MULTIPROXY EVIDENCE OF MAIN DECCAN VOLCANIC PULSE NEAR THE CRETACEOUS-TERTIARY BOUNDARY

Recent studies indicate that the bulk (80%) of Deccan trap eruptions occurred over a relatively short time interval in magnetic polarity C29r, whereas multiproxy studies from central and southeastern India place the Cretaceous-Tertiary (KT) mass extinction near the end of this main phase of Deccan volcanism suggesting a cause-and-effect relationship.

In India a strong floral response is observed as a direct response to Deccan volcanic phase-2. In Lameta (infratrappean) sediments preceding the volcanic eruptions, palynoflora are dominated by gymnosperms and angiosperms with a rich canopy of gymnosperms (Conifers and Podocarpaceae) and an understory of palms and herbs. Immediately after the onset of Deccan phase-2, this floral association was decimated leading to dominance of angiosperms and pteridophytes at the expense of gymnosperms. In subsequent intertrappean sediments a sharp decrease in pollen and spores coupled with the appearance of fungi mark increasing stress conditions apparently as a direct result of volcanic activity. The inter-trappean sediments corresponding to Phase-2 (80% of Deccan basalt emissions, latest Maastrichtian) are characterized by the highest alteration CIA index values. Values of mass specific magnetic susceptibility are two order lower than analogue lake sediments developed under basaltic bedrock, suggesting phenomena of iron oxides dissolution by reduction/acidity. This is probably better explained by increased acid rains due to SO₂ emissions than a global climatic shift; since clay minerals from the corresponding sediments do not reflect a significant climatic change. This increased alteration is coeval with the sharp decline in pollen and an increase in fungal spores and corresponds to the main phase of Deccan activity.