Paleoenvironmental implications of Deccan volcanism relative to the Cretaceous-Paleogene (K-Pg) mass extinction: evidence from the ‘red bole’ record

• Red boles record chemical weathering during volcanic pauses in Deccan Traps. • Smectite-dominated clays indicate semi-arid conditions with fluctuating moisture. • Weathering proxies and isotopes show climate instability before the K–Pg mass extinction event. Large Igneous Provinces (LIPs) have been widely investigated for their potential role in mass extinction events. High-precision U-Pb zircon geochronology of the Deccan Traps indicates that peak eruptive activity began approximately 250 kyr before the Cretaceous-Paleogene (K-Pg) boundary and persisted into the early Danian, suggesting a causal link between Deccan volcanism and the K-Pg mass extinction. Within the Deccan stratigraphy, intra-volcanic weathered horizons known as red boles represent intervals of volcanic quiescence and serve as critical archives of paleoenvironmental conditions during the Deccan Traps emplacement. These red boles have been studied using a suite of geochemical proxies including major element composition, bulk rock and clay mineralogy, weathering indices, paleo-precipitation estimates, and stable isotope analyses to assess climatic and environmental changes induced by volcanism. Our multiproxy geochemical analysis of 26 red bole sections across the Deccan stratigraphy reveals that they are enriched in immobile elements such as Al and Fe 3+ . The clay fraction is dominated by smectite, suggesting semi-arid conditions with fluctuating moisture availability rather than persistent monsoonal climate. Weathering indices indicate progressive chemical weathering, likely exacerbated by acid rain associated with increasing volcanic emissions. Stable hydrogen and oxygen isotope compositions further suggest episodes of hydroclimatic instability that intensified alongside peak Deccan eruption rates, particularly near the K-Pg boundary. These findings reinforce the hypothesis that Deccan volcanism played a significant role in shaping Late Cretaceous climate variability and contributed to the environmental stresses leading up to the K-Pg mass extinction.