A scientific challenge is to assess the role of Deccan volcanism in the
Cretaceous-Tertiary boundary (KTB) mass extinction. Here we report on
the stratigraphy and biologic effects of Deccan volcanism in eleven deep
wells from the Krishna-Godavari (K-G) Basin, Andhra Pradesh, India. In
these wells, two phases of Deccan volcanism record the world's largest
and longest lava mega-flows interbedded in marine sediments in the K-G
Basin about 1500 km from the main Deccan volcanic province. The main
phase-2 eruptions (similar to 80% of total Deccan Traps) began in C29r
and ended at or near the KTB, an interval that spans planktic
foraminiferal zones CF1-CF2 and most of the nannofossil Micula prinsii
zone, and is correlative with the rapid global warming and subsequent
cooling near the end of the Maastrichtian. The mass extinction began in
phase-2 preceding the first of four mega-flows. Planktic foraminifera
suffered a 50% drop in species richness. Survivors suffered another
50% drop after the first mega-flow, leaving just 7 to 8 survivor
species. No recovery occurred between the next three mega-flows and the
mass extinction was complete with the last phase-2 mega-flow at the KTB.
The mass extinction was likely the consequence of rapid and massive
volcanic CO(2) and SO(2) gas emissions, leading to high continental
weathering rates, global warming, cooling, acid rains, ocean
acidification and a carbon crisis in the marine environment.
Deccan volcanism phase-3 began in the early Danian near the C29R/C29n
boundary correlative with the planktic foraminiferal zone P1a/P1b
boundary and accounts for similar to 14% of the total volume of Deccan
eruptions, including four of Earth's longest and largest mega-flows. No
major faunal changes are observed in the intertrappeans of zone P1b,
which suggests that environmental conditions remained tolerable,
volcanic eruptions were less intense and/or separated by longer time
intervals thus preventing runaway effects. Alternatively, early Danian
assemblages evolved in adaptation to high-stress conditions in the
aftermath of the mass extinction and therefore survived phase-3
volcanism. Full marine biotic recovery did not occur until after Deccan
phase-3. These data suggest that the catastrophic effects of phase-2
Deccan volcanism upon the Cretaceous planktic foraminifera were a
function of both the rapid and massive volcanic eruptions and the highly
specialized faunal assemblages prone to extinction in a changing
environment. Data from the K-G Basin indicates that Deccan phase-2 alone
could have caused the KTB mass extinction and that impacts may have had
secondary effects.