TIMING, TEMPO AND PALEOENVIRONMENTAL IMPLICATIONS OF DECCAN VOLCANISM RELATIVE TO THE KTB EXTINCTION : EVIDENCES FROM THE RED BOLE RECORD
A typical red bole begins with the fresh underlying basalt and evolves into weathered basalt, a layer of ‘bole’-shaped basalt infilled with, and overlain by, clays, which is overlain by the next lava flow. The upper clay layer is composed of red silty clays characterized by high-concentrations of immobile elements such as Al and Fe3+ that are typical of paleo-laterites, which probably developed during the short periods of weathering between eruptions. Clay minerals consist mostly of smectite suggesting semi-arid monsoonal conditions. At least 30 thick red bole layers are present between the lava flows forming the main volcanic phase. The short duration of exposure of these red boles are reflected in the mineralogical and geochemical data that indicate rapid weathering (high CIA) probably linked to increasing acid rains. ∂D and ∂18O measured on smectite clays from the red boles approximate the meteoric water composition that prevailed during Deccan eruptions. Preliminary isotopic data from these red boles suggest significant and rapid changes in rainfall intensity and/or altitude linked to the accumulation of 3400m of basalt that erupted over about 750 ky.