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<p>The Lower Silurian Longmaxi Formation is a key stratigraphic layer for shale gas exploration and development in the Middle Yangtze Block. The organic matter content of this formation is a crucial indicator of the shale gas enrichment. However, no systematic comparative research has been conducted on the factors controlling the organic matter enrichment of the shale in the western Middle Yangtze Block. In this paper, we compare the sedimentological and geochemical characteristics of the Longmaxi Formation shales in the passive continental margin and cratonic depression in the western Middle Yangtze Block in order to explore the main controlling factors and formation patterns of the differential organic matter enrichment. The results show that the section of the shale with a total high organic carbon (TOC) content is located at the bottom of the Longmaxi Formation, and it formed in a foreland flexural subsidence setting characterized by low terrestrial input, high paleoproductivity, and good preservation conditions. Subsequently, as the flexural migration gradually strengthened and the sea level continued to decline, the shale experienced increased terrestrial input and deteriorating preservation conditions. However, the paleoproductivity level was weakly affected by the sea level decline, exhibiting a gradual increase; this was mainly due to the fact that the flexural migration caused the gradual opening of the barrier in the northern Yangtze Basin and the gradual increase in the influx of ocean currents. Therefore, vertically, the decrease in the TOC content in the Longmaxi Formation was mainly controlled by the deterioration of the preservation conditions and the increase in the terrestrial input. Laterally, the shale transitioned from the passive continental margin to the cratonic depression, with decreasing sea level and ocean current activity, along with deteriorating preservation conditions and paleoproductivity levels, leading to a decrease in the TOC content. As a result, the focus of shale gas exploration and development in the Longmaxi Formation should be focused the northwest region. The results of this study have significant implications for gaining a deeper understanding of the evolution of the paleoenvironment of the Longmaxi Formation shales and the mechanisms of organic matter enrichment and thus provide guidance for shale gas exploration practices.</p>

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Paleoenvironmental Changes in Organic Matter Deposition in Shales and Their Significance for Shale Gas Exploration

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • Xuefeng Bai,
  • Haibin Zhao,
  • Pengwan Wang,
  • Ping Jiang,
  • Famu Huang,
  • Tao Yang

摘要

The Lower Silurian Longmaxi Formation is a key stratigraphic layer for shale gas exploration and development in the Middle Yangtze Block. The organic matter content of this formation is a crucial indicator of the shale gas enrichment. However, no systematic comparative research has been conducted on the factors controlling the organic matter enrichment of the shale in the western Middle Yangtze Block. In this paper, we compare the sedimentological and geochemical characteristics of the Longmaxi Formation shales in the passive continental margin and cratonic depression in the western Middle Yangtze Block in order to explore the main controlling factors and formation patterns of the differential organic matter enrichment. The results show that the section of the shale with a total high organic carbon (TOC) content is located at the bottom of the Longmaxi Formation, and it formed in a foreland flexural subsidence setting characterized by low terrestrial input, high paleoproductivity, and good preservation conditions. Subsequently, as the flexural migration gradually strengthened and the sea level continued to decline, the shale experienced increased terrestrial input and deteriorating preservation conditions. However, the paleoproductivity level was weakly affected by the sea level decline, exhibiting a gradual increase; this was mainly due to the fact that the flexural migration caused the gradual opening of the barrier in the northern Yangtze Basin and the gradual increase in the influx of ocean currents. Therefore, vertically, the decrease in the TOC content in the Longmaxi Formation was mainly controlled by the deterioration of the preservation conditions and the increase in the terrestrial input. Laterally, the shale transitioned from the passive continental margin to the cratonic depression, with decreasing sea level and ocean current activity, along with deteriorating preservation conditions and paleoproductivity levels, leading to a decrease in the TOC content. As a result, the focus of shale gas exploration and development in the Longmaxi Formation should be focused the northwest region. The results of this study have significant implications for gaining a deeper understanding of the evolution of the paleoenvironment of the Longmaxi Formation shales and the mechanisms of organic matter enrichment and thus provide guidance for shale gas exploration practices.