Tectonic inferences from palynology of Permian sequences of the Godavari Valley Coalfield, Southern India

Abstract

Core samples from four boreholes (SAV-1, SAV-117, SAV-124, SAV-125) within the Vaddugudem block of the Godavari Valley Coalfield, Southern India have been palynologically investigated to understand the stratigraphic setting of that area. Only 60 out of the 172 samples yielded identifiable palynoassemblages. From the observed palynofloral composition, five distinct palynoassemblages (Scheuringipollenites Assemblage: PA-I, Striatopodocarpites + Faunipollenites Assemblage: PA-II, Striates + Striasulcites Assemblage: PA-III, Striates + Guttulapollenites Assemblage: PA-IV, Lundbladispora + Verrucosisporites Assemblage: PA-V) were identified. Furthermore, five distinct palynozones (Scheuringipollenites barakarensis Zone = PZ-1, Striatopodocarpites + Faunipollenites Zone = PZ-2, Gondisporites raniganjensis Zone = PZ-3, Guttulapollenites gondwanensis-Striatopodocatpites tiwarii Zone = PZ-4 and Playfordiaspora cancellosa Zone = PZ-5) were identified. These correspond to the Artinskian (PZ-1), Wordian–Capitanian (PZ-2 and PZ-3), Wuchiapingian–Changhsingian (PZ-4) and Induan–Olenekian (PZ-5), respectively. The study site is situated within a geologically active region within the basin, primarily attributed to the exposure of elevated basement rocks on the eastern side of the borehole locations. Notably, the palynozones appear as relatively narrow layers in the boreholes investigated within this tectonically disturbed basin. The repetition of palynoassemblages and palynozones at small intervals suggests that the boreholes are located in a fault zone with multiple fault planes and that palynomorphs were reworked along these fault planes. Fault slices of different lithological units containing palynoassemblages may have intersected the boreholes. Specifically, the recurrence of thin marker palynoassemblages and palynozones, which show similarities in age to the Barakar and Lower Kamthi/Raniganj formations, is likely attributable to tectonic disturbances, such as faulting. This disturbance may have induced the reworking or migration of palynomorphs along the fault plane. As a result, it is concluded that variations in the stratigraphic abundance of these reworked palynomorphs can serve as indicators of tectonic settings, even when these settings are not readily discernible in the geological record.