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ABSTRACT

Deccan volcanism likely triggered environmental stress that controlled biotic transformations and Cretaceous/Paleogene (K/Pg) boundary mass extinction in the Indian subcontinent, but these revelations still remain inconclusive. Thus, we conducted high-resolution organo-molecular studies on a marine Um-Sohryngkew River K/Pg boundary succession. The results were used as standard reference for comparison with biotic attributes of the brackish water (Jhilmili) to freshwater (Anjar) intertrappean sediments and bole beds of the Deccan Traps. Organo-molecular compounds of the former section show strong correlation with the global stratotype section and point. High amounts of short-chain n-fatty acids and n-alkanes derived from autochthonous marine algal remains were observed in this section. However, the dominance of mid- and long-chain n-alkanes over short-chain n-alkanes in the Jhilmili intertrappean and intravolcanic bole beds of the eastern Deccan volcanic province suggested a terrestrial origin from higher plants under semiarid climatic conditions. The prolific abundance of n-alkanes in the Um-Sohryngkew River succession implies a mixture of terrestrial input from emergent and submerged/floating aquatic macrophytes. Low-molecular-weight aromatic hydrocarbon markers peak in biozone CF2 of the Um-Sohryngkew River succession. Possibly, this corresponds to greenhouse effects linked to the second phase of Deccan volcanism in the latest Maastrichtian, chron 29r. Abundant n-fatty acids found in the eastern Deccan bole beds suggest an origin from bacteria developed in a terrestrial environment. Depleted δ13Cbulk values recorded from Jhilmili intertrappean and eastern Deccan bole beds are indicative of low primary productivity and burning of terrestrial biomass. Total organic carbon (TOC) maxima observed in the lowermost Danian P1a foraminiferal biozone of the Um-Sohryngkew River succession are also linked to late Deccan phase-two eruptions. The presence of three low-molecular-weight aromatic hydrocarbon markers in the eastern Deccan bole bed implies incomplete combustion of organic compounds in a terrestrial environment. Moreover, the dominance of high-molecular-weight aromatic hydrocarbon markers in biozone CF3 of the Um-Sohryngkew River succession is akin to that reported from other well-established K/Pg boundary successions, suggestive of their possible derivation from regional fire induced by the heat supplied by Deccan volcanism, which has been linked to the K/Pg boundary transition. Thus, regional wildfire played a significant role and affected the ecosystem, which perhaps accounts for the mass extinction.

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