC content, with an average of 3.99%, and the upper part was a continuously low value with an average of 1.22%. The paleoproductivity proxies (Ba bio , Cu/Al, Ni/Al, Si excess ) showed that in the Katian and Rhuddanian-Aeronian Stages, the Upper Yangtze Sea had high primary productivity, indicating that organic matter accumulation was more affected by terrigenous influx and redox conditions. Al, Zr, and Zr/Al indicated that terrigenous influx was relatively high in the Kaitian-Hirnantian Stages, it was at a constant low in the Rhuddanian Stage, and increased again in the Aeronian Stage. The correlations between redox-sensitive trace elements (Mo, U, V) and TOC indicate that the organic-rich shale of the Wufeng Formation was deposited in the anoxic–euxinic environment. In the Longmaxi Formation, organic-rich shales formed in a more hypoxic environment, and overlying organic-lean shales formed in a suboxic environment. Therefore, the anoxic–euxinic conditions of the Late Ordovician Yangtze Sea were the main reason for the organic matter accumulation, but the high terrigenous influx caused by regression and/or structural controls diluted the organic matter to some extent. For the Early Silurian, a complete transgression–regression cycle changed terrigenous influx and redox conditions, resulting in significant differences in organic matter accumulation.

Suggested Citation

  • Zisang Huang & Xingzhi Wang & Xiyan Yang & Rukai Zhu & Jingwei Cui & Wenrui Shi & Yiqing Zhu, 2020. "Paleoenvironment and Organic Matter Accumulation of the Upper Ordovician-Lower Silurian, in Upper Yangtze Region, South China: Constraints from Multiple Geochemical Proxies," Energies, MDPI, vol. 13(4), pages 1-16, February.
    • Handle: RePEc:gam:jeners:v:13:y:2020:i:4:p:858-:d:321256
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    References listed on IDEAS

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    1. Ruibo Guo & Jinchuan Zhang & Panwang Zhao & Xuan Tang & Ziyi Liu, 2019. "Accumulation Conditions and an Analysis of the Origins of Natural Gas in the Lower Silurian Shiniulan Formation from Well Anye 1, Northern Guizhou Province," Energies, MDPI, vol. 12(21), pages 1-29, October.
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    Cited by:

    1. Yao Du & Xingzhi Wang & Ruifeng Tang & Yiqing Zhu & Cong Yang & Hongfei Zhou & Qian Pang, 2022. "Extraordinarily High Organic Matter Enrichment in Upper Permian Wujiaping Formation in the Kaijiang-Liangping Trough, Sichuan Basin," Energies, MDPI, vol. 16(1), pages 1-17, December.

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