Unraveling the Charred Past: Microscopic Insights and Advanced Techniques in Understanding Permian Palaeofires

This study conducts a comprehensive palynofacies and geochemical analysis to characterize organic matter (OM) in shale samples from the Godavari Basin. Palynofacies analysis identified three types of organic matter under transmitted light: translucent organic matter (TrOM), comprising palynomorphs, structured phytoclasts, and degraded organic matter; and two types of opaque phytoclasts/charcoal (CH), distinguished as palaeofire-induced (PAL-CH) and oxidized (OX-CH). The multifaceted approach is applied through Raman spectroscopy, Rock-Eval, and Fourier transform infrared spectroscopy (FTIR) to assess organic carbon's thermal evolution and structural integrity required to substantiate the palynological evidence on microcharcoal. The intensity ratio (ID/IG) ranged from 0.20 to 0.47, indicating varying impacts of thermal events on carbon structures. Higher ID/IG ratios corresponded with samples affected by palaeofires. Additionally, D-FWHM and G-FWHM parameters were analyzed, revealing larger D-FWHM values in thermally matured samples, indicating greater disorder in the carbon structure. The D-FWHM/G-FWHM ratio, exceeding unity, suggested significant structural shifts toward disordered carbon domains. Consequently, the presence of overmaturation of organic matter ranging from 411 to 609 °C indicates the alteration of organic matter due to the impact of heat causing the removal of hydrogen from the samples. FTIR spectroscopy suggests the presence of aromatic and aliphatic deformation due to thermal maturation. This integrated approach combining palaeofire history, Raman spectroscopy, and geochemical analysis provides valuable insights into the palaeofire history and structural evolution of charcoal in the Godavari Basin shales.