Impact of Deccan Volcanism on evolution of higher plant terpenoids

The Deccan volcanism represents one of the largest volcanic eruptions in Earth’s history. The volcanic activity significantly impacted global environmental changes and played a crucial role in the Maastrichtian period's floral and faunal diversification. The present study aims to explore the palaeovegetation during the Deccan Volcanism for better understanding of floral occurrences using biomarker proxy. The sediment samples from the Early Cretaceous Kutch Basin and Late Cretaceous Deccan Intertrappean samples were investigated. The samples were analysed by extracting the bitumen fraction and separating it into saturates and aromatics using column chromatography. Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry was employed to analyse the resulting fractions. The saturated fractions of Early Cretaceous Kutch Basin were dominated by n-alkanes and acyclic isoprenoids with a slight OEP predominance and high CPI. In the Kutch samples, diterpenoids such as labdane, ent-beyerene, isopimarane etc were detected. However, in the Late Cretaceous samples only dihydrorimuene and abeitane were identified in the saturated fractions, showing limited gymnosperm contribution. Hopanes series showed C27-32 hopanoids in the Intertrappeans along with mono-unsaturated hopanes. Mono- and di-unsaturated A-ring degraded compounds, including des-A-olean-13(18)-ene, des-A-olean-12-ene, olean-12-ene, olean-18-ene, urs-12-ene, olean-2, 13(18)-diene, and A-ring degraded compounds like des-A-ursane and des-A-lupane, related to angiosperm input were recorded in the Late Cretaceous samples. Additionally, various angiosperm-derived aromatic triterpenoids were detected in the Intertrappean samples. Based on the biomarker distribution, it was inferred that the palaeovegetation during the Cretaceous period showed a remarkable shift from gymnosperm dominated paleo-assemblage to angiosperm- dominated palaeovegetation and that the angiosperm evolved during the Cretaceous time. Overall, this study aims to shed light on the palaeovegetation during the Deccan Volcanism, providing insights into how the massive volcanic eruptions can impact the palaeoflora and paleoecology of the region.