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Role of tectonic activities on kerogen maturity and carbon stable isotope signature of coal

Abstract

Higher ranked Permian and Cenozoic coals are reported in tectonically affected regions of northeast India. The geochemical signature of the tectonically induced higher-ranked coals has not been studied carefully, although such coals' hydrocarbon potential is assessed using parameters, such as kerogen maturity. Notably, published data of stable isotope ratio of organic carbon (δ13C) analysis in Indian coal is rare, and only a few researchers attempted to study the δ13C signature of tectonically affected coals. We have studied the δ13C and kerogen maturity parameters in the Permian sub-bituminous coal from Arunachal Pradesh, Permian Anthracite from Sikkim, Late Oligocene bituminous coal from Tirap and Ledo Open Cast Projects in Assam, Eocene lignites from Umarsar, Matanomadh and Panandhro and Upper Eocene to Oligocene lignite from the Tadkeshwar lignite mines in Gujarat, and Mio-Pliocene lignite from Neyveli lignite mine in Tamil Nadu. The results are compared with the published data to understand the tectonic effect on the kerogen character and δ13C signature of coal. Cenozoic lignites, not affected by thrusting, are mainly composed of mixed type-II to III (oil–gas prone) and/or type-III kerogen (gas prone). Low Tmax (maximum pyrolysis temperature) values of the lignites further indicate the thermally immature character of the kerogen. In contrast, tectonically affected Cenozoic sub-bituminous coals show higher maturity of kerogen. Permian coals, affected by the shear stress of the Main Boundary Thrust (MBT), show type-IV (inert) and post-mature character of kerogen. The study reflects that tectonic activities strongly influence kerogen maturity. Enriched δ13C values of Permian coals compared to the younger Cenozoic coals are attributed to the enrichment of the heavier carbon isotope during coalification. Tectonically driven alteration of coal is evidenced by the enriched δ13C values of the thrust-affected coals. Nonetheless, an overall C3 plant source of the coal organic matter irrespective of the age, rank and tectonic history is reflected by the δ13C values (–21‰ to –27‰). The stable isotope composition further assigns an angiosperm source to the Cenozoic coals and a gymnosperm source to the Permian coals. The results indicate that kerogen maturity and δ13C of coal reflect the influence of tectonic activities, although the stable isotope source signature of coal remains unaffected.

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source of coal OM (after Khan et al. 2015).

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Acknowledgements

The authors gratefully acknowledge the financial help of the DST, Government of West Bengal, India (Memo No.: 173 (Sanc.)/ST/P/S&T/10G-23/2017) and DST (No: DST/INT/JSPS/P-232/2016) is acknowledged for providing fund for the research. The authors are also thankful to the authority of NLC, RSMML, CIL and GMDC for their permission for sampling and fieldwork. Sumit K Ray, Kalyan Halder, Arunabha Dey, Sourav P Adhya are acknowledged for helping with the sampling.

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Supriyo Kumar Das: Conceptualization, methodology, validation, investigation, resources, writing – original draft, visualization, supervision, project administration, funding acquisition. Madhurima Ganguly: Writing – review and editing. Mainak Ghosh: Formal analysis, fieldwork and sample collection. Devleena Mani: Formal analysis. Kalpana M S: Formal analysis, review and editing. Subhadeep Kumar: Resources.

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Correspondence to Supriyo Kumar Das.

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Communicated by Santanu Banerjee

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Das, S.K., Ganguly, M., Ghosh, M. et al. Role of tectonic activities on kerogen maturity and carbon stable isotope signature of coal. J Earth Syst Sci 130, 214 (2021). https://doi.org/10.1007/s12040-021-01707-x

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Keywords

  • Kerogen maturity
  • stable isotopes
  • Rock-Eval pyrolysis
  • thrusts
  • coal
  • India