Palynofloral, palynofacies and carbon isotope of Permian coal deposits from the Godavari Valley Coalfield, South India: Insights into the age, palaeovegetation and palaeoclimate

Abstract

Palynological studies of the present Permian sediments play a vital role in biostratigraphic and palaeoecological interpretations. Additionally, the palynofacies analysis, Total Organic Carbon (TOC) content and δ13C value in the present study focus largely for the palaeoenvironmental and palaeoclimatic reconstruction and also provides information about processes responsible for sedimentary deposits along with their lithological counter parts. The palynological investigation of 306 m deep borehole (MSM-25) from the Somavaram area of the Godavari Valley Coalfield has led to infer five distinct palynofloral assemblages. The Artinskian (Palynofloral assemblage-I and II), Guadalupian (Palynofloral assemblage-III and IV), and Lopingian (Palynofloral assemblage-V) ages have been assigned to the palynofloral assemblages based on the palynofloral evidence. The distinct stable carbon isotope ratios also comprehend these ages with extreme climatic events. The Artinskian age (−22.4‰) is characterized by relatively higher average δ13C values, whereas lowest average δ13C values are observed at the Lopingian age (−24.0‰) with intermediate average δ13C value (−23.2‰) during Guadalupian age. In the present study, the Permian-Triassic (P-T) transition is marked by the distinct negative carbon-isotope excursion followed by a distinct recovery during the early Triassic time period. The relative variability of palynofacies components, such as palynomorphs, structured terrestrial phytoclasts, opaque phytoclasts, degraded organic matter (OM) and amorphous OM, is related to hydrodynamic perturbations during the deposition time. Based on the dominance and sub-dominance of the palynofacies, three distinct depositional phases have been identified, representing differential environmental settings. The palynomorphs and structured terrestrial phytoclasts dominate the Palynofacies assemblage A suggesting forest swamp environment, while in the Palynofacies assemblage B the dominance of degraded OM and amorphous OM characterize Reed marshes/lakeshore setting and the abundance of opaque phytoclasts in the Palynofacies assemblage C indicate oxidized swamp environment.