MAIN DECCAN VOLCANISM PHASE ENDS AT K-T MASS EXTINCTION: EVIDENCE FROM THE KRISHNA-GODAVARI BASIN, SE INDIA

Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous-Tertiary (K-T) boundary. Determining just where within this major eruptive phase the K-T mass extinction occurred has remained problematic. For this reason, models estimating the biotic and environmental consequences have generally underestimated the rate and quantity of Deccan gaseous emissions by orders of magnitude leading to conclusions that volcanism could not have caused the K-T mass extinction. In this study we report that the end of the most massive Deccan trap eruption coincided precisely with the K-T mass extinction. This suggests that volcanism, in addition to a large K-T impact, caused the end-Cretaceous mass extinction. These results are based on sedimentologic, microfacies and biostratigraphic data (planktic foraminifera and calcareous nannofossils) of 4-9 m thick intertrappean sediments in four quarry outcrops in the Rajahmundry area of the Krishna-Godavari Basin of southeastern India. In this area two Deccan basalt flows, known as the Rajahmundry traps, mark the most extensive lava flows extending 1000 km across the Indian continent and into the Bay of Bengal. The sediments directly overlying the lower Rajahmundry trap contain claysone clasts with the earliest Danian planktic foraminiferal assemblages of zones P0-P1a that mark the initial evolution in the aftermath of the K-T mass extinction. These claystone clasts were originally deposited on top of the Deccan trap and subsequently eroded during a sea level regression. Upsection, early Danian zone P1a deposition prevailed through the intertrappean sediments. The upper Rajahmundry trap was deposited in magnetic polarity C29n. These results show direct correlations between (1) the most massive Deccan flood basalt eruption and the K-T mass extinction and (2) the last major volcanic eruption in the early Danian and the long delayed post-K-T mass extinction biotic recovery that has remained an enigma for so long. Volcanism may have played a decisive role in both the K-T mass extinction and delayed biotic recovery.