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<p>The Lesser Himalayan (Extra-Peninsular) Gondwana coal of Permian age remains rarely explored relative to its Peninsular counterparts with respect to its paleodepositional setting, provenance, and paleoclimate. This study offers an integrated petrological and geochemical examination of Extra-Peninsular Gondwana (Upper Permian) coals from Arunachal Pradesh and Darjeeling, Northeastern India, to determine their organic matter sources, paleoenvironments, provenance, and paleoclimatic conditions. A total of 27 coal samples were collected, with representative samples analysed for maceral composition, mineralogy, major oxides, and trace elements using reflected-light microscopy, X-ray Diffraction (XRD), X-ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), respectively. Vitrinite Reflectance (%VR<sub>o</sub>) values (0.88–1.79%) indicate medium to high thermal maturity, corresponding to medium-volatile bituminous to semi-anthracite rank. Maceral examination shows vitrinite-rich assemblages (64.5–93.2%), with subordinate inertinite (6.8–35.4%) and negligible liptinite content (ranging from 0% to 0.3%), suggesting dominance of woody vegetation during peat accumulation. Mineralogical data reveal quartz and kaolinite as dominant phases, along with illite, siderite, dolomite, and pyrite, suggesting appreciable terrigenous input. Geochemical data indicate enrichment of SiO₂, Al₂O₃, and Fe₂O₃, suggesting an intermediate to felsic provenance. Facies indices and maceral-based ternary plots suggest deposition in forested to limnic swamp environments with fluctuating water tables, alternating oxic and anoxic conditions, and predominantly humid climates with pockets of aridity. Sr/Cu ratios and oxide association indicate predominantly humid conditions with an irregular drier phase. Redox-sensitive element concentrations further suggest fluctuating oxic-to-suboxic conditions, with possible episodic brackish water during peat accumulation. This study offers new insights into the origin, evolution, and paleoenvironmental context of the Extra-Peninsular Gondwana coals, emphasising their potential as repositories of critical elements for future resource exploitation.</p>

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Geochemical and petrological investigation of extra-peninsular Gondwana coals from NE India: Insights into provenance, paleoclimate, and paleoenvironment

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  • 发表日期：

    2026年8月4日

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  • Manuranjan Konwar,
  • Dhrubajyoti Neog,
  • Diganta Bhuyan,
  • Alok Kumar,
  • Prakash K. Singh

摘要

The Lesser Himalayan (Extra-Peninsular) Gondwana coal of Permian age remains rarely explored relative to its Peninsular counterparts with respect to its paleodepositional setting, provenance, and paleoclimate. This study offers an integrated petrological and geochemical examination of Extra-Peninsular Gondwana (Upper Permian) coals from Arunachal Pradesh and Darjeeling, Northeastern India, to determine their organic matter sources, paleoenvironments, provenance, and paleoclimatic conditions. A total of 27 coal samples were collected, with representative samples analysed for maceral composition, mineralogy, major oxides, and trace elements using reflected-light microscopy, X-ray Diffraction (XRD), X-ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), respectively. Vitrinite Reflectance (%VRo) values (0.88–1.79%) indicate medium to high thermal maturity, corresponding to medium-volatile bituminous to semi-anthracite rank. Maceral examination shows vitrinite-rich assemblages (64.5–93.2%), with subordinate inertinite (6.8–35.4%) and negligible liptinite content (ranging from 0% to 0.3%), suggesting dominance of woody vegetation during peat accumulation. Mineralogical data reveal quartz and kaolinite as dominant phases, along with illite, siderite, dolomite, and pyrite, suggesting appreciable terrigenous input. Geochemical data indicate enrichment of SiO₂, Al₂O₃, and Fe₂O₃, suggesting an intermediate to felsic provenance. Facies indices and maceral-based ternary plots suggest deposition in forested to limnic swamp environments with fluctuating water tables, alternating oxic and anoxic conditions, and predominantly humid climates with pockets of aridity. Sr/Cu ratios and oxide association indicate predominantly humid conditions with an irregular drier phase. Redox-sensitive element concentrations further suggest fluctuating oxic-to-suboxic conditions, with possible episodic brackish water during peat accumulation. This study offers new insights into the origin, evolution, and paleoenvironmental context of the Extra-Peninsular Gondwana coals, emphasising their potential as repositories of critical elements for future resource exploitation.