The Carboniferous-Permian transition in Arunachal Pradesh, North East India: A palynological and palynofacies study

Palynology and palynofacies analyses were carried out from an outcrop of the Bichom Formation located in Arunachal Pradesh, North-East India. The age of the Bichom Formation at this locality is inferred based on palynological investigation and correlation with coeval assemblages from India and across Gondwana, suggesting that these deposits may represent the Permo-Carboniferous transitional phase, dated as latest Carboniferous to Permian (Asselian). The recovered palynocomposition shows the dominance of Cordaitales, different spore taxa, followed by Glossopteridales, Coniferales, and Algae. Palynofacies (PF) analysis identifies three assemblage zones reflecting variable depositional settings. PF-I, dominated by phytoclasts, represents proximal fluvio-deltaic to floodplain environments, with subzones (IA–IC) marking a transition from low-energy floodplain facies to higher-energy distributary channels. PF-II, characterized by the dominance of bacterially derived amorphous organic matter (AOM), indicates distal low-energy conditions such as prodelta to restricted shelf or lacustrine settings, where persistent anoxia promoted organic matter preservation. PF-III, with a balanced phytoclast–AOM composition and contrasting lithologies, reflects transitional delta-front to shallow marine environments shaped by fluctuating sediment supply, redox variability, and possible sea-level oscillations. The palynofacies analysis of the Bichom Formation reveals a complex mosaic of depositional environments influenced by fluctuating terrestrial and aquatic inputs under variable energy and redox conditions during deposition. • Palynoassemblage comprises Cordaitales, Filicales, Lycopsidales, Equisetopsidales, Glossopteridales, Coniferales, and algae, reflecting a diverse and complex terrestrial vegetation. • The palynoassemblage is dominated by Cordaitales pollen grains and trilete spores, indicating a late Carboniferous to Asselian (early Permian) transition time. • Palynofacies assemblage zones indicate a dynamic fluvio-deltaic to shallow marine system. • The prevalence of monosaccate (Cordaitales) pollen grains suggests a cold, low-humidity climate during deposition, reflecting post-glacial conditions with seasonally dry, cold-tolerant vegetation dominating the basinal lowlands.