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<p>A comprehensive geochemical study was conducted on the Late Cretaceous–Eocene Coal Measure succession exposed at the mine faces in the West Coast Basin, New Zealand. This study employed organic geochemical and biomarker investigations, combined with carbon isotope analysis, to assess the input of organic matter (OM) and paleoenvironmental conditions. This work also aims to understand the characteristics of the source rocks and the exploitation of the basin's natural resources. The studied coal samples exhibit a total organic carbon (TOC) content exceeding 60 wt.% and a low sulfur content of less than 1 wt.% (0.17–0.72%), resulting in very low TS/TOC values of less than 0.1, which suggests a predominantly freshwater environment and well-oxygenated conditions. This studied coal succession is characterized by a high pristane-to-phytane (Pr/Ph) ratio &gt; 4, and low C<sub>32</sub>R/C<sub>30</sub> hopane and dibenzothiophene-to-phenanthrene (DBT/P) ratios, indicate deposition under highly oxygenated environments, transitioning from fluvial to fluvio-deltaic settings. The studied Coal Measure succession also shows an elevated Tm/Ts ratio and a significant abundance of C<sub>29</sub> regular sterane compared to C<sub>27</sub> and C<sub>28</sub> regular sterane, indicating that the organic matter is predominantly derived from terrestrial organic matter. The Late Cretaceous–Eocene Coal Measure succession is also characterized by a predominance of Type III kerogen to mixed Type II/III kerogen, with hydrogen index (HI) values ranging from 92 to 333 mg HC/g TOC, indicating both oil and gas potential, with a substantial prospect for mainly gas generation. However, the studied Coal Measure succession has reached the early–moderate mature stage of the oil generation window, and therefore, this organic-rich coal has not yet released commercial amounts of oil for expulsion, because the adsorption of oil on the organic macromolecules of the coal, derived from higher plants, prevents this. Therefore, an intensive hydrocarbon exploration of the Late Cretaceous–Eocene Coal Measure succession is recommended in the deeper structural units of the West Coast Basin. </p>

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Evaluating the organic matter input, paleoenvironmental conditions, and hydrocarbon prospective of the Late Cretaceous–Eocene Coal Measure succession in the West Coast Basin, New Zealand

  • 期刊论文

  • 发表日期：

    2025年5月19日

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  • Mohammed Hail Hakimi,
  • Mahdi Ali Lathbl,
  • Akm Eahsanul Haque,
  • Hassan Soleimani,
  • Ali Y. Kahal,
  • Afikah Rahim,
  • Madyan M. A. Yahya

摘要

A comprehensive geochemical study was conducted on the Late Cretaceous–Eocene Coal Measure succession exposed at the mine faces in the West Coast Basin, New Zealand. This study employed organic geochemical and biomarker investigations, combined with carbon isotope analysis, to assess the input of organic matter (OM) and paleoenvironmental conditions. This work also aims to understand the characteristics of the source rocks and the exploitation of the basin's natural resources. The studied coal samples exhibit a total organic carbon (TOC) content exceeding 60 wt.% and a low sulfur content of less than 1 wt.% (0.17–0.72%), resulting in very low TS/TOC values of less than 0.1, which suggests a predominantly freshwater environment and well-oxygenated conditions. This studied coal succession is characterized by a high pristane-to-phytane (Pr/Ph) ratio > 4, and low C32R/C30 hopane and dibenzothiophene-to-phenanthrene (DBT/P) ratios, indicate deposition under highly oxygenated environments, transitioning from fluvial to fluvio-deltaic settings. The studied Coal Measure succession also shows an elevated Tm/Ts ratio and a significant abundance of C29 regular sterane compared to C27 and C28 regular sterane, indicating that the organic matter is predominantly derived from terrestrial organic matter. The Late Cretaceous–Eocene Coal Measure succession is also characterized by a predominance of Type III kerogen to mixed Type II/III kerogen, with hydrogen index (HI) values ranging from 92 to 333 mg HC/g TOC, indicating both oil and gas potential, with a substantial prospect for mainly gas generation. However, the studied Coal Measure succession has reached the early–moderate mature stage of the oil generation window, and therefore, this organic-rich coal has not yet released commercial amounts of oil for expulsion, because the adsorption of oil on the organic macromolecules of the coal, derived from higher plants, prevents this. Therefore, an intensive hydrocarbon exploration of the Late Cretaceous–Eocene Coal Measure succession is recommended in the deeper structural units of the West Coast Basin.